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Sample records for polyoxometalate keggin clusters

  1. Trapping the δ Isomer of the Polyoxometalate-Based Keggin Cluster with a Tripodal Ligand.

    PubMed

    Sartzi, Harikleia; Miras, Haralampos N; Vilà-Nadal, Laia; Long, De-Liang; Cronin, Leroy

    2015-12-14

    We report the synthesis, structural, and electronic characterization of the theoretically predicted, but experimentally elusive δ-isomer of the Keggin polyoxometalate polyanion. A family of δ-Keggin polyoxoanions of the general formula, (TEA)Hp Naq [H2 M12 (XO4 )O33 (TEA)]⋅r H2 O where p, q, r=[2,3,8] for 1 and [4,1,4] for 2 were isolated by the reaction of tungstate(VI) and vanadium(V) with triethanolammonium ions (TEAH), acting as a tripodal ligand grafted to the surface of the cluster thereby stabilizing the polyanionic δ-Keggin archetype. The δ-Keggin species were characterized by single-crystal X-ray diffraction, FT-IR, UV/Vis, NMR, and ESI-MS spectrometry. Electronic structure and structure-stability correlations were evaluated by means of DFT calculations. The compounds exhibited multi-electron transfer and reversible photochromic properties by undergoing single-crystal-to-single-crystal (SC-SC) transformations accompanied with color changes under light. PMID:26511859

  2. Effects of support on bifunctional methanol oxidation pathways catalyzed by polyoxometallate keggin clusters

    SciTech Connect

    Liu, Haichao; Iglesia, Enrique

    2003-12-26

    H5PV2Mo10O40 polyoxometallate Keggin clusters supported on ZrO2, TiO2, SiO2, and Al2O3 are effective catalysts for CH3OH oxidation reactions to form HCHO, methyl formate (MF), and dimethoxymethane (DMM). Rates and selectivities and the structure of supported clusters depend on the surface properties of the oxide supports. Raman spectroscopy showed that Keggin structures remained essentially intact on ZrO2, TiO2, and SiO2 after treatment in air at 553 K, but decomposed to MoOx and VOx oligomers on Al2O3. Accessible protons per Keggin unit (KU) were measured during CH3OH oxidation by titration with 2,6-di-tert-butyl pyridine. For similar KU surface densities (0.28 0.37 KU/nm2), the number of accessible protons was larger on SiO2 than on ZrO2 and TiO2 and much smaller on Al2O3 supports, even though residual dimethyl ether (DME) synthesis rates after titrant saturation indicated that the fractional dispersion of KU was similar on the first three supports. These effects of support on structure and on H+ accessibility reflect varying extents of interaction between polyoxometallate clusters and supports. Rates of CH3OH oxidative dehydrogenation per KU were higher on ZrO2 and TiO2 than on SiO2 at similar KU surface densities (0.28 0.37 KU/nm2) and dispersion, indicating that redox properties of Keggin clusters depend on the identity of the support used to disperse them. ZrO2 and TiO2 supports appear to enhance the reducibility of anchored polyoxometallate clusters. Rates were much lower on Al2O3, because structural degradation led to less reactive MoOx and VOx domains. CH3OH reactions involve primary oxidation to form HCHO and subsequent secondary reactions to form DMM and MF. These reactions involve HCHO CH3OH acetalization steps leading to methoxymethanol (CH3OCH2OH) or hemiacetal intermediates, which condense with CH3OH on acid sites to form DMM or dehydrogenate to form MF. COx formation rates are much lower than those of other reactions, and DME forms in parallel

  3. Two new polyoxometalate-based hybrids consisting of Keggin-type cluster modified by (Ag{sub 4}) group

    SciTech Connect

    Zhao, Xiaofang; Sun, Xiaowei; Han, Zhangang; Zhao, Chuan; Yu, Haitao; Zhai, Xueliang

    2013-11-15

    Two new supramolecular polyoxometalate compounds [Ag{sub 2}(mbpy){sub 3}][Ag(mbpy){sub 2}][PW{sub 12}O{sub 40}] (1) and [Ag{sub 2}(mbpy){sub 3}]{sub 2}[SiW{sub 12}O{sub 40}] (2) (mbpy=4,4'-dimethyl-2,2'-dipyridyl), have been hydrothermally synthesized and characterized by IR, TG, and single-crystal X-ray diffraction techniques. The structural feature of 1–2 is in the cationic moiety of a tetra-core (Ag{sub 4}) cluster through weak Ag…Ag interactions. The silver(I) centers show three-, four- and five-coordinated geometries. In 1 the tetrameric silver atoms in ([Ag{sub 2}(mbpy){sub 3}]{sub 2}){sup 4+} covalently bind to [PW{sub 12}O{sub 40}]{sup 3−} anion via Ag3O bonds, while there is only intermolecular hydrogen bonding between ([Ag{sub 2}(mbpy){sub 3}]{sub 2}){sup 4+} and [SiW{sub 12}O{sub 40}]{sup 4−} in 2. The coordination environments of the tetrameric silver cations have a great influence on the structure richness of the Keggin-based hybrids. The fluorescence properties of compounds 1 and 2 also have been discussed. - Graphical abstract: New polyoxometalate-based hybrids consisting of Keggin-type clusters modified by (Ag{sub 4}) groups had been synthesized and characterized, and their photoluminescence properties were also discussed. Display Omitted - Highlights: • Two Keggin-type polyoxometalates consisting of (Ag{sub 4}) clusters through weak Ag…Ag interactions have been synthesized. • There exist face-to-face and dot-to-face π…π interactions in (Ag-ligand){sub 4} fragment. • The fluorescence properties of (Ag{sub 4}) modified POMs are also discussed.

  4. Bi-antimony capped Keggin polyoxometalate modified with Cu-ligand fragment

    SciTech Connect

    Huang, Jiao; Han, Zhangang; Zhang, Heng; Yu, Haitao; Zhai, Xueliang

    2012-10-15

    Three polyoxometalates consisting of bi-antimony capped Keggin-type clusters: [Cu(mbpy){sub 2}]{sub 2}[PMo{sub 12}O{sub 40}Sb{sub 2}]{center_dot}4H{sub 2}O (1), [Cu(mbpy){sub 2}][PMo{sub 12}O{sub 40}Sb{sub 2}] (2) and {l_brace}Cu(mbpy)[Cu(mbpy){sub 2}]{sub 2}{r_brace}[VMo{sub 8}V{sub 4}O{sub 40}Sb{sub 2}]{center_dot}2H{sub 2}O (3) (mbpy=4,4 Prime -dimethyl-2,2 Prime - dipyridyl in 1 and 2; 5,5 Prime -dimethyl-2,2 Prime -dipyridyl in 3) have been synthesized and characterized by IR, X-ray powder diffraction, TG analysis and electrochemical property. Single-crystal analysis revealed that all of three compounds are built upon bi-antimony capped Keggin-type polyoxoanions and Cu-mbpy cations. In 1-3, two Sb{sup III} centers located at the two opposite of anionic surface adopt fundamentally tetragonal pyramidal coordination geometry. Both compounds 1 and 2 consist of P-centered Keggin structure, while compound 3 presents a V-centered Keggin anion. The Keggin-type anions present different structural features: isolated cluster in 1 and Cu-ligand-supported cluster in 2 and 3. - Graphical abstract: Three hybrid compounds consisting of bi-antimony capped Keggin-type clusters modified with Cu-ligand cations have been synthesized and characterized. Highlights: Black-Right-Pointing-Pointer Three hybrid compounds consisting of bi-antimony capped Keggin-type clusters have been synthesized. Black-Right-Pointing-Pointer Two Sb{sup III} centers located at the two opposite of anionic surface adopt tetragonal pyramidal coordination geometry. Black-Right-Pointing-Pointer The anions present different structural features: isolated and Cu-ligand-supported cluster.

  5. Two polyoxometalate-based coordination polymers constructed from Mn(II)-4,4'-bipyridine-N,N'-dioxide building blocks and Keggin-type clusters: Syntheses, crystal structures and spectral properties.

    PubMed

    Bai, Yan; Li, Meng-Meng; Huang-Fu, You-Jing; Dang, Dong-Bin

    2013-11-01

    Two polyoxometalate-based coordination polymers {[Mn2(dpdo)4(H2O)6](GeMo12O40)(H2O)4}n (1) and {[Mn2(dpdo)4(H2O)6](GeW12O40)(H2O)3}n (2) (dpdo=4,4'-bipyridine-N,N'-dioxide) have been synthesized and characterized by IR, elemental analysis, XRPD, TG technique and X-ray crystallography. The polymers 1 and 2 are basically isostructural and feature a 3D supramolecular framework decorated with Keggin-type polyanion clusters based on one-dimension polymeric chains, which formed through the coordination interaction of Mn(II) and dpdo. The luminescent properties of the polymers were investigated in the solid state at room temperature. PMID:23880411

  6. Monolacunary Keggin polyoxometalates connected to ten 4d or 4f metal atoms.

    PubMed

    Pang, Haijun; Gómez-García, Carlos J; Peng, Jun; Ma, Huiyuan; Zhang, Chunjing; Wu, Qingyin

    2013-12-21

    The rational self-assembly of mono-lacunary Keggin clusters with 4d and 4f metal salts via a conventional method has yielded two novel polyoxometalate-based 4d-4f heterometallic compounds containing lacunary Keggin anions connected to ten metal atoms: {[Ag{Ag2(H2O)4}{Ln(H2O)6}2H ⊂ {SiW11Ln(H2O)4O39}2]·nH2O (Ln = Ce and n = 7 for 1, Ln = Pr and n = 3 for 2). Their structures were determined by single crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. A structural feature in 1 and 2 is that each [SiW11O39](8-) cluster (SiW11) is connected to ten metals (five Ag(+) and five Ln(3+) cations), representing the highest number of connected metal atoms to any mono-lacunary Keggin anion to date. This large connectivity leads to a structure with a purely inorganic 3D framework with two kinds of channels along the [100] and [010] directions. The magnetic properties of both compounds show the expected magnetic moments (0.8 and 1.6 amu K mol(-1) per Ce(3+) and Pr(3+) ion, respectively) and confirm the presence of isolated Ce(3+) and Pr(3+) ions. PMID:24067933

  7. A multifunctional lanthanide metal-organic framework supported by Keggin type polyoxometalates.

    PubMed

    Zhu, Wen-Hua; Zeng, Min; Wang, Juan; Li, Chen-Yang; Tian, Li-Hong; Yin, Jia-Cheng; Liu, Yu-Kun

    2016-06-21

    A neodymium metal-organic framework with 1D nanotubular channels incorporating Keggin type [SiWWO38](3-) has been synthesized by utilizing pyridine-2,5-dicarboxylic acid as an organic ligand. It represents an unusual polyoxometalate-templated framework with the multifunctionality of magnetism, near-infrared luminescence and the selective adsorption of Rhodamine B dye molecules. PMID:27242190

  8. Synergistic combination of multi-Zr(IV) cations and lacunary Keggin germanotungstates leading to a gigantic Zr24-cluster-substituted polyoxometalate.

    PubMed

    Huang, Ling; Wang, Sa-Sa; Zhao, Jun-Wei; Cheng, Lin; Yang, Guo-Yu

    2014-05-28

    Synergistic directing roles of six lacunary fragments resulted in an unprecedented Zr24-cluster substituted poly(polyoxotungstate) Na10K22[Zr24O22(OH)10(H2O)2(W2O10H)2(GeW9O34)4(GeW8O31)2]·85H2O (Na10K22·1·85H2O), which contains the largest [Zr24O22(OH)10(H2O)2] (Zr24) cluster in all the Zr-based poly(polyoxometalate)s to date. The most remarkable feature is that the centrosymmetric Zr24-cluster-based hexamer contains two symmetry-related [Zr12O11(OH)5(H2O)(W2O10H)(GeW9O34)2(GeW8O31)](16-) trimers via six μ3-oxo bridges and was simultaneously trapped by three types of different segments of B-α-GeW9O34, B-α-GeW8O31, and W2O10. The other interesting characteristic is that there are two pairs of intriguing triangular atom alignments: one is composed of the Zr(2,4,6,8,11) and W21 atoms and the other contains the Ge(1-3), Zr(3,5,7,9,10,12) and W26 atoms, and the Zr5 atom is inside the triangle; a linking mode is unobserved. The oxygenation reactions of thioethers by H2O2 were evaluated when Na10K22·1·85H2O served as a catalyst. Results show that it is an effective catalyst for oxygenation of thioethers by H2O2. The unique redox property of oxygen-enriched polyoxotungstate fragments and Lewis acidity of the Zr cluster imbedded in Na10K22·1·85H2O provide a sufficient driving force for the catalytic conversion from thioethers to sulfoxides/sulfones. PMID:24819708

  9. Energetics of Al13 Keggin cluster compounds

    PubMed Central

    Armstrong, Christopher R.; Casey, William H.; Navrotsky, Alexandra

    2011-01-01

    The ϵ-Al13 Keggin aluminum hydroxide clusters are essential models in establishing molecular pathways for geochemical reactions. Enthalpies of formation are reported for two salts of aluminum centered ϵ-Keggin clusters, Al13 selenate, (Na(AlO4)Al12(OH)24(SeO4)4•12H2O) and Al13 sulfate, (NaAlO4Al12(OH)24(SO4)4•12H2O). The measured enthalpies of solution, ΔHsol, at 28 °C in 5 N HCl for the ε-Al13 selenate and sulfate are −924.57 (± 3.83) and −944.30 ( ± 5.66) kJ·mol-1, respectively. The enthalpies of formation from the elements, ΔHf,el, for Al13 selenate and sulfate are −19,656.35 ( ± 67.30) kJ·mol-1, and −20,892.39 ( ± 70.01) kJ·mol-1, respectively. In addition, ΔHf,el for sodium selenate decahydrate was calculated using data from high temperature oxide melt solution calorimetry measurements: −4,006.39 ( ± 11.91) kJ·mol-1. The formation of both ε-Al13 Keggin cluster compounds is exothermic from oxide-based components but energetically unfavorable with respect to a gibbsite-based assemblage. To understand the relative affinity of the ϵ-Keggin clusters for selenate and sulfate, the enthalpy associated with two S-Se exchange reactions was calculated. In the solid state, selenium is favored in the Al13 compound relative to the binary chalcogenate, while in 5 N HCl, sulfur is energetically favored in the cluster compound compared to the aqueous solution. This contribution represents the first thermodynamic study of ε-Al13 cluster compounds and establishes a method for other such molecules, including the substituted versions that have been created for kinetic studies. Underscoring the importance of ε-Al13 clusters in natural and anthropogenic systems, these data provide conclusive thermodynamic evidence that the Al13 Keggin cluster is a crucial intermediate species in the formation pathway from aqueous aluminum monomers to aluminum hydroxide precipitates. PMID:21852572

  10. Preparation and application of L-cysteine-doped Keggin polyoxometalate microtubes

    SciTech Connect

    Shen Yan; Peng Jun; Zhang Huanqiu; Meng Cuili; Zhang Fang

    2012-01-15

    L-cysteine-doped tungstosilicate (Lcys-SiW{sub 12}) microtubes are prepared, and the amount of L-cysteine doped in the microtubes can be tuned to some extent. The as-prepared Lcys-SiW{sub 12} microtubes are sensitive to ammonia gas exhibited through the distinct color change of the microtubes from light purple to dark blue after exposing to ammonia gas. A possible mechanism of the coloration is that the adsorbed ammonia molecules increase the basicity of the Lcys-SiW{sub 12} microtubes and promote the redox reaction between L-cysteine and polyoxometalate. This is a pH-dependent solid-solid redox reaction, which is triggered by proton capture agent. The Lcys-SiW{sub 12} microtubes show application in chemical sensors for alkaline gases. - Graphical abstract: The Lcys-SiW{sub 12} microtubes were formed during transformation of the monolacunary Keggin-type [{alpha}-SiW{sub 11}O{sub 39}]{sup 8-} to the saturated Keggin-type [{alpha}-SiW{sub 12}O{sub 40}]{sup 4-}, meanwhile L-cysteine molecules were doped during the growth of the microtubes. Highlights: Black-Right-Pointing-Pointer L-cysteine-doped polyoxometalate microtubes are prepared. Black-Right-Pointing-Pointer Amount of L-cysteine doped in the microtubes can be tuned to some extent. Black-Right-Pointing-Pointer Lcys-SiW{sub 12} microtubes can be applied as a sensor for detecting alkaline gases. Black-Right-Pointing-Pointer This is a proton capture agent-triggered solid-solid redox reaction.

  11. Synthesis and structural characterization of Keggin polyoxometalate compounds with argininium(2+) cations

    NASA Astrophysics Data System (ADS)

    Santos, F. M.; Brandão, P.; Félix, V.; Cavaleiro, A. M. V.; de Matos Gomes, E.; Belsley, M. S.

    2010-01-01

    New organic-inorganic hybrid compounds, with formula (H 2Arg) 3[PM 12O 40] 2·4H 2O and (H 2Arg) 4[SiM 12O 40]· nH 2O ( n = 0-1), where Arg = L-arginine and M = Mo, W, were prepared and characterized by analytical, spectroscopic, and X-ray diffraction techniques. Thermal analysis was performed to study their thermal stability. The crystal structure of (H 2Arg) 3[PMo 12O 40] 2·15H 2O·EtOH (triclinic, space group P1, Z = 1) was determined by X-ray diffraction. The chiral H 2Arg 2+ cations and the Keggin anions are involved in hydrogen bonding interactions which lead to the formation of an infinite three-dimensional network. This study adds new members to the important family of argininium/inorganic anions hybrid salts. To our best knowledge these are the first compounds of diprotonated arginine and Keggin-type polyoxoanions and also the first crystal structure determination of an argininium(2+) compound with an inorganic anion of the polyoxometalate family.

  12. Photocatalytic degradation of dye naphthol blue black in the presence of zirconia-supported Ti-substituted Keggin-type polyoxometalates

    SciTech Connect

    Jiang Chunjie; Guo Yihang; Hu Changwen; Wang Chungang; Li Danfeng

    2004-02-02

    Zirconia-supported Ti-substituted Keggin-type polyoxometalates, Li{sub 5}PW{sub 11}TiO{sub 40}/ZrO{sub 2} (PW{sub 11}Ti/ZrO{sub 2}) and K{sub 7}PW{sub 10}Ti{sub 2}O{sub 40}/ZrO{sub 2} (PW{sub 10}Ti{sub 2}/ZrO{sub 2}), were prepared by incorporating PW{sub 11}Ti and PW{sub 10}Ti{sub 2} cluster into a zirconia matrix via a sol-gel technique. These insoluble and readily separable composites were characterized by DR-UV (DR: diffuse reflectance) and FT-IR spectra, {sup 31}P MAS NMR, ICP-AES, and nitrogen adsorption determination, indicating that the clusters were chemically attached to the zirconia supports, and the primary Keggin structure remained intact. The photocatalytic activity of the supported PW{sub 11}Ti and PW{sub 10}Ti{sub 2} was tested via degradation of an aqueous dye naphthol blue black (NBB). It indicated that the dye NBB can be degraded totally and mineralized into the inorganic products such as CO{sub 2}, NH{sub 4}{sup +}, NO{sub 3}{sup -}, and SO{sub 4}{sup 2-} ions by irradiating the composite slurry in the near-UV area. Dropped of PW{sub 11}Ti or PW{sub 10}Ti{sub 2} cluster from the zirconia matrix into the reaction system was hardly observed during the photocatalytic tests, attributed to the strong chemical interactions between the Keggin units and the zirconia support.

  13. Keggin-Type Polyoxometalate-Based Metal-Organic Networks for Photocatalytic Dye Degradation.

    PubMed

    Hao, Hong-Fang; Zhou, Wen-Zhe; Zang, Hong-Ying; Tan, Hua-Qiao; Qi, Yan-Fei; Wang, Yong-Hui; Li, Yang-Guang

    2015-08-01

    The reaction of Keggin-type polyoxometalate (POM) units, transition-metal (TM) ions, and a rigid bis(imidazole) ligand (1,4-bis(1-imidazolyl)benzene (bimb)) in a hydrothermal environment led to the isolation of four new POM-based metal-organic networks, [H2 L][CuL][SiW12 O40 ]⋅2 H2 O (1), [H2 L]2 [Co(H2 O)3 L][SiW11 CoO39 ]⋅6 H2 O (2), KH[CuL]2 [SiW11 CoO39 (H2 O)]⋅2 H2 O (3), and [CuL]4 [GeW12 O40 ]⋅H2 O (4; L=bimb). All four compounds were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. Compounds 1 and 3 are new 3D networks with 1D channels. Compounds 2 and 4 contain 2D networks, which further stack into 3D supramolecular networks. The contributions of pH value, the negative charge of the POM, and the TM coordination modes to the construction of 3D networks were elucidated by comparing the synthetic conditions and structures of compounds 1-4. The photocatalytic properties of compounds 1-4 were investigated using methylene blue (MB) degradation under UV light. All compounds showed good catalytic activity and structural stability. The possible catalytic mechanism was discussed on the basis of active-species trapping experiments. The different photocatalytic activities of compounds 1-4 were explained by comparison of the band gaps of different POM species and different packing modes of POM units in these hybrid compounds. PMID:26033779

  14. Design, synthesis and excellent third-order NLO properties of two new polyoxometalates constructed from Keggin polyanions bonded by a solvent molecule.

    PubMed

    Miao, Hao; Dong, Yayu; Chen, Ziwang; He, Xingxiang; Hu, Gonghao; Xu, Yan

    2016-08-01

    Two new monosubstituted Keggin structural polyoxometalates [H5PMo11O39Zn(C5H5N)]·(C5H5N)5·H2O (1) and [H5PW11O39Co(C5H5N)]·(C5H5N)2·(C6H8N)2·1.5CH3OH (2) have been successfully synthesized under hydrothermal conditions. Structural analysis indicates that the polyoxoanion of compound 1 is a solvent molecule-bonded zinc-monosubstituted Keggin structural cluster, [PMo11O39Zn(C5H5N)](5-), while the polyoxoanion of compound 2 is a cobalt-monosubstituted phosphotungstate polyanion bonded with one pendant pyridine molecule. Both 1 and 2 show 3D supramolecular interpenetrating structures constructed of inorganic polyanion layers and organic layers. Very interestingly, compounds 1 and 2 exhibit excellent third-order NLO properties, and the TPA cross section σ of 1 and 2 is 2571.3 GM and 2876.3 GM, respectively. PMID:27453327

  15. Ferrihydrite Formation: The Role of Fe13 Keggin Clusters.

    PubMed

    Weatherill, Joshua S; Morris, Katherine; Bots, Pieter; Stawski, Tomasz M; Janssen, Arne; Abrahamsen, Liam; Blackham, Richard; Shaw, Samuel

    2016-09-01

    Ferrihydrite is the most common iron oxyhydroxide found in soil and is a key sequester of contaminants in the environment. Ferrihydrite formation is also a common component of many treatment processes for cleanup of industrial effluents. Here we characterize ferrihydrite formation during the titration of an acidic ferric nitrate solution with NaOH. In situ SAXS measurements supported by ex situ TEM indicate that initially Fe13 Keggin clusters (radius ∼ 0.45 nm) form in solution at pH 0.12-1.5 and are persistent for at least 18 days. The Fe13 clusters begin to aggregate above ∼ pH 1, initially forming highly linear structures. Above pH ∼ 2 densification of the aggregates occurs in conjunction with precipitation of low molecular weight Fe(III) species (e.g., monomers, dimers) to form mass fractal aggregates of ferrihydrite nanoparticles (∼3 nm) in which the Fe13 Keggin motif is preserved. SAXS analysis indicates the ferrihydrite particles have a core-shell structure consisting of a Keggin center surrounded by a Fe-depleted shell, supporting the surface depleted model of ferrihydrite. Overall, we present the first direct evidence for the role of Fe13 clusters in the pathway of ferrihydrite formation during base hydrolysis, showing clear structural continuity from isolated Fe13 Keggins to the ferrihydrite particle structure. The results have direct relevance to the fundamental understanding of ferrihydrite formation in environmental, engineered, and industrial processes. PMID:27480123

  16. Hydrolysis of the RNA model substrate catalyzed by a binuclear Zr(IV)-substituted Keggin polyoxometalate.

    PubMed

    Luong, Thi Kim Nga; Absillis, Gregory; Shestakova, Pavletta; Parac-Vogt, Tatjana N

    2015-09-21

    The reactivity and solution behaviour of the binuclear Zr(IV)-substituted Keggin polyoxometalate (Et2NH2)8[{α-PW11O39Zr(μ-OH)(H2O)}2]·7H2O (ZrK 2 : 2) towards phosphoester bond hydrolysis of the RNA model substrate 2-hydroxypropyl-4-nitrophenyl phosphate (HPNP) was investigated at different reaction conditions (pD, temperature, concentration, and ionic strength). The hydrolysis of the phosphoester bond of HPNP, followed by means of (1)H NMR spectroscopy, proceeded with an observed rate constant, kobs = 11.5(±0.42) × 10(-5) s(-1) at pD 6.4 and 50 °C, representing a 530-fold rate enhancement in comparison with the spontaneous hydrolysis of HPNP. (1)H and (31)P NMR spectra indicate that at these reaction conditions the only products of hydrolysis are p-nitrophenol and the corresponding cyclic phosphate ester. The pD dependence of kobs exhibits a bell-shaped profile, with the fastest rate observed at pD 6.4. The formation constant (Kf = 455 M(-1)) and catalytic rate constant (kc = 42 × 10(-5) s(-1)) for the HPNP-ZrK 2 : 2 complex, activation energy (Ea) of 63.35 ± 1.82 kJ mol(-1), enthalpy of activation (ΔH(‡)) of 60.60 ± 2.09 kJ mol(-1), entropy of activation (ΔS(‡)) of -133.70 ± 6.13 J mol(-1) K(-1), and Gibbs activation energy (ΔG(‡)) of 102.05 ± 0.13 kJ mol(-1) at 37 °C were calculated from kinetic experiments. Binding between ZrK 2 : 2 and the P-O bond of HPNP was evidenced by the change in the (31)P chemical shift and signal line-broadening of the (31)P atom in HPNP upon addition of ZrK 2 : 2. Based on (31)P NMR experiments and isotope effect studies, a mechanism for HPNP hydrolysis in the presence of ZrK 2 : 2 was proposed. PMID:26256057

  17. Influence of metal ions on the structures of Keggin polyoxometalate-based solids: Hydrothermal syntheses, crystal structures and magnetic properties

    NASA Astrophysics Data System (ADS)

    Shi, Zhenyu; Peng, Jun; Gómez-García, Carlos J.; Benmansour, Samia; Gu, Xiaojun

    2006-01-01

    Three new Keggin polyoxometalate (POM)-based compounds linked to 3d metal complexes have been synthesized under hydrothermal conditions: [Cu(phen) 2] 2{[Cu(phen)] 2 [SiMo 12O 40(VO) 2]} ( 1), {[Zn(phen) 2] 2[GeMo 12O 40(VO) 2]}{[Zn(phen) 2(H 2O)] 2 [GeMo 12O 40(VO) 2]}·3H 2O ( 2) and {[Co(phen) 2] 2[PMo 12O 40(VO) 2]}{[Co(phen) 2(OH)] 2 [PMo 12O 40(VO) 2]}·2.5H 2O ( 3) (phen=1,10-phenanthroline). These three compounds present, as building blocks, the bicapped Keggin anions [ XMo 12O 40(VO) 2] ( X=Si, Ge and P). Compound 1 consists of a bicapped Keggin anion [SiMo 12O 40(VO) 2] 2- linked to two [Cu(phen)] + complexes with two [Cu(phen) 2] + countercations. Compound 2 contains two bicapped Keggin anions [GeMo 12O 40(VO) 2] 4-, one linked to two [Zn(phen) 2(H 2O)] 2+ cations and the other one linked to two [Zn(phen) 2] 2+ cations. Compound 3 is a two-dimensional POM-based square network formed by bicapped Keggin anions [PMo 12O 40(VO) 2] 4- connected by [Co(phen) 2] 2+ cations. Discrete bicapped Keggin anions [PMo 12O 40(VO) 2] linked to two [Co(phen) 2(OH)] + cations are located between the layers. The magnetic properties show the presence of antiferromagnetic interactions among the reduced Mo(V) atoms (in the three compounds) plus a paramagnetic contribution from the V(IV) atoms (in 1 and 2). Compound 3 shows, in addition, an antiferromagnetic interaction between the Co(II) and the V(IV) ions directly linked through an oxygen bridge. The low-temperature ESR spectra of compound 3 confirm the presence of the reduced Mo(V) ions and the antiferromagnetic coupling between the Co(II) and the V(IV) ions.

  18. Synthesis and characterization of molecular hexagons and rhomboids and subsequent encapsulation of Keggin-type polyoxometalates by molecular hexagons.

    PubMed

    Uehara, Kazuhiro; Oishi, Takamichi; Hirose, Takayuki; Mizuno, Noritaka

    2013-10-01

    Structural control among hexagonal (trimer), rhomboidal (dimer), and infinite-chain supramolecular complexes with three different supporting ligands of ethylenediamine (en), N,N,N',N'-tetramethylethylenediamine (en*), and 1,2-bis(diphenyl)phosphinoethane (dppe) [(en)Pd(L)]3(OTf)6 1t·OTf, [(en*)Pd(L)]2(PF6)4 2d·PF6, and [(dppe)Pd(L)(OTf)2]∞ 3·OTf (OTf = trifluoromethane sulfonate; L = 1,3-bis(4-pyridylethynyl)benzene) in the solid and solution states was investigated. The encapsulation of a large Keggin-type polyoxometalate [α-PW12O40](3-) by these complexes was also examined. As the steric bulkiness of the supporting ligands increased in the order of en < en* < dppe, the hexagonal, rhomboidal, and infinite-chain structures were obtained, as confirmed by X-ray crystallography. In solution, equilibrium between the molecular hexagon (1t·OTf/2t·PF6) and the molecular rhomboid (1d·OTf/2d·PF6) was observed in the en/en* ligand systems, whereas 3·OTf with the dppe ligand did not exhibit equilibrium and instead existed as a single species. These phenomena were established by cold-spray ionization mass spectroscopy (CSI-MS) and (1)H diffusion ordered NMR spectroscopy (DOSY). The addition of the highly negatively charged Keggin-type phosphododecatungstate [α-PW12O40](3-) to a solution of 2t/2d·PF6 resulted in the encapsulation of the tungstate species in the cavity of the molecular hexagon to form {[(en*)Pd(L)]3[⊃α-PW12O40]}(PF6)3 2t·[α-PW12O40](3-), as confirmed by a combination of (1)H and (31)P DOSY and CSI-MS spectral data. PMID:24050509

  19. Photoelectrocatalytic performance of a titania-keggin type polyoxometalate-gold nanocomposite modified electrode in methanol oxidation.

    PubMed

    Pandiyarajan, Chinnappan; Pandikumar, Alagarsamy; Ramaraj, Ramasamy

    2013-11-01

    Aminosilicate sol-gel supported titania-keggin type polyoxometalate-gold nanocomposite materials (APS/(P25-PTA-Au)NCM) (APS, (3-aminopropyl)triethoxysilane; P25, Degussa-TiO2; PTA, Na3PW12O40·xH2O) were prepared by a simple chemical reduction method and characterized by diffuse reflectance spectroscopy, photoluminescence, x-ray diffraction, transmission electron microscopy and energy-dispersive x-ray analysis. The as-prepared APS/(P25-PTA-Au)NCM was used to fabricate the photoelectrode for a photoelectrochemical cell. The photoelectrocatalytic activity of the APS/(P25-PTA-Au)NCM modified photoelectrode in methanol oxidation was investigated. The APS/(P25-PTA-Au)NCM modified photoelectrode showed a higher photocurrent for methanol oxidation than control photoelectrodes. The modification of titania using PTA and Au nanoparticles significantly boosted the photoelectrocatalytic performance by a synergistic effect and thus improved the interfacial charge transfer processes. The presence of Au nanoparticles enhances the interfacial electron transfer process. The APS silicate sol-gel matrix acts as a very good support material for the preparation of the nanocomposite material and for preparation of the chemically modified electrode. This newly fabricated APS/(P25-PTA-Au)NCM modified photoelectrode could be a promising candidate for photoelectrochemical cells. PMID:24077520

  20. Photodegradation of malachite green dye catalyzed by Keggin-type polyoxometalates under visible-light irradiation: Transition metal substituted effects

    NASA Astrophysics Data System (ADS)

    Liu, Chun-Guang; Zheng, Ting; Liu, Shuang; Zhang, Han-Yu

    2016-04-01

    In the present paper, Keggin-type polyoxometalates (POMs) (NH4)3[PW12O40] and its mono-transition-metal-substituted species (NH4)5[{PW11O39}MII(H2O)] (M = Mn, Fe, Co, Ni, Cu, Zn) have been synthesized and used as photocatalyst to activate O2 for the degradation of dye molecule under visible-light irradiation. Because of the strong adsorption on the surface of POM catalyst, malachite green (MG) molecule was employed as a molecular probe to test their photocatalytic activity. The photodegradation study shows that introduction of transition metal ion leads to an increase in the degradation of MG in the following order: Mn < Fe < Co < [PW12O40]3- < Ni < Cu < Zn, which indicates that the photocatalytic activity of these POMs is sensitive to the transition metal substituted effects. Electronic structure analysis based on the density functional theory calculations shows that a moderate decrease of oxidizing ability of POM catalyst may improve the photocatalytic activity in the degradation of dye molecule under visible-light irradiation. Meanwhile, intermediate products about the photocatalytic oxidation of MG molecule were proposed on the basis of gas chromatograph mass spectrometer analysis.

  1. Amide bond hydrolysis in peptides and cyclic peptides catalyzed by a dimeric Zr(IV)-substituted Keggin type polyoxometalate.

    PubMed

    Ly, Hong Giang T; Absillis, Gregory; Parac-Vogt, Tatjana N

    2013-08-14

    Detailed kinetic studies on the hydrolysis of glycylserine (Gly-Ser) and glycylglycine (Gly-Gly) in the presence of the dimeric zirconium(IV)-substituted Keggin type polyoxometalate (Et2NH2)8[{α-PW11O39Zr(μ-OH)(H2O)}2]·7H2O (1) were performed by a combination of (1)H, (13)C and (31)P NMR spectroscopy. The observed rate constants for the hydrolysis of Gly-Ser and Gly-Gly at pD 5.4 and 60 °C were 63.3 × 10(-7) s(-1) and 4.44 × 10(-7) s(-1) respectively, representing a significant acceleration as compared to the uncatalyzed reactions. The pD dependence of the rate constant for both reactions exhibited a bell-shaped profile with the fastest hydrolysis observed in the pD range of 5.5-6.0. Interaction of 1 with Gly-Ser and Gly-Gly via their amine nitrogen and amide oxygen was proven by (13)C NMR spectroscopy. The effective hydrolysis of Gly-Ser in the presence of 1 is most likely a combination of the polarization of the amide oxygen due to its binding to the Zr(IV) ion in 1 and the intramolecular attack of the Ser hydroxyl group on the amide carbonyl carbon. The effect of temperature, inhibitors, and ionic strength on the hydrolysis rate constant was also examined. The solution structure of 1 was investigated by means of (31)P NMR spectroscopy, revealing that its stability is highly dependent on pH, concentration and temperature. A 2.0 mM solution of 1 was found to be fully stable under hydrolytic conditions (pD 5.4 and 60 °C) both in the presence and in the absence of the dipeptides. PMID:23787813

  2. Hybrid Coordination Networks Constructed from ɛ-Keggin-Type Polyoxometalates and Rigid Imidazole-Based Bridging Ligands as New Carriers for Noble-Metal Catalysts.

    PubMed

    Yang, Xiao-Jian; Sun, Meng; Zang, Hong-Ying; Ma, Yuan-Yuan; Feng, Xiao-Jia; Tan, Hua-Qiao; Wang, Yong-Hui; Li, Yang-Guang

    2016-03-18

    Three hybrid coordination networks that were constructed from ɛ-Keggin polyoxometalate building units and imidazole-based bridging ligands were prepared under hydrothermal conditions, that is, H[(Hbimb)2 (bimb){Zn4 PMo(V8) Mo(VI) 4O40}]⋅6 H2O(1), [Zn(Hbimbp)(bimbp)3 {Zn4 PMo(V8) Mo(VI) 4O40}]⋅DMF⋅3.5 H2O(2), and H[Zn2 (timb)2 (bimba)2 Cl2 {Zn4 PMo(V8) Mo(VI) 4O40}]⋅7 H2O(3) (bimb=1,4-bis(1-imidazolyl)benzene, bimbp=4,4'-bis(imidazolyl)biphenyl, timb=1,3,5-tris(1-imidazolyl)benzene, bimba=3,5-bis(1-imidazolyl)benzenamine). All three compounds were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, and single-crystal X-ray diffraction. The mixed valence of the Mo centers was analyzed by XPS spectroscopy and bond-valence sum calculations. In all three compounds, the ɛ-Keggin polyoxometalate (POM) units acted as nodes that were connected by rigid imidazole-based bridging ligands to form hybrid coordination networks. In compound 1, 1D zigzag chains extended to form a 3D supramolecular architecture through intermolecular hydrogen-bonding interactions. Compound 2 consisted of 2D curved sheets, whilst compound 3 contained chiral 2D networks. Because of the intrinsic reducing properties of ɛ-Keggin POM species, noble-metal nanoparticles were loaded onto these POM-based coordination networks. Thus, compounds 1-3 were successfully loaded with Ag nanoparticles, and the corresponding composite materials exhibited high catalytic activities for the reduction of 4-nitrophenol. PMID:26807960

  3. Effect of the Keggin anions on assembly of Cu{sup I}-bis(tetrazole) thioether complexes containing multinuclear Cu{sup I}-cluster

    SciTech Connect

    Wang Xiuli; Gao Qiang; Tian Aixiang; Hu Hailiang; Liu Guocheng

    2012-03-15

    In order to investigate the effect of polyoxometalate (POM) on the assembly of transition metal-bis(tetrazole) thioether complexes, three new complexes based on different Keggin anions and multinuclear Cu{sup I}-cluster [Cu{sup I}{sub 12}(bmtr){sub 9}(HSiMo{sub 12}O{sub 40}){sub 4}] (1), [Cu{sup I}{sub 3}(bmtr){sub 3}(PM{sub 12}O{sub 40})] (M=W for 2; Mo for 3) (bmtr=1,3-bis(1-methyl-5-mercapto-1,2,3,4-tetrazole)propane), have been hydrothermally synthesized and characterized by routine physical methods and single crystal X-ray diffraction. In compound 1, two kinds of nanometer-scale tetranuclear subunits linked by [SiMo{sub 12}O{sub 40}]{sup 4-} polyanions assemble a (3, 4)-connected three-dimensional (3D) self-penetrating framework. Compounds 2 and 3 are isostructural, exhibiting a 1D chain with [PW{sub 12}O{sub 40}]{sup 3-}/[PMo{sub 12}O{sub 40}]{sup 3-} polyanions and trinuclear clusters arranging alternately. The distinct structural differences between these POM-based Cu{sup I}-bmtr complexes of 1 and 2/3 maybe rest on the contrast of Keggin-type polyoxometalate with different central heteroatoms, which have been discussed in detail. In addition, the electrochemical properties of the title complexes have been investigated. - Graphical abstract: Three new complexes based on different Keggin anions and multinuclear Cu{sup I}-cluster have been synthesized under hydrothermal conditions. The Keggin polyanions with different central heteroatoms play a key role. Highlights: Black-Right-Pointing-Pointer The flexible bis(tetrazole)-based thioether ligand with some advantages have been used. Black-Right-Pointing-Pointer The effect of Keggin anions with different central heteroatoms has been discussed in detail. Black-Right-Pointing-Pointer The electrochemical behaviors and electrocatalysis property have been investigated.

  4. Super-reduced polyoxometalates: excellent molecular cluster battery components and semipermeable molecular capacitors.

    PubMed

    Nishimoto, Yoshio; Yokogawa, Daisuke; Yoshikawa, Hirofumi; Awaga, Kunio; Irle, Stephan

    2014-06-25

    Theoretical investigations are presented on the molecular and electronic structure changes that occur as α-Keggin-type polyoxometalate (POM(3-)) clusters [PM12O40](3-) (M = Mo, W) are converted toward their super-reduced POM(27-) state during the discharging process in lithium-based molecular cluster batteries. Density functional theory was employed in geometry optimization, and first-principles molecular dynamics simulations were used to explore local minima on the potential energy surface of neutral POM clusters adorned with randomly placed Li atoms as electron donors around the cluster surface. On the basis of structural, electron density, and molecular orbital studies, we present evidence that the super-reduction is accompanied by metal-metal bond formation, beginning from the 12th to 14th excess electron transferred to the cluster. Afterward, the number of metal-metal bonds increases nearly linearly with the number of additionally transferred excess electrons. In α-Keggin-type POMs, metal triangles are a prominently emerging structural feature. The origin of the metal triangle formation during super-reduction stems from the formation of characteristic three-center two-electron bonds in triangular metal atom sites, created under preservation of the POM skeleton via "squeezing out" of oxygen atoms bridging two metal atoms when the underlying metal atoms form covalent bonds. The driving force for this unusual geometrical and electronic structure change is a local Jahn-Teller distortion at individual transition-metal octahedral sites, where the triply degenerate t2 d orbitals become partially filled during reduction and gain energy by distortion of the octahedron in such a way that metal-metal bonds are formed. The bonding orbitals show strong contributions from mixing with metal-oxygen antibonding orbitals, thereby "shuffling away" excess electrons from the cluster center to the outside of the cage. The high density of negatively charged yet largely separated

  5. Asymmetrically fused polyoxometalate-silver alkynide composite cluster.

    PubMed

    Kurasawa, Mariko; Arisaka, Fumio; Ozeki, Tomoji

    2015-02-16

    We demonstrate that an asymmetric composite cluster, [Ag25{C≡CC(CH3)3}16(CH3CN)4(P2W15Nb3O62)] (1), consisting of directly fused polyoxometalate and silver alkynide moieties can be facilely synthesized by a one-pot reaction between a Nb-substituted Dawson-type polyoxometalate, H4[α-P2W15Nb3O62](5-), and the mixture of (CH3)3CC≡CAg and CF3SO3Ag. Single-crystal X-ray diffraction revealed the structure of 1, where Ag atoms are selectively attached to the Nb-substituted hemisphere of the pedestal Dawson anion. Its structural integrity in the solution was demonstrated by (31)P NMR spectroscopy and analytical ultracentrifugation. The latter method also unveiled the stepwise formation mechanism of 1. PMID:25586879

  6. A new Keggin-like niobium-phosphate cluster that reacts reversibly with hydrogen peroxide.

    PubMed

    Son, Jung-Ho; Casey, William H

    2015-08-18

    Polyoxoniobate clusters that are stable in acidic solutions are rare and particularly useful in industrial processes. Here we report a new pentaphosphate niobate polyoxometalate cluster (TMA)9H3Nb9P5O41·28H2O (Nb9P5) that is stable over a wide pH range and that can be converted reversibly into the peroxo form. PMID:26133686

  7. Two hybrid compounds constructed from Ni-tris(imidazolyl) complexes and Keggin clusters: Syntheses, structures and electrochemical properties

    NASA Astrophysics Data System (ADS)

    Zhang, Zhuanfang; Sun, Xiaojun; Ma, Huiyuan; Pang, Haijun; Li, Shaobin; Zhao, Chunyan

    2016-07-01

    By introducing different polyoxotungstates into the Ni-tib (tib = 1, 3, 5-tris (1-imidazolyl)benzene) system, two new polyoxometalate-based inorganic-organic hybrids with distinct architectures, [Ni(Htib)4][PW12O40]2 (1) and [Nitib]2(H2O)4](GeW12O40)·2H2O (2) have been synthesized under the same hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (PXRD) patterns and thermogravimetic (TG) analyses. Structural analyses show that compound 1 is a dimer, in which two neighboring mono-connected [PW12O40]3- (PW12) clusters are linked together by a [Ni(Htib)4] complex cation. In contrast to compound 1, compound 2 presents a 2D grid layer formed by bi-connected [GeW12O40]4- (GeW12) clusters and [Ni2(H2O)4(tib)2] complex cations, and the adjacent layers are further linked together by the hydrogen bondings to form a highly opened 3D framework. The distinct structural features of two hybrids suggest that the charge of the Keggin anions should play a key role in the process of assembly. Additionally, the electrochemical properties of compounds 1 and 2 have been investigated, and the results indicated that 1 and 2 have good electrocatalytic activities towards reduction of nitrite and oxidation of ascorbic acid.

  8. Two hybrid compounds constructed from Ni-tris(imidazolyl) complexes and Keggin clusters: Syntheses, structures and electrochemical properties

    NASA Astrophysics Data System (ADS)

    Zhang, Zhuanfang; Sun, Xiaojun; Ma, Huiyuan; Pang, Haijun; Li, Shaobin; Zhao, Chunyan

    2016-07-01

    By introducing different polyoxotungstates into the Ni-tib (tib = 1, 3, 5-tris (1-imidazolyl)benzene) system, two new polyoxometalate-based inorganic-organic hybrids with distinct architectures, [Ni(Htib)4][PW12O40]2 (1) and [Nitib]2(H2O)4](GeW12O40)·2H2O (2) have been synthesized under the same hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (PXRD) patterns and thermogravimetic (TG) analyses. Structural analyses show that compound 1 is a dimer, in which two neighboring mono-connected [PW12O40]3- (PW12) clusters are linked together by a [Ni(Htib)4] complex cation. In contrast to compound 1, compound 2 presents a 2D grid layer formed by bi-connected [GeW12O40]4- (GeW12) clusters and [Ni2(H2O)4(tib)2] complex cations, and the adjacent layers are further linked together by the hydrogen bondings to form a highly opened 3D framework. The distinct structural features of two hybrids suggest that the charge of the Keggin anions should play a key role in the process of assembly. Additionally, the electrochemical properties of compounds 1 and 2 have been investigated, and the results indicated that 1 and 2 have good electrocatalytic activities towards reduction of nitrite and oxidation of ascorbic acid.

  9. Polyoxometalate-directed assembly of water-soluble AgCl nanocubes.

    PubMed

    Neyman, Alevtina; Wang, Yifeng; Sharet, Shelly; Varsano, Neta; Botar, Bogdan; Kögerler, Paul; Meshi, Louisa; Weinstock, Ira A

    2012-02-21

    "Out-of-pocket" association of Ag(+) to the tetradentate defect site of mono-vacant Keggin and Wells-Dawson polyoxometalate (POM) cluster-anions is used to direct the formation of water-soluble AgCl nanocubes. PMID:22252035

  10. Uranium pyrophosphate / methylenediphosphonate polyoxometalate cage clusters

    SciTech Connect

    Ling, Jie; Qiu, Jie; Sigmon, Ginger E.; Ward, Matt; Szymanowski, Jennifer E.S.; Burns, Peter C

    2010-09-29

    Despite potential applications in advanced nuclear energy systems, nanoscale control of uranium materials is in its infancy. In its hexavalent state, U occurs as (UO{sub 2}){sup 2+} uranyl ions that are coordinated by various ligands to give square, pentagonal, or hexagonal bipyramids. Creation and design of nanostructured uranyl materials requires interruption of the tendency of uranyl bipyramids to share equatorial edges to form infinite sheets that occur in extended structures. Where a bidentate peroxide group bridges uranyl bipyramids, the configuration is inherently bent, fostering formation of cage clusters. Here the bent configurations of four- and five-membered rings of uranyl peroxide hexagonal bipyramids are bridged by pyrophosphate or methylenediphosphonate, creating eight chemically complex cage clusters with specific topologies. Chemical complexity in such clusters provides opportunities for the tuning of cage sizes, pore sizes, and properties such as aqueous solubility. Several of these are topological derivatives of simpler clusters that contain only uranyl bipyramids, whereas others exhibit new topologies.

  11. Two new helical compounds based on Keggin clusters and N-donor multidentate ligand: Syntheses, structures and properties

    SciTech Connect

    Zhou, Shi; Liu, Bo; Li, Xiao-Min; Shi, Tian; Chen, Ya-Guang

    2014-11-15

    Two isostructural polyoxometalate-based inorganic–organic hybrids with 1D helical chain, [CuH{sub 3}L{sub 2}(GeMo{sub 12}O{sub 40})]·2H{sub 2}O (1) and [CuH{sub 3}L{sub 2}(SiMo{sub 12}O{sub 40})]·2H{sub 2}O (2), where L=2,4,5-tri(4-pyridyl)-imidazole have been synthesized under hydrothermal conditions. It is the first time to use the L ligand to synthesis the Keggin-type polyoxometalate-based inorganic–organic hybrids. The two compounds possess the left- and right-handed helical chains and the POMs as pendants attach in the helical chains through Cu–O bonds. The two compounds have been characterized by elemental analyses, infrared (IR) spectroscopy, powder X-ray diffraction (PXRD), X-ray photoelectron spectra (XPS), thermogravimetric analysis (TGA) and photoluminescent spectroscopy. Moreover, nitrogen adsorption−desorption measurement, electrochemical and photocatalysis properties for degradation of methylene blue (MB) upon a UV irradiation of compound 1 have been examined. - Graphical abstract: Two new compounds, [CuH{sub 3}L{sub 2}(GeMo{sub 12}O{sub 40})]·2H{sub 2}O (1) and [CuH{sub 3}L{sub 2}(SiMo{sub 12}O{sub 40})]·2H{sub 2}O (2) have been synthesized under hydrothermal conditions. The two compounds possess the left- and right-handed helical chains. - Highlights: • The tridentate L ligand is first used to synthesis Keggin-type polyoxometalates. • The two compounds possess the left- and right-handed Cu–L helical chains. • Relationship between surface properties and photocatalytic activity was studied. • Two compounds exhibit photoluminescence of ligand-to-metal charge transfer.

  12. Design of polystyrene latex particles covered with polyoxometalate clusters via multiple covalent bonding.

    PubMed

    Chen, Xinyue; Li, Hui; Yin, Panchao; Liu, Tianbo

    2015-04-11

    Polyoxometalates (POMs) covalently functionalized with methyl methacrylate groups were applied as surfactants in the emulsion polymerization reaction of styrene. Due to the copolymerization of the methyl methacrylate groups and the styrene monomers, the polyoxometalate clusters are covalently grafted onto the surface of polystyrene latex nanoparticles. Such latex particles are fully covered with catalytic POM clusters and might serve as quasi-homogeneous catalysts. PMID:25743436

  13. Design of polystyrene latex particles covered with polyoxometalate clusters via multiple covalent bonding

    SciTech Connect

    Chen, Xinyue; Li, Hui; Yin, Panchao; Liu, Tianbo

    2015-02-27

    In this study, polyoxometalates (POMs) covalently functionalized with methyl methacrylate groups were applied as surfactants in the emulsion polymerization reaction of styrene. Due to the copolymerization of the methyl methacrylate groups and the styrene monomers, the polyoxometalate clusters are covalently grafted onto the surface of polystyrene latex nanoparticles. Finally, such latex particles are fully covered with catalytic POM clusters and might serve as quasi-homogeneous catalysts.

  14. Designed Assembly of Heterometallic Cluster Organic Frameworks Based on Anderson-Type Polyoxometalate Clusters.

    PubMed

    Li, Xin-Xiong; Wang, Yang-Xin; Wang, Rui-Hu; Cui, Cai-Yan; Tian, Chong-Bin; Yang, Guo-Yu

    2016-05-23

    A new approach to prepare heterometallic cluster organic frameworks has been developed. The method was employed to link Anderson-type polyoxometalate (POM) clusters and transition-metal clusters by using a designed rigid tris(alkoxo) ligand containing a pyridyl group to form a three-fold interpenetrated anionic diamondoid structure and a 2D anionic layer, respectively. This technique facilitates the integration of the unique inherent properties of Anderson-type POM clusters and cuprous iodide clusters into one cluster organic framework. PMID:27061042

  15. Heteroanionic Materials Based on Copper Clusters, Bisphosphonates, and Polyoxometalates: Magnetic Properties and Comparative Electrocatalytic NO(x) Reduction Studies.

    PubMed

    Oms, Olivier; Yang, Shu; Salomon, William; Marrot, Jérôme; Dolbecq, Anne; Rivière, Eric; Bonnefont, Antoine; Ruhlmann, Laurent; Mialane, Pierre

    2016-02-15

    Three compounds associating for the first time polyoxotungstates, bisphosphonates, and copper ions were structurally characterized. They consist in heteropolyanionic monodimensional materials where [Cu6(Ale)4(H2O)4](4-) (Ale = alendronate = [O3PC(O)(C3H6NH3)PO3](4-)) complexes alternate with polyoxometalate (POM) units. In Na12[{SiW9O34Cu3(Ale)(H2O)}{Cu6(Ale)4(H2O)4}]·50H2O (SiW9CuAle), the polyoxometalate core consists in a {SiW9Cu3} monomer capped by a pentacoordinated Ale ligand, while sandwich-type Keggin {(SbW9O33)2Cu3(H2O)(2.5)Cl(0.5)} and Dawson {(P2W15O56)2Cu4(H2O)2} complexes are found in Na8Li29[{(SbW9O33)2Cu3(H2O)(2.5)Cl(0.5)}2{Cu6(Ale)4(H2O)4}3]·163H2O (SbW9CuAle) and Na20[{(P2W15O56)2Cu4(H2O)2}{Cu6(Ale)4(H2O)4}]·50H2O (P2W15CuAle), respectively. A comparative magnetic study of the SiW9CuAle and SbW9CuAle compounds enabled full quantification of the Cu(II) superexchange interactions both for the POM and non-POM subunits, evidencing that, while the paramagnetic centers are anti-ferromagnetically coupled in the polyoxometalate units, both anti-ferromagnetic and ferromagnetic interactions coexist in the {Cu6(Ale)4(H2O)4} cluster. All the studied compounds present a good efficiency upon the reduction of HNO2 or NO2(-), the POM acting as a catalyst. However, it has been found that SbW9CuAle is inactive toward the reduction of nitrates, highlighting that both the {(SbW9O33)2Cu3} unit and the {Cu6(Ale)4(H2O)4} cluster do not act as electrocatalysts for this reaction. In contrast, SiW9CuAle and P2W15CuAle have shown a significant activity upon the reduction of NO3(-) and thus both at pH 1 and pH 5, evidencing that the chemical nature of the polyoxometalate is a crucial parameter even if it acts as precatalyst. Moreover, comparison of the activities of P2W15CuAle and [(P2W15O56)2Cu4(H2O)2](16-) evidenced that if the [Cu6(Ale)4(H2O)4](4-) cluster does not act as electrocatalyst, it acts as a cofactor, significantly enhancing the catalytic efficiency of the

  16. Ionic self-assembly affords mesoporous ionic networks by crosslinking linear polyviologens with polyoxometalate clusters.

    PubMed

    Chen, Guojian; Hou, Wei; Li, Jing; Wang, Xiaochen; Zhou, Yu; Wang, Jun

    2016-03-21

    Ionic-bonded mesoporous ionic networks were prepared by the ionic self-assembly of polyoxometalate (POM) clusters with linear cationic polyviologens in water. The POM-enriched PMIN-2(V) possesses a high surface area up to 120 m(2) g(-1), exhibiting superior non-noble metal heterogeneous catalytic performance in the ambient aerobic selective oxidation of 5-hydroxymethylfurfural. PMID:26898883

  17. Polyoxometalate Cluster-Incorporated Metal-Organic Framework Hierarchical Nanotubes.

    PubMed

    Xu, Xiaobin; Chen, Shuangming; Chen, Yifeng; Sun, Hongyu; Song, Li; He, Wei; Wang, Xun

    2016-06-01

    A simple method to prepare metal-organic framework (MOF) nanotubes is developed by employing polyoxometalates (POMs) as modulators. The local structure of the MOF nanotubes is investigated combining XANES and EXAFS studies. These nanotubes show both an excellent catalytic performance in the detoxification of sulfur compounds in O2 atmosphere and a remarkable cycling stability as the anode material for lithium-ion batteries. PMID:27101564

  18. The effect of counteranions on the molecular structures of phosphanegold(i) cluster cations formed by polyoxometalate (POM)-mediated clusterization.

    PubMed

    Nagashima, Eri; Yoshida, Takuya; Matsunaga, Satoshi; Nomiya, Kenji

    2016-09-14

    The effect of counteranions on the molecular structures of phosphanegold(i) cluster cations formed by polyoxometalate (POM)-mediated clusterization was investigated. A novel intercluster compound, [{(AuLCl)2(μ-OH)}2]3[α-PMo12O40]2·3EtOH (1-PMo12), was obtained as orange-yellow plate crystals in 12.0% yield from a 6 : 1 molar ratio reaction of the monomeric phosphanegold(i) carboxylato complex [Au(RS-pyrrld)(LCl)] (RS-Hpyrrld = RS-2-pyrrolidone-5-carboxylic acid; LCl = tris(4-chlorophenyl)phosphane) in CH2Cl2 with the free acid-form of Keggin polyoxometalate (POM), H3[α-PMo12O40]·14H2O. An EtOH/H2O (5 : 1, v/v) solvent mixture was used. The dimeric cation [{(AuLCl)2(μ-OH)}2](2+) in 1-PMo12 was in a parallel-edge arrangement that was formed by self-assembly through the inter-cationic aurophilic interactions of the μ-OH-bridged dinuclear phosphanegold(i) cation. The POM anion in 1-PMo12 was successfully exchanged with a smaller PF6(-) anion by the use of an anion-exchange resin. POM-free, colorless block crystals of [{(AuLCl)3(μ3-O)}2](PF6)2·4CH2Cl2 (2-PF6) were obtained by vapor diffusion in 14.1% yield. During the synthesis of 2-PF6, a compound with mixed counteranions (one POM and one PF6(-) anion), i.e. [{(AuLCl)4(μ4-O)}]2[α-PMo12O40]PF6 (3-PMo12PF6), was obtained in 66.4% yield. Both products were characterized by elemental analysis, TG/DTA, FT-IR, (31)P{(1)H} NMR, (1)H NMR, and X-ray crystallography. X-ray crystallography revealed that the countercation in 2-PF6 was the dimeric cation of the μ3-O-bridged tris{phosphanegold(i)} species, whereas that in 3-PMo12PF6 consisted of an unusual μ4-O-bridged tetragonal-pyramidal tetrakis{phosphanegold(i)} cation. Therefore, we concluded that the POM anion significantly contributed to the stabilization of these countercations (parallel-edged arrangement in 1-PMo12 and μ4-O-bridged tetragonal-pyramid in 3-PMo12PF6). Moreover, the previously reported yellow crystals of [{(AuLF)2(μ-OH)}2]3[PMo12O40]2·3

  19. Effects of isolobal heteroatoms in divanadium-substituted γ-Keggin-type polyoxometalates on (OV)2(μ-OH)2 diamond and (OV)2(μ-O) core structures and the transformation.

    PubMed

    Uehara, Kazuhiro; Taketsugu, Tatsuya; Yonehara, Kazuhiro; Mizuno, Noritaka

    2013-01-18

    Effects of isolobal heteroatoms in divanadium-substituted γ-Keggin-type polyoxometalates, (TBA)(4)[γ-XV(2)W(10)O(38)(μ-OH)(2)] 1(X) and (TBA)(4)[γ-XV(2)W(10)O(38)(μ-O)] 2(X) (where X = Ge or Si), on (OV)(2)(μ-OH)(2) and (OV)(2)(μ-O) core structures and transformations from 2(X) to 1(X) have been investigated. X-ray crystallography of 1(X) and 2(X) reveals that larger Ge (covalent radius 1.22 Å; covalent radius of Si 1.11 Å) induces (a) expansion of (OV)(2)(μ-OH)(2) and (OV)(2)(μ-O) cores, (b) expansion of lacunary sites, and (c) deep location of divanadium cores inside their lacunary sites. Density functional theory (DFT) calculations for anionic moieties of 1(X) and 2(X) reveal that energy levels of the highest occupied molecular orbital (HOMO)-1 in 1(Ge) and HOMO in 2(Ge) are lower than those in 1(Si) and 2(Si), respectively, because of smaller contribution of p(z) orbitals of oxygen atoms in 1(Ge) and 2(Ge), which would result from shorter V···O(-Ge) distances. Compound 2(Ge) reacts with water vapor to form (TBA)(4)[γ-GeV(2)W(10)O(38)(μ-OH)(2)] 1'(Ge) via a crystal-to-crystal transformation, and the water dissociation proceeds heterolytically. DFT calculations reveal that the reaction proceeds through (1) coordination of water on a coordinatively unsaturated site of vanadium in the lowest unoccupied molecular orbital (LUMO), followed by (2) proton transfer to the bridging oxo moiety. The order is different from that in 2(Si), which would result from the lower energy level of HOMO of 2(Ge) (i.e., lower nucleophilicity toward a proton of water) than that of 2(Si). PMID:23301537

  20. X-ray and Neutron Scattering Study of the Formation of Core–Shell-Type Polyoxometalates

    DOE PAGESBeta

    Yin, Panchao; Wu, Bin; Mamontov, Eugene; Daemen, Luke L.; Cheng, Yongqiang; Li, Tao; Seifert, Soenke; Hong, Kunlun; Bonnesen, Peter V.; Keum, Jong Kahk; et al

    2016-02-05

    A typical type of core-shell polyoxometalates can be obtained through the Keggin-type polyoxometalate-templated growth of a layer of spherical shell structure of {Mo72Fe30}. Small angle X-ray scattering is used to study the structural features and stability of the core-shell structures in aqueous solutions. Time-resolved small angle X-ray scattering is applied to monitor the synthetic reactions and a three-stage formation mechanism is proposed to describe the synthesis of the core-shell polyoxometalates based on the monitoring results. Quasi-elastic and inelastic neutron scattering are used to probe the dynamics of water molecules in the core-shell structures and two different types of water molecules,more » the confined and structured water, are observed. These water molecules play an important role in bridging core and shell structures and stabilizing the cluster structures. A typical type of core shell polyoxometalates can be obtained through the Keggin-type polyoxometalate-templated growth of a layer of spherical shell structure of {Mo72Fe30}. Small-angle X-ray scattering is used to study the structural features and stability of the core shell structures in aqueous solutions. Time-resolved small-angle X-ray scattering is applied to monitor the synthetic reactions, and a three-stage formation mechanism is proposed to describe the synthesis of the core shell polyoxometalates based on the monitoring results. New protocols have been developed by fitting the X-ray data with custom physical models, which provide more convincing, objective, and completed data interpretation. Quasi-elastic and inelastic neutron scattering are used to probe the dynamics of water molecules in the core shell structures, and two different types of water molecules, the confined and structured water, are observed. These water molecules play an important role in bridging core and shell structures and stabilizing the cluster structures.« less

  1. Crystallographic Studies on the Mechanisms of the Cluster Formation and the Higher Order Structure Evolution of Mixed-valence Polyoxometalates

    NASA Astrophysics Data System (ADS)

    Ozeki, Tomoji

    The advantages of the use of synchrotron radiation for single crystal X-ray diffraction experiments were exploited to obtain a deeper understanding of the chemistry of polyoxometalates through structural investigations. The pH dependence of the structures of {Mo154-x} mixed-valence oxomolybdate clusters were investigated by analyzing the structures of systematically prepared compounds containing wheel-shaped mixed-valence polyoxometalates with 138, 142, 148, 150, or 152 molybdenum atoms. Direct correlation was observed between the nuclearity of the clusters with the pH of the mother liquor. On the other hand, the geometries of extended structures do not show apparent correlation with the pH. They turned out to be determined by the structures of the constituent polyoxometalate. The pH of the mother liquor exerts influence on the extended structure through the structures of the constituent clusters. Such systematic preparation—structure determination study was enabled by the use of synchrotron radiation.

  2. 2D-network of inorganic-organic hybrid material built on Keggin type polyoxometallate and amino acid: [L-C{sub 2}H{sub 6}NO{sub 2}]{sub 3}[(PO{sub 4})Mo{sub 12}O{sub 36}].5H{sub 2}O

    SciTech Connect

    Alizadeh, M.H. Mirzaei, M.; Razavi, H.

    2008-03-04

    A new inorganic-organic hybrid material based on polyoxometallate, [L-C{sub 2}H{sub 6}NO{sub 2}]{sub 3}[(PO{sub 4})Mo{sub 12}O{sub 36}].5H{sub 2}O, has been successfully synthesized and characterized by single-crystal X-ray analysis, elemental analysis, infrared and ultraviolet spectroscopy, proton nuclear magnetic resonance and differential thermal analysis techniques. The title compound crystallizes in the monoclinic space group, P2{sub 1}/c{sub ,} with a = 12.4938 (8) A, b = 19.9326 (12) A, c = 17.9270 (11) A, {beta} = 102.129 (1){sup o}, V = 4364.8 (5) A{sup 3}, Z = 4 and R{sub 1}(wR{sub 2}) = 0.0513, 0.0877. The most remarkable structural feature of this hybrid can be described as two-dimensional inorganic infinite plane-like (2D/{infinity} [(PO{sub 4})Mo{sub 12}O{sub 36}]{sup 3-}) which forming via weak Van der Waals interactions along the z axis. The characteristic band of the Keggin anion [(PO{sub 4})Mo{sub 12}O{sub 36}]{sup 3-} appears at 210 nm in the UV spectrum. Thermal analysis indicates that the Keggin anion skeleton begins to decompose at 520 deg. C.

  3. Time-resolved assembly of cluster-in-cluster {Ag₁₂}-in-{W₇₆} polyoxometalates under supramolecular control.

    PubMed

    Zhan, Caihong; Cameron, Jamie M; Gao, Jing; Purcell, Jamie W; Long, De-Liang; Cronin, Leroy

    2014-09-22

    We report the time-resolved supramolecular assembly of a series of nanoscale polyoxometalate clusters (from the same one-pot reaction) of the form: [H(10+m)Ag18Cl(Te3W38O134)2]n, where n=1 and m=0 for compound 1 (after 4 days), n=2 and m=3 for compound 2 (after 10 days), and n=∞ and m=5 for compound 3 (after 14 days). The reaction is based upon the self-organization of two {Te3W38} units around a single chloride template and the formation of a {Ag12} cluster, giving a {Ag12}-in-{W76} cluster-in-cluster in compound 1, which further aggregates to cluster compounds 2 and 3 by supramolecular Ag-POM interactions. The proposed mechanism for the formation of the clusters has been studied by ESI-MS. Further, control experiments demonstrate the crucial role that TeO3(2-), Cl(-), and Ag(+) play in the self-assembly of compounds 1-3. PMID:25087861

  4. Sequential Synthesis of 3d-3d'-4f Heterometallic Heptanuclear Clusters in between Lacunary Polyoxometalates.

    PubMed

    Sato, Rinta; Suzuki, Kosuke; Minato, Takuo; Yamaguchi, Kazuya; Mizuno, Noritaka

    2016-03-01

    In this work, we have successfully created several unprecedented discrete 3d-3d'-4f heterotrimetallic clusters in between lacunary polyoxometalates (POMs). By the three-step sequential introduction of metal cations into a trivacant lacunary POM TBA4H6[A-α-SiW9O34] (TBA = tetra-n-butylammonium) in organic media, five kinds of sandwich-type POMs with double-diamond-shaped 3d-3d'-4f heptanuclear clusters (IIIFeM4Ln2, TBAnHm[FeM4{Ln(L)2}2O2(A-α-SiW9O34)2], M = Mn(3+), Cu(2+); Ln = Gd(3+), Dy(3+), Lu(3+); L = acac (acetylacetonate), hfac (hexafluoroacetylacetonate)) were successfully synthesized for the first time. By introduction of two [Ln(L)2](+) units on the ends of pentanuclear clusters [FeMn4O18(OH)2](23-) and [FeCu4O18(OH)2](27-), the magnetic interactions between Mn(3+)-Mn(3+) and Cu(2+)-Cu(2+) could be modulated. Among a series of the heterometallic heptanuclear compounds, IIIFeMn4Lu2 exhibited the slow magnetic relaxation characteristic for a single-molecule magnet under the zero applied magnetic fields. PMID:26914662

  5. Development of Dodecaniobate Keggin Chain Materials as Alternative Sorbents for SR and Actinide Removal from High-Level Nuclear Waste Solutions

    SciTech Connect

    Nyman, May; Bonhomme, Francois

    2004-03-28

    The current baseline sorbent (monosodium titanate) for Sr and actinide removal from Savannah River Site's high level wastes has excellent adsorption capabilities for Sr but poor performance for the actinides. We are currently investigating the development of alternative materials that sorb radionuclides based on chemical affinity and/or size selectivity. The polyoxometalates, negatively-charged metal oxo clusters, have known metal binding properties and are of interest for radionuclide sequestration. We have developed a class of Keggin-ion based materials, where the Keggin ions are linked in 1- dimensional chains separated by hydrated, charge-balancing cations. These Nb-based materials are stable in the highly basic nuclear waste solutions and show good selectivity for Sr and Pu. Synthesis, characterization and structure of these materials in their native forms and Sr-exchanged forms will be presented.

  6. Design and fabrication of memory devices based on nanoscale polyoxometalate clusters

    NASA Astrophysics Data System (ADS)

    Busche, Christoph; Vilà-Nadal, Laia; Yan, Jun; Miras, Haralampos N.; Long, De-Liang; Georgiev, Vihar P.; Asenov, Asen; Pedersen, Rasmus H.; Gadegaard, Nikolaj; Mirza, Muhammad M.; Paul, Douglas J.; Poblet, Josep M.; Cronin, Leroy

    2014-11-01

    Flash memory devices--that is, non-volatile computer storage media that can be electrically erased and reprogrammed--are vital for portable electronics, but the scaling down of metal-oxide-semiconductor (MOS) flash memory to sizes of below ten nanometres per data cell presents challenges. Molecules have been proposed to replace MOS flash memory, but they suffer from low electrical conductivity, high resistance, low device yield, and finite thermal stability, limiting their integration into current MOS technologies. Although great advances have been made in the pursuit of molecule-based flash memory, there are a number of significant barriers to the realization of devices using conventional MOS technologies. Here we show that core-shell polyoxometalate (POM) molecules can act as candidate storage nodes for MOS flash memory. Realistic, industry-standard device simulations validate our approach at the nanometre scale, where the device performance is determined mainly by the number of molecules in the storage media and not by their position. To exploit the nature of the core-shell POM clusters, we show, at both the molecular and device level, that embedding [(Se(IV)O3)2]4- as an oxidizable dopant in the cluster core allows the oxidation of the molecule to a [Se(V)2O6]2- moiety containing a {Se(V)-Se(V)} bond (where curly brackets indicate a moiety, not a molecule) and reveals a new 5+ oxidation state for selenium. This new oxidation state can be observed at the device level, resulting in a new type of memory, which we call `write-once-erase'. Taken together, these results show that POMs have the potential to be used as a realistic nanoscale flash memory. Also, the configuration of the doped POM core may lead to new types of electrical behaviour. This work suggests a route to the practical integration of configurable molecules in MOS technologies as the lithographic scales approach the molecular limit.

  7. Gel-assisted crystallization of [Ir4(IMe)7(CO)H10](2+) and [Ir4(IMe)8H9](3+) clusters derived from catalytic glycerol dehydrogenation.

    PubMed

    Sharninghausen, Liam S; Mercado, Brandon Q; Crabtree, Robert H; Balcells, David; Campos, Jesús

    2015-11-14

    The two title clusters were formed during iridium-catalyzed glycerol dehydrogenation and display a remarkably high NHC content. They were crystallized in either agarose or polyethylene oxide gel matrices, while more conventional crystallization techniques proved unsuccessful. Cluster [Ir4(IMe)8H9](3+), with a net charge of +3, was only crystallizable with a polyoxometalate Keggin trianion. The crystal packing of this intercluster compound is discussed. Computational studies position the iridium hydrides and provide insights into the bonding. PMID:26435314

  8. Nanoscale control of polyoxometalate assembly: a {Mn8W4} cluster within a {W36Si4Mn10} cluster showing a new type of isomerism.

    PubMed

    Winter, Ross S; Yan, Jun; Busche, Christoph; Mathieson, Jennifer S; Prescimone, Alessandro; Brechin, Euan K; Long, De-Liang; Cronin, Leroy

    2013-02-25

    Two near isomeric clusters containing a novel {Mn(8)W(4)} Keggin cluster within a [W(36)Mn(10)Si(4)O(136)(OH)(4)(H(2)O)8](24-) cluster are reported: K(10)Li(14)[W(36)Si(4)O(136)Mn(II)(10)(OH)(4)(H(2)O)(8)] (1) and K(10)Li1(3.5)Mn(0.25)[W(36)Si(4)O(136)Mn(II)(10)(OH)(4)(H(2)O)(8) ] (1'). Bulk characterization of the clusters has been carried out by single crystal X-ray structure analysis, ICP-MS, TGA, ESI-MS, CV and SQUID-magnetometer analysis. X-ray analysis revealed that 1' has eight positions within the central Keggin core that were disordered W/Mn whereas 1 contained no such disorder. This subtle difference is due to a differences is how the two clusters assemble and recrystallize from the same mother liquor and represents a new type of isomerism. The rapid recrystallization process was captured via digital microscopy and this uncovered two "intermediate" types of crystal which formed temporarily and provided nucleation sites for the final clusters to assemble. The intermediates were investigated by single crystal X-ray analysis and revealed to be novel clusters K(4)Li(22)[W(36)Si(4)Mn(7)O(136)(H(2)O)(8)]·56H(2)O (2) and Mn(2)K(8)Li(14)[W(36)Si(4)Mn(7)O(136)(H(2)O)(8)]·45H(2)O (3). The intermediate clusters contained different yet related building blocks to the final clusters which allowed for the postulation of a mechanism of assembly. This demonstrates a rare example where the use X-ray crystallography directly facilitated understanding the means by which a POM assembled. PMID:23362186

  9. Cobalt Clusters with Cubane-Type Topologies Based on Trivacant Polyoxometalate Ligands.

    PubMed

    Duan, Yan; Clemente-Juan, Juan M; Giménez-Saiz, Carlos; Coronado, Eugenio

    2016-01-19

    Four novel cobalt-substituted polyoxometalates having cobalt cores exhibiting cubane or dicubane topologies have been synthesized and characterized by IR, elemental analysis, electrochemistry, UV-vis spectroscopy, X-ray single-crystal analysis, and magnetic studies. The tetracobalt(II)-substituted polyoxometalate [Co4(OH)3(H2O)6(PW9O34)](4-) (1) consists of a trilacunary [B-α-PW9O34](9-) unit which accommodates a cubane-like {Co(II)4O4} core. In the heptacobalt(II,III)-containing polyoxometalates [Co7(OH)6(H2O)6(PW9O34)2](9-) (2), [Co7(OH)6(H2O)4(PW9O34)2]n(9n-) (3), and [Co7(OH)6(H2O)6(P2W15O56)2](15-) (4), dicubane-like {Co(II)6Co(III)O8} cores are encapsulated between two heptadentate [B-α-PW9O34](9-) (in 2 and 3) or [α-P2W15O56](15-) (in 4) ligands. While 1, 2, and 4 are discrete polyoxometalates, 3 exhibits a polymeric, chain-like structure that results from the condensation of polyoxoanions of type 2. The magnetic properties of these complexes have been fitted according to an anisotropic exchange model in the low-temperature regime and discussed on the basis of ferromagnetic interactions between Co(2+) ions with angles Co-L-Co (L = O, OH) close to orthogonality and weakly antiferromagnetic interactions between Co(2+) ions connected through central diamagnetic Co(3+) ion. Moreover, we will show the interest of the unique spin structures provided by these cubane and dicubane cobalt topologies in molecular spintronics (molecular spins addressed though an electric field) and quantum computing (spin qu-gates). PMID:26731303

  10. Synthesis and characterization of Lanthanide Aluminotungstates and Rhenium Polyoxometalates: Potential Application in Molecular Information Storage Devices

    NASA Astrophysics Data System (ADS)

    Bian, Fang

    2011-12-01

    Polyoxometalates (abbreviated as POMs) are metal-oxide clusters with frameworks built from group 5 or 6 transition metals linked by shared oxide ions. The Keggin structure is one of the most famous structural forms of POMs. Keggin anions have a general formula of [XM12O40 ]n-, where X is a p-block atom and M is a transition metal atom such as W or Mo. Upon removal of one MO4+ unit from the Keggin anion, the monovacant structure [XM11O39] n- is formed. Those POMs that have lost one or more metal center are called lacunary POMs, which are very nice building blocks for the fabrication of coordination polymers. My research focuses on two facets of POM chemistry: 1) Lanthanide chemistry of aluminum tungstate monovacant Keggin and 2) Rhenium chemistry of aluminum tungstate Keggin and Wells-Dawson POM alpha1 -P2W17O61. In lanthanide POM research area, we obtained the following results: 1) The starting material aluminum tungstate monovacant Keggin α-K 9AlW12O39 was synthesized. Its single crystal was firstly identified by multinuclear NMR and X-ray crystallography. Its redox properties on the nano-scale solid state were determined by Conducting Electrostatic Force Mode (EFM) probes. It is well known that for POMs, a number of varies redox states are normally stable and reversible. Thus we estimated that POMs can potentially be used in molecular information storage applications, which we refer to as "redox disk drives". 2) Eight lanthanide aluminum tungstate Keggin complexes were synthesized. In their molecular structures (identified by multinuclear NMR and X-ray crystallography), each α-AlW11O39 is connected by lanthanide (III) cations to form 1D and 2D networks. All AlW11O39 Keggin POMs are regularly aligning on a flat plane. Microscopic data also verified that there is layer-by-layer morphology in this series of compounds. Overall, we postulate that aluminum tungstate Keggin POMs are a very promising materials for making future information storage device because they

  11. Decisive Interactions between the Heterocyclic Moiety and the Cluster Observed in Polyoxometalate-Surfactant Hybrid Crystals

    PubMed Central

    Otobe, Saki; Fujioka, Natsumi; Hirano, Takuro; Ishikawa, Eri; Naruke, Haruo; Fujio, Katsuhiko; Ito, Takeru

    2015-01-01

    Inorganic-organic hybrid crystals were successfully obtained as single crystals by using polyoxotungstate anion and cationic dodecylpyridazinium (C12pda) and dodecylpyridinium (C12py) surfactants. The decatungstate (W10) anion was used as the inorganic component, and the crystal structures were compared. In the crystal comprising C12pda (C12pda-W10), the heterocyclic moiety directly interacted with W10, which contributed to a build-up of the crystal structure. On the other hand, the crystal consisting of C12py (C12py-W10) had similar crystal packing and molecular arrangement to those in the W10 crystal hybridized with other pyridinium surfactants. These results indicate the significance of the heterocyclic moiety of the surfactant to construct hybrid crystals with polyoxometalate anions. PMID:25894221

  12. TETRAALKYLPHOSPHONIUM POLYOXOMETALATES AS NOVEL IONIC LIQUIDS.

    SciTech Connect

    DIETZ,M.L.; RICKERT, P.G.; ANTONIO, M.R.; FIRESTONE, M.A.; WISHART, J.F.; SZREDER, T.

    2007-11-30

    The pairing of a Lindqvist or Keggin polyoxometalate (POM) anion with an appropriate tetraalkylphosphonium cation, [R{sub 3}R{prime}P]{sup +}, has been shown to yield an original family of ionic liquids (POM-ILs), among them salts liquid at or near ambient temperature. The physicochemical properties of several such 'inorganic liquids', in particular their thermal properties, suggests the possible application of these compounds as robust, thermally-stable solvents for liquid-liquid extraction. A preliminary evaluation of the potential of POM-ILs in this application is presented.

  13. Synthesis, structures and properties of new hybrid solids containing ruthenium complexes and polyoxometalates

    SciTech Connect

    Yan Bangbo; Hodsdon, Samantha A.; Li Yanfen; Carmichael, Christopher N.; Cao Yan; Pan Weiping

    2011-12-15

    Two new organic-inorganic hybrid solids containing Keggin ions and ruthenium complexes have been synthesized and characterized by FT-IR, UV-vis, luminescence, X-ray, and TG analysis. In KNa[Ru(bpy){sub 3}]{sub 2}[H{sub 2}W{sub 12}O{sub 40}]{center_dot}8H{sub 2}O (1), the [Ru(bpy){sub 3}]{sup 2+} (bpy=2,2 Prime -bipyridine) complex ions are located in between the infinite one-dimensional double-chains formed by adjacent Keggin anions [H{sub 2}W{sub 12}O{sub 40}]{sup 6-} linked through {l_brace}KO{sub 7}{r_brace} and {l_brace}NaO{sub 6}{r_brace} polyhedra, while in K{sub 6}[Ru(pzc){sub 3}]{sub 2}[SiW{sub 12}O{sub 40}] Bullet 12H{sub 2}O (2), the [Ru(pzc){sub 3}]{sup -} (pzc=pyrazine-2-carboxylate) complex anions are confined by layered networks of the [SiW{sub 12}O{sub 40}]{sup 4-} clusters connected by potassium ions. Both compounds exhibit three-dimensional frameworks through noncovalent interactions such as hydrogen bonds and anion Midline-Horizontal-Ellipsis {pi} interactions. Additionally, compound 1 shows strong luminescence at 604 nm in solid state at room temperature. - Graphical abstract: Two three-dimensional framework solids are constructed from polyoxoanions and ruthenium-organic complexes through noncovalent interactions. Highlights: Black-Right-Pointing-Triangle Ru complexes form hybrid solids with polyoxometalates. Black-Right-Pointing-Triangle Anion Midline-Horizontal-Ellipsis {pi} interaction between polyoxometalates and metal complexes was observed. Black-Right-Pointing-Triangle Noncovalent interactions play an important role in the assembly of solids. Black-Right-Pointing-Triangle The hybrid solid shows luminescence properties.

  14. Isolation and characterization of the [Ga2Al18O8(OH)36(H2O)12](8+) cluster: cationic variations on the Wells-Dawson topology.

    PubMed

    Fairley, M; Corum, K W; Johns, A; Unruh, D K; Basile, M; de Groot, J; Mason, S E; Forbes, T Z

    2015-08-11

    The structural chemistry of Group 13 polyoxometalates lags far behind related negatively charged transition metal species and limits the development of advanced materials. A novel heterometallic cluster [Ga2Al18O8(OH)36(H2O)12](8+) (Ga2Al18) has been isolated using a supramolecular approach and structurally characterized using single-crystal X-ray diffraction. Ga2Al18 represents the Wells-Dawson structure polycations and variations in the structural topology may be related to the initial stabilization of the Keggin isomer. DFT calculations on the related ε-Keggins (GaAl12 and Al13), Ga2Al18, and theoretical Al2Al18 clusters reveal similar features of electronic structure, suggesting additional heteroatom substitution in other isostructural clusters should be possible. PMID:26146343

  15. Cluster-controlled dimerisation in supramolecular ruthenium photosensitizer-polyoxometalate systems.

    PubMed

    Heussner, Kirsten; Peuntinger, Katrin; Rockstroh, Nils; Rau, Sven; Streb, Carsten

    2015-01-01

    A supramolecular reaction system is reported where a labile molecular metal oxide cluster enables the unprecedented dimerisation of ruthenium photosensitizers [Ru(L)2(tmbiH2)](2+) (L = 4,4'-di-tert-butyl-2,2'-bipyridine (1a) or 2,2'-bipyridine (1b); tmbiH2 = 5,5',6,6'-tetramethyl-2,2'-bibenzimidazole). In the presence of [Mo8O26](4-) clusters (2) the dimerisation is triggered by the in situ conversion of [Mo8O26](4-) to [Mo6O19](2-) which results in the release of hydroxide ions. Simultaneous deprotonation of the pH-sensitive tmbiH2-ligands starts the dimerisation, resulting in the formation of the dinuclear complex [(Ru(L)2)2(tmbi)](2+) (L = 4,4'-di-tert-butyl-2,2'-bipyridine (3) or 2,2'-bipyridine (4)). The dimerisation reaction can be suppressed when 2 is replaced by a stable polyoxomolybdate cluster, [Mo5O15(PhPO3)2](4-) (5) and the reaction between 1a and 5 leads to the formation of hydrogen-bonded supramolecular aggregates 6. The solution and solid-state interactions in these systems were investigated using a range of spectroscopic and crystallographic techniques and compounds 3, 4 and 6 were characterized using single-crystal XRD. PMID:25381808

  16. A silver-alkynyl cluster encapsulating a fluorescent polyoxometalate core: enhanced emission and fluorescence modulation.

    PubMed

    Song, Chao-Yu; Chai, Dong-Feng; Zhang, Rui-Ren; Liu, Hong; Qiu, Yun-Feng; Guo, Hua-Dong; Gao, Guang-Gang

    2015-03-01

    A new silver(I)-alkynyl cluster with a [Eu(W5O18)2](9-) polyoxoanionic core of [Ag42{Eu(W5O18)2}((t)BuC≡C)28Cl4] [OH]·H2O (1) has been designed and synthesized. The [Eu(W5O18)2](9-) polyoxoanion acts as a template to induce the formation of the surrounding 42-core Ag(I) cage. Due to the hydrophobic silver(I)-alkynyl shell, 1 features an unusual fluorescence enhancement as compared to the precursor of the [Eu(W5O18)2](9-) polyoxoanionic core. Interestingly, the silver ions in the shell silver(I)-alkynyl cage can only be reduced to silver atoms by irradiation with high energy UV light (2 kW). Upon high UV irradiation, fluorescence quenching of 1 has been observed. Moreover, the solution fluorescence of 1 can be modulated by addition of S(2-) ions into the system, which also leads to the fluorescence quenching phenomenon. The successful synthesis of 1 demonstrates a new route to the detection of high energy UV irradiation or S(2-) ions by elaborate design of fluorescence quenching of silver(I)-alkynyl clusters. PMID:25612008

  17. Mixed addenda polyoxometalate "solutions" for stationary energy storage.

    PubMed

    Pratt, Harry D; Anderson, Travis M

    2013-11-28

    A series of redox flow batteries utilizing mixed addenda (vanadium and tungsten), phosphorus-based polyoxometalates (A-α-PV3W9O40(6-), B-α-PV3W9O40(6-), and P2V3W15O62(9-)) were prepared and tested. Cyclic voltammetry and bulk electrolysis experiments on the Keggin compounds (A-α-PV3W9O40(6-) and B-α-PV3W9O40(6-)) established that the vanadium centers of these compounds could be used as the positive electrode (PV(IV)3W(VI)9O40(9-)/PV(V)3W(VI)9O40(6-)), and the tungsten centers could be used as the negative electrode (PV(IV)3W(VI)9O40(9-)/PV(IV)3W(V)3W(VI)6O40(12-)) since these electrochemical processes are separated by about 1 V. The results showed that A-α-PV3W9O40(6-) (where A indicates adjacent, corner-sharing vanadium atoms) had coulombic efficiencies (charge in divided by charge out) above 80%, while the coulombic efficiency of B-α-PV3W9O40(6-) (where B indicates adjacent edge-sharing vanadium atoms) fluctuated between 50% and 70% during cycling. The electrochemical yield, a measurement of the actual charge or discharge observed in comparison with the theoretical charge, was between 40% and 50% for A-α-PV3W9O40(6-), and (31)P NMR showed small amounts of PV2W10O40(5-) and PVW11O40(4-) formed with cycling. The electrochemical yield for B-α-PV3W9O40(6-) decreased from 90% to around 60% due to precipitation of the compound on the electrode, but there were no decomposition products detected in the solution by (31)P NMR, and infrared data on the electrode suggested that the cluster remained intact. Testing of P2V3W15O62(9-) (Wells-Dawson structure) suggested higher charge density clusters were not as suitable as the Keggin structures for a redox flow battery due to the poor stability and inaccessibility of the highly reduced materials. PMID:24042471

  18. A polyoxometalate flow battery

    SciTech Connect

    Pratt, Harry D.; Hudak, Nicholas S.; Fang, Xikui; Anderson, Travis M.

    2013-08-01

    A redox flow battery utilizing two, three-electron polyoxometalate redox couples (SiVV3WVI9O407–/SiVIV3WVI9O4010- and SiVIV3WVI9O4010-/SiVIV3WV3WVI6O4013-) was investigated for use in stationary storage in either aqueous or non-aqueous conditions. The aqueous battery had coulombic efficiencies greater than 95% with relatively low capacity fading over 100 cycles. Infrared studies showed there was no decomposition of the compound under these conditions. The non-aqueous analog had a higher operating voltage but at the expense of coulombic efficiency. The spontaneous formation of these clusters by self-assembly facilitates recovery of the battery after being subjected to reversed polarity. Polyoxometalates offer a new approach to stationary storage materials because they are capable of undergoing multi-electron reactions and are stable over a wide range of pH values and temperatures.

  19. Molecule-Based Water-Oxidation Catalysts (WOCs): Cluster-Size-Dependent Dye-Sensitized Polyoxometalates for Visible-Light-Driven O2 Evolution

    PubMed Central

    Gao, Junkuo; Cao, Shaowen; Tay, Qiuling; Liu, Yi; Yu, Lingmin; Ye, Kaiqi; Mun, Peter Choon Sze; Li, Yongxin; Rakesh, Ganguly; Loo, Say Chye Joachim; Chen, Zhong; Zhao, Yang; Xue, Can; Zhang, Qichun

    2013-01-01

    From atomic level to understand the cluster-size-dependant behavior of dye-sensitized photocatalysts is very important and helpful to design new photocatalytic materials. Although the relationship between the photocatalytic behaviors and particles' size/shape has been widely investigated by theoretical scientists, the experimental evidences are much less. In this manuscript, we successfully synthesized three new ruthenium dye-sensitized polyoxometalates (POM-n, n relate to different size clusters) with different-sized POM clusters. Under visible-light illumination, all three complexes show the stable O2 evolution with the efficient order POM-3 > POM-2 > POM-1. This cluster-size-dependent catalytic behavior could be explained by the different numbers of M = Ot (terminal oxygen) bonds in each individual cluster because it is well-known that Mo = Ot groups are the catalytically active sites for photooxidation reaction. The proposed mechanism of water oxidation for the dye-sensitized POMs is radical reaction process. This research could open up new perspectives for developing new POM-based WOCs. PMID:23676701

  20. Assembly of Cu/Ag-quinoxaline-polyoxotungstate hybrids: Influence of Keggin and Wells-Dawson polyanions on the structure

    NASA Astrophysics Data System (ADS)

    Chi, Ying-Nan; Cui, Feng-Yun; Lin, Zheng-Guo; Xu, Yan; Ma, Xiao-Yu; Shen, Pan-Pan; Huang, Kun-Lin; Hu, Chang-Wen

    2013-03-01

    In order to investigate the influence of Keggin and Wells-Dawson polyoxometalates on the resultant structure, four new organic-inorganic hybrid compounds [Cu4(qx)5(SiW12O40)] (1), [Cu6(qx)6(P2W18O62)(H2O)1.5]·4.5H2O (2), [Ag4(qx)4(SiW12O40)(H2O)]·H2O (3), [Ag6(qx)6(P2W18O62)]·8H2O (4) (qx=quinoxaline) were synthesized and structurally characterized by single-crystal X-ray diffraction. In 1, the 2D layers are linked by the SiW12O404- (SiW12) anions to construct a 3D framework. When the Wells-Dawson type P2W18O626- (P2W18) is used, 2 is prepared, in which the 1D helical chains are connected by P2W18 to form a 3D network. In 3, two kinds of 1D metal-organic chains are connected by SiW12 clusters to construct a 3D framework. In 4, there are also two kinds of 1D chains one kind of 1D chain combines with P2W18 by the AgO weak interaction and the other kind is just metal-organic chain. In addition, the electrochemistry properties of compounds 1-4 have been studied.

  1. New polyoxometalates containing hybrid polymers and their potential for nano-patterning.

    PubMed

    Kalyani, Vishwanath; Satyanarayana, V S V; Singh, Vikram; Pradeep, Chullikkattil P; Ghosh, Subrata; Sharma, Satinder K; Gonsalves, Kenneth E

    2015-01-26

    Two new polyoxometalate (POM)-based hybrid monomers (Bu4 N)5 (H)[P2 V3 W15 O59 {(OCH2 )3 CNHCO(CH3 )CCH2 }] (2) and (S(CH3 )2 C6 H4 OCOC(CH3 )=CH2 )6 [PV  2Mo10 O40 ] (5) were developed by grafting polymerizable organic units covalently or electrostatically onto Wells-Dawson and Keggin-type clusters and were characterized by analytical and spectroscopic techniques including ESI-MS and/or single-crystal X-ray diffraction analyses. Radical initiated polymerization of 2 and 5 with organic monomers (methacryloyloxy)phenyldimethylsulfonium triflate (MAPDST) and/or methylmethacrylate (MMA) yielded a new series of POM/polymer hybrids that were characterized by (1) H, (31) P NMR and IR spectroscopic techniques, gel-permeation chromatography as well as thermal analyses. Preliminary tests were conducted on these POM/polymer hybrids to evaluate their properties as photoresists using electron beam (E-beam)/extreme ultraviolet (EUV) lithographic techniques. It was observed that the POM/polymer hybrid of 2 with MAPDST exhibited improved sensitivity under EUV lithographic conditions in comparison to the MAPDST homopolymer resist possibly due to the efficient photon harvesting by the POM clusters from the EUV source. PMID:25431365

  2. Controlling the dispersion of supported polyoxometalate heterogeneous catalysts: impact of hybridization and the role of hydrophilicity-hydrophobicity balance and supramolecularity.

    PubMed

    Raj, Gijo; Swalus, Colas; Arendt, Eglantine; Eloy, Pierre; Devillers, Michel; Gaigneaux, Eric M

    2014-01-01

    The hybridization of polyoxometalates (POMs) through an organic-inorganic association offers several processing advantages in the design of heterogeneous catalysts. A clear understanding of the organization of these hybrid materials on solid surfaces is necessary to optimise their properties. Herein, we report for the first time the organization of Keggin phosphotungstic [PW12O40](3-) and Wells-Dawson (WD) phosphomolybdic [P2Mo18O62](6-) anions deposited on mica (hydrophilic), and highly oriented pyrolytic graphite (HOPG) (hydrophobic) surfaces. Next, the supramolecular organization of the organic-inorganic hybrid materials formed from the association of POM anions and dimethyldioctadecylammonium bromide (DODA) is investigated as a function of the hydrophilic or hydrophobic nature of the surfaces. The height of the Keggin-POM anions, measured with tapping mode (TM-AFM) is always in good agreement with the molecular dimension of symmetric Keggin-POM anions (ca. 1 nm). However, the asymmetric WD-POM anions form monolayer assemblies on the surfaces with the orientation of their long molecular axis (ca. 1.6 nm) depending on the hydrophilic or hydrophobic properties of the substrate. Namely, the long axis is parallel on mica, and perpendicular on HOPG. When hybridized with DODA, the organization of the hybrid material is dictated by the interaction of the alkyl side chains of DODA with the substrate surface. On HOPG, the DODA-POM hybrid forms small domains of epitaxially arranged straight nanorod structures with their orientation parallel to each other. Conversely, randomly distributed nanospheres are formed when the hybrid material is deposited on freshly cleaved mica. Finally, a UV-ozone treatment of the hybrid material allows one to obtain highly dispersed isolated POM entities on both hydrophilic and hydrophobic surfaces. The hybridization strategy to prevent the clustering of POMs on various supports would enable to develop highly dispersed POM-based heterogeneous

  3. Shrink wrapping redox-active crystals of polyoxometalate open frameworks with organic polymers via crystal induced polymerisation.

    PubMed

    Takashima, Yohei; Miras, Haralampos N; Glatzel, Stefan; Cronin, Leroy

    2016-06-14

    We report examples of crystal surface modification of polyoxometalate open frameworks whereby the use of pyrrole or aniline as monomers leads to the formation of the corresponding polymers via an oxidative polymerization process initiated by the redox active POM scaffolds. Guest-exchange experiments demonstrate that the polymers can finely tune the guest exchange rate and their structural integrity is retained after the surface modifications. In addition, the formation of polyoxometalate-based self-fabricating tubes by the dissolution of Keggin-based network crystals were also modulated by the polymers, allowing a new type of hybrid inorganic polymer with an organic coating to be fabricated. PMID:27203804

  4. Stabilization of Tetravalent 4f (Ce), 5d (Hf), or 5f (Th, U) Clusters by the [α-SiW9O34](10-) Polyoxometalate.

    PubMed

    Duval, Sylvain; Béghin, Sébastien; Falaise, Clément; Trivelli, Xavier; Rabu, Pierre; Loiseau, Thierry

    2015-09-01

    The reaction of Na10[α-SiW9O34] with tetravalent metallic cations such as 4f ((NH4)2Ce(NO3)6), 5d (HfCl4), or 5f (UCl4 and Th(NO3)4) in a pH 4.7 sodium acetate buffer solution leads to the formation of four sandwich-type polyoxometalates [Ce4(μ(3)-O)2(SiW9O34)2(CH3COO)2](10-) (1), [U4(μ(3)-O)2(SiW9O34)2(CH3COO)2](10-) (2), [Th3(μ(3)-O)(μ(2)-OH)3(SiW9O34)2](13-) (3), and [Hf3(μ(2)-OH)3(SiW9O34)2](11-) (4). All four compounds consist of a polynuclear cluster fragment stabilized by two [α-SiW9O34](10-) polyanions. Compounds 1 and 2 are isostructural with a tetranuclear core (Ce4, U4), while compound 3 presents a trinuclear Th3 core bearing a μ(3)-O-centered bridge. It is an unprecedented configuration in the case of the thorium(IV) cluster. Compound 4 also possesses a trinuclear Hf3 core but with the absence of the μ(3)-O bridge. The molecules have been characterized by single-crystal X-ray diffraction, (183)W and (29)Si nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) analysis. PMID:26301948

  5. Polyoxometalate flow battery

    DOEpatents

    Anderson, Travis M.; Pratt, Harry D.

    2016-03-15

    Flow batteries including an electrolyte of a polyoxometalate material are disclosed herein. In a general embodiment, the flow battery includes an electrochemical cell including an anode portion, a cathode portion and a separator disposed between the anode portion and the cathode portion. Each of the anode portion and the cathode portion comprises a polyoxometalate material. The flow battery further includes an anode electrode disposed in the anode portion and a cathode electrode disposed in the cathode portion.

  6. On the effect of ion pairing of Keggin type polyanions with quaternary ammonium cations on redox potentials in organic solvents.

    PubMed

    Chen, Bo; Neumann, Ronny

    2016-08-10

    The electrochemical properties of Keggin type polyoxometalates Qn[XW12O40] (X = P, Si, B; Q = n-tetraoctylammonium and n-trioctylmethylammonium) in organic solvents were investigated in order to understand the interrelation between the redox potentials, solvents and ion pairing. A logarithmic correlation between the dielectric constant of the solvent (ε ranged from 4.8 to 46.6) and the reduction potential of the [PW12O4](3-)/[PW12O4](4-) couple was found. This reduction potential increased significantly when the surface charge of the polyoxometalate went from 3- to 5-. The investigation of the ion pairing properties by diffusion NMR revealed the presence of intimate ion pairs in less polar solvents (e.g. dichloromethane) and less compact ion pairs in more polar solvents (e.g. DMSO). Using a V atom within the polyoxometalate an NMR experiment showed that a n-trioctylmethyl ammonium cation bonded to the polyoxometalate anion more intimately than a n-tetraoctyl ammonium cation. PMID:27465599

  7. A fluorophosphate-based inverse Keggin structure

    SciTech Connect

    Fielden, John; Quasdorf, Kyle; Cronin, Leroy; Kogerler, Paul

    2012-07-17

    An unusual PFO(3)(2-)-templated "inverse Keggin" polyanion, [Mo(12)O(46)(PF)(4)](4-), has been isolated from the degradation reaction of an {Mo(132)}-type Keplerate to [PMo(12)O(40)](3-) by [Cu(MeCN)(4)](PF(6)) in acetonitrile. (31)P-NMR studies suggest a structure-directing role for [Cu(MeCN)(4)](+) in the formation of the highly unusual all-inorganic inverse Keggin structure.

  8. Efficient visible-light photocatalytic activity by band alignment in mesoporous ternary polyoxometalate-Ag2S-CdS semiconductors

    NASA Astrophysics Data System (ADS)

    Kornarakis, I.; Lykakis, I. N.; Vordos, N.; Armatas, G. S.

    2014-07-01

    Porous multicomponent semiconductor materials show improved photocatalytic performance due to the large and accessible pore surface area and high charge separation efficiency. Here we report the synthesis of well-ordered porous polyoxometalate (POM)-Ag2S-CdS hybrid mesostructures featuring a controllable composition and high photocatalytic activity via a two-step hard-templating and topotactic ion-exchange chemical process. Ag2S compounds and polyoxometalate cluster anions with different reduction potentials, such as PW12O403-, SiW12O404- and PMo12O403-, were employed as electron acceptors in these ternary heterojunction photocatalysts. Characterization by small-angle X-ray scattering, X-ray diffraction, transmission electron microscopy and N2 physisorption measurements showed hexagonal arrays of POM-Ag2S-CdS hybrid nanorods with large internal BET surface areas and uniform mesopores. The Keggin structure of the incorporated POM clusters was also verified by elemental X-ray spectroscopy microanalysis, infrared and diffuse-reflectance ultraviolet-visible spectroscopy. These new porous materials were implemented as visible-light-driven photocatalysts, displaying exceptional high activity in aerobic oxidation of various para-substituted benzyl alcohols to the corresponding carbonyl compounds. Our experiments show that the spatial separation of photogenerated electrons and holes at CdS through the potential gradient along the CdS-Ag2S-POM interfaces is responsible for the increased photocatalytic activity.Porous multicomponent semiconductor materials show improved photocatalytic performance due to the large and accessible pore surface area and high charge separation efficiency. Here we report the synthesis of well-ordered porous polyoxometalate (POM)-Ag2S-CdS hybrid mesostructures featuring a controllable composition and high photocatalytic activity via a two-step hard-templating and topotactic ion-exchange chemical process. Ag2S compounds and polyoxometalate cluster

  9. Construct Polyoxometalate Frameworks through Covalent Bonds.

    PubMed

    Chen, Hong; Zhao, Huishuang; Yu, Zheng-Bao; Wang, Lei; Sun, Licheng; Sun, Junliang

    2015-09-01

    An emerging strategy for exploring the application of polyoxometalates (POMs) is to assemble POM clusters into open-framework materials, especially inorganic-organic hybrid three-dimensional (3D) open-framework materials, via the introduction of different organic linkers between the POM clusters. This strategy has yielded a few 3D crystalline POMs of which a typical class is the group of polyoxometalate metal-organic frameworks (POMMOFs). However, for reported POMMOFs, only coordination bonds are involved between the linkers and POM clusters, and it has not yet produced any covalently bonded polyoxometalate frameworks. Here, the concept of "covalently bonded POMs (CPOMs)" is developed. By using vanadoborates as an example, we showed that the 3D CPOMs can be obtained by a condensation reaction through the oxolation mechanism of polymer chemistry. In particular, suitable single crystals were harvested and characterized by single-crystal X-ray diffraction. This work forges a link among polymer science, POM chemistry, and open-framework materials by demonstrating that it is possible to use covalent bonds according to polymer chemistry principles to construct crystalline 3D open-framework POM materials. PMID:26286321

  10. A Stable Polyoxometalate-Pillared Metal-Organic Framework for Proton-Conducting and Colorimetric Biosensing.

    PubMed

    Zhou, En-Long; Qin, Chao; Huang, Peng; Wang, Xin-Long; Chen, Wei-Chao; Shao, Kui-Zhan; Su, Zhong-Min

    2015-08-10

    A stable metal-organic framework pillared by Keggin-type polyoxometalate, Cu6 (Trz)10 (H2O)4 [H2 SiW12 O40 ]⋅8 H2O (Trz=1,2,4-triazole) (1), has been prepared under hydrothermal condition. The 2D layer structure with a 22-member ring was formed by Cu(2+) ions, which are connected with each other via the Trz ligands on the ab plane. Thus, the 2D layers are further interconnected through Keggin polyoxoanions to generate a 3D porous network with a small 1D channel. Moreover, the presence of polyoxoanions make it exhibit selective adsorption of water and proton-conducting properties. Additionally it showed efficient intrinsic peroxidase-like activity, providing a simple and sensitive colorimetric assay to detect H2O2 . PMID:26179161

  11. A new hybrid constructed from Dawson-like polyoxometalates and dicopper coordination compounds containing a discrete tridecameric water cluster

    NASA Astrophysics Data System (ADS)

    Yang, Hongxun; Cao, Minna; Gao, Shuiying; Cao, Rong

    2014-01-01

    A new organic-inorganic hybrid polyoxotungstates, [Cu2Cl(H2O)3(phen)2]2[H3SbW18O60]·7H2O (phen = 1,10-phenanthroline, 1), has been synthesized and characterized by elemental analyses, FTIR, TG, UV-DRS, XRPD, magnetic property and X-ray single crystal diffraction. The structure analyses reveal that complex 1 based on Dawson-like polyoxoanions and dicopper coordination cations exhibits 3D supramolecular network via hydrogen bonding and π-π stacking containing a new discrete tridecameric water cluster. The magnetic property of 1 was also investigated between 2 and 300 K, indicating the existence of antiferromagnetic exchange interaction between the Cu(II) centres.

  12. Functionalization of cotton fiber by partial etherification and self-assembly of polyoxometalate encapsulated in Cu3(BTC)2 metal-organic framework.

    PubMed

    Lange, Laura E; Obendorf, S Kay

    2015-02-25

    A combination of a Keggin-type polyoxometalate (POM), [CuPW11O39](5-), with a Cu3(BTC)2 metal-organic framework (MOF-199/HKUST-1; where BTC is benzene-1,3,5-tricarboxylate), was successfully self-assembled on a cellulose substrate (cotton) with a room-temperature process. Cotton fibers were functionalized by partial etherification. Cu3(BTC)2 metal-organic framework and polyoxometalate encapsulated in Cu3(BTC)2 metal-organic framework were self-assembled on the carboxymethylate ion sites initiated with copper nitrate using ethanol and water as solvents. Octahedral crystals were observed on both MOF-cotton and POM-MOF-cotton; both contained copper while the POM-MOF-cotton also contained tungsten. Occupancy of POM in MOF cages was calculated to be about 13%. Moisture content remained at 3 to 4 wt % similar to that of untreated cotton. Reactivity to both hydrogen sulfide and methyl parathion was higher for POM-MOF-cotton due to the Keggin polyoxometalate and the extra-framework cations Cu(2+) ions compensating the charges of the encapsulated Keggins. The POM-MOF material was found to effectively remove 0.089 mg of methyl parathion per mg of MOF from a hexane solution while MOF-cotton removed only 0.054 mg of methyl parathion per mg of MOF. PMID:25647089

  13. Tetrairon and hexairon hydroxo/acetato clusters stabilized by multiple polyoxometalate scaffolds. Structures, magnetic properties, and chemistry of a dimer and a trimer.

    PubMed

    Botar, Bogdan; Kögerler, Paul; Hill, Craig L

    2007-06-25

    Investigation of the catalytically relevant gamma-diiron(III) Keggin complexes in aqueous acetate buffer leads to a dimeric C(2v)-symmetric polyanion, [{Fe(OH)(OAc)}(4)(gamma-SiW(10)O(36))(2)](12-) (3) and a trimeric C(2)-symmetric polyanion, [{Fe(6)(OH)(9)(H(2)O)(2)(OAc)(2)}(gamma-SiW(10)O(36))(3)](17-) (4). Polyanion 3 incorporates a hydroxo/acetato-bridged tetrairon(III) core, while 4 incorporates a trigonal prismatic hydroxo/acetato-bridged hexairon(III) core. The monomeric building unit of 3 and 4, {gamma-SiW(10)Fe(2)}, adopts the "out-of-pocket" structural motif (with two corner-sharing FeO(6) coordination polyhedra no longer connected to the internal SiO(4) tetrahedron of the Keggin unit) also observed in the {gamma-SiW(10)Fe(2)}(-)type structures isolated from nonbuffered aqueous solutions. Following hydrolysis, 3 is converted to 4 as confirmed by (29)Si NMR. Magnetic measurements establish that in both 3 and 4 all exchange interactions are antiferromagnetic. PMID:17518464

  14. Adsorption of volatile organic compounds in porous metal-organic frameworks functionalized by polyoxometalates

    SciTech Connect

    Ma Fengji; Liu Shuxia; Liang Dadong; Ren Guojian; Wei Feng; Chen Yaguang; Su Zhongmin

    2011-11-15

    The functionalization of porous metal-organic frameworks (Cu{sub 3}(BTC){sub 2}) was achieved by incorporating Keggin-type polyoxometalates (POMs), and further optimized via alkali metal ion-exchange. In addition to thermal gravimetric analysis, IR, single-crystal X-ray diffraction, and powder X-ray diffraction, the adsorption properties were characterized by N{sub 2} and volatile organic compounds (VOCs) adsorption measurements, including short-chain alcohols (C<4), cyclohexane, benzene, and toluene. The adsorption enthalpies estimated by the modified Clausius-Clapeyron equation provided insight into the impact of POMs and alkali metal cations on the adsorption of VOCs. The introduction of POMs not only improved the stability, but also brought the increase of adsorption capacity by strengthening the interaction with gas molecules. Furthermore, the exchanged alkali metal cations acted as active sites to interact with adsorbates and enhanced the adsorption of VOCs. - Graphical Abstract: The adsorption behavior of volatile organic compounds in porous metal-organic frameworks functionalized by polyoxometalates has been systematically evaluated. Highlights: > Functionalization of MOFs was achieved by incorporating Keggin-type POMs. > Introduction of POMs improved the thermal stability and adsorption capacity. > Alkali metal ion-exchange modified the inclusion state and also enhanced the adsorption. > Adsorption enthalpies were estimated to study the impact of POMs and alkali metal cations.

  15. Two types of tetranuclear phosphanegold(I) cations as dimers of dinuclear units, [{(Au{P(p-RPh)3})2(μ-OH)}2]2+ (R = Me, F), synthesized by polyoxometalate-mediated clusterization.

    PubMed

    Yoshida, Takuya; Matsunaga, Satoshi; Nomiya, Kenji

    2013-08-28

    Novel intercluster compounds [{(Au{P(p-RPh)3})2(μ-OH)}2]3[α-PM12O40]2·nEtOH (R = Me, M = W for 1; R = Me, M = Mo for 2; R = F, M = Mo for 3) were synthesized by the polyoxometalate (POM)-mediated clusterization of monomeric phosphanegold(I) complexes, and unequivocally characterized by elemental analysis, TG/DTA, FTIR, X-ray crystallography, and (1)H and (31)P{(1)H} NMR. In each cluster cation, two digold(I) units, {Au{P(p-RPh)3})2(μ-OH)}(+), dimerized to form the tetragold(I) cluster cation by interdimer aurophilic interactions, i.e., a dimer of dinuclear units, and these cations showed different forms of structural dimerization, i.e., a crossed-edge arrangement for 1 and 2 and a parallel-edge arrangement for 3, depending upon the substituent on the aryl group of triarylphosphanes. The dimerization of digold(I) cations was affected by not only the type of the POMs, but also the phosphane ligand of the monomeric phosphanegold(I) precursors. PMID:23817364

  16. A highly aluminum-doped β-isomer Keggin-type tungstoaluminate.

    PubMed

    Han, Zhangang; Zhang, Huixia; Yan, Jinshuang; Zhai, Xueliang

    2016-09-28

    A trialuminum-substituted β-isomer Keggin-type tungstoaluminate was synthesized and characterized, in which the pure metal-oxygen cluster [AlW8.5Al0.5{Al(OH2)}3(OH)3O34](6.5-) consists of three kinds of aluminum sites: the central Al(1), the doped Al(5), and the substituted Al(2) and Al(3) centers. PMID:27549221

  17. Highly Amino Acid Selective Hydrolysis of Myoglobin at Aspartate Residues as Promoted by Zirconium(IV)-Substituted Polyoxometalates.

    PubMed

    Ly, Hong Giang T; Absillis, Gregory; Janssens, Rik; Proost, Paul; Parac-Vogt, Tatjana N

    2015-06-15

    SDS-PAGE/Edman degradation and HPLC MS/MS showed that zirconium(IV)-substituted Lindqvist-, Keggin-, and Wells-Dawson-type polyoxometalates (POMs) selectively hydrolyze the protein myoglobin at Asp-X peptide bonds under mildly acidic and neutral conditions. This transformation is the first example of highly sequence selective protein hydrolysis by POMs, a novel class of protein-hydrolyzing agents. The selectivity is directed by Asp residues located on the surface of the protein and is further assisted by electrostatic interactions between the negatively charged POMs and positively charged surface patches in the vicinity of the cleavage site. PMID:25950869

  18. Hydrothermal synthesis and characterization of the tri-capped and mono-supported pseudo-Keggin-type tungstovanadophosphate: {l_brace}PW{sub 4}{sup VI}W{sub 5}{sup V}V{sub 3}{sup IV}O{sub 40}(V{sup IV}O){sub 3}[Cu(en){sub 2}]{r_brace}{sup 6-}

    SciTech Connect

    Liu Jian; Xu Jianing; Liu Yabing; Lu Yukun; Song Jiangfeng; Zhang Xiao; Cui Xiaobing; Xu Jiqing Wang Tiegang

    2007-12-15

    A novel polyoxometalate [Cu(phen){sub 2}]{sub 3}{l_brace}PW{sub 4}{sup VI}W{sub 5}{sup V}V{sub 3}{sup IV}O{sub 40}(V{sup IV}O){sub 3}[Cu(en){sub 2}]{r_brace}.4H{sub 2}O 1 (en=ethylenediamine, phen=1,10-phenanthroline) has been synthesized hydrothermally and characterized by elemental analysis, IR, XPS, TG, EPR and single-crystal X-ray diffraction analysis. The crystal structure analysis shows that compound 1 contains a novel highly reduced tri-capped and mono-supported pseudo-Keggin-type heteropolyanion, {l_brace}PW{sub 4}{sup VI}W{sub 5}{sup V}V{sub 3}{sup IV}O{sub 40}(V{sup IV}O){sub 3}[Cu(en){sub 2}]{r_brace}{sup 6-}, three [Cu(phen){sub 2}]{sup 2+} cations and four lattice water molecules. They are further linked to form three-dimensional supramolecular networks through extensive hydrogen bonding and {pi}-{pi} stacking interactions. Interestingly, the water dimer and terminal oxygen of the cluster polyanion constitute a beautiful supramolecular helix chain. The heteropolyanion is the first example of tri-capped and mono-supported pseudo-Keggin-type tungstovanadophosphate and the pH value is crucial for obtaining compound 1 in synthetic procedure. - Graphical abstract: A novel complex [Cu(phen){sub 2}]{sub 3}{l_brace}PW{sub 4}{sup VI}W{sub 5}{sup V}V{sub 3}{sup IV}O{sub 40}(V{sup IV}O){sub 3}[Cu(en){sub 2}]{r_brace}.4H{sub 2}O, the first example of tri-capped and mono-supported highly reduced pseudo-Keggin-type tungstovanadophosphate was synthesized under hydrothermal condition. And the heteropolyanions are linked by water dimer and cation [Cu(phen){sub 2}]{sup 2+} through the hydrogen bond forming a three-dimensional (3D) supramolecular network. Interestingly, the water dimer and terminal oxygen of the polyanion cluster constitute a beautiful supramolecular helix chain.

  19. Polyoxometalate-based Supramolecular Gel

    NASA Astrophysics Data System (ADS)

    He, Peilei; Xu, Biao; Liu, Huiling; He, Su; Saleem, Faisal; Wang, Xun

    2013-05-01

    Self-assemblyings of surfactant-encapsulated Wells-Dawson polyoxometalates (SEPs) nanobuilding blocks in butanone and esters yielded supramolecular gels showing thermo and photo responsive properties. The gels can be further polymerized if unsaturated esters were used and subsequently electrospinned into nanowires and non-woven mats. The as-prepared non-woven mats have a Young's modulus as high as 542.55 MPa. It is believed that this supramolecular gel is a good platform for polyoxometalates processing.

  20. Surface charge of polyoxometalates modulates polymerization of the scrapie prion protein

    PubMed Central

    Wille, Holger; Shanmugam, Maheswaran; Murugesu, Muralee; Ollesch, Julian; Stubbs, Gerald; Long, Jeffrey R.; Safar, Jiri G.; Prusiner, Stanley B.

    2009-01-01

    Prions are composed solely of an alternatively folded isoform of the prion protein (PrP), designated PrPSc. N-terminally truncated PrPSc, denoted PrP 27–30, retains infectivity and polymerizes into rods with the ultrastructural and tinctorial properties of amyloid. We report here that some polyoxometalates (POMs) favor polymerization of PrP 27-30 into prion rods, whereas other POMs promote assembly of the protein into 2D crystals. Antibodies reacting with epitopes in denatured PrP 27-30 also bound to 2D crystals treated with 3 M urea. These same antibodies did not bind to either native PrPSc or untreated 2D crystals. By using small, spherical POMs with Keggin-type structures, the central heteroatom was found to determine whether prion rods or 2D crystals were preferentially formed. An example of a Keggin-type POM with a phosphorous heteroatom is the phosphotungstate anion (PTA). Both PTA and a Keggin-type POM with a silicon heteratom have low-charge densities and favor formation of prion rods. In contrast, POMs with boron or hydrogen heteroatoms exhibiting higher negative charges encouraged 2D crystal formation. The 2D crystals of PrP 27-30 produced by selective precipitation with POMs were larger and more well ordered than those obtained by sucrose gradient centrifugation. Our findings argue that the negative charge of Keggin-type POMs determines the quaternary structure adopted by PrP 27-30. The mechanism by which POMs function in competing prion polymerization pathways—one favoring 2D crystals and the other, amyloid fibrils—remains to be established. PMID:19223590

  1. Charge and pressure-tuned surface patterning of surfactant-encapsulated polyoxometalate complexes at the air-water interface.

    PubMed

    Xu, Miao; Li, Haolong; Zhang, Liying; Wang, Yizhan; Yuan, Yuan; Zhang, Jianming; Wu, Lixin

    2012-10-16

    In this paper, four organic-inorganic hybrid complexes were prepared using a cationic surfactant dimethyldioctadecylammonium (DODA) to replace the counter cations of four Keggin-type polyoxometalate (POM) clusters with gradually increased negative charges, PW(12)O(40)(3-), SiW(12)O(40)(4-), BW(12)O(40)(5-), and CoW(12)O(40)(6-). The formed surfactant-encapsulated POM (SEP) complexes showed typical amphiphilic properties and can be spread onto the air-water interface to form Langmuir monolayers. The interfacial behavior of the SEP monolayer films was systemically studied by multiple in situ and ex situ characterization methods including Brewster angle microscopy (BAM), atomic force microscopy (AFM), reflection-absorption infrared (RAIR), and X-ray photoelectron spectroscopy (XPS). We found that the increasing alkyl chain density of SEPs leads to an enhanced stability and a higher collapse pressure of SEP Langmuir monolayers. Moreover, a second layer evolved as patterns from the initial monolayers of all the SEPs, when the surface pressures approached the collapse values. The rational combination of alkyl chain density and surface pressure can precisely control the size and the morphology of SEP patterns transforming from disk-like to leaf-like structures on a micrometer scale. The pattern formation was demonstrated to be driven by the self-optimized surface energy of SEP monolayers. This finding can direct a new strategy for the fabrication of POM-hybrid films with controllable patterns, which should be instructive for designing POM-based thin film devices. PMID:22991980

  2. Preparation of periodic mesoporous silica-included divacant Keggin units for the catalytic oxidation of styrene to synthesize styrene oxide

    NASA Astrophysics Data System (ADS)

    Yu, Xiaodan; Xu, Leilei; Yang, Xia; Guo, Yingna; Li, Kexin; Hu, Jianglei; Li, Wei; Ma, Fengyan; Guo, Yihang

    2008-05-01

    Periodic mesoporous composite catalysts, [( n-C 4H 9) 4N] 4[γ-SiW 10O 34(H 2O) 2]/SBA-15 (TBA-1*/SBA-15, where TBA-1* = [( n-C 4H 9) 4N] 4[γ-SiW 10O 34(H 2O) 2]), with TBA-1* loadings of 4.3-14.8% were prepared by simultaneous hydrolysis and co-condensation of the tetraethoxysilane (TEOS) in the presence of divacant Keggin-type polyoxometalate and triblock copolymer surfactant (P123) followed by hydrothermal treatment process. Structure integrity of the Keggin unit in as-prepared composites was studied by Fourier transform infrared spectroscopy (FT-IR), Raman scattering spectra, and 29Si magic-angle spinning (MAS) NMR. Periodic mesoporous structure of the composites was evaluated by low-angle X-ray powder diffraction (LXRD) patterns, nitrogen porosimetry, and transmission electron microscope (TEM) measurements. As-prepared TBA-1*/SBA-15 was used as an heterogeneous oxidation catalyst for the styrene epoxidation reaction to synthesize styrene oxide in the presence of dilute H 2O 2 (30%), and influences of solvent, molar ratio of styrene to H 2O 2, TBA-1* loading on the styrene conversion, styrene oxide yield and selectivity were considered.

  3. Classical Keggin Intercalated into Layered Double Hydroxides: Facile Preparation and Catalytic Efficiency in Knoevenagel Condensation Reactions.

    PubMed

    Jia, Yueqing; Fang, Yanjun; Zhang, Yingkui; Miras, Haralampos N; Song, Yu-Fei

    2015-10-12

    The family of polyoxometalate (POM) intercalated layered double hydroxide (LDH) composite materials has shown great promise for the design of functional materials with numerous applications. It is known that intercalation of the classical Keggin polyoxometalate (POM) of [PW12 O40 ](3-) (PW12 ) into layered double hydroxides (LDHs) is very unlikely to take place by conventional ion exchange methods due to spatial and geometrical restrictions. In this paper, such an intercalated compound of Mg0.73 Al0.22 (OH)2 [PW12 O40 ]0.04 ⋅0.98 H2 O (Mg3 Al-PW12 ) has been successfully obtained by applying a spontaneous flocculation method. The Mg3 Al-PW12 has been fully characterized by using a wide range of methods (XRD, SEM, TEM, XPS, EDX, XPS, FT-IR, NMR, BET). XRD patterns of Mg3 Al-PW12 exhibit no impurity phase usually observed next to the (003) diffraction peak. Subsequent application of the Mg3 Al-PW12 as catalyst in Knoevenagel condensation reactions of various aldehydes and ketones with Z-CH2 -Z' type substrates (ethyl cyanoacetate and malononitrile) at 60 °C in mixed solvents (V2-propanol :Vwater =2:1) demonstrated highly efficient catalytic activity. The synergistic effect between the acidic and basic sites of the Mg3 Al-PW12 composite proved to be crucial for the efficiency of the condensation reactions. Additionally, the Mg3 Al-PW12 -catalyzed Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate demonstrated the highest turnover number (TON) of 47 980 reported so far for this reaction. PMID:26337902

  4. Synthesis of polyoxometalate-loaded epoxy composites

    DOEpatents

    Anderson, Benjamin J

    2014-10-07

    The synthesis of a polyoxometalate-loaded epoxy uses a one-step cure by applying an external stimulus to release the acid from the polyoxometalate and thereby catalyze the cure reaction of the epoxy resin. Such polyoxometalate-loaded epoxy composites afford the cured epoxy unique properties imparted by the intrinsic properties of the polyoxometalate. For example, polyoxometalate-loaded epoxy composites can be used as corrosion resistant epoxy coatings, for encapsulation of electronics with improved dielectric properties, and for structural applications with improved mechanical properties.

  5. Polyoxometalate immobilization in Cu{sup I}/Ag-pz porous coordination polymers: The influences of them on the structural properties of frameworks

    SciTech Connect

    Zhu, Min; Peng, Jun; Pang, Hai-Jun; Zhang, Peng-Peng; Chen, Yuan; Wang, Dan-Dan; Liu, Ming-Guan; Wang, Yong-Hui

    2011-05-15

    Three new high dimensional Cu{sup I}/Ag-pz porous coordination polymers (PCPs) with different Keggin polyoxometalate templates have been hydrothermally synthesized: [Cu{sup I}{sub 5}(pz){sub 6}Cl][HPMo{sup VI}{sub 10}Mo{sup V}{sub 2}O{sub 40}] (1) [Ag{sub 5}(pz){sub 7}(BW{sub 12}O{sub 40})] (2) and [Cu{sup I}{sub 5}(pz){sub 6}H(H{sub 2}W{sub 12}O{sub 40})].4H{sub 2}O (3) (pz=pyrazine). The choice of the particular Keggin POM templates is shown to influence the structural properties of the Cu/Ag PCPs. Compound 1 shows a Cl-bridged Cu-pz-Cl double layer, between which two kinds of [HPMo{sup VI}{sub 10}Mo{sup V}{sub 2}O{sub 40}]{sup 4-}(PMo{sub 12}) polyanions are located. Compound 2 presents a 3D Ag-pz framework with parallelogram-like voids, into which BW{sub 12}O{sub 40}{sup 5-} (BW{sub 12}) Keggin ions are incorporated. Compound 3 contains a Cu-pz cationic layer framework, between which are located [H(H{sub 2}W{sub 12}O{sub 40})]{sup 5-} (W{sub 12}) Keggin ions. Primary photocatalytic experiment indicates that compound 1 presents excellent photocatalytic activity. The photoluminescence properties and electrochemistry properties of the compounds are also discussed. -- Graphical abstract: The choice of the particular Keggin template is shown to influence the structural properties of the Cu/Ag PCPs. Their photocatalytic activities have been studied. Display Omitted highlights: > In this paper, three Keggin POM-templated metal-pyrazine frameworks are reported. > The choice of template can influence the structural properties of the frameworks. > Further, compound 1 exhibits excellent photocatalytic activity.

  6. Correlating Acid Properties and Catalytic Function: A First-Principles Analysis of Alcohol Dehydration Pathways on Polyoxometalates

    SciTech Connect

    Janik, Michael J.; Macht, Josef; Iglesia, Enrique; Neurock, Matthew

    2009-02-05

    Density functional theory calculations and reactivity data were used to examine the mechanism of alcohol dehydration on Keggin-type polyoxometalate (POM) catalysts and the influence of the POM composition and the degree of substitution of the alcohol on kinetically relevant elimination steps. Dehydration was found to proceed through E1 pathways in which the alcohol CsO bond is cleaved heterolytically via a carbeniumion transition state. Dehydration rates were found to depend on the elimination rate constant and the equilibrium constant for the formation of unreactive alcohol dimers. E2-type elimination transition states, involving concerted CsH and CsO bond cleavage, were not found. The extent of substitution at the R-carbon on the alcohol was found to lead to marked effects on elimination barriers, because substitution increases the proton affinity of the alcohol and the stability of the carbenium-ion transition state. Changes in the central and addenda atoms of the POM cluster and the presence of n-donors, a support, vicinal POM clusters, or charge-compensating cations were found to lead to changes in the deprotonation energy (DPE) of the POM cluster, activation barriers to dehydration, and the stability of the unreactive dimer. These effects are all captured in a general linear relation between activation barriers and deprotonation energy, a rigorous measure of acid strength. The explicit dependence of the E1 activation barrier on the acid deprotonation energy is much weaker than that on reactant proton affinity. This results from the more effective compensation between the acid deprotonation energy and the interaction energy between the cationic hydrocarbon fragment and the anionic POM cluster at the transition state. The direct interactions between the POM protons and the support, other POM clusters, n-donors, base probe molecules, and charge-compensating cations increased the negative charge of the oxide shell of the W12O40 conjugate base, which increased the

  7. An unusual 3D interdigitated architecture assembled from Keggin polyoxometalates and dinuclear copper(II) complexes

    SciTech Connect

    Pang, Haijun; Yang, Ming; Kang, Lu; Ma, Huiyuan; Liu, Bo; Li, Shaobin; Liu, Heng

    2013-02-15

    A novel organic-inorganic hybrid compound, [Cu{sub 2}(bipy){sub 3}({mu}{sub 1}-H{sub 2}O){sub 2}({mu}{sub 2}-H{sub 2}O)({mu}{sub 2}-OH)(H{sub 2}BW{sub 12}O{sub 40})]{center_dot}4 H{sub 2}O (1) (bipy=4,4 Prime -bipy), has been synthesized in hydrothermal condition and characterized by elemental analysis, IR spectrum, TG analysis and single-crystal X-ray diffraction. Compound 1 possesses poly-pendant layered motifs composed of 12-tungstoborates and dinuclear copper(II) complexes, in which the mono-coordinated bipy molecules are orderly appended to both sides of the layer, respectively. Adjacent layers mutually engage in a zipper-like pattern to result in a novel 3D interdigitated architecture. The variable-temperature magnetic susceptibility of 1 showed that there existed weak antiferromagnetic interaction in 1. Toward the reduction of hydrogen peroxide, 1 has good electrocatalytic activity and remarkable stability. - A new compound has been obtained, which represents the first interdigitated architecture assembled by POMs and dinuclear copper(II) complexes. Highlights: Black-Right-Pointing-Pointer The first example of interdigitated architecture assembled by POMs and dinuclear copper(II) complexes is observed. Black-Right-Pointing-Pointer A zipper-like pattern is observed in the structure. Black-Right-Pointing-Pointer The IR, TG, XRPD, magnetism and electrochemical property of the title compound were studied.

  8. Polyoxometalate-based Supramolecular Gel

    PubMed Central

    He, Peilei; Xu, Biao; Liu, Huiling; He, Su; Saleem, Faisal; Wang, Xun

    2013-01-01

    Self-assemblyings of surfactant-encapsulated Wells-Dawson polyoxometalates (SEPs) nanobuilding blocks in butanone and esters yielded supramolecular gels showing thermo and photo responsive properties. The gels can be further polymerized if unsaturated esters were used and subsequently electrospinned into nanowires and non-woven mats. The as-prepared non-woven mats have a Young's modulus as high as 542.55 MPa. It is believed that this supramolecular gel is a good platform for polyoxometalates processing. PMID:23666013

  9. Visible-light-driven hydrogen production in a dye sensitized polyoxometalate system without noble metals

    NASA Astrophysics Data System (ADS)

    Liu, Xing; Li, Yuexiang; Peng, Shaoqin; Lai, Hua; Yi, Zhengji

    2016-05-01

    In this work, a noble-metal-free homogeneous system was constructed in one step with Keggin-type polyoxometalate (POM) SiW12O404- as a catalyst, Eosin Y as a photosensitizer, and triethanolamine (TEOA) as a sacrificial electron donor for water splitting to produce hydrogen under visible-light irradiation. A two-electron reduced heteropoly blue SiW12O406- is produced by photosensitization under visible-light irradiation. The effect of various component concentrations and POMs with different central atoms (PW12O403-, GeW12O404-, etc.) on hydrogen production was discussed. This simple system made of earth-abundant elements is expected to contribute toward the development of functional and efficient artificial photosynthetic system.

  10. Ionic liquid polyoxometalates as light emitting materials

    SciTech Connect

    Ortiz-acosta, Denisse; Del Sesto, Rico E; Scott, Brian; Bennett, Bryan L; Purdy, Geraldine M; Muenchausen, Ross E; Mc Kigney, Edward; Gilbertson, Robert

    2008-01-01

    The low melting point, negligible vapor pressure, good solubility, and thermal and chemical stability make ionic liquids useful materials for a wide variety of applications. Polyoxometalates are early transition metal oxygen clusters that can be synthesized in many different sizes and with a variety of heterometals. The most attractive feature of POMs is that their physical properties, in particular electrical, magnetic, and optical properties, can be easily modified following known procedures. It has been shown that POMs can exhibit cooperative properties, as superconductivity and energy transfer. POM ionic liquids can be obtained by selecting the appropliate cation. Different alkyl ammonium and alkyl phosphonium salts are being used to produce new POM ionic liquids together with organic or inorganic luminescent centers to design light emitting materials. Ammonium and phosphonium cations with activated, polymerizable groups are being used to further polymerize the ionic liquid into transparent, solid materials with high metal density.

  11. Systematic Studies on 3 d- and 4 f-Metal Containing Polyoxometalates Suitable for Organic Derivatization.

    PubMed

    Artetxe, Beñat

    2016-06-01

    Premium polyoxometalates! The organic functionalization of 3 d-metalsubstituted polyoxometalates and the synthesis of new metal-oxo clusters with accessible 3 d- and 4 f-metal centers suitable for organic derivatization are discussed in this thesis. A total number of 39 compounds were structurally characterized, and their luminescent and magnetic properties analyzed. The solution behavior was studied by NMR spectroscopy, mass spectrometry, and light-scattering techniques. PMID:27551662

  12. Robust Cluster Building Unit: Icosanuclear Heteropolyoxocopperate Templated by Carbonate.

    PubMed

    Liu, Fu-Ling; Kozlevčar, Bojan; Strauch, Peter; Zhuang, Gui-Lin; Guo, Ling-Yu; Wang, Zhi; Sun, Di

    2015-12-14

    The encapsulation of carbonate derived from atmospheric CO2 has resulted in an icosanuclear heteropolyoxocopperate, isolated as a metal-organic 1D chain, 2D sheet, or 3D framework, in which the Cu20 nanocluster represents the first eight-capped α-Keggin polyoxometalate with the late-transition-metal Cu(II) as the polyatom, CO3(2-) as the heteroanion, and OH(-) and suc(2-) or glu(2-) (H2suc=succinic acid; H2glu=glutaric acid) as the terminal ligands, which suggests a conceptual similarity to classical polyoxometalates. Even in the presence of competitive SO4(2-) in the assembly system, the CO3(2-) anion is still captured as a template to direct the formation of the Cu20 nanocluster, which indicates the stronger templation ability of CO3(2-) compared with SO4(2-). When other aliphatic dicarboxylates, such as glutaric acid, were used as ligands, the CO3(2-)-templated Cu20 nanocluster was maintained and acted as a cluster building unit (CBU) to be linked by two glutarate bridges to generate a distinct 1D metal-organic chain. This report presents not only a rare example of a huge anion-templated transition-metal cluster, but also its use as a robust CBU to construct novel coordination architectures. Variable-temperature magnetic susceptibility studies revealed that an antiferromagnetic interaction exists within the Cu20 nanocluster. The correlation between the coordination structure and the electron paramagnetic resonance spectra recorded of both powder and single-crystal samples are discussed in detail. PMID:26541877

  13. Polymers incorporating covalently attached organoimido polyoxometalates

    DOEpatents

    Maatta, Eric A.; Moore, Aaron R.

    2004-03-16

    New polyoxometalate compounds and polymers comprising recurring monomers of those compounds are provided. The compounds are formed by replacing at least one oxide of the starting polyoxometalate with an organoimido (NR) group bonded to the polyoxometalate via a triple bond to the nitrogen atom. The R of the (NR) group comprises a reactive functional group which renders the compound readily polymerizable, alone or with other monomers (e.g., divinylbenzene), to form the inventive polymers. Additionally, a countercation (e.g., bis(tetra-n-butylammonium)) can be mixed with the polyoxometalate compounds in order to neutralize the negative charge thereof as well as to make those compounds more soluble in organic solvents.

  14. Efficient Synthesis of Ir-Polyoxometalate Cluster Using a Continuous Flow Apparatus and STM Investigation of Its Coassembly Behavior on HOPG Surface.

    PubMed

    Zhang, Junyong; Chang, Shaoqing; Suryanto, Bryan H R; Gong, Chunhua; Zeng, Xianghua; Zhao, Chuan; Zeng, Qingdao; Xie, Jingli

    2016-06-01

    Taking advantage of a continuous-flow apparatus, the iridium(III)-containing polytungstate cluster K12Na2H2[Ir2Cl8P2W20O72]·37H2O (1) was obtained in a reasonable yield (13% based on IrCl3·H2O). Compound 1 was characterized by Fourier transform IR, UV-visible, (31)P NMR, electrospray ionization mass spectrometry (ESI-MS), and thermogravimetric analysis measurements. (31)P NMR, ESI-MS, and elemental analysis all indicated 1 was a new polytungstate cluster compared with the reported K14[(IrCl4)KP2W20O72] compound. Intriguingly, the successful isolation of 1 relied on the custom-built flow apparatus, demonstrating the uniqueness of continuous-flow chemistry to achieve crystalline materials. The catalytic properties of 1 were assessed by investigating the activity on catalyzing the electro-oxidation of ruthenium tris-2,2'-bipyridine [Ru(bpy)3](2+/3+). The voltammetric behavior suggested a coupled catalytic behavior between [Ru(bpy)3](3+/2+) and 1. Furthermore, on the highly oriented pyrolytic graphite surface, 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB) was used as the two-dimensional host network to coassemble cluster 1; the surface morphology was observed by scanning tunneling microscope technique. "S"-shape of 1 was observed, indicating that the cluster could be accommodated in the cavity formed by two TCDB host molecules, leading to a TCDB/cluster binary structure. PMID:27163481

  15. Aqueous formation and manipulation of the iron-oxo Keggin ion

    NASA Astrophysics Data System (ADS)

    Sadeghi, Omid; Zakharov, Lev N.; Nyman, May

    2015-03-01

    There is emerging evidence that growth of synthetic and natural phases occurs by the aggregation of prenucleation clusters, rather than classical atom-by-atom growth. Ferrihydrite, an iron oxyhydroxide mineral, is the common form of Fe3+ in soils and is also in the ferritin protein. We isolated a 10 angstrom discrete iron-oxo cluster (known as the Keggin ion, Fe13) that has the same structural features as ferrihydrite. The stabilization and manipulation of this highly reactive polyanion in water is controlled exclusively by its counterions. Upon dissolution of Fe13 in water with precipitation of its protecting Bi3+-counterions, it rapidly aggregates to ~22 angstrom spherical ferrihydrite nanoparticles. Fe13 may therefore also be a prenucleation cluster for ferrihydrite formation in natural systems, including by microbial and cellular processes.

  16. Two Keggin-type heteropolytungstates with transition metal as a central atom: Crystal structure and magnetic study with 2D-IR correlation spectroscopy

    SciTech Connect

    Chai, Feng; Chen, YiPing; You, ZhuChai; Xia, ZeMin; Ge, SuZhi; Sun, YanQiong; Huang, BiHua

    2013-06-01

    Two Keggin-type heteropolytungstates, [Co(phen)₃]₃[CoW₁₂O₄₀]·9H₂O 1 (phen=1,10-phenanthroline) and [Fe(phen)₃]₂[FeW₁₂O₄₀]·H₃O·H₂O 2, have been synthesized via the hydrothermal technique and characterized by single crystal X-ray diffraction analyses, IR, XPS, TG analysis, UV–DRS, XRD, thermal-dependent and magnetic-dependent 2D-COS IR (two-dimensional infrared correlation spectroscopy). Crystal structure analysis reveals that the polyanions in compound 1 are linked into 3D supramolecule through hydrogen bonding interactions between lattice water molecules and terminal oxygen atoms of polyanion units, and [Co(phen)₃]²⁺ cations distributed in the polyanion framework with many hydrogen bonding interactions. The XPS spectra indicate that all the Co atoms in 1 are +2 oxidation state, the Fe atoms in 2 existing with +2 and +3 mixed oxidation states. - Graphical abstract: The magnetic-dependent synchronous 2D correlation IR spectra of 1 (a), 2 (b) over 0–50 mT in the range of 600–1000 cm⁻¹, the obvious response indicate two Keggin polyanions skeleton susceptible to applied magnetic field. Highlights: • Two Keggin-type heteropolytungstates with transition metal as a central atom has been obtained. • Compound 1 forms into 3D supramolecular architecture through hydrogen bonding between water molecules and polyanions. • Magnetic-dependent 2D-IR correlation spectroscopy was introduced to discuss the magnetism of polyoxometalate.

  17. Manganese carbonyl derivatives based on Keggin- or Dawson-type polyoxoanions

    NASA Astrophysics Data System (ADS)

    Zhao, Juan; Zhao, Junwei; Ma, Pengtao; Wang, Jingping; Niu, Jingyang; Wang, Junsheng

    2012-07-01

    The reactions of [Mn(CO)5]Br with saturated Keggin- or Dawson-type polyoxometalate precursors in the CH3CN/H2O mixed solvent have led to the formation of a series of compounds based on polyoxoanions and manganese carbonyl groups [Mn(CO)3(CH3CN)3]n[α-XM12O40] [n = 3, X = PV, M = MoVI (1), WVI (2)], [Mn(CO)3(CH3CN)3]n[α-XM12O40]·1.5H2O [n = 4, X = SiIV, M = MoVI, (3)], [Mn(CO)3(CH3CN)3]nH[α-XM12O40] [n = 3, X = GeIV, M = MoVI (4)] and [Mn(CO)3(CH3CN)3]6[α-X2M18O62]·H2O [X = PV, M = MoVI (5), WVI (6); X = AsV, M = MoVI (7), WVI (8)], which have been characterized by elemental analyses, IR spectra, X-ray photoelectron spectroscopy (XPS), thermogravimatric (TG) analyses and single-crystal X-ray diffraction. 1, 2 and 4 are isomorphous and crystallize in the trigonal space group P-3. While 5-8 are also isostructural and belong to the monoclinic space group P2(1)/c, but 3 crystallizes in the triclinic space group P-1. Single-crystal X-ray diffraction analyses indicate that 1-8 commonly consist of [Mn(CO)3(CH3CN)3]+ cations and polyoxoanions, which are combined by electrostatic interaction.

  18. Self-Assembly of a Giant Tetrahedral 3 d-4 f Single-Molecule Magnet within a Polyoxometalate System.

    PubMed

    Ibrahim, Masooma; Mereacre, Valeriu; Leblanc, Nicolas; Wernsdorfer, Wolfgang; Anson, Christopher E; Powell, Annie K

    2015-12-14

    A giant tetrahedral heterometallic polyoxometalate (POM) [Dy30 Co8 Ge12 W108 O408 (OH)42 (OH2 )30 ](56-) , which shows single-molecule magnet (SMM) behavior, is described. This hybrid contains the largest number of 4f ions of any polyoxometalate (POM) reported to date and is the first to incorporate two different 3d-4f and 4f coordination cluster assemblies within same POM framework. PMID:26390858

  19. Synthesis and energy band characterization of hybrid molecular materials based on organic–polyoxometalate charge-transfer salts

    SciTech Connect

    Tan, Chunxia; Bu, Weifeng

    2014-11-15

    A cationic amphiphilic molecule was synthesized and employed to encapsulate Lindqvist ([M{sub 6}O{sub 19}]{sup 2−}) and Keggin polyoxometalates ([SiM{sub 12}O{sub 40}]{sup 4−}, M=Mo, W) to form hybrid molecules through electrostatic interaction. The X-ray diffraction results illustrate that the former hybrids possess lamellar nanostructures in their solid states, while the latter hybrids show a cubic Im3m packing model with low intensities and poor long-range order. These hybrids have clear charge-transfer characters as shown in their deeper colors and UV–vis diffuse reflectance spectra. According to the reported reduction potentials of the POM acceptors and the band gaps deduced from their diffuse reflectance spectra, we have calculated the theoretical values of the lowest unoccupied molecular orbital (LUMO) position similar to the electron affinity (E{sub A}) of solid materials. Such energy level parameters are comparable to those of electroluminescence and electron-transport materials commonly used in organic electroluminescence devices. These organic–polyoxometalate charge-transfer salts have more advantages, such as higher decomposition temperatures, easier film fabrication and better electron affinities, which presumably would be used for electron-transport materials in the area of the electroluminescence. - Graphical abstract: Hybrid molecular materials with charge-transfer characters formed by a positively charged donor L and acceptors of the Lindqvist-type and Keggin-type POMs have lamellar and cubic structures in their solid state. - Highlights: • Charge-transfer salts are obtained by self-assembling POMs with an anthracene cation. • Their energy parameters are comparable to those of optoelectronic materials in OLEDs. • These POM-based hybrids could be applied in the area of optoelectronic devices.

  20. Thermodynamic study of the interaction between hen egg white lysozyme and Ce(IV)-Keggin polyoxotungstate as artificial protease.

    PubMed

    Stroobants, K; Saadallah, D; Bruylants, G; Parac-Vogt, T N

    2014-10-21

    The molecular interactions of the Keggin polyoxometalate [Me2NH2]10[Ce(PW11O39)2] (1), which promotes selective hydrolysis of hen egg white lysozyme (HEWL) under physiological conditions, were investigated in detail by isothermal titration calorimetry (ITC), (31)P NMR and circular dichroism (CD) spectroscopy. ITC experiments showed that mixing of 1 and HEWL at pH 7.4 and 25 or 37 °C resulted in complexes having 1 : 1 and 2 : 1 POM : HEWL stoichiometries, respectively, and thermodynamic profiles are in agreement with binding in the vicinity of the Trp28-Val29 and Asn44-Arg45 peptide bonds, which were previously shown to undergo selective hydrolysis by 1. Mixing of HEWL with (NH4)4Ce(SO4)4·4H2O salt indicated the absence of any binding accentuating the importance of the polyoxometalate scaffold for selective interaction with the HEWL surface. In contrast, the lacunary Na9[A-α-PW9O34] polyoxometalate showed an increased binding stoichiometry as compared to 1. Increasing the ionic strength resulted in thermodynamic signatures which indicate preservation of the interaction at the Trp28-Val29 site, while interaction at the Asn44-Arg45 appears disrupted due to competition with the salt ions. Decreasing the pH to 4.4 at 37 °C resulted in energetic contributions which suggest that binding at the Trp28-Val29 site is favored, while more pronounced binding at the Asn44-Arg45 site was anticipated when the pH was increased to 9.2. The absence of binding between 1 and α-lactalbumin (α-LA), a protein which is highly isostructural to HEWL but with an overall negative charge, was confirmed at pH 7.4 and 37 °C. The influence of the pH on the binding between 1 and α-LA was investigated, demonstrating that at lower pH values, where α-LA becomes more positively charged, a 1 : 1 interaction with 1 is observed. PMID:25199500

  1. Controlled Triol-Derivative Bonding and Decoration Transformation on Cu-Centered Anderson-Evans Polyoxometalates.

    PubMed

    Wang, Yang; Li, Bao; Qian, Hujun; Wu, Lixin

    2016-05-01

    To create new types of organic ligands covalently grafted onto polyoxometalates and identify the reaction mechanism, we selected Cu(II) as the central heteroatom for the synthesis of a series of disklike Anderson-Evans clusters bearing different triol derivatives on both their faces via one-pot and/or step-by-step routes. By using a [(n-C4H9)4N]4[Mo8O26] precursor cluster and copper acetate as the starting materials, several organically modified χ isomers with Cu(II) heteroatom centers were obtained. Starting from a [(n-C4H9)4N]2[Mo2O7] subcluster, however, a half-malposition coordination fashion of triol ligands with a δ isomer on one face and a χ isomer on the other face of the Anderson-Evans cluster was obtained. By changing the reaction solvent from acetonitrile to methanol, we realized a secondary organic modification of the triol-grafted clusters and obtained a triol ligand/methanol codecoration on the Anderson-Evans polyoxometalate. In addition, by changing the reaction environment, we succeeded in modulating the transformation of triol ligands from one site to another on the polyoxometalate cluster. Importantly, by control of the reaction condition, the methanol molecules were also taken off from the cluster. PMID:27074087

  2. Synthesis, crystal structure, and properties of a 1-D terbium-substituted monolacunary Keggin-type polyoxotungstate

    NASA Astrophysics Data System (ADS)

    Ma, Pengtao; Si, Yanan; Wan, Rong; Zhang, Shaowei; Wang, Jingping; Niu, Jingyang

    2015-03-01

    A new 1-D linear chainlike terbium-substituted polyoxometalate [Tb(H2O)2(α-PW11O39)]4- (1) has been synthesized in aqueous solution and characterized by elemental analysis, inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray powder diffraction (XRPD), IR spectrum, thermal analysis, electrospray ionization mass spectrometry (ESI-MS), and X-ray single-crystal diffraction. X-ray structural analysis reveals that 1 displays a 1-D linear chain containing [Tb(H2O)2(α-PW11O39)]4- moieties. The Tb(III) cation incorporated into the monolacunary Keggin-type [α-PW11O39]7- unit resides in a distorted monocapped triangular prismatic geometry and acts as a linker to join two adjacent [α-PW11O39]7- units to form a 1-D chain structure. Solid-state photoluminescent property of 1 has been investigated at room temperature and the photoluminescent emission mainly results from the synergistic effect of the TbIII cation and the Na7[α-PW11O39] precursor. The ESI-MS spectrum of 1 confirms that the polyanion [Tb(H2O)(HPW11O39)]3- is stable in aqueous solution.

  3. Synthesis, crystal structure, and properties of a 1-D terbium-substituted monolacunary Keggin-type polyoxotungstate.

    PubMed

    Ma, Pengtao; Si, Yanan; Wan, Rong; Zhang, Shaowei; Wang, Jingping; Niu, Jingyang

    2015-03-01

    A new 1-D linear chainlike terbium-substituted polyoxometalate [Tb(H2O)2(α-PW11O39)](4-) (1) has been synthesized in aqueous solution and characterized by elemental analysis, inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray powder diffraction (XRPD), IR spectrum, thermal analysis, electrospray ionization mass spectrometry (ESI-MS), and X-ray single-crystal diffraction. X-ray structural analysis reveals that 1 displays a 1-D linear chain containing [Tb(H2O)2(α-PW11O39)](4-) moieties. The Tb(III) cation incorporated into the monolacunary Keggin-type [α-PW11O39](7-) unit resides in a distorted monocapped triangular prismatic geometry and acts as a linker to join two adjacent [α-PW11O39](7-) units to form a 1-D chain structure. Solid-state photoluminescent property of 1 has been investigated at room temperature and the photoluminescent emission mainly results from the synergistic effect of the Tb(III) cation and the Na7[α-PW11O39] precursor. The ESI-MS spectrum of 1 confirms that the polyanion [Tb(H2O)(HPW11O39)](3-) is stable in aqueous solution. PMID:25541394

  4. Ternary Porphyrinato Hf(IV) and Zr(IV) - Polyoxometalate Complexes

    PubMed Central

    Falber, Alexander; Burton-Pye, Benjamin P.; Radivojevic, Ivana; Todaro, Louis; Saleh, Raihan; Francesconi, Lynn; Drain, Charles Michael

    2010-01-01

    We report a facile, high yield synthesis and characterization of discrete, ternary porphyrin-metal-polyoxometalate (Por-M-POM) complexes where a group (IV) transition metal ion is bound both to the porphyrin core and to the lacunary site of a Keggin POM, PW11O39−7. The remarkably robust complexes exploit the fact that Hf(IV) and Zr(IV) are 7–8 coordinate and reside outside the plane of the porphyrin macrocycle, thus enabling the simultaneous coordination to meso-tetraphenylporphyrin (TPP) or meso-tetra(4-pyridyl)porphyrin (TPyP) and to the defect site in the Keggin framework. The physical properties of the (TPP)Hf(PW11O39)[TBA]5, (TPyP)Hf(PW11O39)[TBA]5, and (TPP)Zr(PW11O39)[TBA]5 complexes are similar because the metal ions have similar oxidation states, and coordination chemistry. This architecture couples the photonic properties of the porphyrin to the POM because the metal ion is incorporated into both frameworks. Thus the ternary complexes can serve as a basis for the characterization of Hf(IV) and Zr(IV) porphyrins bound to oxide surfaces via the group (IV) metal ions. The Hf(Por) and Zr(Por) bind strongly to TiO2 nanoparticles and indium tin oxide (ITO) surfaces, but significantly less binds to crystalline SiO2 or TiO2 surfaces. Together, the strong binding of the metalloporphyrins to the POM, nanoparticles, and the ITO surfaces, and paucity of binding to crystalline surfaces, suggests that the 3–4 open coordination sites on the Hf(Por) and Zr(Por) are predominantly bound at surface defect sites. PMID:20543903

  5. Assembly and spontaneous resolution of the chiral inorganic polyoxometalates-based frameworks via helical chains association.

    PubMed

    Tang, Qun; Liu, Shuxia; Liu, Yiwei; Li, Shujun; Ma, Fengji; Li, Jianxin; Wang, Shengtian; Liu, Chengzhan

    2013-06-21

    Two pairs of enantiomerically pure three-dimensional (3D) chiral polyoxometalate (POM) framework materials l,d-[K(H2O)]6·[H2GeW12O40]3·35H2O (1a and 1b) and l,d-[K(H2O)]6·[H2SiW12O40]3·29H2O (2a and 2b) based on inorganic achiral building blocks, have been synthesized and characterized by X-ray crystallography, elemental analysis, powder X-ray diffraction (PXRD), UV-Vis spectroscopy, circular dichroism (CD) spectra. Single-crystal X-ray diffraction analyses revealed that 1a and 1b, 2a and 2b are enantiomers, respectively. In 1a and 1b, 2a and 2b, {K(H2O)}n link terminal oxygen and μ2-bridging oxygen of Keggin-type polyanion moieties to generate 1D 31 helical infinite chiral chains, which are further connected by the achiral Keggin-type polyoxoanions to form 3D 4,8-connected chiral self-assembly frameworks with {4(12)·6(10)·8(6)}{4(6)}2 topology. 1 and 2 are isostructural. They are obtained by spontaneous resolution upon crystallization in the absence of any chiral source. They represent new examples of chiral self-penetrating pure inorganic frameworks known for POM systems. Compounds 1 and 2 display adsorption activity toward volatile organic compounds (VOCs). PMID:23629579

  6. New Vistas for Functionalized Polyoxometalates

    SciTech Connect

    Maatta, Eric A.

    2006-04-21

    Polyoxometalates (POMs) - the multimetallic oxoanions [MxOyXz]n? formed by Mo, W, and, to a lesser extent, V, Nb and Ta ? have been described as "a class of inorganic compounds that is unmatched in terms of molecular and electronic structural versatility, reactivity, and relevance". The remarkable breadth of POM chemistry, which extends to areas as diverse as catalysis, medicine, imaging, photo- and electrochromism, and magnetic materials, derives from the confluence of the species' attractive intrinsic characteristics and their extraordinary compositional range. While many of these systems are easy to prepare, it is often difficult to modify POMs in a rational manner. Our goal is to provide for the intrinsic modifcation of POM systems so as to enable their further utility: our approach has provided many examples of fundamentally new types of polyoxometalates in which their ubiquitous oxo [O]2? ligands have been replaced by other isoelectronic entities including organoimido [N-R]2? and diazoalkane [NNCR2]2?ligands. These nitrogenous POM derivatives retain the attractive attributes typical of the class but with altered and tunable characteristics including their redox behavior and electronic absorption patterns. The organoimido and diazoalkane species provide the ability to couple remote and useful functionality via the appended substituents R. We also are now engaged in the preparation and study of nitrido-POM systems: these unprecedented inorganic complexes offer the possibility of effecting various types of nitrido-based transformations (such as nitrogen transfer) which could benefit from the superior oxidative and thermal stability of the POM ligation environment.

  7. Study on the Keggin zinctungstates based hybrid compound with like DNA spiral chain

    NASA Astrophysics Data System (ADS)

    Li, Liang; Sha, Jing-Quan; Zong, Xi-Ming; Liu, Cui-Juan; Zhang, Qian-Nan; Wang, Dong-Wen; Yang, Xiao-Ning; Wang, Yu

    2014-05-01

    A new compound based on polyoxometalates (POMs) and the quinolone antibacterial pipemidic acid (HPPA), {[Zn(HPPA)2H2O]2[H2ZnW12O40]}ṡ9H2O (1), was hydrothermally synthesized and characterized by elemental analyses, IR and XPRD. Single-crystal X-ray diffraction analysis reveals that the [ clusters and Zn-HPPA complexes constructed both right- and left-double-stranded like DNA helical chains in the title compound, and these helical chains are further connected together forming the fascinating quadruple-stranded helices via sharing the ZnW12 clusters. Note that the compound 1 represents the first example of zinctungstate POMs modified by antibacterial drugs. In addition, the antibacterial properties of the compound 1 were investigated.

  8. A novel single-side azobenzene-grafted Anderson-type polyoxometalate for recognition-induced chiral migration.

    PubMed

    Zhang, Bin; Yue, Liang; Wang, Yang; Yang, Yang; Wu, Lixin

    2014-09-25

    A three-component supramolecular hybrid system based on host-guest recognition and electrostatic interaction has been developed for a consecutive chiral transfer from an alpha-cyclodextrin to cationic dyes via the bridge of a new azobenzene-grafted Anderson-type polyoxometalate cluster. PMID:25089807

  9. Polyoxometalates as antitumor agents: Bioactivity of a new polyoxometalate with copper on a human osteosarcoma model.

    PubMed

    León, I E; Porro, V; Astrada, S; Egusquiza, M G; Cabello, C I; Bollati-Fogolin, M; Etcheverry, S B

    2014-10-01

    Polyoxometalates (POMs) are early transition metal oxygen anion clusters. They display interesting biological effects mainly related to their antiviral and antitumor properties. On the other hand, copper compounds also show different biological and pharmacological effects in cell culture and in animal models. We report herein for the first time, a detailed study of the mechanisms of action of a copper(II) compound of the group of HPOMs with the formula K7Na3[Cu4(H2O)2(PW9034)2]20H2O (PW9Cu), in a model of human osteosarcoma derived cell line, MG-63. The compound inhibited selectively the viability of the osteosarcoma cells in the range of 25-100μM (p<0.01). Besides, we have clearly shown a more deleterious action of PW9Cu on tumor osteoblasts than in normal cells. Cytotoxicity studies also showed deleterious effects for PW9Cu. The increment of reactive oxygen species (ROS) and the decrease of the GSH/GSSG ratio were involved in the antiproliferative effects of PW9Cu. Moreover, the compound caused cell cycle arrest in G2 phase, triggering apoptosis as determined by flow cytometry. As a whole, these results showed the main mechanisms of the deleterious effects of PW9Cu in the osteosarcoma cell line MG-63, demonstrating that this compound is a promissory agent for cancer treatments. PMID:25451568

  10. Tungsten polyoxometalate molecules as active nodes for dynamic carrier exchange in hybrid molecular/semiconductor capacitors

    SciTech Connect

    Balliou, A.; Douvas, A. M.; Normand, P.; Argitis, P.; Glezos, N.; Tsikritzis, D.; Kennou, S.

    2014-10-14

    In this work we study the utilization of molecular transition metal oxides known as polyoxometalates (POMs), in particular the Keggin structure anions of the formula PW₁₂O₄₀³⁻, as active nodes for potential switching and/or fast writing memory applications. The active molecules are being integrated in hybrid Metal-Insulator/POM molecules-Semiconductor capacitors, which serve as prototypes allowing investigation of critical performance characteristics towards the design of more sophisticated devices. The charging ability as well as the electronic structure of the molecular layer is probed by means of electrical characterization, namely, capacitance-voltage and current-voltage measurements, as well as transient capacitance measurements, C (t), under step voltage polarization. It is argued that the transient current peaks observed are manifestations of dynamic carrier exchange between the gate electrode and specific molecular levels, while the transient C (t) curves under conditions of molecular charging can supply information for the rate of change of the charge that is being trapped and de-trapped within the molecular layer. Structural characterization via surface and cross sectional scanning electron microscopy as well as atomic force microscopy, spectroscopic ellipsometry, UV and Fourier-transform IR spectroscopies, UPS, and XPS contribute to the extraction of accurate electronic structure characteristics and open the path for the design of new devices with on-demand tuning of their interfacial properties via the controlled preparation of the POM layer.

  11. Crystal Structure and Band Gap Engineering in Polyoxometalate-Based Inorganic-Organic Hybrids.

    PubMed

    Roy, Soumyabrata; Sarkar, Sumanta; Pan, Jaysree; Waghmare, Umesh V; Dhanya, R; Narayana, Chandrabhas; Peter, Sebastian C

    2016-04-01

    We have demonstrated engineering of the electronic band gap of the hybrid materials based on POMs (polyoxometalates), by controlling its structural complexity through variation in the conditions of synthesis. The pH- and temperature-dependent studies give a clear insight into how these experimental factors affect the overall hybrid structure and its properties. Our structural manipulations have been successful in effectively tuning the optical band gap and electronic band structure of this kind of hybrids, which can find many applications in the field of photovoltaic and semiconducting devices. We have also addressed a common crystallographic disorder observed in Keggin-ion (one type of heteropolyoxometalate [POMs])-based hybrid materials. Through a combination of crystallographic, spectroscopic, and theoretical analysis of four new POM-based hybrids synthesized with tactically varied reaction conditions, we trace the origin and nature of the disorder associated with it and the subtle local structural coordination involved in its core picture. While the crystallography yields a centrosymmetric structure with planar coordination of Si, our analysis with XPS, IR, and Raman spectroscopy reveals a tetrahedral coordination with broken inversion symmetry, corroborated by first-principles calculations. PMID:26986739

  12. Structural, magnetic, EPR, and electrochemical characterizations of a spin-frustrated trinuclear Cr(III) polyoxometalate and study of its reactivity with lanthanum cations.

    PubMed

    Compain, Jean-Daniel; Mialane, Pierre; Dolbecq, Anne; Mbomekallé, Israël Martyr; Marrot, Jérôme; Sécheresse, Francis; Duboc, Carole; Rivière, Eric

    2010-03-15

    The asymmetric Cr(III) polyoxometalate complex Cs(10)[(gamma-SiW(10)O(36))(2)(Cr(OH)(H(2)O))(3)] x 17 H(2)O (1) has been synthesized in water under atmospheric pressure from the trinuclear precursor [Cr(3)(CH(3)COO)(7)(OH)(2)] and the divacant ligand [gamma-SiW(10)O(36)](8-). Complex 1 is built up of two [gamma-SiW(10)O(36)](8-) Keggin units sandwiching a trinuclear {(Cr(III)(OH)(H(2)O))(3)} fragment where the paramagnetic centers are bridged by three mu-OH ligands forming a nearly isosceles triangle. The magnetic properties of this spin-frustrated system have thus been interpreted considering a 2-J Hamiltonian showing that the Cr(III) ions are antiferromagnetically coupled and that 1 possesses an S = 3/2 ground state with an S = 1/2 first excited state located at 11 cm(-1). These results have been confirmed by EPR spectroscopy measurements (Q-band), which have also enabled the quantification of the electronic parameters characterizing the quadruplet spin ground state. The magnitude of the magnetic exchange interactions and the nature of the ground state are discussed in light of previously reported isosceles triangular S = 3/2 clusters. UV-visible and electrochemical studies have shown that 1 is stable in aqueous media in a 1-7 pH range. This stability is chemically confirmed by the study of the reactivity of 1 with La(III) cations, which has allowed the isolation of the Cs(4)[(gamma-SiW(10)O(36))(2)(Cr(OH)(H(2)O))(3)(La(H(2)O)(7))(2)] x 20 H(2)O compound (2). Indeed, during the synthetic process of this 3d-4f system, the integrity of the [(gamma-SiW(10)O(36))(2)(Cr(OH)(H(2)O))(3)](10-) building unit constituting 1 is maintained despite the high oxophilic character of the La(III) ions. The single crystal X-ray diffraction study of 2 has revealed that in the solid state the rare earth cations connect these subunits, affording a 3d-4f double-chain monodimensional system. PMID:20146426

  13. Steam-Assisted Synthesis of an Extra-Stable Polyoxometalate-Encapsulating Metal Azolate Framework: Applications in Reagent Purification and Proton Conduction.

    PubMed

    Zhou, En-Long; Qin, Chao; Wang, Xin-Long; Shao, Kui-Zhan; Su, Zhong-Min

    2015-09-01

    Different from the conventional synthesis approaches, such as hydrothermal or solvothermal synthesis, a porous metal azolate framework encapsulating Keggin-type [SiW12 O40 ](4-) anions was prepared by an environmentally friendly, low-cost, and highly efficient steam-assisted conversion method for the first time. The nanosized polyoxometalates as a template were encapsulated by a zeotype 6(4) 4(8) cage constructed by 28 nuclear zinc atoms connected through 32 Trz ligands. The obtained composite exhibits excellent thermal and chemical stability; meanwhile, its special ability to selectively absorb water from alcohols makes it efficiently separate water from analytically pure ethanol, with the result that water content decreases from 0.23 to 0.05 wt %, which is superior to the standard of chromatographic grade ethanol (<0.1 wt %). Besides, alternating current (ac) impedance experiments also reveal that the hybrid is a kind of proton conductive material. PMID:26235593

  14. Investigation of the formation process of zeolite-like 3D frameworks constructed with ε-Keggin-type polyoxovanadomolybdates with binding bismuth ions and preparation of a nano-crystal.

    PubMed

    Zhang, Zhenxin; Sadakane, Masahiro; Murayama, Toru; Ueda, Wataru

    2014-09-28

    Reaction conditions for the synthesis of an ε-Keggin-type polyoxometalate-based 3D framework, (NH4)2.8H0.9[ε-VMo9.4V2.6O40Bi2]·7.2H2O (denoted as Mo-V-Bi oxide), are studied. It is found that the reaction time, temperature, pH of the solution, and starting compounds affect the production of Mo-V-Bi oxide. The crystal size of Mo-V-Bi oxide is controllable by changing bismuth compounds. Nanometer-sized Mo-V-Bi oxide is produced using a water-soluble bismuth compound, Bi(NO3)3·5H2O, whereas micrometer to submicrometer-sized Mo-V-Bi oxide is produced using Bi(OH)3, which is less soluble in water. The particle size of the material affects the properties of the material, such as surface area and catalysis. The investigation of the formation process of the material is carried out with Raman spectroscopy, which indicates that mixing (NH4)6Mo7O24·4H2O, VOSO4·5H2O, and bismuth ions in water produces the ε-Keggin polyoxovanadomolybdate together with a ball-shaped polyoxovanadomolybdate, [Mo72V30O282(H2O)56(SO4)12](36-) (denoted as {Mo72V30}). By heating the reaction mixture, the ε-Keggin polyoxovanadomolybdate assembles with bismuth ions to form Mo-V-Bi oxide, whereas {Mo72V30} assembles with other vanadium and molybdenum ions to form orthorhombic Mo-V oxide. PMID:25096969

  15. FINAL REPORT. POLYOXOMETALATES FOR RADIOACTIVE WASTE TREATMENT

    EPA Science Inventory

    The research was directed primarily towards the use of polyoxometalate complexes for separationof lanthanide, actinide, and technetium species from aqueous waste solutions, such as the HanfordTank Wastes. Selective binding of these species responsible for much of the high level...

  16. Polyoxometalates--potent and selective ecto-nucleotidase inhibitors.

    PubMed

    Lee, Sang-Yong; Fiene, Amelie; Li, Wenjin; Hanck, Theodor; Brylev, Konstantin A; Fedorov, Vladimir E; Lecka, Joanna; Haider, Ali; Pietzsch, Hans-Jürgen; Zimmermann, Herbert; Sévigny, Jean; Kortz, Ulrich; Stephan, Holger; Müller, Christa E

    2015-01-15

    Polyoxometalates (POMs) are inorganic cluster metal complexes that possess versatile biological activities, including antibacterial, anticancer, antidiabetic, and antiviral effects. Their mechanisms of action at the molecular level are largely unknown. However, it has been suggested that the inhibition of several enzyme families (e.g., phosphatases, protein kinases or ecto-nucleotidases) by POMs may contribute to their pharmacological properties. Ecto-nucleotidases are cell membrane-bound or secreted glycoproteins involved in the hydrolysis of extracellular nucleotides thereby regulating purinergic (and pyrimidinergic) signaling. They comprise four distinct families: ecto-nucleoside triphosphate diphosphohydrolases (NTPDases), ecto-nucleotide pyrophosphatases/phosphodiesterases (NPPs), alkaline phosphatases (APs) and ecto-5'-nucleotidase (eN). In the present study, we evaluated the inhibitory potency of a series of polyoxometalates as well as chalcogenide hexarhenium cluster complexes at a broad range of ecto-nucleotidases. [Co4(H2O)2(PW9O34)2](10-) (5, PSB-POM142) was discovered to be the most potent inhibitor of human NTPDase1 described so far (Ki: 3.88 nM). Other investigated POMs selectively inhibited human NPP1, [TiW11CoO40](8-) (4, PSB-POM141, Ki: 1.46 nM) and [NaSb9W21O86](18-) (6, PSB-POM143, Ki: 4.98 nM) representing the most potent and selective human NPP1 inhibitors described to date. [NaP5W30O110](14-) (8, PSB-POM144) strongly inhibited NTPDase1-3 and NPP1 and may therefore be used as a pan-inhibitor to block ATP hydrolysis. The polyoxoanionic compounds displayed a non-competitive mechanism of inhibition of NPPs and eN, but appeared to be competitive inhibitors of TNAP. Future in vivo studies with selected inhibitors identified in the current study are warranted. PMID:25449596

  17. Lithium intercalation reaction into the Keggin type polyoxomolybdates

    NASA Astrophysics Data System (ADS)

    Sonoyama, Noriyuki; Suganuma, Yoshiaki; Kume, Tomohiro; Quan, Zhen

    The electrochemical property of Keggin type hetero polyoxomolybdate K 3[PMo 12O 40] (KPM) as the cathode electrode material for lithium battery was examined. KPM showed charge-discharge performance in the potential region from 4.2 V to 1.5 V with capacity of over 200 mAh g -1. From the result of the ex situ XRD measurement, it is presumed that the electrochemical reaction of KPM proceeds via the lithium (de-)intercalation. The cycle performance of KPM is largely dependent on the charge-discharge potential range. The capacity fade caused by deep discharging seems to be concerned to the < to ® isomerization of KPM.

  18. Immobilization of Polyoxometalate in the Metal-Organic Framework rht-MOF-1: Towards a Highly Effective Heterogeneous Catalyst and Dye Scavenger.

    PubMed

    Sun, Jing-Wen; Yan, Peng-Fei; An, Guang-Hui; Sha, Jing-Quan; Li, Guang-Ming; Yang, Guo-Yu

    2016-01-01

    A series of three remarkable complexes [PMo12O40]@[Cu6O(TZI)3(H2O)9]4·OH·31H2O (H3TZI = 5-tetrazolylisophthalic acid; denoted as HLJU-1, HLJU = Heilongjiang University), [SiMo12O40]@[Cu6O(TZI)3(H2O)9]4·32H2O (denoted as HLJU-2), and [PW12O40]@[Cu6O(TZI)3(H2O)6]4·OH·31H2O (denoted as HLJU-3) have been isolated by using simple one-step solvothermal reaction of copper chloride, 5-tetrazolylisophthalic acid (H3TZI), and various Keggin-type polyoxometalates (POMs), respectively. Crystal analysis of HLJU 1-3 reveals that Keggin-type polyoxoanions have been fitted snuggly in the cages of rht-MOF-1 (MOF: metal-organic framework) with large cell volume in a range of 87968-88800 Å(3) and large pore volume of about 68%. HLJU 1-3 exhibit unique catalytic selectivity and reactivity in the oxidation of alkylbenzene with environmental benign oxidant under mild condition in aqueous phase as well as the uptake capacity towards organic pollutants in aqueous solution. PMID:27157290

  19. Immobilization of Polyoxometalate in the Metal-Organic Framework rht-MOF-1: Towards a Highly Effective Heterogeneous Catalyst and Dye Scavenger

    PubMed Central

    Sun, Jing-Wen; Yan, Peng-Fei; An, Guang-Hui; Sha, Jing-Quan; Li, Guang-Ming; Yang, Guo-Yu

    2016-01-01

    A series of three remarkable complexes [PMo12O40]@[Cu6O(TZI)3(H2O)9]4·OH·31H2O (H3TZI = 5-tetrazolylisophthalic acid; denoted as HLJU-1, HLJU = Heilongjiang University), [SiMo12O40]@[Cu6O(TZI)3(H2O)9]4·32H2O (denoted as HLJU-2), and [PW12O40]@[Cu6O(TZI)3(H2O)6]4·OH·31H2O (denoted as HLJU-3) have been isolated by using simple one-step solvothermal reaction of copper chloride, 5-tetrazolylisophthalic acid (H3TZI), and various Keggin-type polyoxometalates (POMs), respectively. Crystal analysis of HLJU 1−3 reveals that Keggin-type polyoxoanions have been fitted snuggly in the cages of rht-MOF-1 (MOF: metal−organic framework) with large cell volume in a range of 87968−88800 Å3 and large pore volume of about 68%. HLJU 1–3 exhibit unique catalytic selectivity and reactivity in the oxidation of alkylbenzene with environmental benign oxidant under mild condition in aqueous phase as well as the uptake capacity towards organic pollutants in aqueous solution. PMID:27157290

  20. Immobilization of Polyoxometalate in the Metal-Organic Framework rht-MOF-1: Towards a Highly Effective Heterogeneous Catalyst and Dye Scavenger

    NASA Astrophysics Data System (ADS)

    Sun, Jing-Wen; Yan, Peng-Fei; An, Guang-Hui; Sha, Jing-Quan; Li, Guang-Ming; Yang, Guo-Yu

    2016-05-01

    A series of three remarkable complexes [PMo12O40]@[Cu6O(TZI)3(H2O)9]4·OH·31H2O (H3TZI = 5-tetrazolylisophthalic acid; denoted as HLJU-1, HLJU = Heilongjiang University), [SiMo12O40]@[Cu6O(TZI)3(H2O)9]4·32H2O (denoted as HLJU-2), and [PW12O40]@[Cu6O(TZI)3(H2O)6]4·OH·31H2O (denoted as HLJU-3) have been isolated by using simple one-step solvothermal reaction of copper chloride, 5-tetrazolylisophthalic acid (H3TZI), and various Keggin-type polyoxometalates (POMs), respectively. Crystal analysis of HLJU 1‑3 reveals that Keggin-type polyoxoanions have been fitted snuggly in the cages of rht-MOF-1 (MOF: metal‑organic framework) with large cell volume in a range of 87968‑88800 Å3 and large pore volume of about 68%. HLJU 1–3 exhibit unique catalytic selectivity and reactivity in the oxidation of alkylbenzene with environmental benign oxidant under mild condition in aqueous phase as well as the uptake capacity towards organic pollutants in aqueous solution.

  1. Orientations of polyoxometalate anions on gold nanoparticles.

    PubMed

    Sharet, Shelly; Sandars, Ella; Wang, Yifeng; Zeiri, Offer; Neyman, Alevtina; Meshi, Louisa; Weinstock, Ira A

    2012-09-01

    Cryogenic transmission electron microscopy of polyoxometalate-protected gold nanoparticles reveals that the Preyssler ion, [NaP(5)W(30)O(110)](14-), lies "face down" with its C(5) axis perpendicular to the gold surface, while the Finke-Droege ion, [P(4)W(30)Zn(4)(H(2)O)(2)O(112)](16-), is "tilted", with its long axis close to 60° from the normal to the surface. PMID:22510818

  2. Interaction between Mo132 nanocluster polyoxometalate and solvents

    NASA Astrophysics Data System (ADS)

    Ostroushko, A. A.; Safronov, A. P.; Tonkushina, M. O.; Korotaev, V. Yu.; Barkov, A. Yu.

    2014-12-01

    The interaction between solid Mo132 nanocluster polyoxometalate with the structure of a keplerate and solvents of different natures (e.g., water, alcohols, hexane, and tetrachloromethane) is studied thermochemically. NMR spectroscopy is used to analyze interactions in solid polyoxometalate-organic compound systems in a gaseous medium. Data are collected on sorption interactions between a Mo132 nanocluster and camphor.

  3. High-nuclearity magnetic clusters: Magnetic interactions in clusters encapsulated by molecular metal oxides

    NASA Astrophysics Data System (ADS)

    Borras-Almenar, Juan José; Coronado, Eugenio; Galan-Mascaros, Jose Ramón; Gómez-García, Carlos J.

    1995-02-01

    The ability of the molecular metal oxides derived from the Keggin anion [PW 12O 40] 3- to accommodate magnetic ions at specific sites, giving rise to polymetallic clusters with increasing spin nuclearities is discussed. Examples of magnetic clusters with three, four and nine metal ions exhibiting ferromagnetic exchange couplings or a coexistence of ferro- and antiferromagnetic couplings are reported.

  4. Exceptional photosensitivity of a polyoxometalate-based charge-transfer hybrid material.

    PubMed

    Liao, Jian-Zhen; Wu, Chen; Wu, Xiao-Yuan; Deng, Shui-Quan; Lu, Can-Zhong

    2016-05-31

    An unusual room-temperature light sensitivity was realized in a polyoxometalate-based hybrid material due to cooperative multicomponent molecular charge-transfer interactions taking place in this material, mainly among POMs, NDIs, and other molecules. The functional π-acidic NDI linkers and POM clusters in the discussed hybrid material were individually designed as photosensors and electron reservoirs. To propose a photo-induced charge-transfer mechanism, EPR, XPS, UV-Vis and computational studies were carried out, and indicated the presence of active charge-transfer interactions among several of the components. PMID:27192943

  5. Fragmenting gadolinium: mononuclear polyoxometalate-based magnetic coolers for ultra-low temperatures.

    PubMed

    Martínez-Pérez, María-José; Montero, Oscar; Evangelisti, Marco; Luis, Fernando; Sesé, Javier; Cardona-Serra, Salvador; Coronado, Eugenio

    2012-08-16

    The polyoxometalate clusters with formula [Gd(W(5) O(18) )(2) ](9-) and [Gd(P(5) W(30) O(110) )](12-) each carry a single magnetic ion of gadolinium, which is the most widespread element among magnetic refrigerant materials. In an adiabatic demagnetization, the lowest attainable temperature is limited by the presence of magnetic interactions that bring about magnetic order below a critical temperature. We demonstrate that this limitation can be overcome by chemically engineering the molecules in such a way to effectively screen all magnetic interactions, suggesting their use as ultra-low-temperature coolers. PMID:22718245

  6. Reversible proton-switchable fluorescence controlled by conjugation effect in an organically-functionalized polyoxometalate

    PubMed Central

    Lv, Chunlin; Chen, Kun; Hu, Junjie; Zhang, Jin; Khan, Rao Naumaan Nasim; Wei, Yongge

    2016-01-01

    A novel monosubstituted organoimido hexamolybdate containing 6-nitroquinoline moiety has been successfully synthesized. This organically-functionalized polyoxometalate exhibits proton-induced switchable fluorescence property in aqueous acetonitrile solution at room temperature. Experimental and theoretical investigations of this reversible “on” and “off” switching mechanism have been carried out, and it is found that the protonation and deprotonation at the heterocyclic nitrogen atom within quinoline fragment leads to the breaking and reformation of the conjugation through strong d-π interaction between the hexamolybdate anionic cluster and the quinoline moiety, resulting in “on” and “off” luminescence signal. PMID:27321576

  7. Reversible proton-switchable fluorescence controlled by conjugation effect in an organically-functionalized polyoxometalate.

    PubMed

    Lv, Chunlin; Chen, Kun; Hu, Junjie; Zhang, Jin; Khan, Rao Naumaan Nasim; Wei, Yongge

    2016-01-01

    A novel monosubstituted organoimido hexamolybdate containing 6-nitroquinoline moiety has been successfully synthesized. This organically-functionalized polyoxometalate exhibits proton-induced switchable fluorescence property in aqueous acetonitrile solution at room temperature. Experimental and theoretical investigations of this reversible "on" and "off" switching mechanism have been carried out, and it is found that the protonation and deprotonation at the heterocyclic nitrogen atom within quinoline fragment leads to the breaking and reformation of the conjugation through strong d-π interaction between the hexamolybdate anionic cluster and the quinoline moiety, resulting in "on" and "off" luminescence signal. PMID:27321576

  8. Visible-light photochromic nanocomposite thin films based on polyvinylpyrrolidone and polyoxometalates supported on clay minerals

    NASA Astrophysics Data System (ADS)

    Wang, Xiang-yu; Dong, Qi; Meng, Qing-ling; Yang, Jun-Yan; Feng, Wei; Han, Xiang-kui

    2014-10-01

    A novel reversible photochromic nanocomposite film was prepared by entrapping phosphomolybdic acid supported on the sodium bentonite (PMoA/Na-MMT) into polyvinylpyrrolidone (PVPd). The microstructure, thermal stability, photochromic behavior and mechanism of the hybrid film were investigated. Fourier transform infrared spectroscopy (FT-IR) results illustrated that the Keggin geometry of polyoxometalates (PMoA) and organic groups of PVPd were still preserved inside the composites and non-covalent bond interaction was built between PMoA/Na-MMT and PVPd polymer matrix. Transmission electron microscopy (TEM) image showed that PMoA nanoparticles were finely dispersed in Na-MMT which exhibited fine stratified structure. Atomic force microscopy (AFM) images indicated that the surface topography of polymeric matrix changed after adding PMoA/Na-MMT, and the surface appearance of nanocomposite film was different before and after visible-light irradiation. The stability of the hybrid film and the effect of the perturbation of Na-MMT on the stability were determined by means of the thermogravimetric analysis (TG) and differential thermal analysis (DTA). Irradiated with visible light, the ultraviolet--visible spectra (UV-vis) showed that the hybrid films changed from colorless to blue and could recover the colorless state gradually in air, where oxygen played an important role during the bleaching process. The hybrid films exhibited excellent bleaching ability during the heating. According to the X-ray photoelectron spectroscopy (XPS) analysis, the appearance of Mo5+ species indicated the photo-reduction reaction between PMoA/Na-MMT and PVPd matrix occurred according to the proton transfer mechanism, and the photochromic reactions were found to exhibit first-order kinetics.

  9. Pharmacokinetics of antiviral polyoxometalates in rats.

    PubMed Central

    Ni, L; Boudinot, F D; Boudinot, S G; Henson, G W; Bossard, G E; Martellucci, S A; Ash, P W; Fricker, S P; Darkes, M C; Theobald, B R

    1994-01-01

    Polyoxometalates are soluble mineral compounds formed principally of oxide anions and early transition metal cations. The polyoxometalates K12H2[P2W12O48].24H2O (JM 1591), K10[P2W18Zn4(H2O)2O68].20H2O (JM 1596), and [(CH3)3NH]8[Si2W18Nb6O77] (JM 2820) demonstrate potent antiviral activity against human immunodeficiency virus types 1 and 2, herpes simplex virus, and cytomegalovirus in vitro. The preclinical pharmacokinetics of these three compounds were characterized after single-dose intravenous administration of 50 mg/kg to rats. Plasma, urine, and feces were collected for 168 h, and polyoxometalate concentrations were determined by atomic emission. Serum protein binding was measured by equilibrium dialysis. All three compounds were highly bound to serum proteins in a concentration-dependent manner. Total and unbound concentrations of the three compounds in plasma declined in a triexponential manner with terminal half-lives of 246.0 +/- 127.0, 438.4 +/- 129.4, and 32.2 +/- 5.37 h (mean +/- standard deviation) for JM 1591, JM 1596, and JM 2820, respectively. Systemic clearances based on total concentrations in plasma were low, averaging 0.016 +/- 0.002, 0.015 +/- 0.002, and 0.018 +/- 0.003 liter/h/kg for JM 1591, JM 1596, and JM 2820, respectively. The clearances of unbound compounds from plasma averaged 0.966 +/- 0.136, 0.050 +/- 0.005, and 0.901 +/- 0.165 liter/h/kg for JM 1591, JM 1596, and JM 2820, respectively. For JM 1596, the clearance of unbound compound from the kidneys was lower than the glomerular filtration rate (0.086 liter/h/kg), suggesting this polyoxometalate underwent renal tubular reabsorption. However, JM 1591 and JM 2820 appeared to undergo tubular secretion. The fraction of the dose recovered in urine was 11.5, 46.8, and 10.6% for JM 1591, JM 1596, and JM 2820, respectively. Approximately 5% of the dose of each polyoxometalate was recovered in feces. The steady-state volume of distribution based on total concentrations averaged 1.44 liters

  10. A multiunit catalyst with synergistic stability and reactivity: a polyoxometalate-metal organic framework for aerobic decontamination.

    PubMed

    Song, Jie; Luo, Zhen; Britt, David K; Furukawa, Hiroyasu; Yaghi, Omar M; Hardcastle, Kenneth I; Hill, Craig L

    2011-10-26

    A combination of polyanion size and charge allows the Keggin-type polyoxometalate (POM), [CuPW(11)O(39)](5-), a catalyst for some air-based organic oxidations, to fit snuggly in the pores of MOF-199 (HKUST-1), a metal-organic framework (MOF) with the POM countercations residing in alternative pores. This close matching of POM diameter and MOF pore size in this POM-MOF material, [Cu(3)(C(9)H(3)O(6))(2)](4)[{(CH(3))(4)N}(4)CuPW(11)O(39)H] (1), results in a substantial synergistic stabilization of both the MOF and the POM. In addition, this heretofore undocumented POM-MOF interaction results in a dramatic increase in the catalytic turnover rate of the POM for air-based oxidations. While 1 catalyzes the rapid chemo- and shape-selective oxidation of thiols to disulfides and, more significantly, the rapid and sustained removal of toxic H(2)S via H(2)S + 1/2 O(2) → 1/8 S(8) + H(2)O (4000 turnovers in <20 h), the POM or the MOF alone is catalytically slow or inactive. Three arguments are consistent with the catalytic reactions taking place inside the pores. POM activation by encapsulation in the MOF likely involves electrostatic interactions between the two components resulting in a higher reduction potential of the POM. PMID:21913693

  11. Charge retention of soft-landed phosphotungstate Keggin anions on self-assembled monolayers.

    PubMed

    Gunaratne, K Don D; Prabhakaran, Venkateshkumar; Andersen, Amity; Johnson, Grant E; Laskin, Julia

    2016-04-01

    Soft landing of mass-selected ions onto surfaces often results in partial loss of charge that may affect the structure and reactivity of deposited species. In this study, Keggin phosphotungstate anions in two selected charge states, PW12O40(3-) (WPOM(3-)) and PW12O40(2-) (WPOM(2-)), were soft-landed onto different self-assembled monolayer (SAM) surfaces and examined using in situ infrared reflection absorption spectroscopy (IRRAS) and density functional theory (DFT) calculations. Partial retention of the 3- charge was observed when WPOM(3-) was soft-landed onto the fluorinated SAM (FSAM), while the charge state distribution was dominated by the 2- charge after both WPOM(3-) and WPOM(2-) were deposited onto a hydrophilic alkylthiol SAM terminated with cationic NH3(+) functional groups (NH3(+)SAM). We found that during the course of the soft landing of WPOM(3-), the relative abundance of WPOM(3-) on FSAM decreased while that of WPOM(2-) increased. We propose that the higher stability of immobilized WPOM(2-) in comparison with WPOM(3-) makes it the preferred charge state of WPOM on both the FSAM and NH3(+)SAM. We also observe weaker binding of WPOM anions to SAMs in comparison with phosphomolybdate ions (MoPOM) reported previously (J. Phys. Chem. C, 2014, 118, 27611-27622). The weaker binding of WPOM to SAMs is attributed to the lower reactivity of WPOM reported in the literature. This study demonstrates that both the charge retention and the reactivity of deposited anionic POM clusters on surfaces are determined by the type of addenda metal atoms in the cluster. PMID:26966731

  12. Tetraalkylphosphonium polyoxometalates : Electroactive, 'task-specific' ionic liquids.

    SciTech Connect

    Rickert, P. G.; Antonio, M. R.; Firestone, M. A.; Kubatko, K-A.; Szreder, T.; Wishart, J. F.; Dietz, M. L.; BNL; Univ. of Miami

    2007-01-01

    The pairing of selected polyoxometalate (POM) anions with appropriate tetraalkylphosphonium cations is shown to yield an original family of ionic liquids, among them an ambient-temperature 'liquid POM.'

  13. Stable graphene-polyoxometalate nanomaterials for application in hybrid supercapacitors.

    PubMed

    Suárez-Guevara, Jullieth; Ruiz, Vanesa; Gómez-Romero, Pedro

    2014-10-14

    We report the synthesis of hybrid supercapacitor electrodes by a novel reduction of GO with simultaneous incorporation of polyoxometalate. These hybrids show a 30% increase in specific capacitance and excellent stability after 10,000 cycles. PMID:25164153

  14. Novel Polyoxometalate Containing Membranes for PEM Fuel Cells

    SciTech Connect

    Mason K. Harrup; Frederick F. Stewart; Thomas A Luther; Tammy Trowbridge

    2009-03-01

    Current proton exchange membrane (PEM) technologies are inadequate to address the projected needs for fuel cell performance above 80 ºC. Continuing research into traditional ion carriers in novel membrane materials offers the promise of marginal improvement, representing only an evolutionary increase in performance. This conclusion is supported by the role of water in conduction. Thus, the key to better PEMs is not to eliminate water, but to change the role of water by developing ion carriers that will bind water more tightly than traditional sulfur or phosphorus based carriers resulting in materials that will conduct at higher temperatures. This change entails having a carrier structure that interacts more intimately with water and by increasing the ion carrier anionic charge to result in more tightly held inner shell protonated waters of hydration. Both of these factors synergistically act to maintain a critical water concentration at the carrier necessary for conduction. In this work, polyoxometalate (POM) clusters were selected to serve as these different proton carriers.

  15. Characterization of manganese(V)-oxo polyoxometalate intermediates and their properties in oxygen-transfer reactions.

    PubMed

    Khenkin, Alex M; Kumar, Devesh; Shaik, Sason; Neumann, Ronny

    2006-12-01

    A manganese(III)-substituted polyoxometalate, [alpha2-P2MnIII(L)W17O61]7- (P2W17MnIII), was studied as an oxidation catalyst using iodopentafluorobenzene bis(tifluoroacetate) (F5PhI(TFAc)2) as a monooxygen donor. Pink P2W17MnIII turns green upon addition of F5PhI(TFAc)2. The 19F NMR spectrum of F5PhI(TFAc)2 with excess P2W17MnIII at -50 degrees C showed the formation of an intermediate attributed to P2W17MnIII-F5PhI(TFAc)2 that disappeared upon warming. The 31P NMR spectra of P2W17MnIII with excess F5PhI(TFAc)2 at -50 and -20 degrees C showed a pair of narrow peaks attributed to a diamagnetic, singlet manganese(V)-oxo species, P2W17MnV=O. An additional broad peak at -10.6 ppm was attributed to both the P2W17MnIII-F5PhI(TFAc)2 complex and a paramagnetic, triplet manganese(V)-oxo species. The electronic structure and reactivity of P2W17MnV=O were modeled by DFT calculations using the analogous Keggin compound, [PMnV=OW11O39]4-. Calculations with a pure functional, UBLYP, showed singlet and triplet ground states of similar energy. Further calculations using both the UBLYP and UB3LYP functionals for epoxidation and hydroxylation of propene showed lowest lying triplet transition states for both transformations, while singlet and quintet transition states were of higher energy. The calculations especially after corrections for the solvent effect indicate that [PMnV=OW11O39]4- should be highly reactive, even more reactive than analogous MnV=O porphyrin species. Kinetic measurements of the reaction of P2W17MnV=O with 1-octene indicated, however, that P2W17MnV=O was less reactive than a MnV=O porphyrin. The experimental enthalpy of activation confirmed that the energy barrier for epoxidation is low, but the highly negative entropy of activation leads to a high free energy of activation. This result originates in our view from the strong solvation of the highly charged polyoxometalate by the polar solvent used and adventitious water. The higher negative charge of the

  16. {l_brace}XW{sub 12}O{sub 40} [Cu(en){sub 2}(H{sub 2}O)]{sub 3}{r_brace} (X=V, Si): Two novel tri-supported Keggin POMs with transition metal complexes

    SciTech Connect

    Lu Yukun; Cui Xiaobing; Chen Yan; Xu Jianing; Zhang Qingbin; Liu Yabing; Xu Jiqing; Wang Tiegang

    2009-08-15

    Two novel polyoxometalate derivatives, {l_brace}X{sup IV}W{sup VI}{sub 10}W{sup V}{sub 2}O{sub 40}[Cu(en){sub 2}(H{sub 2}O)]{sub 3}{r_brace} [X=V (1), Si (2); en=ethylenediamine], have been hydrothermally synthesized and characterized by elemental analyses, IR, UV-Vis, XPS, EPR, TG and single crystal X-ray diffraction analyses. They represent the first classical Keggin polyoxoanion supported by three transition metal complex moieties, which further act as the neutral molecular unit for the construction of the interesting three-dimensional supramolecular frameworks. The magnetic properties of 1 have also been studied in the temperature range of 4-300 K, and its magnetic susceptibility obeys the Curie-Weiss law, showing antiferromagnetic coupling. - Graphical abstract: The first classical Keggin polyoxoanion tri-supported by TMC moieties via bridge oxygen atoms, {l_brace}X{sup IV}W{sup VI}{sub 10}W{sup V}{sub 2}O{sub 40}[Cu(en){sub 2}(H{sub 2}O)]{sub 3}{r_brace}, act as the neutral molecular unit to construct the interesting 3-D supramolecular frameworks.

  17. Hydrothermal combination of trilacunary Dawson phosphotungstates and hexanickel clusters: from an isolated cluster to a 3D framework.

    PubMed

    Li, Xin-Xiong; Fang, Wei-Hui; Zhao, Jun-Wei; Yang, Guo-Yu

    2014-12-22

    Three novel hexa-Ni-substituted Dawson phosphortungstates [Ni6 (en)3 (H2O)6 (μ3-OH)3 (H3 P2 W15 O56 )]⋅14 H2O (1), [Ni(enMe)2 (H2O)][Ni6 (enMe)3 (μ3-OH)3 (H2O)6 (HP2 W15 O56)]⋅ 10 H2O (2), and [Ni(enMe)2 ]3 [Ni(enMe)2 (H2O)][Ni(enMe)(H2O)2][Ni6 (enMe)3 (μ3-OH)3 (Ac)2 (H2O)(P2 W15 O56)]2 ⋅6 H2O (3) (en=ethylenediamine, enMe=1, 2-diaminopropane, Ac=CH3 COO(-)) have been made under hydrothermal conditions and were characterized by IR spectroscopy, elemental analysis, diffuse reflectance spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. The common structural features of compounds 1-3 contain the similar hexa-Ni-substituted Dawson polyoxometalate (POM) units that can be viewed as a [Ni6 (μ3-OH)3](9+) cluster capping on a [P2 W15 O56](12-) fragment. Compounds 1 and 2 are two isolated clusters, whereas compound 3 is the first 3D POM framework constructed from hexa-Ni-substituted Dawson POM units and Ni(enMe) complex bridges. The preparations of compounds 1-3 not only indicate that triangle coplanar Ni6 clusters are very stable fragments in both trivacant Keggin and trivacant Dawson POM systems, but also offer that the hydrothermal technique can act as an effective strategy for making novel Dawson-type high-nuclear transition-metal cluster substituted POMs by combination of lacunary Dawson precusors with transition-metal cations in the tunable role of organic ligands. In addition, magnetic measurements illustrate that there exist overall ferromagnetic interactions in compound 3. PMID:25376152

  18. Synthesis and characterization of two polyoxometalates consisting of different Cu-ligand hydrogen phosphate units

    SciTech Connect

    Yan, Jinshuang; Zhao, Xiaofang; Huang, Jiao; Gong, Kaining; Han, Zhangang Zhai, Xueliang

    2014-03-15

    Two polyoxometalates [(Cu-mbpy){sub 4}(HPO{sub 4}){sub 2}(H{sub 2}O){sub 2}][PMo{sub 12}O{sub 40}]·H{sub 2}O (1) and [(Cu-mbpy){sub 6}(HPO{sub 4}){sub 4}][PW{sub 12}O{sub 40}]·4H{sub 2}O (2) (mbpy=4,4'-dimethyl-2,2'-dipyridyl in 1; 5,5″-dimethyl-2,2'-dipyridyl in 2) have been synthesized and characterized by IR, X-ray powder diffraction, TG analysis and electrochemical property. The structural features of 1–2 are in their cationic moieties consisting of different linkages of [Cu-mbpy]{sup 2+} and HPO{sub 4}{sup 2−} groups. In 1 four Cu-mbpy bridged by two HPO{sub 4}{sup 2−} ions form a discrete cluster with an interesting octahedron of (Cu{sub 4}P{sub 2}), while in 2 Cu-mbpy fragments are bridged by HPO{sub 4}{sup 2−} ions into 1D structure consisting of trigonal bipyramidal polyhedra of (Cu{sub 3}P{sub 2}). Photocatalytic experiments indicate that compounds 1 and 2 are actively photocatalytic for degradation of methyl orange in the presence of H{sub 2}O{sub 2} under UV light irradiation. -- Graphical abstract: Two polyoxometalate-based supramolecular compounds consisting of different linkages based on Cu-ligand and HPO{sub 4}{sup 2−} groups have been synthesized and characterized. The photocatalytic activity are studied. Highlights: • Two polyoxometalate-based supramolecular compounds consisting of different linkages based on Cu-ligand and HPO{sub 4}{sup 2−} groups have been synthesized. • Hydrogen bonding and π…π interactions play important roles in constructing crystal supramolecular frameworks. • Two compounds represent a high photocatalytic activity in the degradation of methyl orange.

  19. Coupled sensitizer-catalyst dyads: electron-transfer reactions in a perylene-polyoxometalate conjugate.

    PubMed

    Odobel, Fabrice; Séverac, Marjorie; Pellegrin, Yann; Blart, Errol; Fosse, Céline; Cannizzo, Caroline; Mayer, Cédric R; Elliott, Kristopher J; Harriman, Anthony

    2009-01-01

    Ultrafast discharge of a single-electron capacitor: A variety of intramolecular electron-transfer reactions are apparent for polyoxometalates functionalized with covalently attached perylene monoimide chromophores, but these are restricted to single-electron events. (et=electron transfer, cr=charge recombination, csr=charge-shift reaction, PER=perylene, POM=polyoxometalate).A new strategy is introduced that permits covalent attachment of an organic chromophore to a polyoxometalate (POM) cluster. Two examples are reported that differ according to the nature of the anchoring group and the flexibility of the linker. Both POMs are functionalized with perylene monoimide units, which function as photon collectors and form a relatively long-lived charge-transfer state under illumination. They are reduced to a stable pi-radical anion by electrolysis or to a protonated dianion under photolysis in the presence of aqueous triethanolamine. The presence of the POM opens up an intramolecular electron-transfer route by which the charge-transfer state reduces the POM. The rate of this process depends on the molecular conformation and appears to involve through-space interactions. Prior reduction of the POM leads to efficient fluorescence quenching, again due to intramolecular electron transfer. In most cases, it is difficult to resolve the electron-transfer products because of relatively fast reverse charge shift that occurs within a closed conformer. Although the POM can store multiple electrons, it has not proved possible to use these systems as molecular-scale capacitors because of efficient electron transfer from the one-electron-reduced POM to the excited singlet state of the perylene monoimide. PMID:19197929

  20. Gas-Phase Fragmentation Pathways of Mixed Addenda Keggin Anions: PMo12-nWnO40 3- (n = 0-12)

    NASA Astrophysics Data System (ADS)

    Gunaratne, K. Don D.; Prabhakaran, Venkateshkumar; Johnson, Grant E.; Laskin, Julia

    2015-06-01

    We report a collision-induced dissociation (CID) investigation of the mixed addenda polyoxometalate (POM) anions, PMo12-nWnO40 3- (n = 0-12). The anions were generated in solution using a straightforward single-step synthesis approach and introduced into the gas phase by electrospray ionization (ESI). Distinct differences in fragmentation patterns were observed for the range of mixed addenda POMs examined in this study. CID of molybdenum-rich anions, PMo12-nWnO40 3- (n = 0-2), generates an abundant doubly charged fragment containing seven metal atoms (M) and 22 oxygen atoms (M7O22 2-) and its complementary singly charged PM5O18 - ion. In comparison, the doubly charged Lindqvist anion, (M6O19 2-) and its complementary singly charged PM6O21 - ion are the dominant fragments of Keggin POMs containing more than two tungsten atoms, PMo12-nWnO40 3- (n = 3-12). The observed transition in the dissociation pathways with an increase in the number of W atoms in the POM may be attributed to the higher barrier of tungsten-rich anions towards isomerization. We present evidence that the observed distribution of Mo and W atoms in the major M6O19 2- and M7O22 2- fragment ions is different from that predicted by a random distribution, indicating substantial segregation of the addenda metal atoms in the POMs. Charge reduction of the triply charged precursor anion resulting in formation of doubly charged anions is also observed. This is a dominant pathway for mixed POMs having a majority (8-11) of W atoms and a minor channel for other precursors indicating a close competition between fragmentation and charge loss pathways in CID of POM anions.

  1. Gas-Phase Fragmentation Pathways of Mixed-Addenda Keggin Anions: PMo12-nWnO403- (n = 0-12)

    SciTech Connect

    Gunaratne, Kalupathirannehelage Don D.; Prabhakaran, Venkateshkumar; Johnson, Grant E.; Laskin, Julia

    2015-06-01

    We report a collision-induced dissociation (CID) investigation of the mixed addenda polyoxometalate (POM) anions, PMo12-nWnO403- (n = 0-12). The anions were generated in solution using a straightforward single-step synthesis approach and introduced into the gas phase by electrospray ionization (ESI). Distinct differences in fragmentation patterns were observed for the range of mixed POMs examined in this study. CID of molybdenum-rich anions, PMo12- nWnO403- (n = 0-2), generates an abundant doubly charged fragment containing seven metal atoms (M) and twenty-two oxygen atoms (M7O222-) and its complementary singly charged PM5O18- ion, while the Lindqvist anion, (M6O192-) and its complementary PM6O21- ion are the dominant fragments of Keggin POMs containing more than two tungsten atoms, PMo12-nWnO403- (n = 3-12). The observed transition in the dissociation pathways with an increase in the number of W atoms may be attributed to the higher stability of tungsten-rich anions towards isomerization. We find that the observed distribution of Mo and W atoms in the major M6O192- and M7O222- fragment ions is different from that predicted by a random distribution indicating substantial segregation of the addenda metal atoms in the POMs. Electron detachment from the triply charged precursor anion resulting in formation of doubly charged anions is observed. This is a dominant dissociation pathway for mixed POMs having a majority (8-11) of W atoms and a minor channel for other precursors indicating a close competition between fragmentation and electron detachment pathways of POM anions.

  2. Gas-Phase Fragmentation Pathways of Mixed Addenda Keggin Anions: PMo12-nW nO 40 3- (n = 0-12).

    PubMed

    Gunaratne, K Don D; Prabhakaran, Venkateshkumar; Johnson, Grant E; Laskin, Julia

    2015-06-01

    We report a collision-induced dissociation (CID) investigation of the mixed addenda polyoxometalate (POM) anions, PMo(12-n)W(n)O(40)(3-) (n = 0-12). The anions were generated in solution using a straightforward single-step synthesis approach and introduced into the gas phase by electrospray ionization (ESI). Distinct differences in fragmentation patterns were observed for the range of mixed addenda POMs examined in this study. CID of molybdenum-rich anions, PMo(12-n)W(n)O(40)(3-) (n = 0-2), generates an abundant doubly charged fragment containing seven metal atoms (M) and 22 oxygen atoms (M(7)O(22)(2-)) and its complementary singly charged PM(5)O(18)(-) ion. In comparison, the doubly charged Lindqvist anion, (M(6)O(19)(2-)) and its complementary singly charged PM(6)O(21)(-) ion are the dominant fragments of Keggin POMs containing more than two tungsten atoms, PMo(12-n)W(n)O(40)(3-) (n = 3-12). The observed transition in the dissociation pathways with an increase in the number of W atoms in the POM may be attributed to the higher barrier of tungsten-rich anions towards isomerization. We present evidence that the observed distribution of Mo and W atoms in the major M(6)O(19)(2-) and M(7)O(22)(2-) fragment ions is different from that predicted by a random distribution, indicating substantial segregation of the addenda metal atoms in the POMs. Charge reduction of the triply charged precursor anion resulting in formation of doubly charged anions is also observed. This is a dominant pathway for mixed POMs having a majority (8-11) of W atoms and a minor channel for other precursors indicating a close competition between fragmentation and charge loss pathways in CID of POM anions. PMID:25832027

  3. Bridging the opposite chemistries of tantalum and tungsten polyoxometalates.

    PubMed

    Molina, P I; Sures, D J; Miró, P; Zakharov, L N; Nyman, M

    2015-09-28

    The disparate solubility, redox activity, and pH stability of the group V and group VI polyoxometalates (POMs) confer very different functionality on these species, and tailoring cluster properties by varying the ratio of group V to group VI metals poses both an opportunity and a synthetic challenge. A classic series of studies reported over 40 years ago provided some insight into W/Nb POMs, from which researchers have built on to date. However, the analogous W/Ta series has never been addressed in a systematic manner. Three members of this W/Ta series are presented here, synthesized from simple oxo- and peroxocoltanate precursors. [Ta3W3O19](5-) displays the Lindqvist-type structure, while [TaW9O32](5-) and [Ta2W8O32](6-) are isostructural with decatungstate ([W10O32](4-)). Additionally, the use of peroxoniobate instead of hexaniobate as the starting material drives the formation of the decatungstate-type structure [NbW9O32](5-) instead of the Lindqvist ion that was established to be the foundational cluster geometry in prior work. The electronic structure of the Nb/Ta substituted decatungstates is directly related to the degree of substitution inasmuch as the HOMO-LUMO energy gap (Egap) slightly increases as more Nb/Ta atoms are incorporated into the structure. The poor mixing of the d-orbitals of Nb/Ta and W is responsible for the observed trends in the UV spectra and cyclic voltammetry. Moreover, the stability of the molecular frameworks in the gas phase is also related to the extent of substitution as revealed by electrospray mass-spectrometry (ESI-MS). PMID:26262676

  4. Dye removal by surfactant encapsulated polyoxometalates.

    PubMed

    Yao, Lei; Lua, Shun Kuang; Zhang, Lizhi; Wang, Rong; Dong, ZhiLi

    2014-09-15

    A novel surfactant encapsulated polyoxometalate (SEP) has been synthesized by using a simple ion-exchange reaction. The prepared SEP complex was found to self-assemble into nanospherical particles whose morphology and component were characterized by TEM and XPS. The SEP was further incorporated into polyvinylidene fluoride (PVDF) to fabricate SEP incorporated composite membrane (SEP-M). Both the SEP and SEP-M exhibited excellent dye removal activities, which is for the first time reported as an intriguing property of the SEP. A regeneration scheme for SEP-M was successfully proposed without any loss of dye removal efficiency. Detailed mechanism studies were carried out to elucidate the nature of dye decolorization. Ion exchange was revealed to play a dominant role in the dye removal process. The current research not only renders a new example for the simple and direct synthesis of SEP but more importantly provides an efficient dye removal methodology. PMID:25194560

  5. Interaction between nanocluster polyoxometallates and low-molecular-weight organic compounds

    NASA Astrophysics Data System (ADS)

    Ostroushko, A. A.; Adamova, L. V.; Eremina, E. V.; Grzhegorzhevskii, K. V.

    2015-08-01

    The equilibrium sorption of methanol and benzene vapors by spherical porous nanocluster polyoxometallates with keplerate structures of different compositions (Mo132 and Mo72Fe30) and polyoxometallate (Mo138) with a toroidal structure and patterns in the kinetics of these processes are studied. Changes in the chemical potentials of the sorbates and polyoxometallates, specific Gibbs energies of the interaction of the polyoxometallates with the indicated substances, and the partial molar entropy of the interaction of Mo132 with methanol are calculated. The stability of the polyoxometallate structure in the sorbate vapors is studied via IR and Raman spectroscopy.

  6. Polyoxometalate-based organic-inorganic hybrid compounds containing transition metal mixed-organic-ligand complexes of N-containing and pyridinecarboxylate ligands.

    PubMed

    Zhao, De-Chuan; Hu, Yang-Yang; Ding, Hong; Guo, Hai-Yang; Cui, Xiao-Bing; Zhang, Xiao; Huo, Qi-Sheng; Xu, Ji-Qing

    2015-05-21

    Five new organic–inorganic hybrid compounds based on the Keggin-type polyoxoanion [SiW12O40]4−, namely [Cu3(2,2′-bpy)3(inic)(μ2-OH)(H2O)][SiW12O40]·2H2O (1), [Cu6(phen)6(μ3-Cl)2(μ2-Cl)2Cl2(inic)2][SiW12O40]·6H2O (2), [Cu2(hnic)(2,2′-bpy)2Cl]2[H2SiW12O40] (3), [Cu2(nic)(phen)2Cl2]2[SiW12O40] (4) and [Cu2(pic)(2,2′-bpy)2Cl]2[SiW12O40] (5) (inic = isonicotinic acid, hnic = 2-hydroxy-nicotinic acid, nic = nicotinic acid, pic = picolinic acid, 2,2′-bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) have been synthesized and characterized by IR, UV-Vis, XPS, XRD, cyclic voltammetric measurements, photoluminescence analysis and single crystal X-ray diffraction analysis. Crystal analysis reveals that compound 1 exhibits a 2-D double layered framework structure constructed from [SiW12O40]4− and copper-aqua-2,2′-bipy-hydroxyl-isonicotinate complexes. Compound 2 is a 0-D discrete structure formed by [SiW12O40]4− and copper-chloro-isonicotinate-phenanthroline complexes. Compound 3 shows a 1-D single chain structure based on the linkage of copper-2,2-bpy-chloro-2-hydroxy-nicotinate complexes and [SiW12O40]4−. Compounds 4 and 5 both contain polyoxometalate supported transition metal complexes, one is a polyoxometalate supported copper-chloro-nicotinate-phenanthroline complex in 4, and the other is a polyoxometalate supported copper-2,2-bpy-chloro-nicotinate complex in 5. It should be noted that nicotinic, isonicotinic and picolinic acids are structural isomers and 2-hydroxy-nicotinic acid is an in situ hydroxylated product of nicotinic acid. In addition, photocatalytic degradation of Rhodamine B (RhB) by compounds 1–5 has been investigated in aqueous solutions. PMID:25882351

  7. Incorporating polyoxometalates into a porous MOF greatly improves its selective adsorption of cationic dyes.

    PubMed

    Yan, Ai-Xue; Yao, Shuang; Li, Yang-Guang; Zhang, Zhi-Ming; Lu, Ying; Chen, Wei-Lin; Wang, En-Bo

    2014-06-01

    Various polyoxometalates (POMs) were successfully immobilized to the mesoporous coordination polymer MIL-101 resulting in a series of POM-MOF composite materials POM@MIL-101 (POM = K4PW11VO40, H3PW12O40, K4SiW12O40). These materials were synthesized by a simple one-pot reaction of Keggin POMs, tetramethylammonium hydroxide (TMAH), terephthalic acid (H2bdc), and Cr(3+) ions. XRD, FTIR, thermogravimetric analyses (TG), inductively coupled plasma (ICP) spectrometry, and energy-dispersive X-ray spectroscopy (EDX) collectively confirmed the successful combination of POMs and the porous framework. Further, these composites POM@MIL-101 with different loading of POMs were achieved by variation of the POM dosage. Notably, the uptake capacity of MIL-101 towards organic pollutants in aqueous solution was significantly improved by immobilization of hydrophilic POMs into cages of MIL-101. An uptake capacity of 371 mg g(-1), comparable to that of the graphene oxide sponges, and much higher than that of the commercial activated carbon, was achieved at room temperature in 5 min when dipping 20 mg PW11V@MIL-101 in the methylene blue (MB) solution (100 mL of 100 mg L(-1) MB solution). Further study revealed that the POM@MIL-101 composite materials not only exhibited a fast adsorption rate towards dye molecules, but also possessed of selective adsorption ability of the cationic dyes in wastewater. For example, the adsorption efficiency of PW11V@MIL-101 (10 mg) towards MB (100 mL of 10 mg L(-1)) could reach 98 % in the initial 5 min, and it could capture MB dye molecules from the binary mixture of the MB and MO with similar size. Also, the POM@MIL-101 materials could be readily recycled and reused, and no POM leached in the dye adsorption process. PMID:24737342

  8. Spin qubits with electrically gated polyoxometalate molecules.

    PubMed

    Lehmann, Jörg; Gaita-Arino, Alejandro; Coronado, Eugenio; Loss, Daniel

    2007-05-01

    Spin qubits offer one of the most promising routes to the implementation of quantum computers. Very recent results in semiconductor quantum dots show that electrically-controlled gating schemes are particularly well-suited for the realization of a universal set of quantum logical gates. Scalability to a larger number of qubits, however, remains an issue for such semiconductor quantum dots. In contrast, a chemical bottom-up approach allows one to produce identical units in which localized spins represent the qubits. Molecular magnetism has produced a wide range of systems with properties that can be tailored, but so far, there have been no molecules in which the spin state can be controlled by an electrical gate. Here we propose to use the polyoxometalate [PMo12O40(VO)2]q-, where two localized spins with S = 1/2 can be coupled through the electrons of the central core. Through electrical manipulation of the molecular redox potential, the charge of the core can be changed. With this setup, two-qubit gates and qubit readout can be implemented. PMID:18654290

  9. Supramolecular organization in organic-inorganic heterogeneous hybrid catalysts formed from polyoxometalate and poly(ampholyte) polymer.

    PubMed

    Raj, Gijo; Swalus, Colas; Guillet, Alain; Devillers, Michel; Nysten, Bernard; Gaigneaux, Eric M

    2013-04-01

    Hybridization of polyoxometalates (POMs) via the formation of an organic-inorganic association constitutes a new route to develop a heterogeneous POM catalyst with tunable functionality imparted through supramolecular assembly. Herein, we report on strategies to obtain tunable well-defined supramolecular architectures of an organic-inorganic heterogeneous hybrid catalyst formed by the association of a hydrophobically substituted polyampholyte copolymer (poly N, N-diallyl-N-hexylamine-alt-maleic acid) and phosphotungstic acid (H3PW12O40) POMs. The self-assembling property of the initial polyampholyte copolymer matrix is modulated by controlling the pH of the hybridization solution. When deposited on a mica surface, isolated, long and extended polymer chains are formed under basic conditions (pH 7.9), while globular or coiled structures are formed under acidic conditions (pH 2). The supramolecular assembly of the POM-polymer hybrid is found to be directed by the type and quantities of charges present on the polyampholyte copolymer, which themselves depend on the pH conditions. The hypothesis is that the Keggin type [PW12O40](3-) anions, which have a size of ~1 nm, electrostatically bind to the positive charge sites of the polymer backbone. The hybrid material stabilized at pH 5.3 consists of POM-decorated polymer chains. Statistical analysis of distances between pairs of POM entities show narrow density distributions, suggesting that POM entities are attached to the polymer chains with a high level of order. Conversely, under acidic conditions (pH 2), the hybrid shows the formation of a core-shell type of structure. The strategies reported here, to tune the supramolecular assembly of organic-inorganic hybrid materials, are highly valuable for the design and a more rational utilization of POM heterogeneous catalysts in several chemical transformations. PMID:23480273

  10. Controlling the Charge State and Redox Properties of Supported Polyoxometalates via Soft Landing of Mass Selected Ions

    SciTech Connect

    Gunaratne, Kalupathirannehelage Don D.; Johnson, Grant E.; Andersen, Amity; Du, Dan; Zhang, Weiying; Prabhakaran, Venkateshkumar; Lin, Yuehe; Laskin, Julia

    2014-12-04

    We investigate the controlled deposition of Keggin polyoxometalate (POM) anions, PMo12O403- and PMo12O402-, onto different self-assembled monolayer (SAM) surfaces via soft landing of mass-selected ions. Utilizing in situ infrared reflection absorption spectroscopy (IRRAS), ex situ cyclic voltammetry (CV) and electronic structure calculations, we examine the structure and charge retention of supported multiply-charged POM anions and characterize the redox properties of the modified surfaces. SAMs of alkylthiol (HSAM), perfluorinated alkylthiol (FSAM), and alkylthiol terminated with NH3+ functional groups (NH3+SAM) are chosen as model substrates for soft landing to examine the factors which influence the immobilization and charge retention of multiply charged anionic molecules. The distribution of charge states of POMs on different SAM surfaces are determined by comparing the IRRAS spectra with vibrational spectra calculated using density functional theory (DFT). In contrast to the results obtained previously for multiply charged cations, soft landed anions are found to retain charge on all three SAM surfaces. This charge retention is attributed to the substantial electron binding energy of the POM anions. Investigation of redox properties by CV reveals that, while surfaces prepared by soft landing exhibit similar features to those prepared by adsorption of POM from solution, the soft landed POM2- has a pronounced shift in oxidation potential compared to POM3- for one of the redox couples. These results demonstrate that ion soft landing is uniquely suited for precisely controlled preparation of substrates with specific electronic and chemical properties that cannot be achieved using conventional deposition techniques.

  11. An Effective Strategy To Construct Novel Polyoxometalate-Based Hybrids by Deliberately Controlling Organic Ligand Transformation In Situ.

    PubMed

    Wang, Xiu-Li; Zhang, Rui; Wang, Xiang; Lin, Hong-Yan; Liu, Guo-Cheng

    2016-07-01

    Deliberately controlling organic ligand transformation in situ has remained a challenge for the construction of polyoxometalate (POM)-based inorganic-organic hybrids. In this work, four POM-based hybrids assembled from an in situ bifurcating organic ligand-[Cu2(DIBA)4](H3PMo12O40)·6H2O (1), [Cu2(DIBA)4](H4SiW12O40)·6H2O (2), [Ag(HDIBA)2](H2PMo12O40)·2H2O (3), [Ag3(HDIBA)2(H2O)][(P2W18O62)1/2]·4H2O (4) (DIBAH = 3,5-di(1H-imidazol-1-yl) benzoic acid)-have been designed and obtained under hydrothermal conditions. Compounds 1 and 2 are isostructural, displaying a three-dimensional (3D) 2-fold interpenetrating framework with two types of channels, and the bigger channels are occupied by Keggin polyoxoanions and crystallization water molecules, but only crystallization water molecules in the smaller ones. Compound 3 displays a 3D supramolecular structure constructed from {Ag(HDIBA)2} segments and PMo12O40(3-) polyoxoanions through hydrogen bonding interactions. Compound 4 shows a 3D 2-fold interpenetrating framework based on (3, 3, 4)-connected network, which is constructed from {Ag3(HDIBA)2}n chains and P2W18O62(6-) polyoxoanions as linkers. The DIBAH ligand was generated in situ from 3,5-di(1H-imidazol-1-yl)benzonitrile by deliberate design, which illustrates that the strategy to construct novel POM-based hybrids by controlling ligand transformation in situ is rational and feasible. In addition, the effects of the central metal and POMs on the structures of the target compounds were discussed. Finally, the electrochemical and photocatalytic properties of compounds 1-4 have been investigated in this paper. PMID:27322656

  12. Differentiation of stem cells into insulin-producing cells under the influence of nanostructural polyoxometalates.

    PubMed

    Bâlici, Ştefana; Şuşman, Sergiu; Rusu, Dan; Nicula, Gheorghe Zsolt; Soriţău, Olga; Rusu, Mariana; Biris, Alexandru S; Matei, Horea

    2016-03-01

    Two polyoxometalates (POMs) with W were synthesized by a two-step, self-assembling method. They were used for stimulation of mesenchymal stem cell differentiation into insulin-producing cells. The nanocompounds (tris(vanadyl)-substituted tungsto-antimonate(III) anions [POM1] and tris-butyltin-21-tungsto-9-antimonate(III) anions [POM2]) were characterized by analytical techniques, including ultraviolet-visible, Fourier transform infrared, nuclear magnetic resonance spectroscopy, and transmission electron microscopy. We found that these polyoxotungstates, with 2-4 nm diameters, did not present toxic effects at the tested concentrations. In vitro, POM1 stimulated differentiation of a greater number of dithizone-positive cells (also organized in clusters) than the second nanocompound (POM2). Based on our in vitro studies, we have concluded that both the POMs tested had significant biological activity acting as active stimuli for differentiation of stem cells into insulin-producing cells. PMID:26397720

  13. Dye-sensitized polyoxometalate for visible-light-driven photoelectrochemical cells.

    PubMed

    Gao, Junkuo; Miao, Jianwei; Li, Yongxin; Ganguly, Rakesh; Zhao, Yang; Lev, Ovadia; Liu, Bin; Zhang, Qichun

    2015-08-28

    A simple and facile one-step method for the synthesis of an organic dye-functionalized polyoxometalate (POM) hybrid with visible-light photo-response was reported. The POM hybrid was fully characterized via single crystal XRD, powder XRD, FTIR and elemental analysis. The reaction of the organic dye with inorganic salts gave the dye-functionalized POM (MoBB3), in which the POM cluster was formed in situ. The electronic absorption peak of this hybrid was successfully extended beyond 680 nm. Photoelectrochemical measurement indicated that MoBB3 was photoresponsive under visible-light illumination, suggesting that it is an n-type (electron conductive) semiconducting material. This result might offer a method for the design of novel organic dye-functionalized POMs for photoelectric applications. PMID:26200796

  14. Multifunctional radical-doped polyoxometalate-based host-guest material: photochromism and photocatalytic activity.

    PubMed

    Liao, Jian-Zhen; Zhang, Hai-Long; Wang, Sa-Sa; Yong, Jian-Ping; Wu, Xiao-Yuan; Yu, Rongmin; Lu, Can-Zhong

    2015-05-01

    An effective strategy to synthesize multifunctional materials is the incorporation of functional organic moieties and metal oxide clusters via self-assembly. A rare multifunctional radical-doped zinc-based host-guest crystalline material was synthesized with a fast-responsive reversible ultraviolet visible light photochromism, photocontrolled tunable luminescence, and highly selective photocatalytic oxidation of benzylic alcohols as a result of blending of distinctively different functional components, naphthalenediimide tectons, and polyoxometalates (POMs). It is highly unique to link π-electron-deficient organic tectons and POMs by unusual POMs anion-π interactions, which are not only conducive to keeping the independence of each component but also effectively promoting the charge transfer or exchange among the components to realize the fast-responsive photochromism, photocontrolled tunable luminescence, and photocatalytic activity. PMID:25859742

  15. Nanoscale characterization of polyoxometalate catalysts by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Kaba, Mahmoud Samah

    Polyoxometalates (POMs) are dsp0 early transition metal oxide anion clusters that have found applications in acid and oxidation catalysis, electrode functionalization, and anti-retroviral therapy. Scanning tunneling microscopy (STM) is a powerful surface science technique that was used to determine the structural properties of self-assembled monolayers of POMs, and to probe the electronic properties of individual POM molecules. In our studies, POMs were deposited from aqueous solutions onto graphite surfaces, and the STM operated in ambient conditions gave well-resolved images of the POM-derivatized surfaces, showing highly ordered, two-dimensional surface arrays (corrugations). The shape and periodicity of the corrugations were consistent with the molecular dimensions and structures of POMs as determined by X-ray diffraction. Different coadsorbed species were also imaged in air using STM; the species were distinguished based on differences in shapes and on electronic properties. These results are important steps toward real-space STM imaging of chemical reactions. Tunneling spectroscopy (TS) measurements (current-voltage, or I-V spectra) taken atop the corrugations and compared with the I-V spectra of bare graphite, confirmed that the STM imaged individual POM molecules in monolayer arrays on graphite. The characteristics of the POM monolayers, such as the effects of counter-cation substitution and anion-framework substitution on the ordered arrays, were also examined by STM. The ubiquity of the ordered array formation of these metal oxide clusters suggests that they can be utilized to create well-defined surfaces with more complex chemical functions than one typically encounters in studies of metal and oxide single crystal surfaces. The POM corrugations exhibited localized electronic phenomena, referred to as negative differential resistance (NDR), at specific voltages in their I-V spectra. The NDR voltage in the I-V spectrum was dependent on the identity of the

  16. Nucleophilic substitution reaction for post-functionalization of polyoxometalates

    DOE PAGESBeta

    Yin, Panchao; Li, Qiang; Zhang, Jin; Wang, Longsheng; Hao, Jian; Wei, Yongge

    2015-07-06

    In this study, a hexamolybdate-based organic inorganic hybrid molecule containing a chloralkane fragment is synthesized and its Cl atom can be substituted by iodine and nitrate through nucleophilic substitution reactions in high yields, which provide a post-functionalization protocol to bring in various additional functional groups into polyoxometalate-based hybrid materials under mild conditions.

  17. Polyoxometalate salts of cationic nitronyl nitroxide free radicals

    NASA Astrophysics Data System (ADS)

    Coronado, Eugenio; Giménez-Saiz, Carlos; Gómez-García, Carlos J.; Romero, Francisco M.

    2008-12-01

    The cationic nitronyl nitroxide free radical of the N-methylpyridinium type p-MepyNN + has been combined with [Mo 8O 26] 4- and Keggin [SiW 12O 40] 4- polyanions to afford salts ( p-MepyNN) 4[Mo 8O 26]·DMSO (DMSO = dimethylsulfoxide) ( 1) and ( p-MepyNN) 4[SiW 12O 40]·6DMF (DMF = dimethylformamide) ( 2). Herein, their structural and magnetic properties are described.

  18. Towards an understanding of the bonding in polyoxometalates through bond order and bond energy analysis.

    PubMed

    Bridgeman, Adam J; Cavigliasso, Germán

    2003-01-01

    The molecular and electronic structures of transition metal complexes, [MOCl5]n- (n = 2 for M = V,Nb,Ta and n = 1 for Mo,W) and mixed-metal polyoxometalates, [M'M5O19]3-V,Nb,Ta, M = Mo,W) containing a single terminal oxo group on each metal, and of complexes of the uranyl ion [UO2]2+, [UO2(H2O)5]2+ and [UO2Cl4]2-, have been calculated using density functional methods. The calculated structures of the complexes are in good agreement with available experimental parameters. For the mixed-metal hexametalates, for which no crystallographic data is available, the calculations predict a small tetragonal compression of the clusters with only minor structural changes compared to the parent molybdate and tungstate. The metal oxygen bonding in these anions has been probed using Mayer-Mulliken, bond energy and atoms in molecule analyses (AIM). These methods provide a consistent description of the bonding in polyoxometalates. The terminal bonds between transition metal or uranium and oxygen atoms have large sigma and pi components with the pi contributions exceeding the sigma bonding. The transition metals utilize their d orbitals almost exclusively to bond to oxygen whilst uranium uses both its 5f and 6d orbitals. Oxygen atom charges increase and covalency indexes decrease with coordination number, with a marked separation of these terms according to the oxygen atom type. The total valency and AIM energies of the oxygen atoms are predicted to be almost constant for all types of oxygen site. The constancy of the bonding power of the oxygen atoms appears to be an important factor in determining the gross structures and details of the bonding in polyoxometalates. The Mayer Mulliken approach provides direct characterization of the bonding power of atoms and the extent of the interaction between pairs of atoms that is consistent with the results of the considerably more computationally demanding bond energy and AIM approaches. PMID:14527219

  19. Nanostructured polyoxometalate arrays with unprecedented properties and functions.

    SciTech Connect

    Dunphy, Darren Robert; Brinker, C. Jeffrey; Singh, Seema; Nyman, May Devan

    2003-11-01

    Polyoxometalates (POMs) are ionic (usually anionic) metal -oxo clusters that are both functional entities for a variety of applications, as well as structural units that can be used as building blocks if reacted under appropriate conditions. This is a powerful combination in that functionality can be built into materials, or doped into matrices. Additionally, by assembling functional POMs in ordered materials, new collective behaviors may be realized. Further, the vast variety of POM geometries, compositions and charges that are achievable gives this system a high degree of tunability. Processing conditions to link together POMs to build materials offer another vector of control, thus providing infinite possibilities of materials that can he nano-engineered through POM building blocks. POM applications that can be built into POM-based materials include catalysis, electro-optic and electro-chromic, anti-viral, metal binding, and protein binding. We have begun to explore three approaches in developing this field of functional, nano-engineered POM-based materials; and this report summarizes the work carried out for these approaches to date. The three strategies are: (1) doping POMs into silica matrices using sol-gel science, (2) forming POM-surfactant arrays and metal-POM-surfactant arrays, (3) using aerosol-spray pyrolysis of the POM-surfactant arrays to superimpose hierarchical architecture by self-assembly during aerosol-processing. Doping POMs into silica matrices was successful, but the POMs were partially degraded upon attempts to remove the structure-directing templates. The POM-surfactant and metal-POM-surfactant arrays approach was highly successful and holds much promise as a novel approach to nano-engineering new materials from structural and functional POM building blocks, as well as forming metastable or unusual POM geometries that may not be obtained by other synthetic methods. The aerosol-assisted self assembly approach is in very preliminary state of

  20. Modifying Randles circuit for analysis of polyoxometalate layer-by-layer films.

    PubMed

    Vyas, Ritesh N; Li, Kuyen; Wang, Bin

    2010-12-01

    Multilayer films with anionic phosphomolybidic acid (PMo(12)) clusters have been fabricated via the electrostatic layer-by-layer (LbL) method. The charged mass transport phenomena of these thin films have been studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with [Fe(CN)(6)](3-/4-) and [Ru(NH(3))(6)](3+/2+) as the redox probes. By adding a film resistance and a film capacitance to the conventional Randles equivalent circuit, we can calculate the diffusion coefficient values that help understand the microscopic nature of the thin films. When the negatively charged probe [Fe(CN)(6)](3-/4-) was used, lower diffusion coefficients were obtained for multilayers deposited from higher ionic strength solutions. This relationship was less obvious when the positively charged probe [Ru(NH(3))(6)](3+/2+) was used, in which the electrostatic attraction between PMo(12) clusters and the probe ions complicates the mass-transfer process. It is believed that the addition of salt to dipping solutions increases the tortuosity of the films so the mass transport takes longer paths, inducing lower diffusion coefficients. Higher PMo(12) loading causes lower diffusion coefficients due to the polyoxometalate clusters blocking the paths for charged probe ions. PMID:21077668

  1. Microwave assisted synthesis of a mono organoimido functionalized Anderson polyoxometalate.

    PubMed

    Ritchie, C; Bryant, G

    2015-12-28

    The synthesis of an aliphatic organoimido functionalized polyoxometalate has been achieved through a microwave assisted reaction protocol in the absence of any activating reagents. Characterization of the pendant amine containing polyanion [Mo6O18NC(OCH2)3MnMo6O18(OCH2)3CNH2](5-) (1) includes single crystal XRD, NMR, ESI-MS, IR and SAXS. PMID:26583488

  2. Tube-graft-Sheet Nano-Objects Created by A Stepwise Self-Assembly of Polymer-Polyoxometalate Hybrids.

    PubMed

    Tang, Jing; Li, Xue-Ying; Wu, Han; Ren, Li-Jun; Zhang, Yu-Qi; Yao, Hai-Xia; Hu, Min-Biao; Wang, Wei

    2016-01-19

    In this work, we report the preparation of complex nano-objects by means of a stepwise self-assembly of two polymer-polyoxometalate hybrids (PPHs) in solution. The PPHs are designed and synthesized by tethering two linear poly(ε-caprolactone)s (PCL) of different molecular weights (MW) on a complex of a Wells-Dawson-type polyoxometalate (POM) cluster and its countraions. The higher MW PCL-POM self-assembled into nanosheets, while the lower MW PCL-POM assembled into nanotubes just by altering the ratio of water in the DMF-water mixed solvent system. The two nano-objects have a similar membrane structure in which a PCL layer is sandwiched by the two POM-based complex layers. The PCL layer in the nanosheets is semicrystalline, while the PCL layer in the nanotubes is amorphous. We further exploited this MW-dependence to self-assemble the nanotubes on the nanosheet edges to create complex tube-graft-sheet nano-objects. We found that the nanotubes nucleate on the four {110} faces of the PCL crystal and then further grow along the crystallographic b-axis of the PCL crystal. Our findings offer hope for the further development of nano-objects with increasing complexity. PMID:26710830

  3. Keggin (K{sub 5}, H{sub 3}O)[SiV{sub 3}W{sub 9}O{sub 40}H]·xH{sub 2}O: Characterization and crystal structure

    SciTech Connect

    Bonfim, Rodrigo de Paiva Floro; Moura, Luiza Cristina de; Eon, Jean-Guillaume; Mentré, Olivier; Vezin, Hervé; Caldarelli, Stefano

    2014-05-01

    Single crystals of the potassium salt (K{sub 5}, H{sub 3}O)[SiV{sub 3}W{sub 9}O{sub 40}H]·xH{sub 2}O of the vanadium tri-substituted α-Keggin dodecatungstosilicate were prepared and analyzed by vibrational, EPR and {sup 51}V NMR spectroscopy. Varying the synthesis conditions allows crystallization of partially reduced anions. The crystal structure was determined for both oxidized (V{sup 5+}) and partially reduced (V{sup 4+/5+}) potassium salts. Single crystal X-ray diffraction data and solid state {sup 51}V-NMR spectra confirm the occurrence of a single vanadium site in a cubic structure due to rotational disorder of the Keggin ion. Partially reduced compounds crystallize within the same structure as fully oxidized ones. EPR experiments confirm strong interaction of V{sup 4+} with two V{sup 5+} ions, in accordance with insertion of a V{sub 3} subunit into the lacunary Keggin ion as designed in the synthesis method. The 3D-edifice is composed of K{sup +}/H{sub 2}O counter-sublattice with evidence of tunable water occupancy. - Graphical abstract: Relative arrangements of HPA clusters in (K{sub 5}, H{sub 3}O)[SiV{sub 3}W{sub 9}O{sub 40}]·xH{sub 2}O. - Highlights: • We prepared single crystals of the potassium salt (K{sub 5}, H{sub 3}O)[SiV{sub 3}W{sub 9}O{sub 40}H]·xH{sub 2}O. • The synthesis was designed to give the α-1,2,3-[SiV{sub 3}W{sub 9}O{sub 40}] Keggin ion. • Strict pH control was necessary to avoid vanadium partial reduction. • Reduced compounds crystallize within the same structure as fully oxidized ones. • EPR confirms strong interaction of V{sup 4+} with two V{sup 5+} ions in a V{sub 3} subunit.

  4. Thermochromic and solvatochromic properties of Lindqvist polyoxometalates.

    PubMed

    Herrmann, S; Margraf, J T; Clark, T; Streb, C

    2015-09-14

    The thermochromic and solvatochromic properties of Lindqvist metal oxide clusters [V(x)M(6-x)O19](n-) (x = 0, 1, 2, M = Mo, W) are reported. The cluster anions show pronounced changes of their electronic structure depending on their chemical environment (e.g. solvent polarity, temperature). These are rationalized using experimental and theoretical methods. A combined density functional theory and (51)V-NMR study suggests that temperature-dependent changes in the structural dynamics of the metal oxide framework are the underlying cause for the observed thermochromism. The results might open new avenues for the design of molecular optical sensors. PMID:26229997

  5. Syntheses, structures and properties of a series of photochromic hybrids based on Keggin tungstophosphates

    SciTech Connect

    Zhang Lizhi; Gu Wen; Dong Zhili; Liu Xin; Li Bing; Liu Meiling

    2009-05-15

    Three inorganic-organic hybrids based on Keggin tungstophosphates and lanthanides, [Pr(NMP){sub 6}(PW{sub 12}O{sub 40})]{sub n} (1), [Eu(NMP){sub 6}(PW{sub 12}O{sub 40})]{sub n} (2), and [Er{sub 2}(NMP){sub 12}(PW{sub 12}O{sub 40})][PW{sub 12}O{sub 40}] (3) (NMP=N-methyl-2-pyrrolidone), have been synthesized and characterized by elemental analysis, IR, UV-vis, and single-crystal X-ray diffraction. Compounds 1 and 2 exhibit 1D infinite zigzag chain structures, while compound 3 exhibits an ionic asymmetric structure due to lanthanide contraction. The three compounds are all photochromic. The magnetic susceptibility for 1 measured over the range 2-300 K shows that there is the dominant antiferromagnetic interaction in the compound. The results of luminescent properties show that compound 2 displays an interesting selectivity for Zn{sup 2+} ions. - Graphical Abstract: A series of photochromic hybrids based on Keggin tungstophosphates and lanthanides have been synthesized and characterized by elemental analysis, IR, UV-vis, and single-crystal X-ray diffraction. Their photochromic, magnetic, and luminescent properties have been studied.

  6. A novel iron-containing polyoxometalate heterogeneous photocatalyst for efficient 4-chlorophennol degradation by H2O2 at neutral pH

    NASA Astrophysics Data System (ADS)

    Zhai, Qian; Zhang, Lizhong; Zhao, Xiufeng; Chen, Han; Yin, Dongju; Li, Jianhui

    2016-07-01

    An iron-containing polyoxometalate (FeШLysSiW) was synthesized from ferric chloride (FeIII), lysine (Lys) and silicotungstic acid (SiW), and characterized using ICP-AES, TG, FT-IR, UV-vis DRS, XRD and SEM. The chemical formula of FeШLysSiW was determined as [Fe(H2O)5(C6H14N2O2)]HSiW12O40·8H2O, with Keggin-structured SiW12O404- heteropolyanion and lysine moiety. As a heterogeneous catalyst, the as prepared FeШLysSiW showed good performance in the degradation of 4-chlorophenol by H2O2 in both the dark and irradiated systems. Under the conditions of 4-chlorophenol 100 mg/L, FeШLysSiW 1.0 g/L, H2O2 20 mmol/L and pH 6.5, 4-chlorophenol could be completely degraded in ca. 40 min in the dark and ca. 15 min upon irradiation. Prolonging the reaction time to 3 h, the TOC removal reached to ca. 71.3% in the dark and ca. 98.8% under irradiation. The catalytic activity of FeШLysSiW stems from synergetic effect of ferric iron and SiW12O404- in the catalyst, corresponding to Fenton-like catalysis and photocatalysis, respectively. The enhanced degradation of 4-CP under irradiation is due to the simultaneous oxidation of 4-CP through the Fenton-like and photocatalytic processes. The high catalytic activity of FeШLysSiW is also strongly related to the chemisorption of H2O2 on FeШLysSiW surface by hydrogen bonding, which promotes both the Fenton-like and photocatalytic processes.

  7. Multinuclear diffusion NMR spectroscopy and DFT modeling: a powerful combination for unraveling the mechanism of phosphoester bond hydrolysis catalyzed by metal-substituted polyoxometalates.

    PubMed

    Luong, Thi Kim Nga; Shestakova, Pavletta; Mihaylov, Tzvetan T; Absillis, Gregory; Pierloot, Kristine; Parac-Vogt, Tatjana N

    2015-03-01

    A detailed reaction mechanism is proposed for the hydrolysis of the phosphoester bonds in the DNA model substrate bis(4-nitrophenyl) phosphate (BNPP) in the presence of the Zr(IV)-substituted Keggin type polyoxometalate (Et2NH2)8[{α-PW11O39Zr(μ-OH)(H2O)}2]⋅7 H2O (ZrK 2:2) at pD 6.4. Low-temperature (31)P DOSY spectra at pD 6.4 gave the first experimental evidence for the presence of ZrK 1:1 in fast equilibrium with ZrK 2:2 in purely aqueous solution. Moreover, theoretical calculations identified the ZrK 1:1 form as the potentially active species in solution. The reaction intermediates involved in the hydrolysis were identified by means of (1)H/(31)P NMR studies, including EXSY and DOSY NMR spectroscopy, which were supported by DFT calculations. This experimental/theoretical approach enabled the determination of the structures of four intermediate species in which the starting compound BNPP, nitrophenyl phosphate (NPP), or the end product phosphate (P) is coordinated to ZrK 1:1. In the proposed reaction mechanism, BNPP initially coordinates to ZrK 1:1 in a monodentate fashion, which results in hydrolysis of the first phosphoester bond in BNPP and formation of NPP. EXSY NMR studies showed that the bidentate complex between NPP and ZrK 1:1 is in equilibrium with monobound and free NPP. Subsequently, hydrolysis of NPP results in P, which is in equilibrium with its monobound form. PMID:25652658

  8. Theoretical exploration to second-order nonlinear optical properties of new hybrid complexes via coordination interaction between (metallo)porphyrin and [MSiW11O39](3-) (M=Nb(V) or V(V)) polyoxometalates.

    PubMed

    Zhang, Ting; Ma, Nana; Yan, Likai; Wen, Shizheng; Ma, Tengying; Su, Zhongmin

    2013-11-01

    The second-order nonlinear optical (NLO) properties of hybrid complexes via coordination interaction between porphyrin and Keggin-type polyoxometalates (POMs) α-[MSiW11O39](3-) (M=Nb(V) or V(V)) are investigated by time-dependent density functional theory (TDDFT). The calculated results show that this kind of organic-inorganic hybrid complexes possesses remarkably large molecular second-order NLO polarizability, especially for the ZnP3P-C≡C-4-Py-[VSiW11O39](3-) (complex 4), which has a computed β0 value of 261,410 a.u. and might be an excellent second-order NLO material. The effects of substituted metal atom (M), metalloporphyrin, and π-conjugation on NLO response are analyzed, the substituted metal atom (M) with a large electronegativity, the metalloporphyrin, and the lengthening of π-conjugation are helpful in enhancing the optical nonlinearity of these systems, which reveal the general rules to design the complexes with large optical nonlinearities. Furthermore, the solvent effect largely affects the first-order hyperpolarizability of the complex, it implies that the second-order polarizabilities increased with the increase of the solvent in polarity. PMID:24149319

  9. Accurate calculation of (31)P NMR chemical shifts in polyoxometalates.

    PubMed

    Pascual-Borràs, Magda; López, Xavier; Poblet, Josep M

    2015-04-14

    We search for the best density functional theory strategy for the determination of (31)P nuclear magnetic resonance (NMR) chemical shifts, δ((31)P), in polyoxometalates. Among the variables governing the quality of the quantum modelling, we tackle herein the influence of the functional and the basis set. The spin-orbit and solvent effects were routinely included. To do so we analysed the family of structures α-[P2W18-xMxO62](n-) with M = Mo(VI), V(V) or Nb(V); [P2W17O62(M'R)](n-) with M' = Sn(IV), Ge(IV) and Ru(II) and [PW12-xMxO40](n-) with M = Pd(IV), Nb(V) and Ti(IV). The main results suggest that, to date, the best procedure for the accurate calculation of δ((31)P) in polyoxometalates is the combination of TZP/PBE//TZ2P/OPBE (for NMR//optimization step). The hybrid functionals (PBE0, B3LYP) tested herein were applied to the NMR step, besides being more CPU-consuming, do not outperform pure GGA functionals. Although previous studies on (183)W NMR suggested that the use of very large basis sets like QZ4P were needed for geometry optimization, the present results indicate that TZ2P suffices if the functional is optimal. Moreover, scaling corrections were applied to the results providing low mean absolute errors below 1 ppm for δ((31)P), which is a step forward in order to confirm or predict chemical shifts in polyoxometalates. Finally, via a simplified molecular model, we establish how the small variations in δ((31)P) arise from energy changes in the occupied and virtual orbitals of the PO4 group. PMID:25738630

  10. Polyoxometalate-based eight-connected self-catenated network and fivefold interpenetrating framework

    SciTech Connect

    Zhang Zhiming; Liu Jia; Li Yangguang; Yao Shuang; Wang Enbo; Wang Xinlong

    2010-01-15

    Two entangled compounds [(bpy){sub 6}Cu{sup I}{sub 6}Cl{sub 3}(Mo{sup V}W{sub 5}O{sub 19})] (1) and [(bpy){sub 7}Cu{sup I}{sub 7}Cl{sub 2}(BW{sub 12}O{sub 40})].H{sub 2}O (2) (bpy=4,4'-bipyridine), have been successfully synthesized under hydrothermal conditions and characterized by element analysis, IR spectroscopy, thermal gravimetric analysis, X-ray photoelectron spectroscopy, and single crystal X-ray diffraction analyses. Compound 1 represents the first eight-connected self-penetrating network constructed from cuprous chloride clusters [Cu{sub 6}Cl{sub 3}] and Lindquist-type polyoxoanions. Compound 2 exhibits an interesting fivefold interpenetrating network consisting of Keggin polyoxoanions and Cu{sup +}-metal-organic framework. Crystal data of the two compounds are following: 1, triclinic, P1-bar, a=11.502(2) A, b=13.069(3) A, c=13.296(3) A, alpha=90.55(3){sup o}, beta=113.74(3){sup o}, gamma=110.48(3){sup o}, Z=1; 2, triclinic, P1-bar, a=12.341(3) A, b=13.119(3) A, c=15.367(3) A, alpha=99.12(3){sup o}, beta=90.53(3){sup o}, gamma=104.49(3){sup o}, Z=1. - Graphical abstract: Compound 1 is the POM-based unprecedented eight-connected self-penetrating organic-inorganic hybrid network constructed from the cuprous chloride clusters [Cu{sub 6}Cl{sub 3}], Lindquist-type polyoxoanions [Mo{sup V}W{sub 5}O{sub 19}], and the 4,4'-bipyridine ligands.

  11. Immobilization of polyoxometalates in crystalline solids for highly efficient heterogeneous catalysis.

    PubMed

    Ye, Ji-Jie; Wu, Chuan-De

    2016-06-21

    Polyoxometalates (POMs) are a unique class of molecular metal-oxygen clusters with attractive architecture and tunable properties. Due to their strong acidity, redox chemistry, photoactivity, charge distribution and multielectron transformation, POMs have been used as efficient catalysts in a variety of chemical reactions. To meet the requirement of sustainable chemistry, great effort has been focused on immobilization of the active POMs on different solid supports to realize heterogeneous catalysis. This short review summarizes the recent progress on immobilization of POM moieties in crystalline solids with defined crystal structures, including organic-inorganic hybrid materials, POM-based inorganic crystalline solids and POM-encapsulated metal-organic frameworks (POM@MOFs), and their catalytic properties in oxidation, hydrolysis, cyanosilylation, photocatalysis and electrocatalysis. As illustrated in the text, these crystalline solids exhibit interesting catalytic properties, such as high activity, stability and selectivity, and simple recovery and easy recycling, which are much superior to those of the corresponding constituent species in most cases. PMID:27230969

  12. Activation of molecular oxygen, polyoxometalates, and liquid-phase catalytic oxidation.

    PubMed

    Neumann, Ronny

    2010-04-19

    In this Forum Article, we discuss the use of dioxygen (O(2)) in oxidations catalyzed by polyoxometalates. One- and two-electron-transfer oxidation of organic substrates is catalyzed by H(5)PV(2)Mo(10)O(40) and often occurs via an outer-sphere mechanism. The reduced polyoxometalate is reoxidized in a separate step by O(2) with the formation of water. H(5)PV(2)Mo(10)O(40) also catalyzes electron transfer-oxygen transfer reactions. Here, in contrast to the paradigm that high-valent oxo species are often stronger oxygen-transfer species than lower-valent species, the opposite occurs. Thus, oxygen transfer from the catalyst is preceded by electron transfer from the organic substrate. The monooxygenase-type reduction of O(2) with polyoxometalates is also discussed based on the formation of a stable iron(III) hydroperoxide compound that may have implications for the oxidation of other lower-valent polyoxometalates such as vanadium(IV)- and ruthenium(II)-substituted polyoxometalates. Finally, the formation of hybrid compounds through the attachment of electron-accepting polyoxometalates to coordination compounds can modify the reactivity of the latter by making higher-valent oxidation states more accessible. PMID:20380461

  13. Five inorganic–organic hybrids based on Keggin polyanion [SiMo{sub 12}O{sub 40}]{sup 4−}: From 0D to 2D network

    SciTech Connect

    Yu, Xiao-Yang; Cui, Xiao-Bing; Lu, Jing; Luo, Yu-Hui; Zhang, Hong; Gao, Wei-Ping

    2014-01-15

    Five new inorganic–organic hybrids based on 4,4′-bipyridine and Keggin-type polyoxometalate [SiMo{sub 12}O{sub 40}]{sup 4−}, (SiMo{sub 12}O{sub 40})(H{sub 2}bipy){sub 2}·2H{sub 2}O (1), [Cu(Hbipy){sub 4}(HSiMo{sub 12}O{sub 40})(SiMo{sub 12}O{sub 40})](H{sub 2}bipy){sub 0.5}·7H{sub 2}O (2), [Cu{sub 2}(Hbipy){sub 6}(bipy)(SiMo{sub 12}O{sub 40}){sub 3}](Hbipy){sub 2}·6H{sub 2}O (3), [Cu(bipy){sub 2}(SiMo{sub 12}O{sub 40})](H{sub 2}bipy)·2H{sub 2}O (4) and [Cu{sub 2}(bipy){sub 4}(H{sub 2}O){sub 4}](SiMo{sub 12}O{sub 40})·13H{sub 2}O (5) (bipy=4,4′-bipyridine), have been hydrothermally synthesized. 1 consists of H{sub 2}bipy{sup 2+} and [SiMo{sub 12}O{sub 40}]{sup 4−} units. In 2, two [SiMo{sub 12}O{sub 40}]{sup 4−} are bridged by [Cu(Hbipy){sub 4}]{sup 6+} to form a [Cu(Hbipy){sub 4}(SiMo{sub 12}O{sub 40}){sub 2}]{sup 2−} dimmer. In 3, [SiMo{sub 12}O{sub 40}]{sup 4−} polyanions acting as bidentated bridging ligands and monodentated auxiliary ligands connect [Cu{sub 2}(Hbipy){sub 6}(bipy)]{sup 8+} units into a 1D zigzag chain. In 4, [SiMo{sub 12}O{sub 40}]{sup 4−} polyanions bridge neighboring 1D [Cu(bipy){sub 2}]{sup 2+} double chains into a 2D extended layer. In 5, [SiMo{sub 12}O{sub 40}]{sup 4−} polyanions acting as templates site alternately upon the grids from both sides of the square grid [Cu{sub 2}(bipy){sub 4}(H{sub 2}O){sub 4}]{sup 4+} layer. In addition, the electrochemical behaviors of 1, 3 and 4 and the photocatalysis property of 1 have been investigated. - Graphical abstract: Five new compounds based on [SiMo{sub 12}O{sub 40}]{sup 4−} have been successfully generated. [SiMo{sub 12}O{sub 40}]{sup 4−} anions play different roles in the structures of the five compounds. Display Omitted - Highlights: • Five new compounds based on [SiMo{sub 12}O{sub 40}]{sup 4−} have been generated. • [SiMo{sub 12}O{sub 40}]{sup 4−} anions play different roles in the five structures. • The electrochemical behaviors of 1, 3 and 4 have been

  14. An unusual mono-substituted Keggin anion-chain based 3D framework with 24-membered macrocycles as linker units

    SciTech Connect

    Pang Haijun; Ma Huiyuan; Yu Yan; Yang Ming; Xun Ye; Liu Bo

    2012-02-15

    A new compound, [Cu{sup I}(H{sub 2}O)(Hbpp){sub 2}] Subset-Of {l_brace}[Cu{sup I}(bpp)]{sub 2}[PW{sub 11}Cu{sup II}O{sub 39}]{r_brace} (1) (bpp=1,3-bis(4-pyridyl)propane), has been hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction. In compound 1, the unusual -A-B-A-B- array mono-substituted Keggin anion-chains and 24-membered (Cubpp){sub 2} cation-macrocycles are linked together to form a (2, 4) connected 3D framework with channels of ca. 9.784 Multiplication-Sign 7.771 A{sup 2} along two directions, in which the [Cu(H{sub 2}O)(Hbpp){sub 2}] coordination fragments as guest components are trapped. The photocatalytic experiments of compound 1 were performed, which show a good catalytic activity of compound 1 for photodegradation of RhB. Furthermore, the IR, TGA and electrochemical properties of compound 1 were investigated. - Graphical abstract: An unusual example of mono-substituted Keggin anion-chain based hybrid compound that possesses a 3D structure has been synthesized, which offers a feasible route for synthesis of such compounds. Highlights: Black-Right-Pointing-Pointer The first example of -A-B-A-B- array mono-substituted Keggin chain is observed. Black-Right-Pointing-Pointer An unusual three dimensional structure based mono-substituted Keggin anion-chains. Black-Right-Pointing-Pointer The photocatalysis and electrochemical properties of the title compound were studied.

  15. Cationic cure kinetics of a polyoxometalate loaded epoxy nanocomposite

    SciTech Connect

    Anderson, Benjamin J.

    2012-08-06

    The reaction cure kinetics of a novel polyoxometalate (POM) loaded epoxy nanocomposite is described. The POM is dispersed in the epoxy resin up to volume fractions of 0.1. Differential scanning calorimetry measurements show the cure of the epoxy resin to be sensitive to the POM loading. A kinetics study of the cure exotherm confirms that POM acts as a catalyst promoting cationic homopolymerization of the epoxy resin. The cure reaction is shown to propagate through two cure regimes. A fast cure at short time is shown to be propagation by the activated chain end (ACE) mechanism. A slow cure at long time is shown to be propagation by the activated monomer (AM) mechanism. The activation energies for the fast and slow cure regimes agree well with other epoxy based systems that have been confirmed to propagate by the ACE and AM mechanisms.

  16. Self-assembled polyoxometalates nanoparticles as pickering emulsion stabilizers.

    PubMed

    Leclercq, Loïc; Mouret, Adrien; Renaudineau, Séverine; Schmitt, Véronique; Proust, Anna; Nardello-Rataj, Véronique

    2015-05-21

    We easily produced a series of polyoxometalate (POM) nanoparticles by taking benefit from electrostatic attractions between various POMs and alkylammonium cations. These self-assembled supramolecular nanoparticles are fully characterized in terms of shape, nanostructure, and physicochemical properties. The nanoparticle differences are discussed on the basis of the chemical composition of the initial POM. Moreover, such particles have the ability to stabilize water-in-oil Pickering emulsions. Using a gel-trapping technique coupled to atomic force microscopy (AFM) observations, we determined their affinity toward oil by the contact angle of adsorbed nanoparticles. We show that the emulsion droplet size and stability can be directly linked to the nanoparticle hydrophobicity, which is tuned by the charge localization and molecular packing of POMs with the ammonium cations. Such particles are of special interest as they open large possibilities for Pickering interfacial catalysis. PMID:25937090

  17. Polyoxometalate water oxidation catalysts and methods of use thereof

    DOEpatents

    Hill, Craig L.; Gueletii, Yurii V.; Musaev, Djamaladdin G.; Yin, Qiushi; Botar, Bogdan

    2014-09-02

    Homogeneous water oxidation catalysts (WOCs) for the oxidation of water to produce hydrogen ions and oxygen, and methods of making and using thereof are described herein. In a preferred embodiment, the WOC is a polyoxometalate WOC which is hydrolytically stable, oxidatively stable, and thermally stable. The WOC oxidized waters in the presence of an oxidant. The oxidant can be generated photochemically, using light, such as sunlight, or electrochemically using a positively biased electrode. The hydrogen ions are subsequently reduced to form hydrogen gas, for example, using a hydrogen evolution catalyst (HEC). The hydrogen gas can be used as a fuel in combustion reactions and/or in hydrogen fuel cells. The catalysts described herein exhibit higher turn over numbers, faster turn over frequencies, and/or higher oxygen yields than prior art catalysts.

  18. Template-free polyoxometalate-assisted synthesis for ZnO hollow spheres

    SciTech Connect

    Li Qiuyu; Wang Enbo; Li Siheng; Wang Chunlei; Tian Chungui; Sun Guoying; Gu Jianmin; Xu Rui

    2009-05-15

    ZnO hollow spheres with diameters ranging from 400 to 600 nm and the thickness of shell approximate 80 nm were synthesized by a simple polyoxometalate-assisted solvothermal route without using any templates. The effect of polyoxometalate concentration, reaction time and temperature on the formation of the hollow spheres was investigated. The results indicated that the hollow spheres were composed of porous shells with nanoparticles and polyoxometalate play a key role in controlling morphology of ZnO. A possible growth mechanism based on polyoxometalate-assisted assembly and slow Ostwald ripening dissolution in ethanol solution is tentatively proposed. In addition, the room temperature photoluminescence spectrum showed that the ZnO hollow spheres exhibit exciting emission features with wide band covering nearly all the visible region. - Graphical abstract: ZnO hollow spheres with porous shell were synthesized by a one-step polyoxometalate-assisted solvothermal route at low temperature. Room temperature photoluminescence spectrum of the ZnO hollow spheres exhibits exciting emission features with a broad band covering nearly all the visible region.

  19. Crystallization of Keggin Heteropolyanions via a Two-Step Process in Aqueous Solutions.

    PubMed

    Bera, Mrinal K; Antonio, Mark R

    2016-06-15

    Although the analytical simplicity of the one-step classical theory of nucleation facilitates its use to understand crystallization processes, recent experiments and simulations have shown that many occur via multiple steps. According to the contemporary two-stage theory of nucleation, the onset of crystallization in a solution is preceded by large density fluctuations in the mother liquor that results in the formation of dense liquid-like correlated structures of the constituent solute particles. Here we report the observation of dense liquid-like correlated structures of heteropolyacid salts of α-Keggin anions (heteropolyanions) in aqueous solutions as volume is decreased long before the onset of crystallization by in situ time-dependent small-angle X-ray scattering measurements. Experiments were performed on drying drops of solutions of heteropolyacids to monitor their ordering before and during the onset of their crystallization. A continuous change in the density of the correlated structures is observed up to the onset of crystallization. Moreover, the correlated structures and the onset of crystallization are found to depend upon the charge of the heteropolyanions. The crystals formed within the drying drops of solutions during the crystallization process are found to be metastable polymorphic structures that are different from the stable crystal structures obtained after complete drying of the drops. Our results support a two-step process and Ostwald's rule of stages for the crystallization of heteropolyanions in their aqueous solutions upon evaporation. PMID:27249015

  20. Using density functional theory to study shape-reactivity relationships in Keggin Al-nanoclusters.

    PubMed

    Corum, Katie W; Mason, Sara E

    2016-10-01

    Keggin-based aluminum nanoclusters have been shown to be efficient sorbents for the removal of arsenic from water. Obtaining a molecular-level understanding of the adsorption processes associated with these molecules is of fundamental importance, and could pave the way for rational design strategies for water treatment. Due to their size and the availability of experimental crystal structures, Al nanoclusters are computationally tractable at the density functional theory (DFT) level. Here, we compare the reactivity of three aluminum polycations: [Al13O4(OH)24(H2O)12](7+) (Al13), [Al30O8(OH)56(H2O)26](18+) (Al30), and [Al32O8(OH)60(H2O)30](20+) (Al32). We use DFT calculations to determine reactivity as a function of particle topography, using sulfate and chloride as adsorption probes. Our comparative modeling of outer-sphere adsorption of Cl(-) and SO4(2-) on Al13, Al30, and A132 supports that the unique "hourglass" shape characteristic to Al30 gives rise to relatively strong adsorption in the molecular beltway, as well as a wide range of reaction energies as a function of particle topography. PMID:27393966

  1. Noble metal (Ru{sup III}, Pd{sup II}, Pt{sup II}) substituted {open_quotes}sandwich{close_quotes} type polyoxometalates: Preparation, characterization, and catalytic activity in oxidations of alkanes and alkenes by peroxides

    SciTech Connect

    Neumann, R.; Khenkin, A.M.

    1995-11-08

    The polyoxometalates substituted with noble metals, Pd(II), Pt(II) and Ru(III), K{sub 12}([WZnPd{sup II}{sub 2}(H{sub 2}O){sub 2}](ZnW{sub 9}O{sub 34}){sub 2}){center_dot}38H{sub 2}O, K{sub 12}[WZnPt{sup II}{sub 2}(H{sub 2}O){sub 2}][(ZnW{sub 9}O{sub 34}){sub 2}]{center_dot}36H{sub 2}O, and Na{sub 11}[WZnRu{sup III}{sub 2}(OH)(H{sub 2}O)][(ZnW{sub 9}O{sub 34}){sub 2}]{center_dot}42H{sub 2}O, were prepared by exchange of labile zinc atoms with noble metal atoms from the isostructural starting material, N{sub 12}-[WZn{sub 3}(H{sub 2}O){sub 2}][(ZnW{sub 9}O{sub 34}){sub 2}]{center_dot}46H{sub 2}O. Magnetic susceptibility studies as a function of temperature provide convincing evidence of two ruthenium (III) centers with no magnetic interaction between them. The catalytic activity of these compounds was tested for the oxidation of alkenes and alkanes using aqueous 30% hydrogen peroxide and 70% tert-butyl hydroperoxide as oxidants. The alkene oxidation proceeded in high reactivity and moderate selectivity to the epoxide product using 30% H{sub 2}O{sub 2}. Kinetic profiles as well as UV-vis and IR spectra before, during and after the reaction indicate that the catalysts are stable throughout the reaction. Formation of epoxides rather than ketonization in the reaction of terminal alkenes as well as low reactivity with iodosobenzene indicates that the reaction is tungsten centered and not noble metal centered. Oxidation of alkenes with tert-butyl hydroperoxide gave mostly allylic oxidation and/or addition of tert-butyl alcohol to the double bond. Oxidation of cyclic alkanes such as cyclohexane and adamantane was successful with tert-butyl hydroperoxide with catalytic activity 10 times higher than previously found for transition metal substituted Keggin compounds. Ratios of hydroxylation of adamantane at tertiary vs secondary positions indicates different active species in the palladium-, platinum-, and ruthenium substituted-polyoxometalates.

  2. Polyoxometalates as efficient catalysts for transformations of cellulose into platform chemicals.

    PubMed

    Deng, Weiping; Zhang, Qinghong; Wang, Ye

    2012-09-01

    Efficient utilisation of renewable biomass resources, particularly lignocellulosic biomass, for the production of chemicals and fuels has attracted much attention in recent years. The catalytic conversion of cellulose, the main component of lignocellulosic biomass, selectively into a platform chemical such as glucose, 5-hydroxymethyl furfural (HMF), sorbitol or gluconic acid under mild conditions is the most desirable route. Acid catalysis plays a crucial role in the conversion of cellulose via the cleavage of its glycosidic bonds. Owing to their unique features such as strong acidity, water-tolerance, low corrosiveness and recoverability, polyoxometalates have shown promising performances in transformations of cellulose into platform chemicals both in homogeneous and heterogeneous systems. This article highlights recent studies on polyoxometalates and polyoxometalate-based bifunctional catalysts or catalytic systems for the selective conversions of cellulose and cellobiose, a model molecule of cellulose, into platform chemicals. PMID:22653050

  3. Enhanced water splitting at thin film tungsten trioxide photoanodes bearing plasmonic gold-polyoxometalate particles.

    PubMed

    Solarska, Renata; Bienkowski, Krzysztof; Zoladek, Sylwia; Majcher, Aldona; Stefaniuk, Tomasz; Kulesza, Pawel J; Augustynski, Jan

    2014-12-15

    Tungsten trioxide (WO3) is one of a few stable semiconductor materials liable to produce solar fuel by photoelectrochemical water splitting. To enhance its visible light conversion efficiency, we incorporated plasmonic gold nanoparticles (Au NPs) derivatized with polyoxometalate (H3PMo12O40) species into WO3. The combined plasmonic and catalytic effect of Au NPs anchored to the WO3 surface resulted in a large increase of water photooxidation currents. Shielding the Au NPs with polyoxometalates appears to be an effective means to avoid formation of recombination centers at the photoanode surface. PMID:25332175

  4. Lanthanoid Template Isolation of the α-1,5 Isomer of Dicobalt(II)-Substituted Keggin Type Phosphotungstates: Syntheses, Characterization, and Magnetic Properties.

    PubMed

    Gupta, Rakesh; Hussain, Firasat; Sadakane, Masahiro; Kato, Chisato; Inoue, Katsuya; Nishihara, Sadafumi

    2016-09-01

    A new series of heterometallic 3d-4f sandwich type phosphotungstates, [Ln{PCo2W10O38(H2O)2}2](11-) (Ln = Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), and Lu(III), denoted 1a-10a, respectively), have been synthesized by a one-pot reaction procedure on reacting the dilacunary K14[P2W19O69(H2O)]·24H2O precursor with Ln(NO3)3·nH2O and Co(NO3)2·6H2O in an aqueous potassium chloride solution. All the compounds were isolated as potassium salts and further characterized with different analytical techniques such as single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, high-resolution electrospray ionization mass spectrometry, elemental analysis by inductively coupled plasma atomic emission spectroscopy, magnetic measurement, and thermogravimetric analysis. Single-crystal X-ray diffraction analysis of the compounds reveals that all these compounds are isostructural and crystallized in the orthorhombic crystal system in space group Iba2. The polyanions contain the α-1,5 isomer of dicobalt-substituted α-Keggin phosphotungstate, which sandwiched lanthanoid cation and formed novel heterometallic dimer species. The temperature-dependent magnetic susceptibilities of 1a, 2a, 4a, and 7a-10a indicate the dominant contribution of the ferromagnetic interaction between Co(II) and Co(II) within the cluster, while the antiferromagnetic interaction between Co(II) and Ln(III) dominates for 3a, 5a, and 6a. The isothermal magnetizations of 1a-10a show a gradual increase in magnetization at low fields and do not reach saturation even at 50 kOe. PMID:27509227

  5. Two proton-conductive hybrids based on 2-(3-pyridyl)benzimidazole molecules and Keggin-type heteropolyacids

    SciTech Connect

    Wei, Mei-Lin Wang, Yu-Xia; Wang, Xin-Jun

    2014-01-15

    Two proton-conductive organic/inorganic complexes were constructed by Keggin-type heteropolyacids and 2-(3-pyridyl)benzimidazole molecules. Single-crystal X-ray diffraction analyses revealed that two complexes crystallized in the monoclinic space group P2{sub 1}/c, exhibited different unit cell parameters, and presented different hydrogen-bonded networks constructed by 2-(3-pyridyl)benzimidazole molecules, [PMo{sub 12}O{sub 40}]{sup 3−} anions and solvent molecules. The results of thermogravimetric analyses suggest that two supramolecular complexes have different thermal stability based on the different hydrogen-bonded networks. Two complexes at 100 °C under 35–98% relative humidity showed a good proton conductivity of about 10{sup −3} S cm{sup −1}. The proton conductivities of two complexes under 98% relative humidity both increase on a logarithmic scale with temperature range from 25 to 100 °C. At 100 °C, both complexes showed poor proton conductivities of 10{sup −8}–10{sup −9} S cm{sup −1} under acetonitrile or methanol vapor. - Graphical abstract: Two molecular hybrids constructed by Keggin-type heteropolyacids and 2-(3-pyridyl)benzimidazole molecules showed good proton conductivities of 10{sup −3} S cm{sup −1} at 100 °C under 35–98% relative humidity. Display Omitted - Highlights: • 2-(3-Pyridyl)benzimidazole could form hydrogen bonds via the N–H groups. • Heteropolyacids have suitable characteristics to be used excellent proton conductors. • Two proton-conductive hybrids based on Keggin HPAs and 3-PyBim were constructed. • The structures were determined by using single-crystal X-ray diffraction data. • They showed good proton conductivities of 10{sup −3} S cm{sup −1} at 100 °C under 35–98% RH.

  6. Two proton-conductive hybrids based on 2,2 Prime -biimidazole molecules and Keggin-type heteropolyacids

    SciTech Connect

    Wei, Mei-Lin; Wang, Jun-Hua; Wang, Yu-Xia

    2013-02-15

    Two proton-conductive organic/inorganic complexes were constructed by Keggin-type heteropolyacids and 2,2 Prime -biimidazole molecules. Single-crystal X-ray diffraction analyses revealed that two complexes crystallized in the triclinic space group Pi, exhibited very close unit cell parameters, and presented similar three-dimensional (3D) hydrogen-bonded networks constructed by H{sub 2}biim, [PM{sub 12}O{sub 40}]{sup 3-} (M=W for 1 and Mo for 2) and solvent molecules. The results of thermogravimetric analyses (TG) suggest that two supramolecular complexes have similar thermal stability based on the same 3D packing. Two complexes at 100 Degree-Sign C under 98% relative humidity showed a good proton conductivity of about 10{sup -4} S cm{sup -1}. A possible mechanism of the proton conduction was proposed according to the experimental results. - Graphical Abstract: Two molecular hybrids constructed by Keggin-type heteropolyacids and 2,2 Prime -biimidazole molecules showed good proton conductivities of 10{sup -4} S cm{sup -1} in the temperature range of 85-100 Degree-Sign C under 98% relative humidity. Highlights: Black-Right-Pointing-Pointer H{sub 2}biim shows the ability to form hydrogen bonds via the N-H groups in the context of crystal engineering. Black-Right-Pointing-Pointer Heteropolyacids have suitable characteristics to be used excellent proton conductors. Black-Right-Pointing-Pointer Two new supramolecular complexes based-on Keggin-type heteropolyacids and H{sub 2}biim molecules were constructed. Black-Right-Pointing-Pointer The structure was determined by using single-crystal X-ray diffraction data. Black-Right-Pointing-Pointer Both complexes showed good proton conductivities of 10{sup -4} S cm{sup -1} in the temperature range of 85-100 Degree-Sign C.

  7. Dioxygen and water activation processes on multi-Ru-substituted polyoxometalates: comparison with the "blue-dimer" water oxidation catalyst.

    PubMed

    Kuznetsov, Aleksey E; Geletii, Yurii V; Hill, Craig L; Morokuma, Keiji; Musaev, Djamaladdin G

    2009-05-20

    Dioxygen and water activation on multi-Ru-substituted polyoxometalates were studied using the B3LYP density functional method. It was shown that the reaction of the Ru(2)-substituted gamma-Keggin polyoxotungstate {gamma-[(H(2)O)Ru(III)-(mu-OH)(2)-Ru(III)(H(2)O)][SiW(10)O(36)]}(4-), I(H(2)O), with O(2) is a 4-electron highly exothermic [DeltaE(gas) = 62.5 (DeltaE(gas) + DeltaG(solv(water)) = 24.6) kcal/mol] process and leads to formation of (H(2)O){gamma-[(O)Ru-(mu-OH)(2)-Ru(O)](H(2)O)[SiW(10)O(36)]}(4-), IV(H(2)O). Both the stepwise (or dissociative) and the concerted (or associative) pathways of this reaction occurring with and without water dissociation, respectively, were examined, and the latter has been found to be kinetically more favorable. It was shown that the first 1e-oxidation is achieved by the H(2)O-to-O(2) substitution, which might occur with a maximum of 23.1 (10.5) kcal/mol barrier and leads to the formation of {gamma-[(OO)Ru-(mu-OH)(2)-Ru(H(2)O)](H(2)O)[SiW(10)O(36)]}(4-), II(H(2)O). The second 1e-oxidation is initiated by the proton transfer from the coordinated water molecule to the superoxide (OO(-)) ligand in II(H(2)O) and is completed upon formation of hydroperoxo-hydroxo intermediate {gamma-[(OOH)Ru-(mu-OH)(2)-Ru(OH)](H(2)O)[SiW(10)O(36)]}(4-), III-1(H(2)O). The final 2e-oxidation occurs upon the proton transfer from the terminal OH-ligand to the Ru-coordinated OOH fragment and is completed at the formation of (H(2)O)...{gamma-[(O)Ru-(mu-OH)(2)-Ru(O)](H(2)O)[SiW(10)O(36)]}(4-), IV(H(2)O), with two Ru=O bonds. Each step in the associative pathway is exothermic and occurs with small energy barriers. During the process, the oxidation state of Ru centers increases from +3 to +4. The resulting IV(H(2)O) with a {Ru(O)-(mu-OH)(2)-Ru(O)} core should be formulated to have the Ru(IV)=O(*) units, rather than the Ru(V)=O groups. The reverse reaction, water oxidation by IV(H(2)O), is found to be highly endothermic and cannot occur; this finding is

  8. Metal-Directed Self-Assembly of a Polyoxometalate-Based Molecular Triangle: Using Powerful Analytical Tools to Probe the Chemical Structure of Complex Supramolecular Assemblies.

    PubMed

    Izzet, Guillaume; Macdonell, Andrew; Rinfray, Corentin; Piot, Madeleine; Renaudineau, Séverine; Derat, Etienne; Abécassis, Benjamin; Afonso, Carlos; Proust, Anna

    2015-12-21

    A polyoxometalate-based molecular triangle has been synthesized through the metal-driven self-assembly of covalent organic/inorganic hybrid oxo-clusters with remote pyridyl binding sites. The new metallomacrocycle was unambiguously characterized by using a combination of (1)H NMR spectroscopy, 2D diffusion NMR spectroscopy (DOSY), electrospray ionization travelling wave ion mobility mass spectrometry (ESI-TWIM-MS), small-angle X-ray scattering (SAXS) and molecular modelling. The collision cross-sections obtained from TWIM-MS and the hydrodynamic radii derived from DOSY are in good agreement with the geometry-optimized structures obtained by using theoretical calculations. Furthermore, SAXS was successfully employed and proved to be a powerful technique for characterizing such large supramolecular assemblies. PMID:26602994

  9. Polypyrrole-polyoxometalate/reduced graphene oxide ternary nanohybrids for flexible, all-solid-state supercapacitors.

    PubMed

    Chen, Yuyun; Han, Min; Tang, Yujia; Bao, Jianchun; Li, Shunli; Lan, Yaqian; Dai, Zhihui

    2015-08-11

    Novel polypyrrole-polyoxometalate/reduced graphene oxide ternary nanohybrids (TNHs) are synthesized via a one-pot redox relay strategy. The TNHs exhibit high areal specific capacitance (2.61 mF cm(-2)), and the fabricated solid device also exhibits good rate capability, excellent flexibility and mechanical stability. PMID:26140676

  10. Nanostructured H(3+x)PW(12-x)NbxO40 (x = 0-3) Keggin heteropolyacid catalysts.

    PubMed

    Choi, Jung Ho; Park, Dong Ryul; Park, Sunyoung; Song, In Kyu

    2011-09-01

    Nanostructured H(3+x)PW(12-x)NbxO40 (x = 0, 1, 2, 3) Keggin heteropolyacid (HPA) catalysts were investigated by scanning tunneling microscopy (STM) and tunneling spectroscopy to probe their redox property and oxidation catalysis. STM image showed that the HPAs formed two-dimensional well-ordered monolayer arrays on graphite surface. In tunneling spectra of the HPAs deposited on graphite, they exhibited a distinctive current-voltage behavior referred to as negative differential resistance (NDR). NDR peak voltage measured atop HPA molecule was then correlated with reduction potential and absorption edge energy determined by electrochemical method and UV-visible spectroscopy, respectively. It was revealed that NDR peak voltage of the HPAs appeared at less negative voltage with increasing reduction potential and with decreasing absorption edge energy. In order to correlate NDR peak voltage of H(3+x)PW(12-x)NbxO40 Keggin HPAs with oxidation catalysis, oxidative dehydrogenation of isobutyraldehyde to methacrolein was carried out as a model reaction. NDR peak voltage of the HPAs appeared at less negative voltage with increasing yield for methacrolein. PMID:22097499

  11. The supramolecular design of low-dimensional carbon nano-hybrids encoding a polyoxometalate-bis-pyrene tweezer.

    PubMed

    Modugno, Gloria; Syrgiannis, Zois; Bonasera, Aurelio; Carraro, Mauro; Giancane, Gabriele; Valli, Ludovico; Bonchio, Marcella; Prato, Maurizio

    2014-05-18

    A novel bis-pyrene tweezer anchored on a rigid polyoxometalate scaffold fosters a unique interplay of hydrophobic and electrostatic supramolecular interactions, to shape carbon nanostructures (CNSs)-based extended architectures. PMID:24595872

  12. A ternary nanocomposite electrode of polyoxometalate/carbon nanotubes/gold nanoparticles for electrochemical detection of hydrogen peroxide.

    PubMed

    Guo, Shuyue; Xu, Lin; Xu, Bingbing; Sun, Zhixia; Wang, Lihao

    2015-02-01

    In this work, a nanocomposite film electrode containing polyoxometalate (POM) clusters K6P2W18O62 (P2W18), carbon nanotubes (CNTs) and Au nanoparticles (AuNPs) was fabricated by a smart combination of layer-by-layer (LbL) with the self-assembly technique. The synergistic effect of POM, CNTs and AuNPs on the electrocatalysis of H2O2 was investigated to improve the sensitivity of H2O2 detection. The response of (P2W18/CNTs/P2W18/AuNPs)4 electrodes to H2O2 was remarkably enhanced due to large active sites and good electron conducting ability. The sensor exhibited a quick response (less than 1 second) to H2O2 with a high sensitivity (596.1 μAm M(-1) cm(-2)), and a low detection limit (52 nM). Based on the respective advantages of POMs, CNTs and AuNPs, the nanocomposite multilayer POMs/CNTs/POMs/AuNPs will have special properties and high potential for application. PMID:25431885

  13. Three new extended Preyssler-type polyoxometalates modified by transition metal-2,2 Prime -biimidazole complexes

    SciTech Connect

    Yang, Chun-Yue; Zhang, Lan-Cui; Wang, Zan-Jiao; Wang, Lin; Li, Xiao-Hui; Zhu, Zai-Ming

    2012-10-15

    Three extended Preyssler-type ({l_brace}P{sub 5}W{sub 30}{r_brace}) polyoxometalates modified by transition metal (TM)-2,2 Prime -biimidazole (abbreviated as H{sub 2}biim) complexes, namely [Mn(H{sub 2}biim){sub 3}]{sub 5}H{sub 2}[{l_brace}Mn(H{sub 2}biim){sub 2}(H{sub 2}O){r_brace} (NaP{sub 5}W{sub 30}O{sub 110})]{center_dot}39H{sub 2}O (1), [{l_brace}(H{sub 2}biim){sub 2}Zn({mu}-OH)Zn(H{sub 2}biim)({mu}-H{sub 2}biim)Zn(H{sub 2}biim)(H{sub 2}O){r_brace}{sub 2}H{sub 4}(NaP{sub 5}W{sub 30}O{sub 110})]{center_dot}22 H{sub 2}O (2), and {l_brace}(H{sub 4}biim){sub 18}NaH{sub 5}[({mu}-Fe(H{sub 3}biim)(H{sub 2}O){sub 3})({mu}-Fe(H{sub 2}O){sub 4})(NaP{sub 5}W{sub 30}O{sub 110}){sub 2}]{sub 2}{center_dot}78H{sub 2}O{r_brace}{sub n} (3) have been hydrothermally synthesized, and characterized by physicochemical and spectroscopic methods. Their catalytic activities have been investigated. 1 contains mono-supporting {l_brace}P{sub 5}W{sub 30}{r_brace} anions. In compound 2, a {l_brace}P{sub 5}W{sub 30}{r_brace} anion is bi-supported by two symmetrical chains constructed by trinuclear zinc complexes. Compound 3 is composed of infinite 1-D zigzag chains built up of {l_brace}P{sub 5}W{sub 30}{r_brace} polyoxoanions linked via [Fe(H{sub 2}O){sub 4}]{sup 3+} and [Fe(H{sub 3}biim)(H{sub 2}O){sub 3}]{sup 4+} fragments. H{sub 2}biim ligands adopt three coordination modes in the structure. All these compounds have 3-D supramolecular frameworks via extensive hydrogen-bonding interactions. - Graphical abstract: Three new extended Preyssler-type polyoxometalates modified by TM-2,2 Prime -biimidazole complexes are obtained, they display high thermal stabilities. Highlights: Black-Right-Pointing-Pointer Three new extended Preyssler-type polyoxometalates were hydrothermally synthesized. Black-Right-Pointing-Pointer An interesting trinuclear zinc-2,2 Prime -biimidazole-polyanion complex was obtained. Black-Right-Pointing-Pointer The huge {l_brace}P{sub 5}W{sub 30}{r_brace} clusters were

  14. Covalent attachment of Anderson-type polyoxometalates to single-walled carbon nanotubes gives enhanced performance electrodes for lithium ion batteries.

    PubMed

    Ji, Yuanchun; Hu, Jun; Huang, Lujiang; Chen, Wei; Streb, Carsten; Song, Yu-Fei

    2015-04-20

    Single-walled carbon nanotubes (SWNTs) covalently functionalized with redox-active organo-modified polyoxometalate (POM) clusters have been synthesized and employed as electrode materials in lithium ion batteries. The Anderson cluster [MnMo6 O24 ](9-) is functionalized with Tris (NH2 C(CH2 OH)3 ) moieties, giving the new organic-inorganic hybrid [N(nC4 H9 )4 ]3 [MnMo6 O18 {(OCH2 )3 CNH2 }2 ]. The compound is then covalently attached to carboxylic acid-functionalized SWNTs by amide bond formation and the stability of this nanocomposite is confirmed by various spectroscopic methods. Electrochemical analyses show that the nanocomposite displays improved performance as an anode material in lithium ion batteries compared with the individual components, that is, SWNTs and/or Anderson clusters. High discharge capacities of up to 932 mAh g(-1) at a current density of 0.5 mA cm(-2) can be observed, together with high long-term cycling stability and decreased electrochemical impedance. Chemisorption of the POM cluster on the SWNTs is shown to give better electrode performance than the purely physisorbed analogues. PMID:25765945

  15. Vanadogermanate cluster anions.

    PubMed

    Whitfield, T; Wang, X; Jacobson, A J

    2003-06-16

    Three novel vanadogermanate cluster anions have been synthesized by hydrothermal reactions. The cluster anions are derived from the (V(18)O(42)) Keggin cluster shell by substitution of V=O(2+) "caps" by Ge(2)O(OH)(2)(4+) species. In Cs(8)[Ge(4)V(16)O(42)(OH)(4)].4.7H(2)O, 1, (monoclinic, space group C2/c (No. 15), Z = 8, a = 44.513(2) A, b = 12.7632(7) A, c = 22.923(1) A, beta = 101.376(1) degrees ) and (pipH(2))(4)(pipH)(4)[Ge(8)V(14)O(50).(H(2)O)] (pip = C(4)N(2)H(10)), 2 (tetragonal, space group P4(2)/nnm (No. 134), Z = 2, a = 14.9950(7) A, c = 18.408(1) A), two and four VO(2+) caps are replaced, respectively, and each cluster anion encapsulates a water molecule. In K(5)H(8)Ge(8)V(12)SO(52).10H(2)O, 3, (tetragonal, space group I4/m (No. 87), Z = 2, a = 15.573(1) A, c = 10.963(1) A), four VO(2+) caps are replaced by Ge(2)O(OH)(2)(4+) species, and an additional two are omitted. The cluster ion in 3 contains a sulfate anion disordered over two positions. The cluster anions are analogous to the vanadoarsenate anions [V(18)(-)(n)()As(2)(n)()O(42)(X)](m)(-) (X = SO(3), SO(4), Cl; n = 3, 4) previously reported. PMID:12793808

  16. Stabilization of plutonium(III) in the Preyssler polyoxometalate.

    PubMed

    Antonio, Mark R; Chiang, Ming-Hsi

    2008-09-15

    The Na(+) ion encapsulated within the Preyssler heteropolyoxoanion, [NaP5W30O110](14-), was exchanged with Pu(III) under hydrothermal conditions to obtain [Pu(III)P5W30O110](12-) (abbreviated [PuPA](12-)) with hybrid electrochemical properties resulting from the combination of the key redox behaviors of the Pu cation and the P-W-O anion. The electroanalytical chemistry of this two-center, multielectron redox system in a 1 M HCl electrolyte shows that Pu(III) is oxidized to Pu(IV) at the half-wave potential, E(1/2), of +0.960 V versus Ag/AgCl, which is 0.197 V more positive than the corresponding electrode potential for the Pu(III) aqua ion also in 1 M HCl, indicating the stabilization of the trivalent Pu cation by its encapsulation in the Preyssler polyoxometalate (POM). This effect is uncommon in actinide-POM chemistry, wherein electrode potential shifts of the opposite nature (to more negative values), leading to the stabilization of the tetravalent ions by complexation, are renowned. Moreover, in cyclic voltammetry measurements of the Pu(III) aqua ion and [PuPA](12-), the peak currents, i(p), for the one-electron Pu(III)/Pu(IV) processes show different dependencies with the scan rate, nu. The former shows proportionality with nu(1/2), indicating freely diffusing species, whereas the latter shows proportionality with nu, indicating a surface-confined one. The first of the five successive two-electron, W-centered reduction processes in [PuPA](12-) occurs at E(1/2) = -0.117 V versus Ag/AgCl, which is 1.077 V less than the E(1/2) for the Pu(III)/Pu(IV) oxidation, thereby providing an experimental, electrochemical measure of the highest occupied molecular orbital/lowest unoccupied molecular orbital energy gap, which compares well with values previously obtained by density-functional theory, complete active space-self consistent field, and post-Hartree-Fock calculations for a series of M(n+)-exchanged systems, [MPA](n-15) for 1 < or = n < or = 4 (Fernandez, J. A

  17. Synthesis, structure and magnetism of a S-shaped multi-iron substituted arsenotungstate containing a trivacant Keggin [B-{alpha}-As{sup V}W{sub 9}O{sub 34}]{sup 9-} and a hexavacant Keggin [{alpha}-As{sup V}W{sub 6}O{sub 26}]{sup 11-} fragments

    SciTech Connect

    Zhao Junwei; Han Qiuxia; Shi Dongying; Chen Lijuan; Ma Pengtao; Wang Jingping; Niu Jingyang

    2011-10-15

    A S-shaped multi-iron substituted arsenotungstate [enH{sub 2}]{sub 2}[({alpha}-H{sub 2}As{sup V}W{sub 6}O{sub 26})Fe{sub 3}(H{sub 2}O)(B-{alpha}-H{sub 4}As{sup V}W{sub 9}O{sub 34})]{sub 2}[Fe]{sub 2}.8H{sub 2}O (1) (en=ethylenediamine) has been prepared by reaction of K{sub 14}[As{sub 2}{sup III}W{sub 19}O{sub 67}(H{sub 2}O)].nH{sub 2}O with Fe{sub 2}(SO{sub 4}){sub 3}.xH{sub 2}O under hydrothermal conditions and structurally characterized by elemental analyses, IR spectra, UV spectra, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. The skeleton of 1 consists of two asymmetric sandwich-type subunits [({alpha}-H{sub 2}As{sup V}W{sub 6}O{sub 26})Fe{sub 3}(H{sub 2}O)(B-{alpha}-H{sub 4}As{sup V}W{sub 9}O{sub 34})]{sup 5-} linked by a di-Fe{sup III} cluster. Moreover, magnetic susceptibility measurements demonstrate that 1 indicates the antiferromagnetic coupling interactions within Fe{sup III} centers with the best-fitting set of parameters of J{sub 1}=-7.07 cm{sup -1}, J{sub 2}=-0.45 cm{sup -1} and g=2.05, which are generated by the addition of the expressions of the molar susceptibilities of two tri-Fe{sup III} clusters and one di-Fe{sup III} cluster derived from for spin pairs coupled through the isotropic exchange interactions. - Graphical abstract: S-shaped multi-iron substituted arsenotungstate consisting of two asymmetric sandwich-type subunits has been hydrothermally synthesized and structurally characterized. Its magnetic properties have been investigated. Highlights: > Multi-iron substituted arsenotungstate. > Symmetric sandwich-type subunits. > Antiferromagnetic coupling interactions within Fe{sup III} centers. > Hexavacant Keggin POM fragments.

  18. Synthesis and structural characterization of inorganic-organic-inorganic hybrids of dipalladium-substituted γ-Keggin silicodecatungstates.

    PubMed

    Hirano, Tomohisa; Uehara, Kazuhiro; Uchida, Sayaka; Hibino, Mitsuhiro; Kamata, Keigo; Mizuno, Noritaka

    2013-03-01

    Three inorganic-organic-inorganic hybrids of dipalladium-substituted γ-Keggin silicodecatungstates with organic linkers of different lengths, TBA8[{(γ-H2SiW10O36Pd2)(O2C(CH2)nCO2)}2] (n = 1 (II), 3 (III), and 5 (IV), TBA = [(n-C4H9)4N](+)), were synthesized by exchange of the acetate ligands in TBA4[γ-H2SiW10O36Pd2(OAc)2] (ITBA) with malonic, glutaric, and pimelic acids, respectively. The X-ray crystallographic analysis of II, IIIA (IIIA: III with DCE, DCE = 1,2-dichloroethane), and IVA (IVA: IV with 10DCE) revealed that the anion parts of II, IIIA, and IVA were inorganic-organic-inorganic hybrids composed of two dipalladium-substituted γ-Keggin silicodecatungstates connected by two dicarboxylate ligands. In the crystal structure of IVA, 10 DCE molecules per polyanion were present in the vicinity of polyanions. Compound IVB (IVB: IV with 0.2DCE) was obtained by the evacuation of IVA. The DCE sorption-desorption isotherms of IVB showed that the amount of DCE sorbed was saturated at 10.5 mol mol(-1), of which the amount was close to that (10 mol mol(-1)) of crystallographically assigned DCE molecules. In the DCE sorption-desorption isotherms, a low-pressure hysteresis was observed probably because of hydrogen-bonding interaction between DCE molecules and polyanions. The powder X-ray diffraction (XRD) pattern of IVA changed with decrease in the relative DCE vapor pressure to form IVC (IVC: IV with 0.7DCE) at P/P0 = 0.0. The in situ powder XRD study showed reversible structure transformation between IVA and IVC driven by the sorption-desorption of DCE. PMID:23398623

  19. Spontaneous structuration in coacervate-based protocells by polyoxometalate-mediated membrane assembly.

    PubMed

    Williams, David S; Patil, Avinash J; Mann, Stephen

    2014-05-14

    Molecularly crowded, polyelectrolyte/ribonucleotide-enriched membrane-free coacervate droplets are transformed into membrane-bounded sub-divided vesicles by using a polyoxometalate-mediated surface-templating procedure. The coacervate to vesicle transition results in reconstruction of the coacervate micro-droplets into novel three-tiered micro-compartments comprising a semi-permeable negatively charged polyoxometalate/polyelectrolyte outer membrane, a sub-membrane coacervate shell, and an internal aqueous lumen. We demonstrate that organic dyes, ssDNA, magnetic nanoparticles and enzymes can be concentrated into the interior of the micro-compartments by sequestration into the coacervate micro-droplets prior to vesicle formation. The vesicle-encapsulated proteins are inaccessible to proteases in the external medium, and can be exploited for the spatial localization and coupling of two-enzyme cascade reactions within single or between multiple populations of hybrid vesicles dispersed in aqueous media. PMID:24515342

  20. New Electrochemical Evaluation of the Antioxidant Capacity of Beverages with Polyoxometalates as Redox Probes.

    PubMed

    Ueda, Tadaharu; Okumura, Takashi; Tanaka, Yukino; Akase, Saki; Shimamura, Tomoko; Ukeda, Hiroyuki

    2016-01-01

    A new method was developed to evaluate antioxidant activity based on the redox properties of polyoxometalates, which are partially reduced by antioxidants to generate a limiting potential. The polyoxometalates [PMo12O40](3-), [PVW11O40](4-) and [SV2W10O40]4- formed in situ were used as electrochemical probes for the new evaluation method, and their formation conditions were optimized to evaluate the antioxidant activities of gallic acid, ellagic acid, catechin, quercetin, morin, trans-ferulic acid, sesamol, α-tocopherol, δ-tocopherol and L-ascorbic acid. The observed difference between initial potential and limiting potential (ΔE) were compared with spectrophotometrically evaluated antioxidant activities. In addition, the antioxidant capacities of five beverages (Japanese green tea, concentrated catechin-containing green tea, grapefruit juice, red wine and Japanese sake) were evaluated. PMID:27506707

  1. Predicting (17)O NMR chemical shifts of polyoxometalates using density functional theory.

    PubMed

    Sharma, Rupali; Zhang, Jie; Ohlin, C André

    2016-03-21

    We have investigated the computation of (17)O NMR chemical shifts of a wide range of polyoxometalates using density functional theory. The effects of basis sets and exchange-correlation functionals are explored, and whereas pure DFT functionals generally predict the chemical shifts of terminal oxygen sites quite well, hybrid functionals are required for the prediction of accurate chemical shifts in conjunction with linear regression. By using PBE0/def2-tzvp//PBE0/cc-pvtz(H-Ar), lanl2dz(K-) we have computed the chemical shifts of 37 polyoxometalates, corresponding to 209 (17)O NMR signals. We also show that at this level of theory the protonation-induced pH dependence of the chemical shift of the triprotic hexaniobate Lindqvist anion, [HxNb6O19]((8-x)), can be reproduced, which suggests that hypotheses regarding loci of protonation can be confidently tested. PMID:26925832

  2. Donor-acceptor organo-imido polyoxometalates: high transparency, high activity redox-active NLO chromophores.

    PubMed

    Al-Yasari, Ahmed; Van Steerteghem, Nick; El Moll, Hani; Clays, Koen; Fielden, John

    2016-02-21

    We show that polyoxometalates (POMs) are an excellent redox-active acceptor on which to base high performance 2(nd) order non-linear optical (NLO) chromophores. This is demonstrated through three new organoimido-Lindqvist derivatives with HRS β0-values exceeding those of any dipolar organic system with comparable donor, π-system and absorption profile. Thus, organoimido POMs may provide a new generation of high performance, high transparency, and potentially redox-switchable NLO materials. PMID:26815652

  3. Temperature- and salt-responsive polyoxometalate-poly(N-isopropylacrylamide) hybrid macromolecules in aqueous solution.

    PubMed

    Zhou, Jing; Yin, Panchao; Chen, Xinyue; Hu, Lang; Liu, Tianbo

    2015-11-14

    Polyoxometalate (POM) polar head groups were covalently functionalized with poly(N-isopropylacrylamide) (PNIPAM) tails. The macromolecular hybrid demonstrates solution behavior of hydrophilic macroions by self-assembling into blackberry structures at room temperature. The hybrid behaves like an amphiphilic surfactant by forming a vesicular structure when the temperature is above the phase transition of PNIPAM. The reversible self-assembly is also salt-sensitive and the salt-induced smaller vesicular formation results from counterion-association. PMID:26383608

  4. Four Hybrid Materials Based on Preyssler P5W30 Polyoxometalate and First-Row Transition-Metal Complex.

    PubMed

    Hu, Tuo-Ping; Zhao, Ya-Qin; Jagličić, Zvonko; Yu, Kai; Wang, Xing-Po; Sun, Di

    2015-08-01

    Four Preyssler P5W30 based inorganic-organic hybrids, formulated as {[Cu12(pbtz)2(Hpbtz)2(OH)4(H2O)16][Na(H2O)P5W30O110]}·16H2O (1; H2pbtz = 5'-(pyridin-2-yl)-1H,2'H-3,3'-bi(1,2,4-triazole)), {[Cu10(ttbz)2(Httbz)4(OH)6(H2O)8][K(H2O)H2P5W30O110]}·30H2O (2; Httbz = 1-(tetrazo-5-yl)-4-(triazo-1-yl)benzene), {[Ni6(bpz)6(H2O)16][Na(H2O)H2P5W30O110]}·36H2O (3; bpz = 3,3',5,5'-tetramethyl-4,4-bipyrazole), {[Co4(bpz)6(H2O)9][K(H2O)H6P5W30O110]}·46H2O (4), have been isolated and structurally identified via microanalysis, thermogravimetry (TG), infrared (IR) spectroscopy, and X-ray single-crystal diffraction. Compound 1 exhibits a 3D binodal (3,6)-connected ant framework composed of dodeca-supported P5W30 polyoxometalate (POM) clusters and discrete [Cu6(pbtz)(Hpbtz)(OH)2(H2O)8] subunits. Compound 2 is a pillared-layer 3D network constructed from [Cu5(ttbz)(Httbz)2(OH)3(H2O)4] sheets pillared by individual P5W30 clusters. Compound 3 contains octa-supporting P5W30 POM clusters and novel [Ni6(bpz)6] crown-like metallamacrocycles, which construct a (4,4)-connected pts network. Compound 4 displays a complicated 3D (5,5)-connected {4(5)·6(4)·8}{4(5)·6(5)} network built by pentasupporting P5W30 POM clusters and discrete [Co4(bpz)6(H2O)9] subunits. In 1-4, the unified features are the Preyssler-type [P5W30O110] POM as the fundamental building block, which supports the transition-metal compounds with different modes to give the resultant diverse networks. The magnetism studies indicated antiferromagnetically coupled systems for the hexa- and pentanuclear Cu(II) units in 1 and 2, respectively. The electrochemical properties demonstrate that all compounds have electrocatalytic abilities toward the reduction of hydrogen peroxide. Furthermore, the catalytic activities of 1 in the cyanosilylation of aldehydes reaction have been investigated. PMID:26196681

  5. The loading of coordination complex modified polyoxometalate nanobelts on activated carbon fiber: a feasible strategy to obtain visible light active and highly efficient polyoxometalate based photocatalysts.

    PubMed

    Lu, Tingting; Xu, Xinxin; Li, Huili; Li, Zhenyu; Zhang, Xia; Ou, Jinzhao; Mei, Mingliang

    2015-02-01

    To enhance the photocatalytic properties of coordination complex modified polyoxometalates (CC/POMs) in the visible light region, its nanobelts (CC/POMNBs) were loaded on activated carbon fiber (ACF) through a simple colloidal blending process. The resulting coordination complex modified polyoxometalate nanobelts loaded activated carbon fiber composite materials (CC/POMNBs/ACF) exhibited dramatic photocatalytic activity for the degradation of rhodamine B (RhB) under visible light irradiation. Optical and electrochemical methods illustrated the enhanced photocatalytic activity of CC/POMNBs/ACF, which originates from the high separation efficiency of the photogenerated electrons and holes on the interface of the CC/POMNBs and ACF, which results from the synergistic effects between them. In the composite material, the role of ACF could be described as a photosensitizer and a good electron transporter. Furthermore, the influence of the mass ratio between the CC/POMNBs and ACF on the photocatalytic performance of the resulting composite material was discussed, and an ideal value to obtain highly efficient photocatalysts was obtained. The results suggested that the loading of CC/POMNBs on the surface of ACF would be a feasible strategy to enhance their photocatalytic activity. PMID:25529472

  6. Keggin (K5, H3O)[SiV3W9O40H]·xH2O: Characterization and crystal structure

    NASA Astrophysics Data System (ADS)

    Bonfim, Rodrigo de Paiva Floro; de Moura, Luiza Cristina; Eon, Jean-Guillaume; Mentré, Olivier; Vezin, Hervé; Caldarelli, Stefano

    2014-05-01

    Single crystals of the potassium salt (K5, H3O)[SiV3W9O40H]·xH2O of the vanadium tri-substituted α-Keggin dodecatungstosilicate were prepared and analyzed by vibrational, EPR and 51V NMR spectroscopy. Varying the synthesis conditions allows crystallization of partially reduced anions. The crystal structure was determined for both oxidized (V5+) and partially reduced (V4+/5+) potassium salts. Single crystal X-ray diffraction data and solid state 51V-NMR spectra confirm the occurrence of a single vanadium site in a cubic structure due to rotational disorder of the Keggin ion. Partially reduced compounds crystallize within the same structure as fully oxidized ones. EPR experiments confirm strong interaction of V4+ with two V5+ ions, in accordance with insertion of a V3 subunit into the lacunary Keggin ion as designed in the synthesis method. The 3D-edifice is composed of K+/H2O counter-sublattice with evidence of tunable water occupancy.

  7. Enhanced Visible Photovoltaic Response of TiO₂ Thin Film with an All-Inorganic Donor-Acceptor Type Polyoxometalate.

    PubMed

    Li, Jian-Sheng; Sang, Xiao-Jing; Chen, Wei-Lin; Zhang, Lan-Cui; Zhu, Zai-Ming; Ma, Teng-Ying; Su, Zhong-Min; Wang, En-Bo

    2015-06-24

    In the field of material chemistry, it is of great significance to develop abundant and sustainable materials for solar energy harvesting and management. Herein, after evaluating the energy band characteristics of 13 kinds of polyoxometalates (POMs), the trisubstituted POM compound K6H4[α-SiW9O37Co3(H2O)3]·17H2O (SiW9Co3) was first studied due to its relatively smaller band gap (2.23 eV) and higher lowest unoccupied molecular orbital (LUMO) level (-0.63 V vs NHE). Additionally, the preliminary computational modeling indicated that SiW9Co3 exhibited the donor-acceptor (D-A) structure, in which the cobalt oxygen clusters and tungsten skeletons act as the electron donor and electron acceptor, respectively. By employing SiW9Co3 to modify the TiO2 film, the visible photovoltaic and photocurrent response were both enhanced, and the light-induced photocurrent at 420 nm was improved by 7.1 times. Moreover, the highly dispersive and small sized SiW9Co3 nanoclusters loading on TiO2 were successfully achieved by fabricating the nanocomposite film of {TiO2/SiW9Co3}3 with the layer-by-layer method, which can result in the photovoltaic performance enhancement of dye-sensitized solar cells (DSSCs), of which the overall power conversion efficiency was improved by 25.6% from 6.79% to 8.53% through the synergistic effect of POMs and Ru-complex. PMID:26030670

  8. The atomic level journey from aqueous polyoxometalate to metal oxide

    SciTech Connect

    Hou, Yu; Fast, Dylan B.; Ruther, Rose E.; Amador, Jenn M.; Fullmer, Lauren B.; Decker, Shawn R.; Zakharov, Lev N.; Dolgos, Michelle R. Nyman, May

    2015-01-15

    Aqueous precursors tailored for the deposition of thin film materials are desirable for sustainable, simple, low energy production of advanced materials. Yet the simple practice of using aqueous precursors is complicated by the multitude of interactions that occur between ions and water during dehydration. Here we use lithium polyoxoniobate salts to investigate the fundamental interactions in the transition from precursor cluster to oxide film. Small-angle X-ray scattering of solutions, total X-ray scattering of intermediate gels, and morphological and structural characterization of the lithium niobate thin films reveal the atomic level transitions between these states. The studies show that (1) lithium–[H{sub 2}Nb{sub 6}O{sub 19}]{sup 6−} has drastically different solution behaviour than lithium–[Nb{sub 6}O{sub 19}]{sup 8−}, linked to the precursor salt structure (2) in both compositions, the intermediate gel preserves the polyoxoniobate clusters and show similar local order and (3) the morphology and phases of deposited films reflect the ions behaviour throughout the journey from cluster solution to metal oxide. - Graphical abstract: Aqueous lithium polyoxoniobate salts were used to prepare lithium niobate (LiNbO{sub 3}) thin films. Fundamental studies were performed to investigate the interactions in the transition from precursor cluster to the oxide film. It was found that acid–base and ion-association chemistries of the aqueous and gel systems significantly affect the key processes in this atom-level journey. - Highlights: • Lithium polyoxoniobate clusters were synthesized with control over Li:Nb ratio as precursors for LiNbO{sub 3} films. • X-ray scattering studies in solution and the solid-state revealed differences controlled by Li:Nb ratio. • Film deposition studies revealed phase, composition and morphology is controlled by Li:Nb ratio. • Cluster to film transformation was revealed using total X-ray scattering and TGA.

  9. pH-controlled assembly of hybrid architectures based on Anderson-type polyoxometalates and silver coordination units.

    PubMed

    Hu, Ying; An, Haiyan; Liu, Xuan; Yin, Jiqiu; Wang, Huilong; Zhang, Hua; Wang, Lin

    2014-02-14

    Three new architectures based on Anderson-type polyoxometalates, (3-H2pya)[(3-Hpya)2Ag][AgAlMo6H6O24]·3H2O 1, HNa2[(3-pya)(3-Hpya)Ag]2[AlMo6H6O24]·8H2O 2 and [(3-Hpya)2Ag][(H2O)2Ag]2[AlMo6H6O24]·2H2O 3 (3-Hpya = 3-(3-pyridyl)acrylic acid), have been synthesized at the different pH values and characterized by elemental analysis, IR spectroscopy, TG analysis, powder X-ray diffraction and single crystal X-ray diffraction. Compound 1 was obtained at lower pH value (2.50), and represents a 3D host-guest compound containing the Ag-3-Hpya coordination complex guest and the 3D [AgAlMo6H6O24](2-) host. The host framework exhibits a 4-connected diamond topology, and is constructed from [AlMo6H6O24](3-) clusters connected by Ag(+) cations. When the pH value was increased slightly, compound 2 was obtained with a 1D chain structure built up of Anderson polyoxoanions, Ag-3-Hpya coordination complexes and binuclear sodium clusters. By further increasing the pH value (3.50), compound 3 was isolated as a 2D network in which [AlMo6H6O24](3-) clusters are linked together by Ag(+) cations and Ag-3-Hpya coordination complexes. Their structural differences reveal that the pH value of the reaction system is the key factor influencing the structure and topology of three compounds. The UV-visible-NIR diffuse reflectivity spectra of 1-3 show that they can be regarded as a wide gap semiconductor. Furthermore, the pyrolysis of 1-3 produces three nanocomposites 1'-3' composed of silver microparticles dispersed in the metal oxides. The photocatalytic properties of 1'-3' have been investigated. PMID:24306316

  10. A co-crystal of polyoxometalates exhibiting single-molecule magnet behavior: the structural origin of a large magnetic anisotropy

    SciTech Connect

    Fang, Xikui; McCallum, Kendall; Pratt III, Harry D.; Anderson, Travis M.; Dennis, Kevin; Luban, Marshall

    2012-03-29

    A polyoxometalate-based {MnIII3MnIV} single-molecule magnet exhibits a large axial anisotropy (D = −0.86 cm−1) resulting from a near-parallel alignment of Jahn–Teller axes. Its rigorous three-fold symmetry (i.e. rhombicity E → 0) and increased intercluster separation via co-crystallization effectively hamper quantum tunnelling of the magnetization. Graphical abstract: A co-crystal of polyoxometalates exhibiting single-molecule magnet behavior: the structural origin of a large magnetic anisotropy

  11. Controlled chiral electrochromism of polyoxometalates incorporated in supramolecular complexes.

    PubMed

    Zhang, Bin; Guan, Weiming; Zhang, Simin; Li, Bao; Wu, Lixin

    2016-04-01

    A three-component supramolecular system was constructed by combining host-guest recognition and electrostatic interaction for realization of induced circular dichroism of achiral polyanionic clusters in aqueous solution, while the induced chiral heteropoly blue was built and switched off by controlling the redox of the inorganic component via electrochemistry. PMID:27002653

  12. Selective hydrogenation of phenylacetylene on Ni and Ni-Pd catalysts modified with heteropoly compounds of the Keggin type

    NASA Astrophysics Data System (ADS)

    Navalikhina, M. D.; Kavalerskaya, N. E.; Lokteva, E. S.; Peristyi, A. A.; Golubina, E. V.; Lunin, V. V.

    2012-12-01

    It is established that unmodified Ni catalysts and Ni catalysts modified with Mo- and W-heteropoly compounds (HPC) of the Keggin type (6 wt %) along with catalyst containing 6% K4SiW12O40/Al2O3 appear to be active in the reaction of phenylacetylene (PA) hydrogenation. At low temperatures (100-150°C), the selectivity of the process strongly depends on the nature of the modifier or second active metal (Pd). It is demonstrated that in the presence of 6% Ni-0.015% Pd/Al2O3 modified by HPC K4SiMo6W6O40, the conversion of PA at 100°C was 87% at a styrene: ethylbenzene ratio of 1: 1. The acidity of HPC is found to influence the side reactions of alkylation and condensation. Transmission electron microscopy demonstrates that Ni in modified HPC 6% Ni/Al2O3 is present in the form of the particles below 2 nm in size, and these particles of Ni become larger when affected by the reaction medium during PA hydrogenation.

  13. Keggin-type heteropoly compounds supported on montmorillonite clays offering strong option for efficient solid-phase microextraction coating.

    PubMed

    Abolghasemi, Mir Mahdi; Yousefi, Vahid; Rafiee, Ezzat

    2014-01-31

    Keggin-type heteropoly compounds supported on montmorillonite clays were prepared and used as a highly porous fiber coating material for solid-phase microextraction (SPME). The prepared nanomaterial was immobilized onto a stainless steel wire for fabrication of the SPME fiber. The fiber was evaluated for the extraction of some polycyclic aromatic hydrocarbons (PAHs) from aqueous sample solutions in combination with gas chromatography-mass spectrometry (GC-MS). A one at-the-time optimization strategy was applied for optimizing the important extraction parameters such as extraction temperature, extraction time, ionic strength, stirring rate, and desorption temperature and time. In optimum conditions, the repeatability for one fiber (n=3), expressed as relative standard deviation (R.S.D.%), was between 5.1% and 8.4% for the test compounds. The detection limits for the studied compounds were between 0.02 and 0.05pgmL(-1). The developed method offers the advantage of being simple to use, with shorter analysis time, lower cost of equipment, thermal stability of fiber, and high relative recovery in comparison to conventional methods of analysis. PMID:24411139

  14. Low-Dimensional Polyoxometalate Molecules/Tantalum Oxide Hybrids for Non-Volatile Capacitive Memories.

    PubMed

    Balliou, Angelika; Papadimitropoulos, Giorgos; Skoulatakis, George; Kennou, Stella; Davazoglou, Dimitrios; Gardelis, Spiros; Glezos, Nikos

    2016-03-23

    Transition-metal-oxide hybrids composed of high surface-to-volume ratio Ta2O5 matrices and a molecular analogue of transition metal oxides, tungsten polyoxometalates ([PW12O40](3-)), are introduced herein as a charge storage medium in molecular nonvolatile capacitive memory cells. The polyoxometalate molecules are electrostatically self-assembled on a low-dimensional Ta2O5 matrix, functionalized with an aminosilane molecule with primary amines as the anchoring moiety. The charge trapping sites are located onto the metal framework of the electron-accepting molecular entities as well as on the molecule/oxide interfaces which can immobilize negatively charged mobile oxygen vacancies. The memory characteristics of this novel nanocomposite were tested using no blocking oxide for extraction of structure-specific characteristics. The film was formed on top of the 3.1 nm-thick SiO2/n-Si(001) substrates and has been found to serve as both SiO2/Si interface states' reducer (i.e., quality enhancer) and electron storage medium. The device with the polyoxometalates sandwiched between two Ta2O5 films results in enhanced internal scattering of carriers. Thanks to this, it exhibits a significantly larger memory window than the one containing the plain hybrid and comparable retention time, resulting in a memory window of 4.0 V for the write state and a retention time around 10(4) s without blocking medium. Differential distance of molecular trapping centers from the cell's gate and electronic coupling to the space charge region of the underlying Si substrate were identified as critical parameters for enhanced electron trapping for the first time in such devices. Implementing a numerical electrostatic model incorporating structural and electronic characteristics of the molecular nodes derived from scanning probe and spectroscopic characterization, we are able to interpret the hybrid's electrical response and gain some insight into the electrostatics of the trapping medium. PMID

  15. Spectroscopic studies of sulfite-based polyoxometalates at high temperature and high pressure

    SciTech Connect

    Quesada Cabrera, Raul; Firth, Steven; Blackman, Christopher S.; Long, De-Liang; Cronin, Leroy; McMillan, Paul F.

    2012-02-15

    Structural changes occurring within non-conventional Dawson-type [{alpha}/{beta}-Mo{sub 18}O{sub 54}(SO{sub 3}){sub 2}]{sup 4-} polyanions in the form of tetrapentylammonium salts were studied by a combination of IR, Raman and visible spectroscopy at high temperature and high pressure. Evidence of the formation of bronze-type materials above 400 K and also upon pressurization to 8 GPa is presented. This conclusion is suggested to be a general result for polyoxometalate compounds subjected to extreme conditions and it opens opportunities for the design of new materials with interesting optical and electronic properties. - Graphical abstract: Structural changes occurring within non-conventional Dawson-type [{alpha}/{beta}-Mo{sub 18}O{sub 54}(SO{sub 3}){sub 2}]{sup 4-} polyanions in the form of tetrapentylammonium salts were studied by a combination of IR, Raman and visible spectroscopy at high temperature and high pressure. Evidence of the formation of bronze-type materials above 400 K and also upon pressurization to 8 GPa is presented. This conclusion is suggested to be a general result for polyoxometalate compounds subjected to extreme conditions and it opens opportunities for the design of new materials with interesting optical and electronic properties. Highlights: Black-Right-Pointing-Pointer Spectroscopy studies of non-conventional Wells-Dawson polyoxometalates (POMs) at high temperature and high pressure. Black-Right-Pointing-Pointer Discussion on the stability of two POM isomers. Black-Right-Pointing-Pointer Local formation of bronze-like materials: possibilities for a new synthetic method at high pressure from POM precursors.

  16. N-alkylation of organo-imido substituted polyoxometalates: an efficient and stoichiometric approach for the easy post-modification of polyoxometalates.

    PubMed

    Khan, Rao Naumaan Nasim; Lv, Chunlin; Zhang, Jin; Hao, Jian; Wei, Yongge

    2015-03-14

    An efficient protocol for post-functionalization of organo-imido polyoxometalates is developed via creating a remote tertiary “N” atom over the surface of organo-imido hexamolybdates and subsequently post-functionalizing it with the help of allyl or alkyl halides to afford stoichiometric, “in situ” crystalline products at moderate temperatures. The parent organo-imido product 2 and post-functionalized crystalline products 3 and 4 are compared for their solid state structures. The post-functionalization protocol introduced here allows the inclusion of the desired functional groups as remote reactive organic groups over a POM's highly negative surface. The in situ crystallization of post-functionalized products further guarantees an 100% purity of final products, along with 95% yield. PMID:25651928

  17. Reversible photoswitchable fluorescence in thin films of inorganic nanoparticle and polyoxometalate assemblies.

    PubMed

    Qin, Bing; Chen, Hongyue; Liang, Hui; Fu, Lei; Liu, Xinfeng; Qiu, Xiaohui; Liu, Shaoqin; Song, Rui; Tang, Zhiyong

    2010-03-10

    A novel type of inorganic hybridized ultrathin film consisting of Preyssler-type polyoxometalates K(14)[Na(H(2)O)P(5)W(30)O(110)] (Na-POMs) and CdSe@CdS nanoparticles (NPs) was prepared on the solid substrates by a layer-by-layer assembly technique. The film exhibits reversible fluorescence switching behavior under control of irradiation with either UV light or visible light, which is ascribed to the selective occurrence of fluorescence resonance energy transfer between luminescent NPs and different states of photochromic Na-POMs. PMID:20155922

  18. Covalent Photosensitizer-Polyoxometalate-Catalyst Dyads for Visible-Light-Driven Hydrogen Evolution.

    PubMed

    Schönweiz, Stefanie; Rommel, Sebastian A; Kübel, Joachim; Micheel, Mathias; Dietzek, Benjamin; Rau, Sven; Streb, Carsten

    2016-08-16

    A general concept for the covalent linkage of coordination compounds to bipyridine-functionalized polyoxometalates is presented. The new route is used to link an iridium photosensitizer to an Anderson-type hydrogen-evolution catalyst. This covalent dyad catalyzes the visible-light-driven hydrogen evolution reaction (HER) and shows superior HER activity compared with the non-covalent reference. Hydrogen evolution is observed over periods >1 week. Spectroscopic, photophysical, and electrochemical analyses give initial insight into the stability, electronic structure, and reactivity of the dyad. The results demonstrate that the proposed linkage concept allows synergistic covalent interactions between functional coordination compounds and reactive molecular metal oxides. PMID:27418410

  19. Spectroscopic studies of sulfite-based polyoxometalates at high temperature and high pressure

    NASA Astrophysics Data System (ADS)

    Quesada Cabrera, Raul; Firth, Steven; Blackman, Christopher S.; Long, De-Liang; Cronin, Leroy; McMillan, Paul F.

    2012-02-01

    Structural changes occurring within non-conventional Dawson-type [α/β-Mo18O54(SO3)2]4- polyanions in the form of tetrapentylammonium salts were studied by a combination of IR, Raman and visible spectroscopy at high temperature and high pressure. Evidence of the formation of bronze-type materials above 400 K and also upon pressurization to 8 GPa is presented. This conclusion is suggested to be a general result for polyoxometalate compounds subjected to extreme conditions and it opens opportunities for the design of new materials with interesting optical and electronic properties.

  20. On the electronic structure of giant polyoxometalates: Mo132vs. W72Mo60.

    PubMed

    Bo, Carles; Miró, Pere

    2012-09-01

    The molecular and electronic structure of the spherical Keplerates [{(Mo(VI))Mo(VI)(5)O(21)}(12)(Mo(V)(2)O(4))(30)](12-) (Mo(132)) and [{(W(VI))W(VI)(5)O(21)}(12)(Mo(V)(2)O(4))(30)](12-) (W(72)Mo(60)) has been determined, for the first time, using first-principles density functional theory (DFT) based methods including solvent effects. Computed geometric parameters are in very good agreement with X-ray data, whereas the electronic structure reveals the archetypal nature of polyoxometalates. PMID:22717598

  1. Polyoxometalates: introduction to a class of inorganic compounds and their biomedical applications.

    PubMed

    Hasenknopf, Bernold

    2005-01-01

    An increasing number of potential applications for polyoxometalates in human medicine have been reported in the literature. These inorganic complexes are composed of early transition metals (mainly molybdenum, tungsten and vanadium) and oxygen. The present review gives an introduction into the chemistry of these compounds, and an overview of the principal studies of their biological and biochemical effects and their therapeutic potential. The reported antitumoral and antibiotic properties of molybdates and tungstates in vitro and in vivo are compiled and discussed, as are their influences on the blood glucose level in diabetic animals. Aspects of antiviral activities and cell penetration are treated. PMID:15574368

  2. Recent advances in porous polyoxometalate-based metal-organic framework materials.

    PubMed

    Du, Dong-Ying; Qin, Jun-Sheng; Li, Shun-Li; Su, Zhong-Min; Lan, Ya-Qian

    2014-07-01

    Polyoxometalate (POM)-based metal-organic framework (MOF) materials contain POM units and generally generate MOF materials with open networks. POM-based MOF materials, which utilize the advantages of both POMs and MOFs, have received increasing attention, and much effort has been devoted to their preparation and relevant applications over the past few decades. They have good prospects in catalysis owing to the electronic and physical properties of POMs that are tunable by varying constituent elements. In this review, we present recent developments in porous POM-based MOF materials, including their classification, synthesis strategies, and applications, especially in the field of catalysis. PMID:24676127

  3. Cerium Oxyhydroxide Clusters: Formation, Structure and Reactivity

    SciTech Connect

    Aubriet, F.; Gaumet, Jean-Jacques; De Jong, Wibe A.; Groenewold, G. S.; Gianotto, Anita K.; McIIwain, Michael E.; Van Stipdonk, Michael J.; Leavitt, Christopher M.

    2009-05-11

    Cerium oxyhydroxide cluster anions were produced by irradiating ceric oxide particles using 355 nm laser pulses that were synchronized with pulses of nitrogen gas admitted to the irradiation chamber. The gas pulse stabilized the nascent clusters that are largely anhydrous [CexOy] ions and neutrals. These initially-formed species react with water, principally forming closed-shell (c-s) oxohydroxy species that are described by the general formula [CexOy(OH)z]-. In general, the extent of hydroxylation varies from a value of 3 OH per Ce atom when x = 1 to a value slightly greater than 1 for x > 8. The Ce3 and Ce6 species deviate significantly from this trend: the x = 3 cluster accommodates more hydroxyl moieties compared to neighboring congeners at x = 2 and x = 4. Conversely, the x = 6 cluster is significantly less hydroxylated. Density functional theory (DFT) modeling of the cluster structures show that the hydrated clusters are hydrolyzed, and contain one-to-multiple hydroxide moieties, but not datively bound water. DFT also predicts an energetic preference for formation of highly symmetric structures as the size of the clusters increases. The calculated structures indicate that the ability of the Ce3 oxyhydroxide to accommodate more extensive hydroxylation is due to a more open, hexagonal structure in which the Ce atoms can participate in multiple hydrolysis reactions. Conversely the Ce6 oxyhydroxide has an octahedral structure that is not conducive to hydrolysis. In addition to the c-s clusters, open-shell (o-s) oxyhydroxides and superoxides are also formed, and they become more prominent as the size of the clusters increases, suggesting that the larger ceria clusters have an increased ability to stabilize a non-bonding electron. The overall intensity of the clusters tends to monotonically decrease as the cluster size increases, however this trend is interrupted at Ce13, which is significantly more stable compared to neighboring congeners, suggesting formation of

  4. Cerium Oxyhydroxide Clusters: Formation, Structure and Reactivity

    SciTech Connect

    Frederic Aubriet; Jean-Jacques Gaumet; Wibe A de Jong; Groenewold, Gary S; Gianotto, Anita K; McIlwain, Michael E; Michael J. Van Stipdonk; Christopher M. Leavitt

    2009-06-01

    Cerium oxyhydroxide cluster anions were produced by irradiating ceric oxide particles using 355 nm laser pulses that were synchronized with pulses of nitrogen gas admitted to the irradiation chamber. The gas pulse stabilized the nascent clusters that are largely anhydrous [CexOy] ions and neutrals. These initially-formed species react with water, principally forming closed-shell (c-s) oxohydroxy species that are described by the general formula [CexOy(OH)z]-. In general, the extent of hydroxylation varies from a value of 3 OH per Ce atom when x = 1 to a value slightly greater than 1 for x > 8. The Ce3 and Ce6 species deviate significantly from this trend: the x = 3 cluster accommodates more hydroxyl moieties compared to neighboring congeners at x = 2 and x = 4. Conversely, the x = 6 cluster is significantly less hydroxylated. Density functional theory (DFT) modeling of the cluster structures show that the hydrated clusters are hydrolyzed, and contain one-to-multiple hydroxide moieties, but not datively bound water. DFT also predicts an energetic preference for formation of highly symmetric structures as the size of the clusters increases. The calculated structures indicate that the ability of the Ce3 oxyhydroxide to accommodate more extensive hydroxylation is due to a more open, hexagonal structure in which the Ce atoms can participate in multiple hydrolysis reactions. Conversely the Ce6 oxyhydroxide has an octahedral structure that is not conducive to hydrolysis. In addition to the c-s clusters, open-shell (o-s) oxyhydroxides and superoxides are also formed, and they become more prominent as the size of the clusters increases, suggesting that the larger ceria clusters have an increased ability to stabilize a non-bonding electron. The overall intensity of the clusters tends to monotonically decrease as the cluster size increases, however this trend is interrupted at Ce13, which is significantly more stable compared to neighboring congeners, suggesting formation of

  5. Efficient visible light-driven water oxidation catalyzed by an all-inorganic copper-containing polyoxometalate.

    PubMed

    Yu, Li; Du, Xiaoqiang; Ding, Yong; Chen, Hongli; Zhou, Panpan

    2015-12-21

    [Cu5(OH)4(H2O)2(A-α-SiW9O33)2](10-) (1) was tested as the first copper-containing polyoxometalate catalyst for O2 production via visible light-driven water oxidation. Multiple experiments confirm that 1 is an active and dominant catalyst during water oxidation. PMID:26468511

  6. Syntheses, structures and properties of 3D inorganic-organic hybrid frameworks constructed from lanthanide polymer and Keggin-type tungstosilicate

    SciTech Connect

    Gao Yuanzhe; Xu Yanqing; Han Zhangang; Li Chunhong; Cui, Fengyun; Chi Yingnan; Hu Changwen

    2010-05-15

    Inorganic-organic hybrid frameworks, namely [Ce(H{sub 2}O){sub 3}(pdc)]{sub 4}[SiW{sub 12}O{sub 40}].6H{sub 2}O 1, [M(H{sub 2}O){sub 4}(pdc)]{sub 4}[SiW{sub 12}O{sub 40}].2H{sub 2}O (M=Ce for 2a, La for 2b, Nd for 2c; H{sub 2}pdc=pyridine-2,6-dicarboxylic acid) were assembled through incorporation of Keggin-type heteropolyanion [SiW{sub 12}O{sub 40}]{sup 4-} within the voids of lanthanides-pdc network as pillars or guests under hydrothermal condition. Single-crystal X-ray analyses of these crystals reveal that compound 1 presents 3D pillar-layered framework with the [SiW{sub 12}O{sub 40}]{sup 4-} anions located on the square voids of the two-dimensional Ce-pdc bilayer. Compounds 2a-c are isostructural and constructed from 3D Ln-pdc-based metal-organic framework (MOF) incorporating noncoordinating guests Keggin structure [SiW{sub 12}O{sub 40}]{sup 4-}. Solid-state properties of compounds 1 and 2a-c such as thermal stability and photoluminescence have been further investigated. - Graphical abstract: Two types of new inorganic-organic hybrid frameworks through incorporation of Keggin-type heteropolyanion [SiW{sub 12}O{sub 40}]{sup 4-} within the voids of lanthanides-pdc network as pillars or guests under hydrothermal condition were successfully assembled. Solid-state properties of compounds 1 and 2a such as thermal stability and photoluminescence have been further investigated.

  7. Direct synthesis of inverse hexagonally ordered diblock copolymer/polyoxometalate nanocomposite films.

    PubMed

    Lunkenbein, Thomas; Kamperman, Marleen; Li, Zihui; Bojer, Carina; Drechsler, Markus; Förster, Stephan; Wiesner, Ulrich; Müller, Axel H E; Breu, Josef

    2012-08-01

    Nanostructured inverse hexagonal polyoxometalate composite films were cast directly from solution using poly(butadiene-block-2-(dimethylamino)ethyl methacrylate) (PB-b-PDMAEMA) diblock copolymers as structure directing agents for phosphomolybdic acid (H(3)[PMo(12)O(40)], H(3)PMo). H(3)PMo units are selectively incorporated into the PDMAEMA domains due to electrostatic interactions between protonated PDMAEMA and PMo(3-) anions. Long solvophilic PB chains stabilized the PDMAEMA/H(3)PMo aggregates in solution and reliably prevented macrophase separation. The choice of solvent is crucial. It appears that all three components, both blocks of the diblock copolymer as well as H(3)PMo, have to be soluble in the same solvent which turned out to be tetrahydrofuran, THF. Evaporation induced self-assembly resulted in highly ordered inverse hexagonal nanocomposite films as observed from transmission electron microscopy and small-angle X-ray scattering. This one-pot synthesis may represent a generally applicable strategy for integrating polyoxometalates into functional architectures and devices. PMID:22757978

  8. A series of new supramolecular structures constructed from triethylenediamine and different polyoxometalates

    SciTech Connect

    Wang, Yan; Pan, Cheng-Ling; Xiao, Li-Na; Wu, Feng-Qing; Ding, Hong; Liu, Ya-Bing; Gao, Zhong-Min; Zheng, Da-Fang; Wang, Tie-Gang; Yang, Guang-Di; Cui, Xiao-Bing; Xu, Ji-Qing

    2010-12-15

    Three new supramolecular compounds based on triethylenediamine and different polyoxometalates [W{sup VI}{sub 3}V{sup V}{sub 3}O{sub 19}H]{l_brace}[Cu(HDABCO)]{sub 2}(H{sub 2}O){r_brace} (1), [P{sub 2}Mo{sup VI}{sub 18}O{sub 62}][HDABCO]{sub 2}[H{sub 2}DABCO]{sub 2}.12 H{sub 2}O (2) and [Mo{sup VI}{sub 7.5}W{sup VI}{sub 0.5}O{sub 27}][Cu(HDABCO)]{sub 2}.2 H{sub 3}O.2 H{sub 2}O (3) (DABCO=triethylenediamine) have been synthesized hydrothermally and characterized by IR, TG, XPS and X-ray diffraction analyses. Crystal structure analyses reveal that compound 1 exhibits a face-centered cubic packing motif, compound 2 displays a supramolecular structure constructed form the 'chains' arranged hexagonally, compound 3 contains [Mo{sub 7.5}W{sub 0.5}O{sub 27}]{sub {infinity}} chain decorated by [Cu(HDABCO)]{sup 2+} cations, which was then packed into a layer structure. These results show that the same organonitrogen combining with the different POMs will yield different supramolecular networks. -- Graphical abstract: Three new supramolecular compounds based on triethylenediamine and different polyoxometalates have been hydrothermally synthesized and characterized by IR, XPS, TG, elemental analysis and X-ray diffraction analysis.

  9. Controllable fabrication of platinum nanospheres with a polyoxometalate-assisted process

    SciTech Connect

    Sun Guoying; Li Qiuyu; Xu Rui; Gu Jianmin; Ju Mingliang; Wang Enbo

    2010-11-15

    Pt nanospheres with an average diameter of 60{+-}10 nm have been successfully synthesized at room temperature through a facile polyoxometalate(POM)-assisted process. Characterization by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) clearly showed that these Pt nanospheres consisted of 2-7 nm Pt nanodots. During the formation of such unique nanostructures, POMs were found to serve as both catalyst and stabilizer. The size of the as-synthesized Pt nanospheres could be controlled solely by adjusting the molar ratio of POMs to H{sub 2}PtCl{sub 6}. A possible formation mechanism based on POMs-mediated electron transfer from ascorbic acid (AA) to PtCl{sub 6}{sup 2-} and AA-assisted aggregation was tentatively proposed to rationalize the formation of such nanostructures. Importantly, these specific Pt nanospheres exhibited good electrocatalytic activity towards the oxidation of methanol, making them promising for applications in direct methanol fuel cells. - Graphical abstract: Large-scale Pt nanospheres were synthesized through a polyoxometalate-assisted process, and exhibited good electrocatalytic activity towards the oxidation of methanol, making them promising for applications in fuel cells. Display Omitted

  10. Co-adsorbtion of Cu and Keggin type polytungstates on polycrystalline Pt: interplay of atomic and molecular UPD.

    PubMed

    Tsirlina, Galina; Mishina, Elena; Timofeeva, Elena; Tanimura, Nobuko; Sherstyuk, Nataliya; Borzenko, Marina; Nakabayashi, Seiichiro; Petrii, Oleg

    2008-01-01

    Second harmonic generation (SHG), electrochemical quartz microbalance (EQCM), and cyclic voltammetry are applied to clarify the structure and properties of Cu adlayers formed in the presence of Keggin polytungstate anions. For 0.02-10 mM CuSO4 solutions, no pronounced suppression of underpotential copper deposition (Cu UPD) by 0.1-10 mM H3PW12O40 (PW12) or H4SiW12O40 (SiW12) is observed in electrochemical experiments. Moreover, coadsorption with polyanions results in an increase of charge in the Cu UPD region. EQCM data demonstrate high surface coverage with polytungstate in the overall potential range and their pronounced co-adsorption with Cu2+ cations under open circuit. The unusual potential dependence of EQCM response of polytungstates is discovered and discussed in terms of anion interactions with adsorbed hydrogen. The SHG response of Cu UPD demonstrates a non-linear dependence on Cu surface coverage, which is interpreted in terms of discontinuous submonolayers consisting of 2D Cu islands. The additives of PW12 or SiW12 decrease copper SHG response at low and high CuSO4 concentrations, with minor effect for a mid range of concentrations. In all mixed solutions, the potential dependence of the SHG response remains typical for Cu UPD, not for polytungstates. SHG transients measured under potential step mode demonstrate that the initial non-steady-state SHG behavior of the adlayer is more close to the behavior of polytungstates, but typical copper features appear at longer wavelength. These facts favor the hypothesis of Cu adatom penetration through anionic adlayers and formation of a metal submonolayer at the vacant areas between large quasi-spherical polyanions, with subsequent transformation into a Pt/Cu/polytungstate layered structure. PMID:19213321

  11. Synthesis and structural characterization of polyoxometalates incorporating with anilinium cations and facile preparation of hybrid film

    NASA Astrophysics Data System (ADS)

    Fukaya, Keisuke; Srifa, Atthapon; Isikawa, Eri; Naruke, Haruo

    2010-08-01

    The self-assembly reaction of tungstate and copper(II) in the presence of aniline (ANI) and phosphoric acid led to the formation of an anilinium (ANIH +) salt of mono-substituted Keggin-type polyoxotungstophosphate (ANIH) 5[PCu(H 2O)W 11O 39](ANI)·8H 2O ( 1), while the reaction of heptamolybdate in the coexistence of copper(II), phosphoric acid and ANI yielded an ANIH + salt of Strandberg-type pentamolybdodiphosphate, (ANIH) 2[(PO 4) 2Mo 5O 15{Cu(ANI) 2(H 2O)} 2](ANI)·2H 2O ( 2). These compounds were characterized by elemental analysis, infrared spectroscopy and X-ray single-crystal analysis. The compound 1, crystallizing in trigonal, P3¯,a = 13.883(4), c = 10.187(3) Å, Z = 1, consists of copper mono-substituted Keggin-typed [PCu(H 2O)W 11O 39] 5- anion surrounded by six ANI molecules, of which five are protonated (ANIH +). The compound 2, crystallizing in triclinic, P1¯,a = 13.98(2), b = 14.73(1), c = 16.24(1) Å, α = 111.27(3), β = 97.42(3), γ = 99.54(4)°, Z = 2, consists of Strandberg-type pentamolybdodiphospate [(PO 4) 2Mo 5O 15] 6- anions interconnected by two Cu(ANI) 2(H 2O) linkers to form a 1D-chain structure. A potentiostatic electrolysis of 1 in aqueous solution gave rise to electropolymerization of the ANIH + cations (and ANI) and deposition with the [PCu(H 2O)W 11O 39] 5- anion on an ITO electrode, forming a nano-structured polyaniline/[PCu(H 2O)W 11O 39] 5- hybrid thin film.

  12. Hybrid uranium-transition-metal oxide cage clusters.

    PubMed

    Ling, Jie; Hobbs, Franklin; Prendergast, Steven; Adelani, Pius O; Babo, Jean-Marie; Qiu, Jie; Weng, Zhehui; Burns, Peter C

    2014-12-15

    Transition-metal based polyoxometalate clusters have been known for decades, whereas those built from uranyl peroxide polyhedra have more recently emerged as a family of complex clusters. Here we report the synthesis and structures of six nanoscale uranyl peroxide cage clusters that contain either tungstate or molybdate polyhedra as part of the cage, as well as phosphate tetrahedra. These transition-metal-uranium hybrid clusters exhibit unique polyhedral connectivities and topologies that include 6-, 7-, 8-, 10-, and 12-membered rings of uranyl polyhedra and uranyl ions coordinated by bidentate peroxide in both trans and cis configurations. The transition-metal polyhedra appear to stabilize unusual units built of uranyl polyhedra, rather than templating their formation. PMID:25434424

  13. di Synthesis and Characterization of the Platinum-Substituted Keggin Anion alpha-H2SiPtW11O404-

    SciTech Connect

    Klonowski, P; Goloboy, JC; Uribe-Romo, FJ; Sun, FR; Zhu, LY; Gandara, F; Wills, C; Errington, RJ; Yaghi, OM; Klemperer, WG

    2014-12-15

    Acidification of an aqueous solution of K8SiW11O39 and K2Pt(OH)(6) to pH 4 followed by addition of excess tetramethylammonium (TMA) chloride yielded a solid mixture of TMA salts of H2SiPtW11O404- (1) and SiW12O404- (2). The former was separated from the latter by extraction into an aqueous solution and converted into tetra-n-butylammonium (TBA) and potassium salts TBA-1 and K-1. The a-H2SiPtW11O404- was identified as a monosubstituted Keggin anion using elemental analysis, IR spectroscopy, X-ray crystallography, electrospray ionization mass spectrometry, Pt-195 NMR spectroscopy, (183)W NMR spectroscopy, and W-183-W-183 2D INADEQUATE NMR spectroscopy. Both TBA-1 and K-1 readily cocrystallized with their unsubstituted Keggin anion salts, TBA-2 and K-2, respectively, providing an explanation for the historical difficulty of isolating certain platinum-substituted heteropolyanions in pure form.

  14. Polyoxometalate-grafted graphene nanohybrid for electrochemical detection of hydrogen peroxide and glucose.

    PubMed

    Yang, MinHo; Kim, Dong Seok; Lee, Tae Jae; Lee, Seok Jae; Lee, Kyoung G; Choi, Bong Gill

    2016-04-15

    The electrochemical performances of electrochemical biosensors largely depend on electrode characteristics, such as size, composition, surface area, and electron and ion conductivities. Herein, highly efficient electrocatalytic polyoxometalate (POM) was directly deposited on polymeric ionic liquid (PIL)-functionalized reduced graphene oxide (rGO) in a simple manner. The nano-sized POM with PIL functional groups was uniformly distributed on the surface of rGO sheets. The unique nanostructure of the resultant POM-g-rGO nanohybrids enabled well-defined multiple redox reaction of POMs and rapid electron transfer. In particular, as-prepared nanohybrids demonstrated high electrocatalytic activity for the electrochemical detection of H2O2 and glucose molecules in flow-injection biosensor device with high sensitivity, rapid response time, and low detection limit. PMID:26828273

  15. Designing artificial photosynthetic devices using hybrid organic-inorganic modules based on polyoxometalates.

    PubMed

    Symes, Mark D; Cogdell, Richard J; Cronin, Leroy

    2013-08-13

    Artificial photosynthesis aims at capturing solar energy and using it to produce storable fuels. However, while there is reason to be optimistic that such approaches can deliver higher energy conversion efficiencies than natural photosynthetic systems, many serious challenges remain to be addressed. Perhaps chief among these is the issue of device stability. Almost all approaches to artificial photosynthesis employ easily oxidized organic molecules as light harvesters or in catalytic centres, frequently in solution with highly oxidizing species. The 'elephant in the room' in this regard is that oxidation of these organic moieties is likely to occur at least as rapidly as oxidation of water, meaning that current device performance is severely curtailed. Herein, we discuss one possible solution to this problem: using self-assembling organic-polyoxometalate hybrid structures to produce compartments inside which the individual component reactions of photosynthesis can occur without such a high incidence of deleterious side reactions. PMID:23816903

  16. Optically Active Liquid Crystalline Polyoxometalates via Electrostatic Encapsulation with Cholesterol-Containing Amphiphile.

    PubMed

    Zhang, Jing; Li, Jingfang; Yuan, Hong; Zhang, Guohua; Li, Bao; Li, Wen; Wei, Xuehong; Duan, Xin-E; Wu, Lixin

    2016-07-20

    A novel cholesterol-containing amphiphile was designed and prepared in the study, which is a room-temperature ionic liquid crystal over a broad temperature range with pronounced chiroptical properties. Four types of inorganic polyoxometalates (PMs) with different numbers of charges were encapsulated by the chiral amphiphile. The incorporation of chiral organic cations triggers achiral PMs in the complexes to show induced chirality through intermolecular interactions, as demonstrated by circular dichroism spectroscopy. The electrostatic encapsulation with mesomorphic promoters provides the inorganic PMs with liquid crystalline behavior, characterized by differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction. The strategy applied herein represents a unique example of liquid crystalline PM complexes with optical activity. PMID:27197844

  17. Use of Lanthanide-Containing Polyoxometalates to Sensitise the Emission of Fluorescent Labelled Serum Albumin.

    PubMed

    Holmes-Smith, A Sheila; Crisp, Jacob; Hussain, Firasat; Patzke, Greta R; Hungerford, Graham

    2016-02-01

    Monitoring the interaction of biomolecules is important, and the use of energy transfer is a principal technique in elucidating nanoscale interactions. Lanthanide compounds are promising luminescent probes for biological samples as their emission is longer-lived than any native autofluorescence. Polyoxometalates (POMs) are interesting structural motifs to incorporate lanthanides, offering low toxicity and a size pertinent for biological applications. Here, we employ iso-structured POMs containing either terbium or europium and assess their interaction with serum albumin by sensitisation of a fluorescent tag on the protein via LRET (luminescence resonance energy transfer) by exciting the lanthanide. Time-resolved measurements showed energy transfer with an efficiency of over 90% for the POM-protein systems. The Tb-POM results were relatively straightforward, while those with the iso-structured Eu-POM were complicated by the effect of protein shielding from the aqueous environment. PMID:26642428

  18. A new integrated approach for dye removal from wastewater by polyoxometalates functionalized membranes.

    PubMed

    Yao, Lei; Zhang, Lizhi; Wang, Rong; Chou, Shuren; Dong, ZhiLi

    2016-01-15

    Membrane technique is a promising way for the removal of dyes from wastewater. A unique approach combining both the adsorptive and the catalytic membrane processes was proposed on the basis of a new functionalized membrane. The membrane integrating both the adsorptive and catalytic activities was developed by introducing polyoxometalates (POMs) as an ideal candidate for the membrane functionalization via a novel sol-gel method. A two-step protocol, adsorptive separation and catalytic degradation, was designed for dye removal, realizing an excellent dye rejection with easy and economic membrane regeneration through simply soaking the membrane in a limited volume of dilute oxidant solution. This approach is feasible and versatile owing to the flexible selection of distinct POMs and design of catalytic degradation routes as required. As a result, the current research provides insight into a new methodology of the membrane technique in dye removal applications. PMID:26410275

  19. Aqueous solutions of acidic ionic liquids for enhanced stability of polyoxometalate-carbon supercapacitor electrodes

    NASA Astrophysics Data System (ADS)

    Hu, Chenchen; Zhao, Enbo; Nitta, Naoki; Magasinski, Alexandre; Berdichevsky, Gene; Yushin, Gleb

    2016-09-01

    Nanocomposites based on polyoxometalates (POMs) nanoconfined in microporous carbons have been synthesized and used as electrodes for supercapacitors. The addition of the pseudocapacitance from highly reversible redox reaction of POMs to the electric double-layer capacitance of carbon lead to an increase in specific capacitance of ∼90% at 1 mV s-1. However, high solubility of POM in traditional aqueous electrolytes leads to rapid capacity fading. Here we demonstrate that the use of aqueous solutions of protic ionic liquids (P-IL) as electrolyte instead of aqueous sulfuric acid solutions offers an opportunity to significantly improve POM cycling stability. Virtually no degradation in capacitance was observed in POM-based positive electrode after 10,000 cycles in an asymmetric capacitor with P-IL aqueous electrolyte. As such, POM-based carbon composites may now present a viable solution for enhancing energy density of electrical double layer capacitors (EDLC) based on pure carbon electrodes.

  20. Two New Armtype Polyoxometalates Grafted on Titanium Dioxide Films: Towards Enhanced Photoelectrochemical Performance.

    PubMed

    Sun, Hang; Guo, Li-Ying; Li, Jian-Sheng; Bai, Jian-Ping; Su, Fang; Zhang, Lan-Cui; Sang, Xiao-Jing; You, Wan-Sheng; Zhu, Zai-Ming

    2016-05-23

    Two new carboxyethyltin-functionalized polyoxometalates (POMs) were successfully obtained and confirmed with physicochemical and spectroscopic methods including X-ray crystallography. The lowest unoccupied molecular orbitals of both compounds are higher in energy than that of TiO2 , and the optical band gaps of these compounds are smaller than that of TiO2 . Grafting them onto a TiO2 film created two kinds of novel photoanode materials that showed significantly enhanced photovoltaic and photocurrent responses, as well as improved photoelectrooxidation activities for methanol relative to that shown by a single TiO2 film. Further, P2 W15 -Co-SnR produced the largest photocurrent by exploring the photoelectric activities of a series of carboxyethyltin POM derivatives. This work provides new insight into the photoelectrochemical functionalization of POM-based organic-inorganic hybrids. PMID:27098260

  1. Perfluorinated quaternary ammonium salts of polyoxometalate anions: Fluorous biphasic oxidation catalysis with and without fluorous solvents

    SciTech Connect

    Maayan, Galia; Fish, Richard H.; Neumann, Ronny

    2003-05-28

    Perfluorinated quaternary ammonium cations, [CF{sub 3}(CF{sub 2}){sub 7}(CH{sub 2}){sub 3}]{sub 3}CH{sub 3}N{sup +} (RFN{sup +}), were synthesized and used as counter cations for the [WZnM{sub 2}(H{sub 2}O){sub 2}(ZnW{sub 9}O{sub 34}){sub 2}]{sup 12-} (M = Mn(II), Zn(II)), polyoxometalate. The (RFN{sup +}){sub 12}[WZnM{sub 2}(H{sub 2}O){sub 2}(ZnW9O{sub 34}){sub 2}] compounds were fluorous biphasic catalysts for alcohol and alkenol oxidation, and alkene epoxidation with aqueous hydrogen peroxide. Reaction protocols with or without a fluorous solvent were tested. The catalytic activity and selectivity was affected both by the hydrophobicity of the solvent and the substrate.

  2. Light- and Solvent-Controlled Self-Assembly Behavior of Spiropyran-Polyoxometalate-Alkyl Hybrid Molecules.

    PubMed

    Chu, Yang; Saad, Ali; Yin, Panchao; Wu, Jiayingzi; Oms, Olivier; Dolbecq, Anne; Mialane, Pierre; Liu, Tianbo

    2016-08-01

    A molecular photochromic spiropyran-polyoxometalate-alkyl organic-inorganic hybrid has been synthesized and fully characterized. The reversible switching of the hydrophobic spiropyran fragment to the hydrophilic merocyanine one can be easily achieved under light irradiation at different wavelengths. This switch changes the amphiphilic feature of the hybrid, leading to a light-controlled self-assembly behavior in solution. It has been shown that the hybrid can reversibly self-assemble into vesicles in polar solvents and irreversibly into reverse vesicles in non-polar solvents. The sizes of the vesicles and the reverse vesicles are both tunable by the polarity of the solvent, with the hydrophobic interactions being the main driving force. PMID:27404486

  3. Nanosized multilayer films with concurrent photochromism and electrochromism based on Dawson-type polyoxometalate

    NASA Astrophysics Data System (ADS)

    Xu, Bingbing; Xu, Lin; Gao, Guanggang; Jin, Yana

    2007-01-01

    An inorganic-organic composite multilayer film constructed of poly(vinyl alcohol) (PVA) with Dawson-type phosphotungstate anion [P 2W 18O 62] 6- (P 2W 18) and poly(allylamine hydrochloride) (PAH) were fabricated on quartz, ITO, silicon and CaF 2 substrates by a layer-by-layer self-assembly method. The film was provided with concurrent photochromism and electrochromism. IR spectra showed that the structure of the PVA was fully maintained in the multilayer film. And their photochromic and electrochromic properties were investigated by UV-vis spectra, cyclic voltammetry (CV), chronoamperometry (CA) measurement and X-ray photoelectron spectra (XPS). Atomic force microscopy (AFM) was used to investigate the surface topography. This study provides a new route to explore the possibility of application to polyoxometalate-based hybrid inorganic-organic materials.

  4. Development of α-polyoxometalate-polypyrrole-Au nanoparticles modified sensor applied for detection of folic acid.

    PubMed

    Babakhanian, Arash; Kaki, Samineh; Ahmadi, Mahtab; Ehzari, Hosna; Pashabadi, Afshin

    2014-10-15

    In this work, electrochemically synthesized gold nanoparticles (AuNPs) and α-polyoxometalate (α-POM) (K7PMO2W9O39 · H2O) were simultaneously doped into electropolymerized polypyrrole (PPy) film using the cyclic voltammetry (CV) technique. Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and CVs were used to characterize the composite films. The PPy-α-POM-AuNPs modified gold (Au) electrode was used to determine folic acid (FA) using square-wave voltammetry (SWV). The modified electrode exhibited excellent electrocatalytic ability to the reduction of FA at 0.3 V (vs. SCE) with the electron transfer rate constant (ks) of 1.15 × 10(-19)s(-1). The common coexisting substances showed no interferences on the response of modified electrode to FA. The modified electrode indicated reproducible behavior and a high level stability during the experiments, making it particularly suitable for the analytical purposes. PMID:24800683

  5. Transition Metal Substitution Effects on Metal-to-Polyoxometalate Charge Transfer.

    PubMed

    Glass, Elliot N; Fielden, John; Huang, Zhuangqun; Xiang, Xu; Musaev, Djamaladdin G; Lian, Tianquan; Hill, Craig L

    2016-05-01

    A series of hetero-bimetallic transition metal-substituted polyoxometalates (TMSPs) were synthesized based on the Co(II)-centered ligand [Co(II)W11O39](10-). The eight complex series, [Co(II)(M(x)OHy)W11O39]((12-x-y)-) (M(x)OHy = V(IV)O, Cr(III)(OH2), Mn(II)(OH2), Fe(III)(OH2), Co(II)(OH2), Ni(II)(OH2), Cu(II)(OH2), Zn(II)(OH2)), of which six are reported for the first time, was synthesized starting from [Co(III)W11O39](9-) and studied using spectroscopic, electrochemical, and computational techniques to evaluate the influence of substituted transition metals on the photodynamics of the metal-to-polyoxometalate charge transfer (MPCT) transition. The bimetallic complexes all show higher visible light absorption than the plenary [Co(II)W12O40](6-) and demonstrate the same MPCT transition as the plenary complex, but they have shorter excited-state lifetimes (sub-300 ps in aqueous media). The decreased lifetimes are rationalized on the basis of nonradiative relaxation due to coordinating aqua ligands, increased interaction with cations due to increased negative charge, and the energy gap law, with the strongest single factor appearing to be the charge on the anion. The most promising results are from the Cr- and Fe-substituted systems, which retain excited-state lifetimes at least 50% of that of [Co(II)W12O40](6-) while more than tripling the absorbance at 400 nm. PMID:27082443

  6. Mechanism of polyoxometalate-mediated inactivation of DNA polymerases: an analysis with HIV-1 reverse transcriptase indicates specificity for the DNA-binding cleft.

    PubMed Central

    Sarafianos, S G; Kortz, U; Pope, M T; Modak, M J

    1996-01-01

    The anti-DNA polymerase activity of a structural family of polyoxometalates has been determined. Two representative compounds of this family, possessing a saddle-like structure [(O3POPO3)4W12O36]16- (polyoxometalate I) and [(O3PCH2PO3)4W12O36]16- (polyoxometalate II) were found to inhibit all the DNA polymerases tested, with IC50 values ranging from 2 to 10 microM. A comparative study with HIV-1 reverse transcriptase (RT) and Klenow polymerase as representative DNA polymerases indicated that protection from inactivation was achieved by inclusion of DNA but not by deoxynucleotide triphosphates (dNTPs). Kinetic analysis revealed that the mode of HIV-1 RT inhibition is competitive with respect to DNA, and non-competitive with respect to dNTP binding. Cross-linking experiments confirmed that the inhibitors interfere with the DNA-binding function of HIV-1 reverse transcriptase. Interestingly, a number of drug-resistant mutants of HIV-1 RT exhibit a sensitivity to polyoxometalate comparable to the wild-type HIV-1 RT, suggesting that these polyoxometalates interact at a novel site. Because different polymerases contain DNA-binding clefts of various dimensions, it should be possible to modify polyoxometalates or to add a link to an enzyme-specific drug so that more effective inhibitors could be developed. Using a computer model of HIV-1 RT we performed docking studies in a binary complex (enzyme-polyoxometalate I) to propose tentatively a possible interacting site in HIV-1 RT consistent with the available biochemical results as well as with the geometric and charge constraints of the two molecules. PMID:8912703

  7. Enhancement of fuel cell performance with less-water dependent composite membranes having polyoxometalate anchored nanofibrous interlayer

    NASA Astrophysics Data System (ADS)

    Abouzari-lotf, Ebrahim; Jacob, Mohan V.; Ghassemi, Hossein; Ahmad, Arshad; Nasef, Mohamed Mahmoud; Zakeri, Masoumeh; Mehdipour-Ataei, Shahram

    2016-09-01

    Polyoxometalate immobilized nanofiber was used to fabricate low gas permeable layer for composite membranes designed for proton exchange membrane fuel cell (PEMFC) operating at low relative humidity (RH). The composite membranes revealed enhanced proton conductivity in dry conditions compared with state-of-the-art pristine membrane (Nafion 112, N112). This was coupled with a low fuel crossover inheriting the composite membranes about 100 mV higher OCV than N112 when tested in PEMFC at 60 °C and 40% RH. A maximum power density of up to 930 mW cm-2 was also achieved which is substantially higher than the N112 under similar conditions (577 mW cm-2). Such remarkable performance enhancement along with undetectable leaching of immobilized polyoxometalate, high dimensional stability and low water uptake of the composite membranes suggest a strong potential for PEMFC under low RH operation.

  8. A carbon-free polyoxometalate molecular catalyst with a cobalt-arsenic core for visible light-driven water oxidation.

    PubMed

    Chen, Wei-Chao; Wang, Xin-Long; Qin, Chao; Shao, Kui-Zhan; Su, Zhong-Min; Wang, En-Bo

    2016-07-21

    A carbon-free, stable, homogeneous water oxidation catalyst based on the unique hepta-nuclear cobalt-arsenic core ("fused" double-quasi-cubane) and polyoxometalate ligands, Na12[{Co(II)7As(III)6O9(OH)6}(A-α-SiW9O34)2]·8H2O (1), was synthesized, thoroughly characterized and employed to catalyze water oxidation under visible-light-driven conditions. PMID:27383015

  9. Solid state and aqueous behavior of uranyl peroxide cage clusters

    NASA Astrophysics Data System (ADS)

    Pellegrini, Kristi Lynn

    Uranyl peroxide cage clusters include a large family of more than 50 published clusters of a variety of sizes, which can incorporate various ligands including pyrophosphate and oxalate. Previous studies have reported that uranyl clusters can be used as a method to separate uranium from a solid matrix, with potential applications in reprocessing of irradiated nuclear fuel. Because of the potential applications of these novel structures in an advanced nuclear fuel cycle and their likely presence in areas of contamination, it is important to understand their behavior in both solid state and aqueous systems, including complex environments where other ions are present. In this thesis, I examine the aqueous behavior of U24Pp 12, as well as aqueous cluster systems with added mono-, di-, and trivalent cations. The resulting solutions were analyzed using dynamic light scattering and ultra-small angle X-ray scattering to evaluate the species in solution. Precipitates of these systems were analyzed using powder X-ray diffraction, X-ray fluorescence spectrometry, and Raman spectroscopy. The results of these analyses demonstrate the importance of cation size, charge, and concentration of added cations on the aqueous behavior of uranium macroions. Specifically, aggregates of various sizes and shapes form rapidly upon addition of cations, and in some cases these aggregates appear to precipitate into an X-ray amorphous material that still contains U24Pp12 clusters. In addition, I probe aggregation of U24Pp12 and U60, another uranyl peroxide cage cluster, in mixed solvent water-alcohol systems. The aggregation of uranyl clusters in water-alcohol systems is a result of hydrogen bonding with polar organic molecules and the reduction of the dielectric constant of the system. Studies of aggregation of uranyl clusters also allow for comparison between the newer uranyl polyoxometalate family and century-old transition metal polyoxometalates. To complement the solution studies of uranyl

  10. Efficiency of Polyoxometalate-Based Mesoporous Hybrids as Covalently Anchored Catalysts.

    PubMed

    Bentaleb, Faiza; Makrygenni, Ourania; Brouri, Dalil; Coelho Diogo, Cristina; Mehdi, Ahmad; Proust, Anna; Launay, Franck; Villanneau, Richard

    2015-08-01

    Polyoxometalate (POM) hybrids have been covalently immobilized through the formation of amide bonds on several types of mesoporous silica. This work allows the comparison of three POM-based mesoporous systems, obtained with three different silica supports in which either the organic functions of the support (amine vs carboxylic acid) and/or the structure of the support itself (SBA-15 vs mesocellular foams (MCF)) were varied. The resulting POM-based mesoporous systems have been studied in particular by high resolution transmission electronic microscopy (HR-TEM) in order to characterize the nanostructuration of the POMs inside the pores/cells of the different materials. We thus have shown that the best distribution and loading in POMs have been reached with SBA-15 functionalized with aminopropyl groups. In this case, the formation of amide bonds in the materials has led to the nonaggregation of the POMs inside the channels of the SBA-15. The catalytic activity of the anchored systems has been evaluated through the epoxidation of cyclooctene and cyclohexene with H2O2 in acetonitrile. The reactivity of the different grafted POMs hybrids has been compared to that in solution (homogeneous conditions). Parallels can be drawn between the distribution of the POMs and the activity of the supported systems. Furthermore, recycling tests together with catalyst filtration experiments during the reaction allowed us to preclude the hypothesis of a significant leaching of the supported catalyst. PMID:26161980