Sample records for magnetochemistry

  1. Reflection spectra and magnetochemistry of iron oxides and natural surfaces

    NASA Technical Reports Server (NTRS)

    Wasilewski, P.


    The magnetic properties and spectral characteristics of iron oxides are distinctive. Diagnostic features in reflectance spectra (0.5 to 2.4 micron) for alpha Fe2O3, gamma Fe2O3, and FeOOH include location of Fe3(+) absorption features, intensity ratios at various wavelengths, and the curve shape between 1.2 micron and 2.4 micron. The reflection spectrum of natural rock surfaces are seldom those of the bulk rock because of weathering effects. Coatings are found to be dominated by iron oxides and clay. A simple macroscopic model of rock spectra (based on concepts of stains and coatings) is considered adequate for interpretation of LANDSAT data. The magnetic properties of materials associated with specific spectral types and systematic changes in both spectra and magnetic properties are considered.

  2. The Magnetochemistry of Supramolecular Particles: The Transition from the Molecular to the Solid-State

    DTIC Science & Technology


    of incipient solid-state phenomena - such as the emergence of a conduction band in metallic clusters and collective magnetic interactions responsible...of technological utility. The iron- oxo clusters also present interest as synthetic analogue or model systems of biomineralization processes such as...the accumulation of iron mineral nanophases by the iron storage protein ferritin. 4 I. Introduction The disciplines of atomic and molecular physics on

  3. Combined analysis of chemical bonding in a Cu(II) dimer using QTAIM, Voronoi tessellation and Hirshfeld surface approaches.


    Vologzhanina, Anna V; Kats, Svitlana V; Penkova, Larisa V; Pavlenko, Vadim A; Efimov, Nikolay N; Minin, Vadim V; Eremenko, Igor L


    Interaction of 1-(1H-pyrazol-5-yl)ethanone oxime (H2PzOx) with copper(II) chloride in the presence of pyridine afforded a binuclear discrete [Cu2(HPzOx)2Cl2py2] complex, which was characterized by Fourier transform-IR and electron paramagnetic resonance (EPR) spectra, magnetochemistry and high-resolution X-ray diffraction experiments. Multipole refinement of X-ray diffraction data and density-functional theory (DFT) calculations of an isolated molecule allowed charge and spin distributions to be obtained for this compound. Magnetochemistry data, EPR spectra and DFT calculations of an isolated molecule show antiferromagnetic coupling between copper(II) ions. The spin distribution suggests an exchange pathway via the bridging pyrazole ring in the equatorial plane of the CuN4Cl coordination polyhedron, thus providing support for the classical superexchange mechanism; the calculated value of the magnetic coupling constant -2J is equal to 220 cm(-1), which compares well with the experimental value of 203 ± 2 cm(-1). Chemical connectivity was derived by Bader's 'quantum theory of atoms in molecules' and compared with Voronoi tessellation and Hirshfeld surface representations of crystal space. All methodologies gave a similar qualitative and semi-quantitative description of intra- and intermolecular connectivity.

  4. Droplet Merging on a Lab-on-a-Chip Platform by Uniform Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Varma, V. B.; Ray, A.; Wang, Z. M.; Wang, Z. P.; Ramanujan, R. V.


    Droplet microfluidics offers a range of Lab-on-a-chip (LoC) applications. However, wireless and programmable manipulation of such droplets is a challenge. We address this challenge by experimental and modelling studies of uniform magnetic field induced merging of ferrofluid based droplets. Control of droplet velocity and merging was achieved through uniform magnetic field and flow rate ratio. Conditions for droplet merging with respect to droplet velocity were studied. Merging and mixing of colour dye + magnetite composite droplets was demonstrated. Our experimental and numerical results are in good agreement. These studies are useful for wireless and programmable droplet merging as well as mixing relevant to biosensing, bioassay, microfluidic-based synthesis, reaction kinetics, and magnetochemistry.

  5. Annual Conference on Magnetism and Magnetic Materials, 29th, Pittsburgh, PA, November 8-11, 1983, Proceedings

    SciTech Connect

    Hasegawa, R.; Koon, N.C.; Cooper, B.R.


    Various topics on magnetism and magnetic materials are addressed. The subjects considered include: spin glasses, amorphous magnetism, actinide and rare earth intermetallics, magnetic excitation, itinerant magnetism and magnetic structure, valence instabilities, Kondo effect, transport and Hall effects, mixed valence and Kondo compounds, superconductivity and magnetism, d and f electron magnetism and superconductivity, Fe-based microcrystalline and permanent magnetic alloys, hard and soft magnetic materials, and magnetooptics. Also discussed are: numerical methods for magnetic field computation, recording theory and experiments, recording heads and media, magnetic studies via hyperfine interactions, magnetic semiconductors, magnet insulators, transition metal systems, random fields, critical phenomena and magnetoelastic effects and resonance, surfaces and interfaces, magnetostatic waves and resonance, bubble materials and implantation, bubble devices and physics, magnetic separation, ferrofluids, magnetochemistry, new techniques and materials, and new applications.

  6. Droplet Merging on a Lab-on-a-Chip Platform by Uniform Magnetic Fields

    PubMed Central

    Varma, V. B.; Ray, A.; Wang, Z. M.; Wang, Z. P.; Ramanujan, R. V.


    Droplet microfluidics offers a range of Lab-on-a-chip (LoC) applications. However, wireless and programmable manipulation of such droplets is a challenge. We address this challenge by experimental and modelling studies of uniform magnetic field induced merging of ferrofluid based droplets. Control of droplet velocity and merging was achieved through uniform magnetic field and flow rate ratio. Conditions for droplet merging with respect to droplet velocity were studied. Merging and mixing of colour dye + magnetite composite droplets was demonstrated. Our experimental and numerical results are in good agreement. These studies are useful for wireless and programmable droplet merging as well as mixing relevant to biosensing, bioassay, microfluidic-based synthesis, reaction kinetics, and magnetochemistry. PMID:27892475

  7. Magnetic behaviour of layered Ag(II) fluorides

    NASA Astrophysics Data System (ADS)

    McLain, Sylvia E.; Dolgos, Michelle R.; Tennant, D. Alan; Turner, John F. C.; Barnes, Ted; Proffen, Thomas; Sales, Brian C.; Bewley, Robert I.


    Fluoride phases that contain the spin-1/2 4d9 Ag(II) ion have recently been predicted to have interesting or unusual magnetochemistry, owing to their structural similarity to the 3d9 Cu(II) cuprates and the covalence associated with this unusual oxidation state of silver. Here we present a comprehensive study of structure and magnetism in the layered Ag(II) fluoride Cs2AgF4, using magnetic susceptometry, inelastic neutron scattering techniques and both X-ray and neutron powder diffraction. We find that this material is well described as a two-dimensional ferromagnet, in sharp contrast to the high-TC cuprates and a previous report in the literature. Analyses of the structural data show that Cs2AgF4 is orbitally ordered at all temperatures of measurement. Therefore, we suggest that orbital ordering may be the origin of the ferromagnetism we observe in this material.

  8. Molecular and electronic structures of the members of the electron transfer series [Mn(bpy)3]n (n = 2+, 1+, 0, 1-) and [Mn(tpy)2]m (m = 4+, 3+, 2+, 1+, 0). An experimental and density functional theory study.


    Wang, Mei; England, Jason; Weyhermüller, Thomas; Wieghardt, Karl


    The members of the electron transfer series [Mn(bpy)3](n) (n = 2+, 1+, 0, 1-) and [Mn(tpy)2](m) (m = 2+, 1+, 0) have been investigated using a combination of magnetochemistry, electrochemistry, and UV-vis-NIR spectroscopy; and X-ray crystal structures of [Mn(II)((Me)bpy(•))2((Me)bpy(0))](0), [Li(THF)4][Mn(II)(bpy(•))3], and [Mn(II)(tpy(•))2](0) have been obtained (bpy = 2,2'-bipyridine; (Me)bpy = 4,4'-dimethyl-2,2'-bipyridine; tpy = 2,2':6,2″-terpyridine; THF = tetrahydrofuran). It is the first time that the latter complex has been isolated and characterized. Through these studies, the electronic structures of each member of both series of complexes have been elucidated, and their molecular and electronic structures further corroborated by broken symmetry (BS) density functional theoretical (DFT) calculations. It is shown that all one-electron reductions that comprise the aforementioned redox series are ligand-based. Hence, all species contain a central high-spin Mn(II) ion (SMn = 5/2). In contrast, the analogous series of Tc(II) and Re(II) complexes possess low-spin electron configurations.

  9. Properties of ferrites at low temperatures (invited)

    SciTech Connect

    Dionne, G.F.


    At cryogenic temperatures magnetic properties of ferrites change significantly from their values at room temperature, which has been the main regime for most device applications. Recently, microwave ferrite devices with superconducting microstrip circuits have been demonstrated at a temperature of 77 K with virtually no electrical conduction losses. Conventional ferrimagnetic garnet and spinel compositions, however, are not generally optimized for low temperatures and may require chemical redesign if the full potential of these devices is to be realized. Saturation magnetizations increase according to the Brillouin{endash}Weiss function dependence that is characteristic of all ferromagnetic materials. Increased magnetocrystalline anisotropy and magnetostriction can have large effects on hysteresis loop squareness and coercive fields that are essential for stable phase shift and efficient switching. Rare-earth impurities and other ions with short spin-lattice relaxation times can cause increased microwave losses. In this article, the basic magnetochemistry pertaining to ferrites will be examined for adaptation of ferrite technology to cryogenic environments. {copyright} {ital 1997 American Institute of Physics.}

  10. Copper(II) complexes with heterocyclic hydroxyimino-containing ligands

    SciTech Connect

    Kogan, V.A.; Burlov, A.S.; Popov, L.D.; Lukov, V.V.; Koshchienko, Yu.V.; Tsupak, E.B.; Barchan, G.P.; Chigarenko, G.G.; Bolotnikov, V.S.


    The reaction of oximes (R = Ph (L'), C=N (L'')) with the copper(II) salts CuA/sub 2/ in methanol has given the complexes CuL/sub 2/ ' x H/sub 2/O and CuL/sub 2//sup ''/ x 2H/sub 2/O (I) (A = Acet/sup -/), CuHLCl/sub 2/ x H/sub 2/O (II) (A = Cl/sup -/), CuLOH(ClO/sub 4/)/sub 2/ x 2H/sub 2/O (III) (A = ClO/sub 4//sup -/) and the complexes Cu/sub 3/L/sub 3//sup '/OH(NO/sub 3/)/sub 2/ and Cu/sub 3/L/sub 3//sup ''/(OH)/sub 2/NO/sub 3/ (IV) (A = NO/sub 3//sup -/). Their physicochemical properties have been studied by the methods of IR spectroscopy and magnetochemistry. It has been shown that complexes I have a chelate structure and that their magnetic moments are not dependent on the temperature. An anti-ferromagnetic exchange interaction takes place in complexes II-IV. On the basis of magnetochemical measurements over a broad temperature range and data calculated in the framework of the Heisenberg-Dirac-Van Vleck model of isotropic exchange interactions, a dimeric structure has been proposed for the complexes of type II, and a trinuclear cluster structure has been proposed for complexes III and IV.

  11. Phosphate diester hydrolysis and DNA damage promoted by new cis-aqua/hydroxy copper(II) complexes containing tridentate imidazole-rich ligands.


    Scarpellini, Marciela; Neves, Ademir; Hörner, Rosmari; Bortoluzzi, Adailton J; Szpoganics, Bruno; Zucco, César; Nome Silva, René A; Drago, Valderes; Mangrich, Antônio S; Ortiz, Wilson A; Passos, Wagner A C; de Oliveira, Maurício C B; Terenzi, Hernán


    The tridentate Schiff base [(2-(imidazol-4-yl)ethyl)(1-methylimidazol-2-yl)methyl)imine (HISMIMI) and its reduced form HISMIMA were synthesized and characterized, as well their mononuclear cis-dihalo copper(II) complexes 1 and 2, respectively. In addition, the dinuclear [CuII(mu-OH)2CuII](2+) complexes (3) and (4) obtained from complexes 1 and 2, respectively, were also isolated and characterized by several physicochemical techniques, including magnetochemistry, electrochemistry, and EPR and UV-vis spectroscopies. The crystal structures of 1 and 2 were determined by X-ray crystallography and revealed two neutral complexes with their tridentate chelate ligands meridionally coordinated. Completing the coordination spheres of the square-pyramidal structures, a chloride ion occupies the apical position and another is bonded in the basal plane. In addition, complexes 1 and 2 were investigated by infrared, electronic, and EPR spectroscopies, cyclic voltammetry, and potentiometric equilibrium studies. The hydrolytic activity on phosphate diester cleavage of 1 and 2 was investigated utilizing 2,4-BDNPP as substrate. These experiments were carried out at 50 degrees C, and the data treatment was based on the Michaelis-Menten approach, giving the following kinetic parameters (complex 1/complex 2): vmax (mol L(-1) s(-1))=16.4x10(-9)/7.02x10(-9); KM (mol L(-1))=17.3x10(-3)/3.03x10(-3); kcat (s(-1))=3.28x10(-4)/1.40x10(-4). Complex 1 effectively promoted the hydrolytic cleavage of double-strand plasmid DNA under anaerobic and aerobic conditions, with a rate constant of 0.28 h(-1) for the decrease of form I, which represents about a 10(7) rate increase compared with the estimated uncatalyzed rate of hydrolysis.

  12. Synthesis, structural characterization and thermal properties of a new copper(II) one-dimensional coordination polymer based on bridging N,N'-bis(2-hydroxybenzylidene)-2,2-dimethylpropane-1,3-diamine and dicyanamide ligands.


    Hopa, Cigdem; Cokay, Ismail


    The design and synthesis of polymeric coordination compounds of 3d transition metals are of great interest in the search for functional materials. The coordination chemistry of the copper(II) ion is of interest currently due to potential applications in the areas of molecular biology and magnetochemistry. A novel coordination polymer of Cu(II) with bridging N,N'-bis(2-hydroxyphenyl)-2,2-dimethylpropane-1,3-diamine (H2L-DM) and dicyanamide (dca) ligands, catena-poly[[[μ2-2,2-dimethyl-N,N'-bis(2-oxidobenzylidene)propane-1,3-diamine-1:2κ(6)O,N,N',O':O,O']dicopper(II)]-di-μ-dicyanamido-1:2'κ(2)N(1):N(5);2:1'κ(2)N(1):N(5)], [Cu2(C19H20N2O2)(C2N3)2]n, has been synthesized and characterized by CHN elemental analysis, IR spectroscopy, thermal analysis and X-ray single-crystal diffraction analysis. Structural studies show that the Cu(II) centres in the dimeric asymmetric unit adopt distorted square-pyramidal geometries, as confirmed by the Addison parameter (τ) values. The chelating characteristics of the L-DM(2-) ligand results in the formation of a Cu(II) dimer with a double phenolate bridge in the asymmetric unit. In the crystal, the dimeric units are further linked to adjacent dimeric units through μ1,5-dca bridges to produce one-dimensional polymeric chains.

  13. The electron transfer series [Mo(III)(bpy)3](n) (n = 3+, 2+, 1+, 0, 1-), and the dinuclear species [{Mo(III)Cl((Me)bpy)2}2(μ2-O)]Cl2 and [{Mo(IV)(tpy·)2}2(μ2-MoO4)](PF6)2⋅4 MeCN.


    Wang, Mei; Weyhermüller, Thomas; Wieghardt, Karl


    The electronic structures of the five members of the electron transfer series [Mo(bpy)3](n) (n = 3+, 2+, 1+, 0, 1-) are determined through a combination of techniques: electro- and magnetochemistry, UV/Vis and EPR spectroscopies, and X-ray crystallography. The mono- and dication are prepared and isolated as PF6 salts for the first time. It is shown that all species contain a central Mo(III) ion (4d(3)). The successive one-electron reductions/oxidations within the series are all ligand-based, involving neutral (bpy(0)), the π-radical anion (bpy·)(1-), and the diamagnetic dianion (bpy(2-))(2-): [Mo(III)(bpy(0))3](3+) (S = 3/2), [Mo(III)(bpy·)(bpy(0))2](2+) (S = 1), [Mo(III)(bpy·)2(bpy(0))](1+) (S = 1/2), [Mo(III)(bpy·)3] (S = 0), and [Mo(III)(bpy·)2(bpy(2-))](1-) (S = 1/2). The previously described diamagnetic dication "[Mo(II)(bpy(0))3](BF4)2" is proposed to be a diamagnetic dinuclear species [{Mo(bpy)3}2(μ2-O)](BF4)4. Two new polynuclear complexes are prepared and structurally characterized: [{Mo(III)Cl((Me)bpy(0))2}2(μ2-O)]Cl2 and [{Mo(IV)(tpy·)2}2(μ2-Mo(VI)O4)](PF6)2⋅4 MeCN.

  14. Corroborative models of the cobalt(II) inhibited Fe/Mn superoxide dismutases.


    Scarpellini, Marciela; Wu, Amy J; Kampf, Jeff W; Pecoraro, Vincent L


    Attempting to model superoxide dismutase (SOD) enzymes, we designed two new N3O-donor ligands to provide the same set of donor atoms observed in the active site of these enzymes: K(i)Pr2TCMA (potassium 1,4-diisopropyl-1,4,7-triazacyclononane-N-acetate) and KBPZG (potassium N,N-bis(3,5-dimethylpyrazolylmethyl) glycinate). Five new Co(II) complexes (1-5) were obtained and characterized by X-ray crystallography, mass spectrometry, electrochemistry, magnetochemistry, UV-vis, and electron paramagnetic resonance (EPR) spectroscopies. The crystal structures of 1 and 3-5 revealed five-coordinate complexes, whereas complex 2 is six-coordinate. The EPR data of complexes 3 and 4 agree with those of the Co(II)-substituted SOD, which strongly support the proposition that the active site of the enzyme structurally resembles these models. The redox behavior of complexes 1-5 clearly demonstrates the stabilization of the Co(II) state in the ligand field provided by these ligands. The irreversibility displayed by all of the complexes is probably related to an electron-transfer process followed by a rearrangement of the geometry around the metal center for complexes 1 and 3-5 that probably changes from a trigonal bipyramidal (high spin, d7) to octahedral (low spin, d6) as Co(II) is oxidized to Co(III), which is also expected to be accompanied by a spin-state conversion. As the redox potentials to convert the Co(II) to Co(III) are high, it can be inferred that the redox potential of the Co(II)-substituted SOD may be outside the range required to convert the superoxide radical (O2*-) to hydrogen peroxide, and this is sufficient to explain the inactivity of the enzyme. Finally, the complexes reported here are the first corroborative structural models of the Co(II)-substituted SOD.

  15. Dinuclear palladium complexes with two ligand-centered radicals and a single bridging ligand: subtle tuning of magnetic properties.


    Broere, Daniël L J; Demeshko, Serhiy; de Bruin, Bas; Pidko, Evgeny A; Reek, Joost N H; Siegler, Maxime A; Lutz, Martin; van der Vlugt, Jarl Ivar


    The facile and tunable preparation of unique dinuclear [(L(⋅))Pd-X-Pd(L(⋅))] complexes (X = Cl or N3), bearing a ligand radical on each Pd, is disclosed, as well as their magnetochemistry in solution and solid state is reported. Chloride abstraction from [PdCl(NNO(ISQ))] (NNO(ISQ) = iminosemiquinonato) with TlPF6 results in an unusual monochlorido-bridged dinuclear open-shell diradical species, [{Pd(NNO(ISQ))}2(μ-Cl)](+), with an unusually small Pd-Cl-Pd angle (ca. 93°, determined by X-ray). This suggests an intramolecular d(8)-d(8) interaction, which is supported by DFT calculations. SQUID measurements indicate moderate antiferromagnetic spin exchange between the two ligand radicals and an overall singlet ground state in the solid state. VT EPR spectroscopy shows a transient signal corresponding to a triplet state between 20 and 60 K. Complex 2 reacts with PPh3 to generate [Pd(NNO(ISQ))(PPh3)](+) and one equivalent of [PdCl(NNO(ISQ))]. Reacting an 1:1 mixture of [PdCl(NNO(ISQ))] and [Pd(N3)(NNO(ISQ))] furnishes the 1,1-azido-bridged dinuclear diradical [{Pd(NNO(ISQ))}2(κ(1)-N;μ-N3](+), with a Pd-N-Pd angle close to 127° (X-ray). Magnetic and EPR measurements indicate two independent S = 1/2 spin carriers and no magnetic interaction in the solid state. The two diradical species both show no spin exchange in solution, likely because of unhindered rotation around the Pd-X-Pd core. This work demonstrates that a single bridging atom can induce subtle and tunable changes in structural and magnetic properties of novel dinuclear Pd complexes featuring two ligand-based radicals. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Synthesis, magnetostructural correlation, and catalytic promiscuity of unsymmetric dinuclear copper(II) complexes: models for catechol oxidases and hydrolases.


    Osório, Renata E H M B; Peralta, Rosely A; Bortoluzzi, Adailton J; de Almeida, Vicente R; Szpoganicz, Bruno; Fischer, Franciele L; Terenzi, Hernán; Mangrich, Antonio S; Mantovani, Karen Mary; Ferreira, Dalva E C; Rocha, Willian R; Haase, Wolfgang; Tomkowicz, Zbigniew; dos Anjos, Ademir; Neves, Ademir


    Herein, we report the synthesis and characterization, through elemental analysis, electronic spectroscopy, electrochemistry, potentiometric titration, electron paramagnetic resonance, and magnetochemistry, of two dinuclear copper(II) complexes, using the unsymmetrical ligands N',N',N-tris(2-pyridylmethyl)-N-(2-hydroxy-3,5-di-tert-butylbenzyl)-1,3-propanediamin-2-ol (L1) and N',N'-bis(2-pyridylmethyl)-N,N-(2-hydroxybenzyl)(2-hydroxy-3,5-di-tert-butylbenzyl)-1,3-propanediamin-2-ol (L2). The structures of the complexes [Cu(2)(L1)(μ-OAc)](ClO(4))(2)·(CH(3))(2)CHOH (1) and [Cu(2)(L2)(μ-OAc)](ClO(4))·H(2)O·(CH(3))(2)CHOH (2) were determined by X-ray crystallography. The complex [Cu(2)(L3)(μ-OAc)](2+) [3; L3 = N-(2-hydroxybenzyl)-N',N',N-tris(2-pyridylmethyl)-1,3-propanediamin-2-ol] was included in this study for comparison purposes only (Neves et al. Inorg. Chim. Acta2005, 358, 1807-1822). Magnetic data show that the Cu(II) centers in 1 and 2 are antiferromagnetically coupled and that the difference in the exchange coupling J found for these complexes (J = -4.3 cm(-1) for 1 and J = -40.0 cm(-1) for 2) is a function of the Cu-O-Cu bridging angle. In addition, 1 and 2 were tested as catalysts in the oxidation of the model substrate 3,5-di-tert-butylcatechol and can be considered as functional models for catechol oxidase. Because these complexes possess labile sites in their structures and in solution they have a potential nucleophile constituted by a terminal Cu(II)-bound hydroxo group, their activity toward hydrolysis of the model substrate 2,4-bis(dinitrophenyl)phosphate and DNA was also investigated. Double electrophilic activation of the phosphodiester by monodentate coordination to the Cu(II) center that contains the phenol group with tert-butyl substituents and hydrogen bonding of the protonated phenol with the phosphate O atom are proposed to increase the hydrolase activity (K(ass.) and k(cat.)) of 1 and 2 in comparison with that found for complex 3. In fact

  17. Molecular and electronic structures of six-coordinate "low-valent" [M((Me)bpy)3]0 (M = Ti, V, Cr, Mo) and [M(tpy)2]0 (M = Ti, V, Cr), and seven-coordinate [MoF((Me)bpy)3](PF6) and [MX(tpy)2](PF6) (M = Mo, X = Cl and M = W, X = F).


    Wang, Mei; Weyhermüller, Thomas; England, Jason; Wieghardt, Karl


    The electronic structures of a series of so-called "low-valent" transition metal complexes [M((Me)bpy)3](0) and [M(tpy)2](0) ((Me)bpy = 4,4'-dimethyl-2,2'-bipyridine and tpy = 2,2',6',2″-terpyridine) have been determined using a combination of X-ray crystallography, magnetochemistry, and UV-vis-NIR spectroscopy. More specifically, the crystal structures of the long-known complexes [Ti(IV)(tpy(2-))2](0) (S = 0, 6), [V(IV)(tpy(2-))2] (S = 1/2, 7), [Ti(III)((Me)bpy(•))3](0) (S = 0, 1), [V(II)((Me)bpy(•))2((Me)bpy(0))](0) (S = 1/2, 2), and [Mo(III)((Me)bpy(•))3](0) (S = 0, 4) have been determined for the first time. In all cases, the experimental results confirm the electronic structure assignments that we ourselves have recently proposed. Additionally, the six-coordinate complex [Mo(III)(bpy(0))2Cl2]Cl·2.5CH3OH (S = 3/2, 13), and seven-coordinate species [Mo(IV)F((Me)bpy(•))2((Me)bpy(0))](PF6) (S = 0, 5), [Mo(IV)Cl(tpy(•))2](PF6)·CH2Cl2 (S = 0, 11), and [W(V)F(tpy(•))(tpy(2-))](PF6)·CH2Cl2 (S = 0, 12) have been synthesized and, for the first time, crystallographically characterized. Using the resulting data, plus that from previously published high-resolution X-ray structures of analogous compounds, it is shown that there is a linear correlation between the average C(py)-C'(py) bond distances in these complexes and the total charge (n) of the ligands, {(bpy)3}(n) and {(tpy)2}(n). Hence, an assignment of the total charge of coordinated bpy or tpy ligands and, by extension, the oxidation state of the central metal ion can reliably be made on the basis of X-ray crystallography alone. In this study, the oxidation states of the metal ions range from +II to +V and in no case has an oxidation state of zero been validated. It is, therefore, highly misleading to use the term "low-valent" to describe any of the aforementioned neutral complexes.

  18. Monomeric, trimeric, and tetrameric transition metal complexes (Mn, Fe, Co) containing N,N-bis(2-pyridylmethyl)-2-aminoethanol/-ate: preparation, crystal structure, molecular magnetism and oxidation catalysis.


    Shin, Jong Won; Rowthu, Sankara Rao; Hyun, Min Young; Song, Young Joo; Kim, Cheal; Kim, Bong Gon; Min, Kil Sik


    The reaction of N,N-bis(2-pyridylmethyl)-2-aminoethanol (bpaeOH), NaSCN/NaN(3), and metal (M) ions [M = Mn(II), Fe(II/III), Co(II)] in MeOH, leads to the isolation of a series of monomeric, trimeric, and tetrameric metal complexes, namely [Mn(bpaeOH)(NCS)(2)] (1), [Mn(bpaeO)(N(3))(2)] (2), [Fe(bpaeOH)(NCS)(2)] (3), [Fe(4)(bpaeO)(2)(CH(3)O)(2)(N(3))(8)] (4), [Co(bpaeOH)(NCS)(2)] (5), and [Co(3)(bpaeO)(2)(NO(3))(N(3))(4)](NO(3)) (6). These compounds have been investigated by single crystal X-ray diffractometry and magnetochemistry. In complex 1 the Mn(II) is bonded to one bpaeOH and two thiocyanate ions, while in complex 2 it is coordinated to a deprotonated bpaeO(-) and two azide ions. The oxidation states of manganese ions are 2+ for 1 and 3+ for 2, respectively, indicating that the different oxidation states depend on the type of binding anions. The structures of monomeric iron(II) and cobalt(II) complexes 3 and 5 with two thiocyanate ions are isomorphous to that of 1. Compounds 1, 2, 3, and 5 exhibit high-spin states in the temperature range 5 to 300 K. 4 contains two different iron(III) ions in an asymmetric unit, one is coordinated to a deprotonated bpaeO(-), an azide ion, and a methoxy group, and the other is bonded to three azide ions and two oxygens from bpaeO(-) and a methoxy group. Two independent iron(III) ions in 4 form a tetranuclear complex by symmetry. 4 displays both ferromagnetic and antiferromagnetic couplings (J = 9.8 and -14.3 cm(-1)) between the iron(III) ions. 6 is a mixed-valence trinuclear cobalt complex, which is formulated as Co(III)(S = 0)-Co(II)(S = 3/2)-Co(III)(S = 0). The effective magnetic moment at room temperature corresponds to the high-spin cobalt(II) ion (∼4.27 μ(B)). Interestingly, 6 showed efficient catalytic activities toward various olefins and alcohols with modest to excellent yields, and it has been proposed that a high-valent Co(V)-oxo species might be responsible for oxygen atom transfer in the olefin epoxidation and

  19. Experimental fingerprints for redox-active terpyridine in [Cr(tpy)2](PF6)n (n = 3-0), and the remarkable electronic structure of [Cr(tpy)2]1-.


    Scarborough, Christopher C; Lancaster, Kyle M; DeBeer, Serena; Weyhermüller, Thomas; Sproules, Stephen; Wieghardt, Karl


    The molecular and electronic structures of the four members, [Cr(tpy)(2)](PF(6))(n) (n = 3-0; complexes 1-4; tpy = 2,2':6',2″-terpyridine), of the electron transfer series [Cr(tpy)(2)](n+) have been determined experimentally by single-crystal X-ray crystallography, by their electro- and magnetochemistry, and by the following spectroscopies: electronic absorption, X-ray absorption (XAS), and electron paramagnetic resonance (EPR). The monoanion of this series, [Cr(tpy)(2)](1-), has been prepared in situ by reduction with KC(8) and its EPR spectrum recorded. The structures of 2, 3, 4, 5, and 6, where the latter two compounds are the Mo and W analogues of neutral 4, have been determined at 100(2) K. The optimized geometries of 1-6 have been obtained from density functional theoretical (DFT) calculations using the B3LYP functional. The XAS and low-energy region of the electronic spectra have also been calculated using time-dependent (TD)-DFT. A consistent picture of the electronic structures of these octahedral complexes has been established. All one-electron transfer processes on going from 1 to 4 are ligand-based: 1 is [Cr(III)(tpy(0))(2)](PF(6))(3) (S = (3)/(2)), 2 is [Cr(III)(tpy(•))(tpy(0))](PF(6))(2) (S = 1), 3 is [Cr(III)(tpy(•))(2)](PF(6)) (S = (1)/(2)), and 4 is [Cr(III)(tpy(••))(tpy(•))](0) (S = 0), where (tpy(0)) is the neutral parent ligand, (tpy(•))(1-) represents its one-electron-reduced π radical monoanion, (tpy(2-))(2-) or (tpy(••))(2-) is the corresponding singlet or triplet dianion, and (tpy(3-))(3-) (S = (1)/(2)) is the trianion. The electronic structure of 2 cannot be described as [Cr(II)(tpy(0))(2)](PF(6))(2) (a low-spin Cr(II) (d(4); S = 1) complex). The geometrical features (C-C and C-N bond lengths) of these coordinated ligands have been elucidated computationally in the following hypothetical species: [Zn(II)Cl(2)(tpy(0))](0) (S = 0) (A), [Zn(II)(tpy(•))Cl(NH(3))](0) (S = (1)/(2)) (B), [Zn(II)(tpy(2-))(NH(3))(2)](0) (S = 0

  20. Dicopper(II) metallacyclophanes as multifunctional magnetic devices: a joint experimental and computational study.


    Castellano, María; Ruiz-García, Rafael; Cano, Joan; Ferrando-Soria, Jesús; Pardo, Emilio; Fortea-Pérez, Francisco R; Stiriba, Salah-Eddine; Julve, Miguel; Lloret, Francesc


    Metallosupramolecular complexes constitute an important advance in the emerging fields of molecular spintronics and quantum computation and a useful platform in the development of active components of spintronic circuits and quantum computers for applications in information processing and storage. The external control of chemical reactivity (electro- and photochemical) and physical properties (electronic and magnetic) in metallosupramolecular complexes is a current challenge in supramolecular coordination chemistry, which lies at the interface of several other supramolecular disciplines, including electro-, photo-, and magnetochemistry. The specific control of current flow or spin delocalization through a molecular assembly in response to one or many input signals leads to the concept of developing a molecule-based spintronics that can be viewed as a potential alternative to the classical molecule-based electronics. A great variety of factors can influence over these electronically or magnetically coupled, metallosupramolecular complexes in a reversible manner, electronic or photonic external stimuli being the most promising ones. The response ability of the metal centers and/or the organic bridging ligands to the application of an electric field or light irradiation, together with the geometrical features that allow the precise positioning in space of substituent groups, make these metal-organic systems particularly suitable to build highly integrated molecular spintronic circuits. In this Account, we describe the chemistry and physics of dinuclear copper(II) metallacyclophanes with oxamato-containing dinucleating ligands featuring redox- and photoactive aromatic spacers. Our recent works on dicopper(II) metallacyclophanes and earlier ones on related organic cyclophanes are now compared in a critical manner. Special focus is placed on the ligand design as well as in the combination of experimental and computational methods to demonstrate the multifunctionality