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Sample records for magnetochemistry

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

    NASA Technical Reports Server (NTRS)

    Wasilewski, P.

    1978-01-01

    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. 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.

    2016-01-01

    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

  3. 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.

    2016-11-01

    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.

  4. 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.

    PubMed

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

    2014-02-17

    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.

  5. Properties of ferrites at low temperatures (invited)

    SciTech Connect

    Dionne, G.F.

    1997-04-01

    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.}

  6. 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.

    1988-05-01

    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.

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

    PubMed

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

    2005-07-11

    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.

  8. 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.

    PubMed

    Wang, Mei; Weyhermüller, Thomas; Wieghardt, Karl

    2014-07-14

    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.

  9. 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.

    PubMed

    Hopa, Cigdem; Cokay, Ismail

    2016-02-01

    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.

  10. 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).

    PubMed

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

    2013-11-04

    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.

  11. 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-.

    PubMed

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

    2012-03-19

    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

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

    PubMed

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

    2015-03-17

    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