High Spin (high + spin)

Distribution by Scientific Domains

Selected Abstracts

Unconventional Spin Crossover in Dinuclear and Trinuclear Iron(III) Complexes with Cyanido and Metallacyanido Bridges

Abstract A nonsymmetrical triamine, 1,6-diamino-4-azahexane, was Schiff-condensed with (X-substituted) o -salicylaldehyde to yield pentadentate ligands X-L5: salpet and MeBu-salpet. These ligands form mononuclear, dinuclear, and trinuclear FeIII complexes, whose structures were determined by single-crystal X-ray analysis. Of the mononuclear complexes, [FeIII(salpet)Cl] and [FeIII(MeBu-salpet)Cl] are high spin (S = 5/2), whereas [FeIII(salpet)CN]·MeOH is low spin (S = 1/2). The dinuclear and trinuclear complexes show a kind ofthermally induced spin crossover. The dinuclear complex [L5FeIII(CN)FeIIIL5](ClO4)·2H2O (L5 = salpet) is a mixed-spin assembly: the C -coordinated FeIII center is low spin (L) and the N -coordinated FeIII center is high spin (H) at low temperature; an antiferromagnetic interaction occurs between them. This LH reference state is mixed with the LL one. Upon heating, the system shows an increasing content of the HH state. Also, the dinuclear complex [L5FeIII(CN)FeIIIL5](BPh4)·2MeCN (L5 = MeBu-salpet) exhibits a spin transition between LH and HH spin pairs. The mixed-valence trinuclear complex [L5FeIII{FeII(CN)5(NO)}FeIIIL5]·0.5MeOH·3.75H2O (L5 = salpet) shows spin crossover with a residual high-spin fraction at liquid He temperature owing to the LL + LH ground state. The metallacyanido-bridged complex [L5FeIII{Ni(CN)4}FeIIIL5]·2MeOH (L5 = MeBu-salpet) contains a high-spin pair, HH, over the whole temperature interval with a ferromagnetic exchange interaction. A theoretical model was outlined that allows simultaneous fitting of all available experimental data (magnetic susceptibility, magnetization, high-spin mole fraction obtained from the Mössbauer spectra) on a common set of parameters. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

A Study of the Electronic Spin-State Crossover in {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2

Daniel L. Reger
Abstract The synthesis, structural, magnetic, and Mössbauer spectroscopic properties of {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2 are reported. The single-crystal X-ray structure results indicate that at 150 K {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2 has a structure which is very similar to that observed at 220 K for the trigonally distorted octahedral, high-spin {Fe[HC(3,5-Me2pz)3]2}(BF4)2 complex. Both the magnetic and Mössbauer spectroscopic results indicate that {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2 is high spin between 160 and 296 K. Upon cooling, {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2 exhibits a complete electronic spin-state crossover from the high-spin to the low-spin state at approximately 110 K and remains completely low spin down to 4.2 K; upon subsequent warming from 4.2 K, the transition from the low-spin to the high-spin state occurs at 148 to 150 K. {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2 exhibits a rather large thermal hysteresis of 38 K in its spin-state crossover. Thus, {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2 behaves differently from both {Fe[HC(3,5-Me2pz)3]2}(BF4)2, which is known to show a unique spin-state crossover of one-half of its iron(II) ions associated with a phase transition, and Fe[HB(3,4,5-Me3pz)3]2, which is known to remain high-spin even upon cooling to 1.7 K. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

Preparation of Uniform, Water-Soluble, and Multifunctional Nanocomposites with Tunable Sizes

Dechao Niu
Abstract Novel, thiol-functionalized, and superparamagnetic, silica composite nanospheres (SH-SSCNs) with diameters smaller than 100,nm are successfully fabricated through the self-assembly of Fe3O4 nanoparticles and polystyrene100 - block -poly(acrylic acid)16 and a subsequent sol-gel process. The size and magnetic properties of the SH-SSCNs can be easily tuned by simply varying the initial concentrations of the magnetite nanoparticles in the oil phase. By incorporating fluorescent dye molecules into the silica network, the composite nanospheres can be further fluorescent-functionalized. The toxicity of the SH-SSCNs is evaluated by choosing three typical cell lines (HUVEC, RAW264.7, and A549) as model cells, and no toxic effects are observed. It is also demonstrated that SH-SSCNs can be used as a new class of magnetic resonance imaging (MRI) probes, having a remarkably high spin,spin (T2) relaxivity (r2*,=,176.1,mM,1 S,1). The combination of the sub-100-nm particle size, monodispersity in aqueous solution, superparamagnetism, and fluorescent properties of the SH-SSCNs, as well as the non-cytotoxicity in vitro, provides a novel and potential candidate for an earlier MRI diagnostic method of cancer. [source]

A DFT study of two diiron (II) synthetic model compounds and their diiron(III) peroxide oxygenation products

R. C. Binning Jr.
Abstract Unrestricted density functional theory calculations have been conducted on two diiron(II) synthetic model compounds. Calculations employed the BPW91 and BOP density functionals with both high-spin and broken symmetry low-spin representations of weakly coupled high-spin irons. Comparison of the calculated and crystallographic structures is made, and good agreement is found with both spin representations. Raman spectral data are available for the diiron(III) product of the reaction with O2 to form a bridged peroxide. Calculated harmonic frequencies confirm the experimental assignments. Small geometry differences between the high spin and broken symmetry results are seen in bond lengths, angles, Raman frequencies, and spin densities associated with oxo and peroxo bridges in the diiron(III) oxidation products. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]

Six-coordinate Co2+ with imidazole, NH3, and H2O ligands: Approaching spin crossover

Ann M. Schmiedekamp
Abstract Octahedral, six-coordinate Co2+ can exist in two spin states: S = 3/2 and S = 1/2. The difference in energy between high spin (S = 3/2) and low spin (S = 1/2) is dependent on both the ligand mix and coordination stereochemistry. B3LYP calculations on combinations of neutral imidazole, NH3, and H2O ligands show that low-spin isomers are stabilized by axial H2O ligands and in structures that also include trans pairs of equatorial NH3 and protonated imidazole ligands, spin crossover structures are predicted from spin state energy differences. Occupied Co d orbitals from the DFT calculations provide a means of estimating effective ligand strength for homoleptic and mixed ligand combinations. These calculations suggest that in a labile biological system, a spin crossover environment can be created. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]

Resonance Raman assignment of myeloperoxidase and the selected mutants Asp94Val and Met243Thr.

Effect of the heme distortion
Abstract Resonance Raman (RR) spectra have been acquired for human myeloperoxidase (MPO), and its Met243Thr and Asp94Val mutants with different excitation wavelengths and in polarized light. The proteins were characterized as ferric, ferrous and ferric,CN complexes in order to study the heme configuration in various coordination, spin and oxidation states. Well-defined spectra of the five-coordinate high spin (ferrous), six-coordinate high spin (ferric) and low spin (ferric,CN) species were obtained. The data allowed us to propose an almost complete assignment of the RR bands. The richness of the RR spectra of MPO is because of the activation of almost all the in-plane skeletal modes observed for the Ni,octaethylporphyrin model compound, induced by the distortion of the heme imposed by the covalent links with the protein. The two mutants, which lost at least one of the covalent links between the protein and the heme group, were useful to determine the effect of the symmetry lowering of the heme group. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Pressure induced high spin to low spin transition in magnesiowüstite

Taku Tsuchiya
Abstract Using a rotationally invariant formulation of LDA + U, we report a successful study of the high spin (HS)/low spin (LS) transition in low solute concentration magnesiowüstite (Mw), (Mg1,xFex )O, (x < 20%), the second most abundant phase in Earth's lower mantle. The HS state crosses over smoothly to the LS state passing through an insulating mixed spins state where properties change continuously, as seen experimentally. These encouraging results indicate this method should enable first principles studies of strongly correlated iron-bearing minerals, a major class of mineral physics problems. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Purification, crystallization and preliminary X-ray analysis of cytochrome P450 219A1 from Novosphingobium aromaticivorans DSM 12444

Chuan Hong
Cytochrome P450 enzymes catalyze a variety of reactions and are widely distributed in living organisms. In recent studies, the first members of five new families of cytochrome P450 enzymes have been identified, including cytochrome P450 219A1 (CYP219A1) from Novosphingobium aromaticivorans DSM 12444. It has also been reported that isolongifolen-9-one (C15H22O), a sesquiterpenoid ketone derivative, is a potential substrate for CYP219A1, inducing a ,95% shift of the haem spin state to high spin upon binding. The CYP219A1 protein has been crystallized and single crystals have been studied by X-ray crystallography. Diffraction data were collected to 2.4,Å resolution. The crystals belonged to space group P6, with unit-cell parameters a = 93.1, b = 93.1, c = 98.0,Å. Preliminary X-ray diffraction data analysis revealed that the asymmetric unit contained one protein molecule. [source]

Structural and Magnetic Resolution of a Two-Step Full Spin-Crossover Transition in a Dinuclear Iron(II) Pyridyl-Bridged Compound

Jarrod J. M. Amoore
Abstract A dinuclear iron(II) complex containing the new pyridyl bridging ligand, 2,5-di(2,,2,,-dipyridylamino)pyridine (ddpp) has been synthesised and characterised by single-crystal X-ray diffraction, magnetic susceptibility and Mössbauer spectral methods. This compound, [Fe2(ddpp)2(NCS)4],4,CH2Cl2, undergoes a two-step full spin crossover. Structural analysis at each of the three plateau temperatures has revealed a dinuclear molecule with spin states HS,HS, HS,LS and LS,LS (HS: high spin, LS: low spin) for the two iron(II) centres. This is the first time that resolution of the metal centres in a HS,LS ordered state has been achieved in a two-step dinuclear iron(II) spin-crossover compound. Thermogravimetric data show that the dichloromethane solvate molecules can be removed in two distinct steps at 120,°C and 200,°C. The partially de-solvated clathrate, [Fe2(ddpp)2(NCS)4],CH2Cl2, undergoes a one-step transition with an increased transition temperature with respect to the as synthesised material. Structural characterisation of this material reveals subtle changes to the coordination geometries at each of the iron(II) centres and striking changes to the local environment of the dinuclear complex. The fully de-solvated material remains high spin over all temperatures. Interestingly, the solvent can be re-introduced into the monosolvated solid to achieve complete conversion back to the original two-step crossover material, [Fe2(ddpp)2(NCS)4],4,CH2Cl2. [source]

High-Spin- and Low-Spin-State Structures of [Fe(chloroethyltetrazole)6](ClO4)2 from Synchrotron Powder Diffraction Data

Eva Dova Dr.
Abstract The spin-crossover complex [Fe(teec)6](ClO4)2 (teec = chloroethyltetrazole) exhibits a 50,% incomplete spin crossover in the temperature range 300,30 K. Time-resolved synchrotron powder diffraction experiments have been carried out to elucidate its structural behavior. We report crystal structure models of this material at 300 K (high spin) and 90 K (low spin), as solved from synchrotron powder diffraction data by using Genetic Algorithm and Parallel Tempering techniques and refined with Rietveld refinement. During short synchrotron powder diffraction experiments (five minutes duration) two distinguishable lattices were observed the quantities of which vary with temperature. The implication of this phenomenon, that is interpreted as a structural phase transition associated with the high-to-low spin crossover, and the structural characteristics of the high-spin and low-spin models are discussed in relation to other compounds showing a similar type of spin-crossover behavior. [source]

Mixed-Valence, Mixed-Spin-State, and Heterometallic [2×2] Grid-type Arrays Based on Heteroditopic Hydrazone Ligands: Synthesis and Electrochemical Features

Lindsay H. Uppadine Dr.
Abstract An extended family of heterometallic [M12M22(L,)4]n+ [2×2] grid-type arrays 1,9 has been prepared. The three-tiered synthetic route encompasses regioselective, redox and enantioselective features and is based on the stepwise construction of heteroditopic hydrazone ligands A,C. These ligands contain ionisable NH and nonionisable NMe hydrazone units, which allows the metal redox properties to be controlled according to the charge on the ligand binding pocket. The 2-pyrimidine (R) and 6-pyridine (R,) substituents have a significant effect on complex geometry and influence both the electrochemical and magnetic behaviour of the system. 1H NMR spectroscopic studies show that the FeII ions in the grid can be low spin, high spin or spin crossover depending on the steric effect of substituents R and R,. This steric effect has been manipulated to construct an unusual array possessing two low-spin and two spin-crossover FeII centres (grid 8). Electrochemical studies were performed for the grid-type arrays 1,9 and their respective mononuclear precursor complexes 10,13. The grids function as electron reservoirs and display up to eight monoelectronic, reversible reduction steps. These processes generally occur in pairs and are assigned to ligand-based reductions and to the CoIII/CoII redox couple. Individual metal ions in the heterometallic grid motif can be selectively addressed electrochemically (e.g., either the CoIII or FeII ions can be targeted in grids 2 and 5). The FeII oxidation potential is governed by the charge on the ligand binding unit, rather than the spin state, thus permitting facile electrochemical discrimination between the two types of FeII centre in 7 or in 8. Such multistable heterometallic [2×2] gridlike arrays are of great interest for future supramolecular devices incorporating multilevel redox activity. Une famille de complexes hétérométalliques [M12M22(L,)4]n+du type grille [2×2] 1,9 a été préparée. Les trois approches synthétiques multiétapes des ligands hydrazone hétéroditopiques A,C possèdent chacune des caractéristiques régio-, rédox-, énantio-sélectives. Ces ligands possèdent un groupement NH ionisable et un groupement hydrazone non-ionisable NMe, qui permettent un contrôle des propriétés rédox du métal complexé en fonction de la charge de la cavité coordinante. Les substituants 2-pyrimidine (R) et 6-pyridine (R,) influencent de manière significative la géométrie des complexes formés ainsi que leurs propriétés électrochimiques et magnétiques. Les études par spectroscopie RMN1H montrent que les ions FeII, dans ces complexes, possèdent une configuration électronique soit de bas spin, soit de haut spin ou encore de transition de spin en fonction de l'encombrement stérique du substituant. Cet effet stérique a été utilisé pour construire des grilles originales possédant deux cations FeIIde bas spin et deux cations FeIIà transition de spin (grille 8). Des études électrochimiques détaillées ont été réalisées pour les assemblages du type grille 1,9 et leurs précurseurs mononucléaires 10,13. Ces grilles fonctionnent comme réservoir à électrons. Jusqu'à huit étapes de réduction monoélectronique réversibles peuvent être observées. Ces transferts d'électrons se font généralement par paire et interviennent sur le ligand à l'exception des deux premières réductions correspondant aux couples CoIII/CoII. Chaque cation métallique d'une grille peut être sollicité sélectivement par voie électrochimique (les ions CoIIIou FeIIpeuvent être ciblés dans les grilles 2 et 5). Le potentiel d'oxydation du FeIIest tributaire de la charge des ligands et non de l'état de spin, permettant une discrimination électrochimique parmi les deux types de FeIIdans 7 ou 8. De telles grilles [2×2] hétérométalliques ont des niveaux de stabilité multiples et présentent un grand intérêt pour des systèmes supramoléculaires possédant une multiplicité de niveaux d'oxydo-réduction. [source]