Home About us Contact
|
Home About us Contact | ||
|
|
||
Magnetic Behaviour (magnetic + behaviour)
Selected AbstractsSynthesis, Structure and Magnetic Behaviour of Manganese(II) Selenolate Complexes ,1[Mn(SePh)2], [Mn(SePh)2(bipy)2] and [Mn(SePh)2(phen)2] (bipy = bipyridyl, phen = phenanthroline)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 30 2007Andreas Eichhöfer Abstract The manganese selenolate complex ,1[Mn(SePh)2] has been prepared by reaction of Mn(OOCCH3)2 with 2 equiv.PhSeSiMe3 in thf. In the crystal structure, the compound forms one-dimensional chains, and the bridging selenolate ligands result in relatively short metal,metal contacts of about 3 Å. Reaction with two equivalents of the Lewis bases 2,2,-bipyridine and 1,10-phenanthroline yielded the monomeric octahedral complexes [Mn(SePh)2(2,2,-bipy)2] and [Mn(SePh)2(1,10-phen)2], respectively. The magnetic and optical properties of these complexes have been investigated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Magnetic behaviour of synthetic Co2SiO4ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2009Andrew Sazonov Synthetic Co2SiO4 crystallizes in the olivine structure (space group ) with two crystallographically non-equivalent Co positions and shows antiferromagnetic ordering below 50,K. We have investigated the temperature variation of the Co2SiO4 magnetic structure by means of non-polarized and polarized neutron diffraction for single crystals. Measurements with non-polarized neutrons were made at 2.5,K (below TN), whereas polarized neutron diffraction experiments were carried out at 70 and 150,K (above TN) in an external magnetic field of 7,T parallel to the b axis. Additional accurate non-polarized powder diffraction studies were performed in a broad temperature range from 5 to 500,K with small temperature increments. Detailed symmetry analysis of the Co2SiO4 magnetic structure shows that it corresponds to the magnetic (Shubnikov) group Pnma, which allows the antiferromagnetic configuration (Gx, Cy, Az) for the 4a site with inversion symmetry (Co1 position) and (0,Cy,0) for the 4c site with mirror symmetry m (Co2 position). The temperature dependence of the Co1 and Co2 magnetic moments obtained from neutron diffraction experiments was fitted in a modified molecular-field model. The polarized neutron study of the magnetization induced by an applied field shows a non-negligible amount of magnetic moment on the oxygen positions, indicating a delocalization of the magnetic moment from Co towards neighbouring O owing to superexchange coupling. The relative strength of the exchange interactions is discussed based on the non-polarized and polarized neutron data. [source] Solid-State Anion,Guest Encapsulation by Metallosupramolecular Capsules Made from Two Tetranuclear Copper(II) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2007Emilio Pardo Abstract A new cationic tetranuclear copper(II) complex self-assembles from one 1,3-phenylenebis(oxamato) (mpba) bridging ligand and four CuII ions partially blocked with N,N,N,,N, -tetramethylethylenediamine (tmen) terminal ligands. In the solid state, two of these tetracopper(II) oxamato complexes of bowl-like shape and helical conformation then serve as a building block for the generation of either hetero- (MP) or homochiral (MM/PP) dimeric capsules depending on the nature of the encapsulated anion guest, perchlorate or hexafluorophosphate. The overall magnetic behaviour of these metallosupramolecular capsules does not depend on the nature of the encapsulated anion guest, but it is consistent with the dimer-of-dimer structure of the tetracopper(II) cation host, where the interdimer magnetic coupling through the meta -phenylenediamidate bridge is negligibly smallrelative to the reasonably strong intradimer one across the oxamato bridge.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] A Ferromagnetically Coupled, Bent, Trinuclear Copper(II) Complex: Synthesis, Structure, Hydrogen-Bonding Network, Magnetic Properties and DNA Interaction StudyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2006Sumana Sarkar Abstract A bent trinuclear copper(II) complex (1) incorporating ,-phenoxo, ,- syn - syn carboxylato, and ,3 -chloro bridges and an O,N,N -coordinated reduced Schiff-base ligand is reported. The complex shows an intramolecular ferromagnetic interaction in the solid state. The EPR spectra also support the magnetic behaviour of the complex. In the compound, each copper centre has a square-pyramidal geometry. The separation between the adjacent copper ions is about 3.05 Å and that between the terminal copper ions is about 5.0 Å. The complex forms a supramolecular architecture through N,H···Cl hydrogen bonding between the amine group of the reduced Schiff-base ligand and the counter chloride anions. Absorption and fluorescence spectral studies and viscosity measurements have been performed to determine the type of interaction with calf-thymus DNA. The nuclease activity of the complex with plasmid DNA is also studied. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Ferromagnetic nanoparticles embedded in self-arranged matricesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2008K. Rumpf Abstract The investigated nanoscopic system, consisting of a non magnetic host material and precipitated ferromagnetic nanostructures shows a magnetic behaviour correlated to the size and shape of the deposited particles but also to their spatial distribution within the template which modifies the magnetic interactions between them. The nanostructures are deposited electrochemically into an etched silicon wafer exhibiting an array of channels of a few ten nanometers in diameter and a length up to 50 µm. The self-assembled grown templates offer the opportunity of tuning the magnetic properties by varying the geometrical characteristics of the membrane which can be loaded with different metals like Ni or Co with variable metal distribution. Magnetic characteristics like coercivity, magnetic anisotropy and temperature dependent magnetization give a survey about the structure and the magnetic interactions of the nanocomposite. This achieved ferromagnetic nanocomposite system is not only of interest for basic research but also gives rise to applications in magneto-optics, spintronics and sensor application. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] FMR study of strain-induced magnetic anisotropies in CrO2 thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2004B. Z. Rameev Abstract Epitaxial CrO2 thin films were grown on TiO2 (100) single-crystalline substrates by chemical vapour deposition (CVD) process with use of CrO3 solid precursor. The films with different thickness (27,530 nm) were studied by Ferromagnetic Resonance (FMR) technique. Strong dependence of FMR signal on the film thickness was observed in the series of CrO2 films deposited onto the pre-etched TiO2 substrates. It is shown that the magnetic behaviour of the CrO2 films arises from competition between magnetocrystalline and strain anisotropies that favour the [001] and [010] magnetization directions, respectively. For the thinnest film the strain anisotropy dominates, and the magnetic easy axis switches from [001] to the [010] direction. On the contrary, the CrO2 film grown on the unetched substrate demonstrates essentially strain-free magnetic anisotropy behaviour. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] On the magnetic behaviour of GdCo2,xCux compoundsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003R. Tetean Abstract The GdCo2,xCux compounds crystallize in a cubic C15 type structure for x , 0.20. The compounds are ferrimagnetically ordered. The mean cobalt magnetic moments, determined at 4.2 K, are little dependent on composition. The saturation moments per formula unit, at 4.2 K, are in rather good agreement with those obtained from band structure calculations. The Gd 5d band polarizations were analyzed. The contributions from 4f,5d, local exchange M5d(Gd), and 5d,3d short range exchange interactions, M5d(0), were determined. The M5d(0) values are proportional to cobalt magnetizations. [source] Temperature dependence of a twofold magnetic behaviour of a nanoscopic metal/silicon hybrid system , a comparison between Ni/Si and Co/SiPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2009K. Rumpf Abstract The investigated hybrid nanocomposite consists of a porous silicon template with electrochemically embedded Ni or Co nanostructures and offers magnetic characteristics which can be tailored by the electrochemical process parameters during fabrication. A twofold magnetic behaviour can be observed, a first one due to the spinmagnetism at magnetic fields below the saturation magnetization of the deposited metals and a second non-saturating term at higher fields (> 1 T up to 7 T) above the saturation magnetization. In case of Ni deposited within the pores this non-saturating term shows a paramagnetic characteristic and follows exactly the Curie-Weiss law, whereas for Co/porous silicon samples the temperature dependent magnetization shows some deviations from the Curie Weiss law. In this high field region a difference in the temperature dependence between Ni and Co is observed whereas the non-saturating term does not depend on the geometry of the embedded nanostructures in contrast to the ferromagnetic behaviour at lower magnetic fields. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystallization and magnetic behaviour of (Fe1,xCox)85.4 Zr5.8Nb1B6.8Cu1 (x = 0, 0.1, 0.3, 0.5) alloysPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004M. Hasiak Abstract Nanocrystallization and low field magnetic properties (i.e. magnetic susceptibility and its disaccommodation) of the (Fe1,xCox)85.4Zr5.8Nb1B6.8Cu1 (x = 0, 0.1, 0.3, 0.5) alloys are investigated. The crystalline phase in the nanocrystalline Fe85.4Zr5.8Nb1B6.8Cu1 alloy consists of ,-Fe grains whereas in the nanocrystalline (Fe1,x Cox)85.4Zr5.8Nb1B6.8Cu1 (x = 0.1, 0.3, 0.5) alloys ,-FeCo phase is present. From Mössbauer spectroscopy studies we have found that ,-FeCo phase for x = 0.3 and 0.5 is atomically ordered. The annealing of the amorphous Fe85.4Zr5.8Nb1B6.8Cu1 sample below the crystallization temperature leads to the decrease of the hyperfine field due to the invar effect. This phenomenon has not been observed in alloys containing Co. In the isochronal disaccommodation curves of the nanocrystalline (Fe1,xCox)85.4Zr5.8Nb1B6.8Cu1 (x = 0.3, 0.5) alloys broad maxima are present. This effect has not been observed in Fe-based nanocrystalline alloys. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spin Crossover versus Low-Spin Behaviour Exhibited in 2D and 3D Supramolecular Isomers of [FeII(2,4-bpt)2],Guest,CHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2010Xin Bao To spin or not to spin: Four supramolecular isomers based on a [Fe(2,4-bpt)2],guest were synthesised by judicious choice of solvents under solvothermal conditions (see figure). They can be categorised into a 2D spin crossover (SCO) branch and a 3D low-spin (LS) branch (all of them exhibit NbO topology, but one is non-interpenetrated and the other two are twofold interpenetrated). The differences in the supramolecular interactions play important roles in their magnetic behaviour. [source] Tuning the Magnetic Moment of [Ru2(DPhF)3(O2CMe)L]+ Complexes (DPhF=N,N, -Diphenylformamidinate): A Theoretical Explanation of the Axial Ligand InfluenceCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2010Carmen Barral Dr. Abstract The magnetic behaviour of the compounds containing the [Ru2(DPhF)3(O2CMe)]+ ion (DPhF,=N,N, -diphenylformamidinate) shows a strong dependence on the nature of the ligand bonded to the axial position. The new complexes [Ru2(DPhF)3(O2CMe)(OPMe3)][BF4],0.5,CH2Cl2 (1, 0.5,CH2Cl2) and [Ru2(DPhF)3(O2CMe)(4-pic)][BF4] (2) (4-pic=4-methylpyridine) clearly display this influence. Complex 1,0.5,CH2Cl2 shows a magnetic moment corresponding to a S=3/2 system affected by the common zero-field splitting (ZFS) and a weak antiferromagnetic interaction, whereas complex 2 displays an intermediate behaviour between S=3/2 and S=1/2 systems. The experimental data of complex 1 are fitted with a model that considers the ZFS effect using the Hamiltonian ,D=S,D,S. The weak antiferromagnetic coupling is introduced as a perturbation, using the molecular field approximation. DFT calculations demonstrate that, in the [Ru2(O2CMe)(DPhF)3(L)]+ complexes, the energy level of the metal,metal molecular orbitals is strongly dependent on the nature of the axial ligand (L). This study reveals that the increase in the ,-acceptor character of L leads to a greater split between the ,* and ,* HOMO orbitals. The influence of the axial ligand in the relative energy between the doublet and quartet states in this type of complexes was also analysed. This study was performed on the new complexes 1,0.5,CH2Cl2 and 2. The previously isolated [Ru2(DPhF)3(O2CMe)(OH2)][BF4],0.5,CH2Cl2 (3, 0.5,CH2Cl2) and [Ru2(DPhF)3(O2CMe)(CO)][BF4],CH2Cl2 (4,CH2Cl2) complexes were also included in this study as representative examples of spin-admixed and low-spin configurations, respectively. The [Ru2(DPhF)3(O2CMe)]+ (5) unit was used as a reference compound. These theoretical studies are in accordance with the different magnetic behaviour experimentally observed. [source] A Family of Ferro- and Antiferromagnetically Coupled Decametallic Chromium(III) WheelsCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2006David M. Low Dr. Abstract The synthesis and crystal structures of a family of decametallic CrIII "molecular wheels" are reported, namely [Cr10(OR)20(O2CR,)10] [R,=Me, R=Me (1), Et (2); R,=Et, R=Me (3), Et (4); R,=CMe3, R=Me (5), Et (6)]. Magnetic studies on 1,6 reveal a remarkable dependence of the magnetic behaviour on the nature of R. In each pair of complexes with a common carboxylate (R,) the nearest neighbour Cr,,,Cr magnetic exchange coupling is more antiferromagnetic for the ethoxide-bridged (R=Et) cluster than for the methoxide analogue. In complexes 2, 4 and 6 the overall coupling is weakly antiferromagnetic resulting in diamagnetic (S=0) ground states for the cluster, whilst in 1 and 5 it is weakly ferromagnetic thus resulting in very high-spin ground states. This ground state has been probed directly in the perdeuterated version of 1 ([D]1) by inelastic neutron scattering experiments, and these support the S=15 ground state expected for ferromagnetic coupling of ten CrIII ions, and they also indicate that a single J -value model is inadequate. The ground state of 5 is large but not well defined. The trends in J on changing R are further supported by density functional calculations on 1,6, which are in excellent agreement with experiment. The very large changes in the nature of the ground state between 1 and 2, and 5 and 6 are the result of relatively small changes in J that happen to cross J=0, hence changing the sign of J. [source] Mixed-Valence, Mixed-Spin-State, and Heterometallic [2×2] Grid-type Arrays Based on Heteroditopic Hydrazone Ligands: Synthesis and Electrochemical FeaturesCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2005Lindsay 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] Templated Synthesis of Mesoporous Superparamagnetic Polymers,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2007B. Fuertes Abstract We present a novel synthetic strategy for fabricating superparamagnetic nanoparticles randomly dispersed in a mesoporous polymeric matrix. This method is based on the use of mesoporous silica materials as templates. The procedure used to obtain these mesoporous magnetic polymers consisted in: a),generating iron oxide ferrite magnetic nanoparticles (FMNP) of size ,,7,8,nm within the pores of the silica, b),loading the porosity of the silica/FMNP composite with a polymer (Polydivinylbenzene), c),selectively removing the silica framework from the resulting silica/FMNP/polymer composite. Such magnetic porous polymeric materials exhibit large surface areas (up to 630,m2,g,1), high pore volumes (up to 0.73,cm3,g,1) and a porosity made up of mesopores. In this way, it is possible to obtain superparamagnetic mesoporous hybrid nanocomposites that are easily manipulated by an external magnetic field and display different magnetic behaviours depending on the textural properties of the template employed. [source] | |||||||||||||