Irina V. Pirog

The novel azomethine ligands for binuclear copper(II) complexes with ferro- and antiferromagnetic properties

A series of novel binuclear ferro- and antiferromagnetic Cu(2+) chelates of structurally broadly varied Schiff bases (derived from o-tosylamino(hydroxyl)benzaldehydes and monoalkylated o-phenylenediamine, o-aminophenol, o-aminothiophenol, 1,2-diaminobenzimidazole, 1-aminobenzimidazoline-2-thione) and β-diketimines (derived from 2,6-di-i-Pr-aniline) has been prepared. The tautomerism of the ligands and structureof their copper complexes have been studied with the use of IR, 1H NMR EPR and EXAFS spectroscopy. Molecular and crystal structure of a β-diketimine copper dimer has been determined by X-ray crystallography. The magnetic measurements (2–300 K) performed for all the complexes showed that the ferro- and antiferromagnetic character of the exchange interaction depends both on the structure of the coordination site (origin of the ligating centers) and the structure of the ligands (in particular, on the type of the cycle annelated to the bridging fragment). Whereas S-binding metal chelates 13 (X = NTs, Y = S, R = H) are diamagnetic, the complexes 15 with annelated azole moieties are ferromagnetic.

The local structure of mixed-ion perovskites

The temperature-dependent Nb K-edge absorption spectra of several mixed-ion Pb-containing perovskite compounds were analysed to determine the Nb displacement and to trace its changes through the phase transitions. Both extended x-ray absorption fine structure (EXAFS) and the pre-edge region of the spectra were involved in the analysis. The results show that, in the compounds studied, Nb occupies an off-centre position with symmetry lower than that implied by macroscopic symmetry. The magnitude and direction of the Nb off-centre displacement do not display any noticeable temperature change and are not affected by the change in macroscopic symmetry. The Nb–O distribution and its temperature evolution do not show any distinct dependence on the degree of compositional ordering and properties of the samples.

Anharmonic pair potential study in face-centred-cubic structure metals

Temperature dependencies of Ni, Cu and Mo metals EXAFS spectra were studied in order to determine the anharmonic pair potential. The potential parameters for metals with cubic structure - Ni, Cu, Mo as well as for Pb (Stern?E?A et al 1991 Phys. Rev. B 43 8850), Au, Ag (Newville?M and Stern?E?A http://krazy.phys.washington.edu/paper/ag-au.html) - obtained earlier, were analysed to find correlations with other physical characteristics. It was found that a, b potential parameter values correlate with cohesive energy and interatomic distance for face-centred-cubic structure metals. Obtained potential parameter values were used to determine thermodynamics parameters, including the linear coefficient of thermal expansion, the Debye temperature, the bulk modulus and the Grunesien parameter.

Study of effective pair potentials in cubic metals

Abstract Temperature dependencies of α-Fe, Mo and W metals EXAFS spectra were studied in order to determine the anharmonic pair potential and Morse potential parameters. Based on the analysis of obtained parameters for α-Fe, Mo and W as well as for Pb, Au, Ag, Ni, and Cu, obtained earlier, the correlations between pair potential parameters and melting temperature and dissociation energy have been found. These correlations were used to estimate the anharmonic pair potential parameters for Pt, Pd, V, Cr. Some thermodynamic characteristics of substances, including linear coefficient of thermal expansion α, Debye temperature TD, and Grunesien parameter γ for α-Fe, Mo, W, Pt, Pd, V and Cr were calculated via anharmonic pair potential parameters. Calculated values of α, γ, TD are in reasonable agreement with those, obtained by thermodynamic methods.

Iron(III) Oxide Nanoparticles in a Polyethylene Matrix

A method is proposed for the preparation of iron(III) oxide nanoparticles via thermal decomposition of iron(III) acetate in a high-temperature solution of polyethylene. The nanoparticles were characterized by EXAFS, EPR, and Mössbauer spectroscopy. The nearest neighbor environment of Fe in the nanoparticles was shown to be similar to that in the structure of γ-Fe2O3 . According to the Mössbauer results, the material contains iron(III) oxide in superparamagnetic and ferromagnetic states similar to γ-Fe2O3 . The particle size determined by high-resolution transmission electron microscopy is consistent with x-ray diffraction data. Experimental data are presented on the field-dependent magnetization of the material.

1-amino-2-thiobenzimidazoleimines as novel ambidentate ligand systems

Azomethine derivatives of 1-amino-2-thiobenzimidazole (H2L) were synthesized and studied by IR and 1H NMR spectroscopy. Thiobenzimidazoline tautomeric form of these compounds was found to predominate in a solid state and DMSO solution. Novel mono-and binuclear metal chelates M(HL)2 and M2L2 (M = Ni(II), Cu(II), Co(II), Zn(II), Cd(II)) were synthesized on the basis of H2L derivatives and their composition and structures were established from IR, 1H NMR, EXAFS, and magnetochemical data. The composition of coordination sphere was shown to produce no effect on ferromagnetic exchange in binuclear Cu(II) complexes.

Structure and dielectric properties of the Aurivillius phase Bi2.25Ca0.5Na0.25Nb2O9

A new layered perovskite-like bismuth-oxide compound with the Bi2.25Ca0.5Na0.25Nb2O9 stoichiometry (Aurivillius phase) has been synthesized in polycrystalline form. As shown by powder x-ray diffraction, Bi2.25Ca0.5Na0.25Nb2O9 has an orthorhombic structure (sp. gr. A21am, no. 36) with unit-cell parameters a = 5.4845 Å, b = 5.4549 Å, and c = 24.9195 Å. Rietveld analysis has been used to determine the atomic positional parameters in its unit cell and the position of the niobium ions. Nb5+ has been shown to be displaced from the center position in the oxygen octahedra by ∼0.15 Å. The Nb K-edge extended x-ray absorption fine structure (EXAFS) spectrum of the new compound has been measured in the range 295 to 960 K. The 295-K EXAFS data have been used to evaluate the Nb-O bond lengths in the octahedra and the corresponding Debye-Waller factors. The bond lengths thus determined agree well with those inferred from powder x-ray data. With increasing temperature, the short Nb-O bonds become longer, while the long bonds become shorter. The dielectric properties of the new compound have been studied between room temperature and 1200 K at frequencies from 1 to 50 kHz. Bi2.25Ca0.5Na0.25Nb2O9 is shown to be a ferroelectric with a Curie temperature of 972 K.

Copper complexes with N-aminotriazolethione azomethines: Structures and magnetochemical properties

Azomethine derivatives of 4-amino-1,2,4-triazole-3-thiones (H2L) and their metal complexes were obtained. The stabilities of the ligand conformers were calculated using quantum-chemical techniques. Ab initio (B3LYP/LANL2DZ) calculations of the complexes in the lower singlet and triplet states were performed with full geometry optimization. The structures and magnetochemical properties of the chelate complexes obtained were examined over a wide temperature range.

Nickel(II) and cobalt(II) chelates with products of condensation of 1,8-diaminonaphthalene and salycylaldehyde

Six Ni(II) and Co(II) chelates were synthesized from different reagents (Ni(II), Co(II) chlorides and 1,8-diaminonaphthalene or the products of a single or double condensation of the latter with salicylaldehyde) and identified and characterized by elemental analysis, powder X-ray diffraction, thermogravimetry, and conductivity methods. The ligand coordination mode and the spatial structure of the complexes were established from the magnetochemistry and spectroscopy (IR, diffuse reflection) data. The dimeric structure of one of the complexes formed due to the chloride bridges was confirmed by EXAFS method.

Temperature-dependent EXAFS-study of tungsten bronze Na2Sr4Nb10O30 and boracite Fe3B7O13Br ferroelectrics

Abstract Local structure of Na2Sr4Nb10O30 and Fe3B7O13Brvhave been studied by means of Nb and Fe K-edges EXAFS spectroscopy at temperatures from 20°C to 500°C. It has been found, that Nb atoms in Na2Sr4Nb10O30 are shifted from the center of the oxygen octahedra (by about 0.085 A) and their displacements exist below and above the phase transition point. Thus it appears that the phase transition is of the order-disorder type. Temperature dependences of Debye-Waller factor (DWF) for FeO and FeBr bonds and interatomic distances (R) in Fe3B7O13Br have pumps in the vicinity of both phase transition points. This indicates the phase transition to be of the displacive type.