ABSTRACT
New iron(II) complexes with 2,6-bis(1H-imidazol-2-yl)-4-methoxypyridine (L) of the composition [FeL2]AnâmH2O (A = SO42-, n = 1, m = 2 (I); A = ReO4-, n = 2, m = 1 (II); A = Br-, n = 2, m = 2 (III)) have been synthesized and investigated. To determine the coordination ability of the ligand, a single crystal of a copper(II) complex of the composition [CuLCl2] (IV) was obtained and studied by X-ray technique. Compounds I-III were studied using methods of X-ray phase analysis, electron (diffuse reflection spectra), infrared and Mössbauer spectroscopy, static magnetic susceptibility. The study of the µeff(T) dependence showed that the 1A1 â 5T2 spin crossover manifests itself in the compounds. The spin crossover is accompanied by thermochromism: there is a distinct color change orange â red-violet.
Subject(s)
Iron , Pyridines , Copper/chemistry , Ferrous Compounds/chemistryABSTRACT
The atom oxidation states were determined using the binding energies of the core S2p-, Cu2p-, Cr2p-, and Ln3d-levels in CuCr0.99Ln0.01S2 (Ln = Dy-Lu) solid solutions. The charge distribution on the matrix elements (Cu, Cr, and S) remained unaffected after cationic substitution. The sulfur atoms were found to be in the S2- oxidation state, the copper-Cu+, and the chromium-Cr3+. The cationic substitution of the initial CuCrS2-matrix occurred via the isovalent mechanism. The obtained results were compared with the electrophysical properties for CuCr0.99Ln0.01S2. The measured carrier concentration was from 1017 to 1018 cm-3. The largest Seebeck coefficient value of 157 µV/K was measured for CuCr0.99Yb0.01S2 at 500 K. The cationic substitution with lanthanides allowed one to enhance the Seebeck coefficient of the initial CuCrS2-matrix.
ABSTRACT
The charge distribution study of metal atoms in CuCr0.99Ln0.01S2 (Ln = Pr-Tb) solid solutions was carried out using X-ray photoelectron spectroscopy (XPS). The analysis of the binding energy of S2p, Cu2p, Cr2p, Ln3d and Ln4d levels allows one to determine the oxidation state of atoms. Copper atoms were found to be monovalent. Chromium and lanthanide atoms were found to be in the trivalent state. Sulfur atoms were found to be in the divalent state. Cationic substitution was found to occur via an isovalent mechanism of Cr3+ to Ln3+. The obtained results were used for the interpretation of the Seebeck coefficient increase for CuCr0.99Ln0.01S2 solid solutions in contrast to the initial CuCrS2 matrix. The largest Seebeck coefficient values of 142 and 148 µV/K were observed at 500 K for CuCr0.99Sm0.01S2 and CuCr0.99Pr0.01S2, respectively. The obtained values are 1.4 times greater in comparison with those for the initial matrix (105 µV/K).
ABSTRACT
Novel iron(II) coordination compounds containing a ligand 2,6-bis(1H-imidazol-2-yl)pyridine (L), having such a composition as [FeL2]SO4·0.5H2O, [FeL2]Br2·H2O, [FeL2](ReO4)2, [FeL2]B10H10âH2O, [FeL2]B12H12â1.5H2O had been synthesized and studied using UV-Vis (diffuse reflectance), infrared, extended X-ray absorption fine structure (EXAFS), and Mössbauer spectroscopy methods, as well as X-ray diffraction and static magnetic susceptibility methods. The analysis of the µeff(T) dependence in the temperature range of 80-600 K have shown that all the obtained complexes exhibit a high-temperature spin crossover 1A1 â 5T2.
ABSTRACT
The comprehensive study of the lanthanide-doped solid solutions CuCr0.99Ln0.01S2 (Ln = La Lu) magnetic properties was carried out using static magnetochemistry and differential scanning calorimetry techniques. It was shown that magnetic properties of CuCr0.99Ln0.01S2 are significantly affected by the magnetic properties of the lanthanide ion. The magnetic susceptibility and the effective magnetic moment were found to deviate from the Curie-Weiss law in the temperature 90 K below and 50 K above the order-disorder transition at 695 K. The observed behavior of the temperature dependence of the effective magnetic moment in the order-disorder transition temperature region was described as a result of copper atoms redistribution over different types of the crystallographic sites.
ABSTRACT
The work reports a comprehensive study of the Seebeck coefficient, electrical resistivity and heat capacity of CuCrS2 in a wide temperature range of 100-740 K. It was shown that the value of the Seebeck coefficient is significantly affected by the sample treatment procedure. The order-to-disorder (ODT) phase transition was found to cause a metal-insulator transition (MIT). It was established that the ODT diminishes the Seebeck coefficient at high temperatures (T > 700 K). The DFT calculations of the CuCrS2 electronic structure showed that the localization of copper atoms in octahedral sites makes the band gap vanish due to the MIT. The decrease of CuCrS2 electrical resistivity in the ODT temperature region corresponds to the MIT.
ABSTRACT
Charge state studies of compounds [Mo3S4(tu)8(H2O)]Cl4·4H2O (1), [Mo3S4Cl3(dbbpy)3]Cl·5H2O (2), [Mo3S4(CuCl)Cl3(dbbpy)3][CuCl2] (3), containing {Mo3S4}4+ and {Mo3CuS4}5+ cluster cores bearing terminal thiourea (tu) or 4,4'-di-tert-butyl-2,2'-bipyridine (dbbpy) ligands, have been performed by X-ray photoelectron and X-ray emission spectroscopies combined with quantum chemical calculations. The best agreement between theory and experiments has been obtained using the B3LYP method. According to the experimental and calculated data, the Mo atoms are in the oxidation state 4+ for all compounds. The energies and shapes of the Cu2p lines indicate formal oxidation states of Cu as 1+. The coordination of Сu(I) to the cluster {Mo3S4} in 3 does not lead to significant changes in the charge state of the molybdenum atoms and the {Mo3S4} unit can be considered as a tridentate metallothia crown ether.
