Том 62, № 7 (2017)

Porous ceramic materials were produced by hot pressing of a nanocrystalline (19 nm) silicon carbide powder synthesized by a hybrid method that combined the sol–gel processing of a finely divided and chemically reactive SiO₂–C system and the carbothermic synthesis at moderate (1400°C) temperature in a vacuum. It was studied how such characteristics as density, porosity, sizes of crystallites and aggregates of SiC particles, specific surface area, and compressive strength depend on pressing temperature (1400, 1500, 1600, and 1700°C).

A method is developed for incorporating praseodymium into magnesium–aluminum hydrotalcites, which are precursors for oxide catalysts for oxidative dehydrogenation (ODH) of alkanes. Oxide catalyst samples that contain praseodymium and various combinations of magnesium, aluminum, chromium, vanadium, molybdenum, and niobium are prepared. The catalytic properties of the prepared catalysts in ethane, propane, and butane ODH reactions are studied. Into some of our studied multicomponent catalysts, the incorporation of praseodymium enhances the reaction selectivity and increases yields of desired products.

o-Tosylaminobenzaldehyde dimethylpyrimidyl hydrazone and its copper(II), nickel(II), and zinc(II) complexesare synthesized and studied. According to the X-ray diffraction data, the zinc(II) complex has the structure of a tetragonal pyramid with the N₃O donor ligand environment. According to EPR and magnetochemistry data, the copper(II) complex has a similar structure of the chelate core. In the nickel(II) complex, the solvent molecule completes the coordination core to an octahedron.

Tetra-para-tolylantimony derivatives (4-MeC₆H₄)₄SbX, X = OC(O)C₆H₄(NO₂-2) (I), OC(O)C≡CPh (II), ON=CHC₆H₄(NMe₂-4) (III)) have been synthesized by the reaction between penta-para-tolylantimony and 2-nitrobenzoic and phenylpropiolic acids and 4-dimethylaminobenzaldoxime in benzene. Using X-ray diffraction, it has been established that the Sb atoms in molecules of complexes I–III are in distorted trigonal bipyramidal coordination to X groups in axial positions. The Sb–O bond lengths are 2.2797(16) (I), 2.2925(17) (II), and 2.1357(17) Å (III). The CSbO axial angles are 178.28(7)° (I), 178.57(9)° (II), 176.09(8)° (III).

Zinc(II) complexes of 4-aminoantipyrine (AAP), [Zn(AAP)₂X₂] (X = Cl^–, I^–) and [Zn(AAP)(CN)₂] · 2H₂O were prepared and characterized by elemental analysis, IR and NMR (¹H & ¹³C) spectroscopy. The crystal structure of [Zn(AAP)₂Cl₂] (1) was determined by X-ray crystallography. The structural analysis of 1 shows that the complex exists as a monomeric nonionic molecule with zinc atom bound to two AAP ligands and two chloride ions adopting a distorted tetrahedral geometry. In [Zn(AAP)₂(CN)₂] · 2H₂O, the appearance of a band at 2162 cm^–1 in IR and resonances around 142 ppm in the ¹³C NMR spectra indicated the binding of cyanide to zinc(II).

The electronic structure of hexagonal TiO₂ nanotubes doped with 3d transition metals from Sc to Zn was calculated by the linearized augmented cylindrical wave method. The calculated densities of states demonstrate that the substitution of Sc, V, Co, Cu, or Fe atoms for a part of Ti atoms leads to the decrease in the band gap width of the material from 4 to 2 eV. Such nanotubes are promising materials for creation of electrodes for electrochemical photolysis of water.

Calculations of two structures of the 3-ClC₆H₄COCl · SnCl₄ complex have been performed by the MP2/LANL2DZ method, and computational results have been compared with the experimental ³⁵Сl NQR data. It has been found that, in contrast to earlier assumptions, the complex has a common arrangement of chlorine atoms and the ligand in a strongly distorted trigonal-bipyramidal coordination sphere of the tin atom. Untypical experimental ³⁵Сl NQR data for this complex are caused by specific features of its crystal structure.

The possibility of the existence of nitrogen molecules with an even number of atoms of composition N₄, N₆, N₈, and N₁₀ has been discussed with the use of the QCISD and G3 quantum-chemical methods. From these data, a conclusion has been made that three new nitrogen allotropes with an even number of atoms in a molecule can exist, namely, N₄ shaped as a rectangle and regular tetrahedron and N₆ with a shape remotely resembling an “open book.” The bond lengths and bond and torsion angles in each of these molecules have been reported.

Optical and vibrational spectra of Bi_1.8Fe_{1.2(1 – x)}Ga_1.2xSbO₇ solid solutions with pyrochlore structure have been studied. It has been shown that the compounds have strongly disordered structure. It has been established that a decrease in iron content causes a marked shift of Bi_1.8Fe_{1.2(1 – x)}Ga_1.2xSbO₇ absorption edge. According to assessment of band gap width, Bi_1.8Ga_1.2SbO₇ is the most wide-band compound (2.90 eV), while Bi_1.8Fe_1.2SbO₇ is the most narrow-band compound (1.88 eV).

Fe_x(O, OH)_y–SiO₂ composite samples are prepared. The composite matrix is amorphous silica prepared by controlled precipitation from silicate solutions or silica derived from rice husks. The iron is shown to exist in the form of acagenite β-FeO(OH) or hematite α-Fe₂O₃. The magnetic properties of the composites are studied at temperatures in the range 2–300 K and fields in the range ±5 T. The composite samples exhibit superparamagnetic properties.

We determined, using a set of physicochemical methods, including X-ray powder diffraction (XRD), differential thermal analysis, and microstructure studies, that the CdAs₂–Cd₃As₂–MnAs ternary system is bounded by three eutectic-type quasi-binary sections: Cd₃As₂–MnAs, CdAs₂–MnAs, and Cd₃As₂–CdAs₂. For Cd₃As₂–MnAs and CdAs₂–MnAs sections, the eutectic coordinates are, respectively, 75 mol % Cd₃As₂ + 25 mol % MnAs, T_m.eut = 604°C; and 92 mol % CdAs₂ + 8 mol % MnAs, T_m.eut = 608°C. These are rod eutectics. Manganese solubilities in Cd₃As₂ and CdAs₂ phases are insignificant and, according to XRD and SEM, they do not exceed 1 at %. The binary eutectics of the quasi-binary sections form ternary eutectic Cd₃As₂ + CdAs₂ + MnAs, whose average composition as probed by SEM is 34.5 at % Cd, 63 at % Cd and 2.5 at % As and T_m.eut = 600°C. Cadmium and manganese arsenide alloys are ferromagnets with the Curie point at ~320 K. The magnetic and electric properties are due to ferromagnetic MnAs microinclusions.

In this work, the solubilities of the salt minerals and the densities of solution in two ternary systems sodium chloride–zinc chloride–water and magnesium chloride–zinc chloride–water were measured at 373 K using an isothermal solution saturation method. Based on the determined equilibrium solubility data and the corresponding equilibrium solid phase, the phase diagrams and density diagrams of the two systems were plotted. The results show that the two ternary systems are complex and the eutectic points, the univariant solubility curves and the solid crystalline phase regions are shown and discussed. The phase diagram of the ternary system NaCl−ZnCl₂−H₂O at 373 K is constituted of two eutectic points, three univariant solubility curves and three solid crystalline phase regions corresponding to NaCl, ZnCl₂ and 2NaCl · ZnCl₂. And the phase diagram of the ternary system MgCl₂−ZnCl₂−H₂O at 373 K includes two eutectic points, three univariant solubility curves and three solid crystalline phase regions corresponding to MgCl₂ · 6H₂O, MgCl₂ · ZnCl₂ · 5H₂O and ZnCl₂. The experimental results were simply discussed.

The main characteristics of extraction system for the conversion of total rare earth chlorides into nitrates with the use of higher isomeric carboxylic acids as extractants have been determined. Laboratory simulation of the process shows that two simplest manipulations: extraction and back extraction, allows conversion of total rare earth chlorides into nitrates with their simultaneous preconcentration by factor larger 40 without evaporation stage. These results can be further used in practice, for example, in the processes of extractive separation of rare earth elements.

Equilibria between gold(I) cysteinate complexes in aqueous solutions are studied by pH-metry, solubility measurements, and potentiometric measurements using a gold electrode at 25°C and I = 0.2 M (NaCl). The stepwise protonation constants logK_iH of cysteinate H_{i – 1}Cys^{i – 3} + H⁺ = H_iCys^{i – 2} are as follows: 10.10 (i = 1), 8.12 (i = 2), and 1.90 (i = 3). Protonation of cysteinate complexes is studied: Au(Cys)₂³⁻ + H⁺ = Au(HCys)(Cys)^2–, logK_{1H Au} = 9.62 and Au(HCys)(Cys)^2– + H⁺ = Au(HCys)₂⁻, logK_2HAu = 9.01. The constant K_S of the heterogeneous equilibrium Au(HCys)_s + HCys^– = Au(HCys)₂⁻ is 3.3. The standard potential of the Au(Cys)₂³⁻ complex is E_1/0⁰ = –0.172 ± 0.011 V. The stability of the Au(HCys)₂⁻ complex is close to that of Au(HS)₂⁻. The constant of substitution Au(HCys)₂⁻ + SO₃²⁻ = Au(HCys)SO₃²⁻ + HCys^– is determined to be logK_11H = –1.3.