卷 62, 编号 5 (2017)

We report the results of developing efficient universal isothermal methods for the determination of compositions of all phases (several solid phases and a liquid) involved in invariant equilibria in multicomponent aqueous systems using chemical analysis (a combination method) or not (an optimized sections method) to determine the composition of an equilibrium liquid phase.

Phase equilibria involving LiMn₂O_4-, Li₂MnO_3-, LiMnO_2-, Mn₃O_4-, and MnO-base solid solutions were studied with varied temperature and partial oxygen pressure. The \({P_{{o_2}}}\)–T and x–y projections of the P–T–x–y phase diagram of the Li–Mn−O system were constructed, as well as the key x–y isotherms of the Li₂O–MnO–MnO₂ quasi-ternary system. In some experiments, the authors’ hydride lithiation method was employed to prepare lithium-rich homogeneous three-component nonstoichiometric phases.

The stable tetrahedron LiF–KI–K₂CrO₄–Li₂CrO₄ of the quaternary reciprocal system Li, K||F, I, CrO₄ was experimentally studied by differential thermal analysis. The compositions and melting points of mixtures of components at two eutectic points were determined. Based on experimental data, a T–x–y–z model of the phase complex was constructed, which allows one to solve problems of building polythermal and isothermal sections. A method for constructing the diagram of material balance of equilibrium phases for a given composition was developed. The diagram enables one to find the ratio between the amounts of the liquid and solid phases at constant temperature and also monitor the change in the composition of the phases within a chosen temperature range.

Topological and geometric images of invariant and monovariant reactions with the participation of melt in quaternary systems were presented. A network of invariant points and monovariant lines characterizes the structure of the liquidus hypersurface. Each invariant reaction produces an association of four solid phases, which is an element of the solidus hypersurface. Its topology is conveniently described by a graph of adjacency of tetrahedra that partition the composition tetrahedron of a system with a given set of binary, ternary, and quaternary compounds. It was demonstrated that it is possible to construct a spatial network of invariant points and monovariant lines on the liquidus hypersurface using the tetrahedron incidence graph with consideration for the phase reactions occurring in the system.

Phase equilibria in the Cu₂S–Cu₃AsS₄–S system were studied by differential thermal analysis and X-ray powder diffraction. Important plots characterizing this system were constructed, namely, the T–x diagrams of the lateral quasi-binary systems Cu₂S–Cu₃AsS₄ and Cu₃AsS₄–S, some internal sections, the isothermal section of the phase diagram at 300 K, and the projection of the liquidus surface. The fields of primary crystallization of phases and the types and coordinates of in- and monovariant equilibria were found. A wide region of separation of liquid phases was detected in the system.

The LiF–KBr–KVO₃–K₂MoO₄ secant tetrahedron of the Li,K||F,Br,VO₃,MoO₄ five-component reciprocal system was studied by differential thermal analysis. The composition corresponding to the quaternary eutectic was determined (mol %): LiF, 7.2; KBr, 16.8; KVO₃, 66.5; and K₂MoO₄, 9.5. The eutectic melting temperature was found to be 419°С.

Heterogeneous equilibria in the zinc perchlorate–urea–perchloric acid–water quaternary system at 25°С were studied by investigating solubility. The crystallization regions were found for the initial solid components, eutonic compositions of the ternary systems constituting the quaternary system, binary compounds of urea with zinc perchlorate and perchloric acid, and also two new coordination compounds containing simultaneously zinc perchlorate, urea, and perchloric acid: ZnClO₄ · 4CO(NH₂)₂ · HClO₄ and ZnClO₄ · 2CO(NH₂)₂ · HClO₄.

Effect of conditions of nanocrystalline cerium dioxide preparation from aqueous solutions on its composition and physicochemical properties and on dielectric characteristics of CeO₂ suspensions in polydimethylsiloxane PMS-20 and the magnitude of electrorheological effect for these suspensions has been analyzed. Relationship between physicochemical properties of CeO₂ nanopowders and polarization and functional characteristics of electrorheological fluids derived therefrom has been established.

We performed the synthesis and studied the extents and compositions of solid solutions (ss) formed by heterovalent substitutions in M₃(VO₄)₂–M₂Me_2/3(VO₄)₂ systems where M = Sr, Ba, or Pb and Me = La or Bi. A continuous solid solution (css) series was shown to be formed only when the initial compounds crystallize in palmierite structure. Bi³⁺ and La³⁺ were shown to occupy different positions (3а and 6с, respectively) in the crystal lattice of Sr₃(VO₄)₂-base ss.

The centrosymmetric binuclear complex of samarium(III) nitrate with bicyclic biscarbamide 2,4,6,8-tetramethyl-2,4,6,8-tetraazabicyclo(3.3.0)octane-3,7-dione, or mebicar (Mk) namely, [Sm(C₈H₁₄N₄O₂)(H₂O)₂(NO₃)₃]₂ (I) has been synthesized. Its crystal structure has been characterized (CIF file CCDC no. 1451436). Crystals of complex I are triclinic, space group P1 a = 9.8661(2) Å, b = 10.2913(3) Å, c = 10.9629(3) Å, α = 74.475(2)°, β = 67.802(2)°, γ = 67.570(2)°, V = 942.68(5) ų, ρcalcd = 2.01028 g/cm³, and Z = 1. The samarium atom is coordinated by the two oxygen atoms of two Mk molecules bonded via the symmetry center, three bidentate nitrate anions, and two water molecules. The coordination number of the samarium atom is 10, the coordination polyhedron of the metal atom is a decahedron and the Sm…Sm distance is 9.7904(4) Å.

N,N-Diethylanilinium dicitratoborate [C₆H₅NH(C₂H₅)₂][(C₆H₆O₇)₂B] (I) has been synthesized for the first time. Single crystals has been synthesized in an aqueous solution to study the crystal structure of complex I by single-crystal X-ray diffraction. Crystals are triclinic, space group Р1 a = 9.6183(2) Å, b = 10.3153(3) Å, c = 13.7364(4) Å, α = 69.0304(12)°, β = 77.0394(13)°, γ = 89.5518(10)°, V = 1236.25(6) ų, Z = 2, ρ_calcd = 1.454 g/cm³. Structural units in a crystal of complex I are large complex dicitratoborate anions with a spirane structure and N,N-diethylanilinium cations. The crystal packing is a three-dimensional framework implemented via a system of hydrogen bonds like О–Н…О, О–Н…О, ОI, and N–Н…О.

The energies and structural and spectroscopic characteristics of endohedral and exohedral isomers of oxovanadate complexes with MO₄ⁿ⁻ tetraoxo anions located in the inner and outer spheres of the V₂₀O₅₀ cluster have been calculated by the density functional theory method (B3LYP). It has been demonstrated that, among the endohedral MO₄@V₂₀O₅₀ⁿ⁻ clusters with strong multiply charged anions (VO₄³⁻, CrO₄²⁻, PO₄³⁻, SO₄²⁻, BO₄⁵⁻, etc.), the isomer in which a distorted “guest” tetrahedron MO₄ is displaced from the cluster center and bonded to the V20O50 cage through two internal oxygen bridges M−O*−V is the most favorable one. Among the exohedral analogues MO4 · V₂₀O₅₀ⁿ⁻, the most favorable isomer contains the guest in the capping position bonded to the cage from the outside through three external M−O−V bridges. The latter isomer is more favorable than the former; however, the “exo–endo” transition between them for the clusters with multiply charged anions is accompanied by small changes in energy of ∼2−10 kcal/mol. Singly charged perchlorate and perbromate anions ClO₄^- and BrO₄⁻ in the inner sphere of V₂₀O₅₀ are unstable: during optimization, they are “reduced” with decomposition into atoms and concurrent “inner-sphere oxidation” of V₂₀O₅₀ to V₂₀O₅₄ with four peroxide cage bridges V−O−O−V. Charge transfer and specific features of the host–guest interaction in oxovanadate complexes and trends in the properties of endo- and exohedral isomers as a function of the charge and bond character of guest anions are discussed.

The solubilities of NiCO₃, ZnCO₃, and CdCO₃ in NaClO₄–NaHCO₃–Na₂CO₃ solutions are studied experimentally at 25°C and ionic strength of 0.1. The resulting data are used to determine the concentration stability constants of NiCO₃⁰, ZnCO₃⁰, and CdCO₃⁰ complexes in aqueous solutions (they are equal to 810, 12700, and 17900, respectively; log \(K'_{MCO_3^0 } \) = 2.90 ± 0.14, 4.10 ± 0.20, and 4.25 ± 0.04) and to calculate their thermodynamic values (6.45 × 10³, 1.01 × 10⁵, and 1.43 × 10⁵, respectively). The logarithms of stability constants of carbonate complexes are found to be inversely dependent on the solubility products of their metal carbonates.

Spectral characteristics (electronic absorption spectra, fluorescence emission spectra, ¹H NMR) of prepared Cu(II) and Zn(II) complexes of 2,7,12,17-tetraphenylporphycene {H₂(β-Ph)₄Por}, their thermal stability, and persistence toward acids, as well as electrochemical and electrocatalytic properties have been discussed. It has been found by cyclic voltammetry that the electrocatalytic activity of metalloporphycenes M(β-Ph)₄Por in the reaction of molecular oxygen reduction is close to that of metalloporphyrins M(ms-Ph)₄P. Thermal stability and persistence of M(β-Ph)₄Por in acidic medium are considerably lower than those of porphyrin analogs. Thus, the kinetic stability of copper(II) complex of 2,7,12,17-tetraphenylporphycene in HOAc–H₂SO₄ medium as compared with Cu(ms-Ph)₄P is lower by more than an order of magnitude, while its thermal stability is almost 200°С lower, which is caused by sterically unfavorable change in the shape of coordination center of ligand H₂(β-Ph)₄Por upon complexation.