Vol 62, No 2 (2017)

A new selective method for the synthesis of nanocrystalline manganese dioxide (α-, β-, and γ-MnO₂) based on the reaction of potassium permanganate with 2,4,6-triamino-1,3,5-triazine (melamine) under hydrothermal conditions has been proposed. Effect of synthesis conditions on the phase composition of the products has been revealed. A new manganese-containing phase with layered structure has been prepared.

Regularities of change in the structural parameters of EuLnCuS₃ (Ln = La–Nd, Sm, Gd, Ho) at an annealing temperature of 970 and 1170 K have been established. A decrease in the Ln³⁺ ionic radius results in the consecutive change of structural types (STs) for the compounds: α-EuLnCuS₃ (Ln = La, Ce, Pr, Nd; BaLaCuS₃ ST) → β-EuLnCuS₃ (Ln = Ce, Pr, Nd; Ba2MnS₃ ST) → γ-EuLnCuS₃ (Ln = Sm, Gd, Ho; Eu₂CuS₃ST). The change of structural types for EuLnCuS₃ leads to a jump-like change in their unit cell parameters and the transformation of coordination polyhedra shaped as a one-capped trigonal prism LnS₇ (α and β phases) into an octahedron LnS₆ (γ phases). The appearance of morphotropic changes correlates with the tetrad effect.

A new Na₂HPO₄ polymorph was prepared with space group Fddd, Z = 8, a = 5.8426(3) Å, b = 9.7908(5) Å, c = 12.2673(5) Å. The crystal structure includes PO₄ tetrahedra and Na atoms, each surrounded by six O atoms positioned in the corners of a heavily distorted octahedron. The proton is equiprobably disordered over the O atoms.

The crystal structures of methoxysalicylidene-2-furfurylamine (HL²) and the related binuclear complex [{MoO₂(L²)(MeOH)}₂(μ-O)] (I) have been determined by single-crystal X-ray diffraction. In complex I, which lies on a crystallographic twofold axis passing through the bridging oxo ligand O(4), the Mo atom has a distorted octahedral coordination (facial isomer) with two terminal oxygen atoms (O(3), O(6)) and the bridging oxo ligand, the O(7) and N(1) atoms of the bidentate chelating ligand (L²)^–, and the O(5) atom of the monodentate methoxy ligand. In the HL² molecule, the intramolecular hydrogen bond O–Н•••N closes the six-membered H-ring HOC₃N.

The conditions of synthesis of a new binary complex salt [Co(Cpl)₆][Hg₂I₆] (Cpl is ε-caprolactam ε-C₆H₁₁NO) have been developed, and its structure has been characterized. The salt crystallizes in triclinic system, space group \(P\bar 1\) , a = 10.1078(4) Å, b = 12.2680(5) Å, c = 13.0782(5) Å, α = 62.872(2)°, β = 72.394(2)°, γ = 76.834(2)°, V = 1367.98(9) ų, Z = 1, and ρ_calc = 2.297 g/cm³. The structure is insular and consists of isolated ions.

Copper(II) complexes isolated from the Cu(CH₃COO)₂–2-(7-bromo-2-oxo-5-phenyl-3H-1,4-benzodiazepin-1-yl)acetohydrazide (Hydr)–salicylaldehyde (HSal)–isopropanol system [Cu₂(HydrSal)₂(μ-CH₃COO)] (I), [Cu(HydrSal)₂] (II) (HydrSal (hydrazone)is the condensation product of hydrazide and salicylaldehide) are synthesized and investigated. The complexes are characterized by elemental analysis, electrical conductivity measurements, and IR spectroscopy. The composition and structure of the Cu²⁺ coordination core are determined by ESR spectroscopy (I), magnetic susceptibility measurements and extended X-ray absorption fine structure (EXAFS) spectroscopy (II).

The heat capacity of Mg(Fe_0.6Ga_0.4)₂O₄ in the temperature range of 4.56–804.9 K is measured by adiabatic and differential scanning calorimetry. The temperature dependence of the heat capacity of Mg(Fe_0.6Ga_0.4)₂O₄ in the 0–800 K range is determined by generalizing the experimental data. The temperature dependences of thermodynamic functions (entropy, enthalpy change, and the reduced Gibbs free energy) are calculated. The abnormal contribution to the heat capacity C_p^an(T) in the temperature range of 5–52 K is estimated.

Arsenates A_0.5Zr₂(AsO₄)₃ (A = Mg, Ca, Sr, Ba), synthesized through sol–gel route with subsequent heat treatment, have been studied by X-ray diffraction, electron probe microanalysis, and IR spectroscopy. Mg_0.5Zr₂(AsO₄)₃ crystallizes in the Sc₂(WO₄)₃ structure type (space group P2₁/n). A_0.5Zr₂(AsO₄)₃ (A = Ca, Sr, Ba) crystallize in the NaZr₂(PO₄)₃ structure type (space group \(R\bar 3\) ). The Ca_0.5Zr₂(AsO₄)₃ and Ba_0.5Zr₂(AsO₄)₃ structures have been refined by the full-profile analysis. The structure frameworks are composed of ZrO₆ octahedra and AsO₄ tetrahedra. The alkaline earth metal atoms occupy one of the two extraframework positions inside the structure columns. The internal vibrational frequencies of the AsO₄^3- tetrahedron have been assigned. The number of the observed bands corresponds to the number predicted by the factor group analysis of vibrations for space groups \(R\bar 3\) and P2₁/n.

A study was made of the effect of synthesis conditions on the properties of a magnetoactive compound obtained by the interaction of iron(II) sulfate with potassium chromate. It was found that, in the formation of the magnetoactive compound, chromium is almost completely coprecipitates with the solid phase. To produce the magnetoactive compound with high relative magnetic susceptibility, it is necessary to precipitate it from the initial solution in no less than 10 min after its preparation at a K₂CrO₄: FeSO₄ molar ratio of 0.16–0.18.

The ternary reciprocal system Na,K‖Br,WO₄ was studied by differential thermal analysis. The compositions and melting points of the alloys corresponding to invariant equilibrium points were determined, and the enthalpies of melting of eutectic mixtures were measured. Phase equilibria in systems were described, and the fields of crystallizing phases were delineated.

The heats of interaction between glycyl-glycyl-glycine and solutions of nitric acid and potassium hydroxide are determined by calorimetry at 298.15 K and ionic strengths of 0.25, 0.50, and 0.75 in the presence of KNO₃. The standard thermodynamic characteristics (Δ_rH°, Δ_rG°, and Δ_rS°) of acid–base interaction in aqueous solutions of the peptide are calculated. The effect of background electrolyte concentration on the enthalpy of dissociation of glycyl-glycyl-glycine is discussed.

The formation of an ion-associated complex between the anionic chelate of Mo(VI)–3,5-dinitrocatehol (3,5-DNC) and the cation of 3-(2-naphthyl)-2,5-diphenyl-2H-tetrazolium chloride (TV) in the liquid–liquid extraction system Mo(VI)–3,5-DNC–TV–H₂O–CHCl₃ was studied by spectrophotometry. The optimum conditions for the complex formation and extraction of the ion-associated complex were established. The effect of co-existing ions and reagents on the process of complex formation was investigated under optimum extraction conditions. The validity of Beer’s law was checked and some analytical characteristics were calculated. The association process in aqueous phase and the extraction equilibria were investigated and quantitatively characterized. The following key constants of the processes were calculated: association constant, distribution constant, extraction constant and recovery factor. The molar ratio of the reagents was determined by independent methods. Based on this, a reaction scheme, a general formula and a structure of the complex were suggested.