Vol 64, No 3 (2019)

Titania-based composites TiO₂/C were manufactured by thermolyzing titanium glycerolate under an inert atmosphere at temperatures in the range 360–850°C. The structure of the compound was shown to be determined by Ti(C₃H₇O₃)₄ heat-treatment conditions. Composite formation (up to 400°C) involves the formation of an X-ray amorphous phase with the short-range order typical of anatase titania. A rise in thermolysis temperature (400–600°C) leads to the formation of anatase TiO₂/C. The composites TiO₂/C manufactured at temperatures above 600°C are anatase + rutile mixtures. TiO₂/C particles have a rod-like morphology 100–250 nm in diameter and up to 6.5 μm long, retaining it up to 850°C. The presence of carbon in samples is verified by Raman spectroscopy and thermogravimetry.

Fine-grained SrWO₄ and NaNd(WO₄)₂ ceramics with the scheelite structure having high relative densities (99 and 95.8%), which can appear candidate matrices for radioactive waste (RAW) management, are prepared by spark plasma sintering (SPS). The phase identity of the ceramics is determined by X-ray powder diffraction; their microstructure is studied by X-ray photoelectron spectroscopy. The tungstates under study are sintered at rather low temperatures (580–665°C). The intensity of compaction of the tungstates at the early sintering stage is determined by the degree of powder agglomeration. The activation energy of fine-grained scheelite ceramics at high temperatures corresponds with the activation energy of grain-boundary oxygen diffusion.

Sorption of uranyl ions from uranyl nitrate UO₂(NO₃)₂ · 6H₂O solutions by natural and synthetic layered silicates was studied by X-ray diffraction, IR spectroscopy, and high-resolution inductively coupled plasma mass spectrometry. The modifications of some structural parameters of the studied species after they were reacted with uranyl ions are due to a partial incorporation of uranyls into the interlayer spaces of the smectite structure, or the rotation of the tetrahedra of a tetrahedral network and the distortion of octahedra in an octahedral layer. The natural bottom clay samples from the Pacific Ocean and the Sea of Okhotsk have the best sorption properties. This is due to structural defects and the formation of uranium complexes with the iron ions of the smectite structure. Iron present in clay minerals improves their sorption potentials.

The structural features of 14 mononuclear d²-Re(V) octahedral monooxo complexes with mono-charged oxygen atoms of bidentate chelate (O, N) ligands (Lⁿ) of the general formula [ReO(Lⁿ)₂(L_mono)] (L_mono is a monodentate ligand) containing five-membered chelate rings ReNC₂O are discussed. The O(Lⁿ) atoms are in the trans positions to the O(oxo) ligands.

Double complex salts [Ln(C₆H₅NO₂)₃(H₂O)₂][Cr(NCS)₆] · 2H₂O, Ln = Lu (I), Ce (II), Y (III), have been synthesized by the reaction between aqueous solutions of Ln(NO₃)₃ (Ln = Lu, Ce, Y), K₃[Cr(NCS)₆], and nicotinic acid (C₅H₅NCOO). The salts representing light lilac crystalline powders have been studied by chemical analysis, IR spectroscopy, and single-crystal X-ray diffraction. The salts crystallize in monoclinic system, space group P2₁/n, Z = 4: a = 9.4969(15) Å, b = 25.606(4) Å, c = 15.541(2) Å, β = 107.126(4)°, V = 3624.34 ų, ρ_calcd = 1.864 g/cm³ for I; a = 9.6559(2) Å, b = 25.8492(5) Å, c = 15.5303(3) Å, β = 106.586(1)°, V = 3715.0(1) ų, ρ_calcd = 1.756 g/cm³ for II; and a = 9.5662(7) Å, b = 25.756(2) Å, c = 15.541(1) Å, β = 107.122(2)°, V = 3659.3(4) ų, ρ_calcd = 1.690 g/cm³ for III. The cations in the crystal structures of complexes I–III have a chain polymer structure, and the coordination polyhedron of chromium(III) represents a slightly distorted octahedron. The steric factor has no appreciable effect on the specific features of the crystal structures in the series of lanthanide hexa(isothiocyanato)chromate(III) complexes with nicotinic acid, and the content of crystallization water molecules is varied alone in their composition.

A new compound with the formula PbUO₂(mac)₄, where mac is the methacrylate ion CH₂C(CH₃)COO⁻, has been synthesized and studied by X-ray diffraction and IR spectroscopy. The equatorial plane of a UO₇ pentagonal bipyramid contains the oxygen atoms of four anions, three of which are coordinated to the uranyl ions monodentately, and one is coordinated bidentately, forming mononuclear complexes [UO₂(mac)₄]²⁻. Each lead ion is bound to eight oxygen atoms of five methacrylate ions of three such complexes. As a result, lead ions bond uranium-containing complexes into electroneutral chains [PbUO₂(mac)₄], which are the main structural units of crystals. The different roles of the four crystallographically nonequivalent methacrylate ions in the crystal structure determine the crystal-chemical formulas of the chains as A′AB⁰¹B¹¹(B²¹)₂, where A′ = Pb²+; A=UO₂²⁺; B⁰¹, B¹¹, and B²¹ = mac. The chains are linked by the system of hydrogen bonds to form a framework. The effect of the nature of R²⁺ cations on the structure of methacrylate uranylates is considered.

A correlation between the molar volumes of nonstoichiometric M_{1 − x}R_xF_{2 + x} (0 ≤ x ≤ 0.5) phases with a fluorite-type (CaF₂) structure and ordered M_mR_nF_{2m + 3n} (m/n = 8/6, 9/5) phases with a fluoritederivative structure has been found in systems MF₂–RF₃ (M = Ca, Sr, Ba, Pb; R = rare-earth elements Y, La-Lu). This correlation validates the cluster concept of the atomic structure of M_{1 − x}R_xF_{2 + x} nonstoichiometric crystals, the concept postulating that the structure is built of matrix fragments {M₁₄F₆₄} and octahedral-cubic clusters {M₈B₆F_68–69}, where the cations 6B are rare-earth cations (6R) or a mixture of cations (5R + M).

The reasons for the difference in coordination numbers of the central atoms (E) in the oxyanions of main-group elements of the second and third periods have been considered using various quantum-chemical methods. Isoelectronic series—triangular EO₃ and tetrahedral EO₄—have been studied both in the isolated state (ions) and with inclusion of the protonic and cationic environment (acids and salts). Simulation of the elementary act of addition reactions like H_kEO₃ + H₂O = H_{k + 2}EO₄ (even in this most simplified form) demonstrates that in the case of E(II), these (often strongly endothermic) reactions do not proceed, whereas in the case of E(III) they proceed without barrier. The available few deviations from this experimental fact have been examined. Possible more complex approaches with inclusion of the environment (primarily, water) have been discussed, and the role of various H-bonds has been analyzed.

The value Δ_fH₀° (CoF₃(cr)) = –861 ± 10 kJ/mol is determined using the data on equilibria of the reactions involving crystalline cobalt(III) fluoride. The features of chemical and thermal behavior of this compound (in particular, its easy hydrolyzability due to hygroscopic properties and vaporization without decomposition to fluorine and difluoride) are explained. The enthalpies of formation of crystalline and gaseous cobalt fluorides CoF_n (n = 2–4), as well as some of their negatively charged ions, and electron affinity energies of CoF₃ and CoF₄ (3.42 and 6.10 eV, respectively) are reported. Quantitative comparison of the efficiencies of iron, manganese, and cobalt trifluorides used as fluorinating agents to synthesize organic and inorganic compounds is performed.

Phase equilibria in the sections Pb₆Sb₂Bi₆Se₁₈-Sb₂Se₃ and Pb₆Sb₂Bi₆Se₁₈-Bi₂Se₃ were studied by differential thermal, X-ray powder diffraction, and microstructural analyses and by microhardness and density measurements, and the state diagrams of these sections were constructed. It was determined that these sections are eutectic-type quasi-binary sections of the Sb₂Se₃-PbSe-Bi₂Se₃ system. The coordinates of the eutectic point in the section Pb₆Sb₂Bi₆Se₁₈-Sb₂Se₃ are 40 mol% Pb₆Sb₂Bi₆Se₁₈ and 700 K, and those in the section Pb₆Sb₂Bi₆Se₁₈-Bi₂Se₃ are 60 mol% Bi₂Se₃ and 725 K. At room temperature, regions of solid solutions based on the initial components in the sections were identified. Procedures were developed for growing single crystals of solid solutions based on both components by the Bridgman-Stockbarger method and chemical transport reactions. The properties of alloys of solid solutions based on Pb₆Sb₂Bi₆Se₁₈ and Bi₂Se₃ were investigated. These alloys were found to be p-type semiconductors.

By differential thermal analysis using the calculation-experimental method, the phase diagram of the quaternary system NaBO₂–Na₂CO₃–Na₂WO4–K₂WO₄ was studied, and the coordinates of ternary eutectics and two quaternary eutectics were determined: E₁^□ (530°C, 5.6% NaBO₂, 30% Na₂CO₃, 55.3% Na₂WO₄, 9.1% K₂WO₄). It was shown that the calculated and experimental data on the coordinates of the quaternary eutectics agree satisfactory.

Extraction of rare earth element(III) (REE) ions from chloride solutions with mixtures of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone and 2-phosphorylphenoxyacetamides in organic solvents has been studied. Observed considerable synergic effect is related to the formation of hydrophobic mixed-ligand REE(III) complexes. The stoichiometry of extracted complexes has been determined and extraction constants have been calculated. Effect of aqueous phase composition, organic solvent nature, and 2-phosphorylphenoxyacetamide structure on the efficiency of REE(III) ions recovery into organic phase has been considered.