Vol 63, No 8 (2018)

A one-step method for preparing composites based on calcium phosphates (CPs) and calcium silicates (CSs) with variable contents of the components is proposed. The combination of chemical analysis, X-ray powder diffraction, and simultaneous thermal analysis with mass-spectrometric detection (STA-MS) showed that the coprecipitation of salts from aqueous solutions yielded mixtures of poorly crystallized carbonate hydroxyapatite (CHA) and xonotlite with minor calcite. Scanning electron microscopy and low-temperature nitrogen adsorption showed that nanosized crystallites of these phases during crystallization were combined into mesoporous aggregates (the mean pore size was 6–11 nm) to form micrometer-sized bulk structures with a developed surface. Two-hour calcination of synthesis products at 1000°С yielded mixtures of well-crystallized Са₁₀(РО₄)₆(ОН)₂ and β-CaSiO₃.

Nanocrystalline tin dioxide modified by Pd and Pt clusters or by bimetallic PdPt nanoparticles was synthesized. Distribution of the modifers on the SnO₂ surface was studied by high-resolution transmission electron microscopy and energy dispersive X-ray microanalysis with element distribution mapping. It was shown that the Pd/Pt ratio in bimetallic particles varies over a broad range and does not depend on the particle diameter. The effect of platinum metals on the reducibility of nanocrystalline SnO₂ by hydrogen was determined. The sensing properties of the resulting materials towards 6.7 ppm CO in air were estimated in situ by electrical conductivity measurements. The sensor response of SnO₂ modified with bimetallic PdPt particles was a superposition of the signals of samples with Pt and Pd clusters.

The synthesis and X-ray diffraction and IR spectroscopic study of (UO₂)₂(mac)₄(L)₃ · H₂O crystals, where mac^– is the methacrylate ion C₃H₅COO^– and L is carbamide (I) or methylcarbamide (II), have been performed. Complexes I and II have a homotypic structure: crystals contain two kinds of mononuclear uranium-containing complexes, i.e., cationic [UO₂(mac)(L)₃]⁺ and anionic [UO₂(mac)₃]^–. The crystallographic formula of complexes in structures I and II is AB⁰¹M₃¹ + AB₃⁰¹ (A =UO₂²⁺ B⁰¹ = mac^–, M¹ = L). The uranium-containing complexes in structures I and II are linked into a framework by means of electrostatic interactions and a system of hydrogen bonds. Despite the similar compositions and structures of the uranium-containing complexes, their packings into a three-dimensional framework appreciably differ from each other.

The method of intersecting spheres and Voronoi–Dirichlet polyhedra are used for crystal chemical analysis of 3817 structures comprising 4533 crystallographically nonequivalent sorts of boron atoms contained in BC_n coordination polyhedra. In these coordination polyhedra, boron has coordination numbers (CNs) from 2 to 6, the CN 4 being most typical. With increasing boron CN, the average B–C interatomic distances of the BC_n polyhedra increase by 0.01–0.13 Å, while the average radii of the spheres whose volumes are equal to the volumes of the Voronoi–Dirichlet polyhedra of boron atoms virtually do not vary within the determination error. The characteristic features of intermolecular contacts in the structures of two crystalline hydrates, Fe[B(CN)₄]₂ · 2H₂O and Fe[B(CN)₄]₃ · 6H₂O, are considered according to the method of Voronoi–Dirichlet molecular polyhedra.

The B−H···H−C specific interactions observed in complexes [M(solv)₆][B₁₀H₁₀], where M= Co(II), Ni(II); solv = DMF or DMSO, are analyzed based on the correlation between the X-ray diffraction data and the results of IR and UV spectroscopic studies. Comparing the experimental data obtained earlier with those reported here allows us to elucidate one of the reasons that do not permit unambiguously determine the presence of long-range contacts when interpreting spectral data.

The geometries of (5676)macrotetracyclic Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes with the (NNNN) coordination of the chelant donor sites, formed through template processes in the M(II)–3,3,8,8-tetramethyl-4,7-diazadecanedihydrazone-1,10-butanedione-2,3 systems have been calculated by the DFT OPBE/TZVP method with the Gaussian 09 program package. The bond lengths and angles and selected nonbonded angles in these complexes with the MN₄ chelate core have been determined. It has been demonstrated that none of the chelate rings is planar: the smallest deviation from coplanarity is always observed for the five-membered rings and the largest, for the six-membered rings not identical to each other. The seven-membered ring resulting from the template cross-linking exhibits deviations from coplanarity intermediate between those for the five- and six-membered rings.

The DFT PBE/3ζ modeling of conformational transformations of an ammonia borane molecule BH₃ ← NH₃ in model single-layer carbon nanotubes indicates an unusual shift of conformational equilibrium to the eclipsed form. In cluster, the В ← N coordination bond demonstrates a noticeable decrease in length and an increase in its order. The increasing diameter of nanoobject weakens the observed effects and shifts conformation equilibrium to the staggered conformer.

This study investigates solvent effect on several electronic structure features, i.e. structural stability, orbital energies, HOMO-LUMO gaps and hardness of an iron aminoborirene complex [(η⁵-C₅H₅)(OC)₂Fe{μ- BN(SiH₃)₂C=C}Ph] (closed-isomer) and its isomer the boryl complex [(η⁵-C₅H₅)(OC)₂FeBN(SiH₃)₂C≡CPh] (open-isomer) through polarizable continuum model. Results revealed that the closed isomer is less stable than the open isomer, in solvent. Further, influence of the solvent on the frontier orbitals energies, HOMOLUMO gap, electrophilicity and chemical potential energies of the isomers was studied. Thermochemical analysis was conducted to study closed-open equilibrium and thermochemical parameters (ΔG and ΔH) were computed.

A computer model of the T–x–y diagram of MgO–SiO₂–Al₂O₃ system is used to show the possibility of analysis of its microstructure constitution in terms of competition between primary and eutectic crystals by means of vertical mass balance diagrams calculated for a given centroid over the whole temperature range. The usefulness of horizontal mass balance diagrams is considered for studying phase relations at a fixed temperature along the chosen isopleth. Mass balances were used to determine the crystallization path at the quasi-peritectic liquidus point with the invariant reaction L + Al₂O₃ = 3Al₂O₃ · 2SiO₂ + MgO · Al₂O₃, whose composition was taken into account in giving a rationale to corundum armor element technology.

The state of silicotungstic acid (STA) in the presence of inorganic salts (Fe₂(SO₄)₃, SnCl₂, and SnSO₄) in aqueous solutions was studied by ¹⁸³W NMR spectroscopy. Silicotungstic acid was found to retain its structure, and no new heteropoly compounds were formed. This finding proves the enhanced stability of STA toward complex formation at high acidities.

The super-high-frequency dielectric properties of aqueous solutions of aluminum chloride were measured at five frequencies (13–25 GHz) at 298 K. The static permittivities and the times and other parameters of dielectric relaxation of the solutions were calculated. The concentration dependences of the hydration properties of the solutions within various concentration ranges were studied.