Vol 64, No 11 (2019)

Powders of nanocrystalline carbide Ta₄HfC₅ were produced by the sol–gel synthesis of a finely divided Ta₂O₅–HfO₂–C composite powder (with tantalum pentaamyloxide and hafnium acetylacetonate as precursors and a phenolformaldehyde resin as a carbon source) with subsequent low-temperature carbothermal synthesis (1200–1300°C, 2–4 h, dynamic vacuum). The composition of the initial Ta₂O₅–HfO₂–C composite powder was optimized by decreasing excess carbon content. The elemental and phase compositions of the obtained carbide product were found. It was shown that, at low temperature of the carbothermal synthesis, single-phase carbide Ta₄HfC₅ can decompose into a mixture of phases of tantalum hafnium carbide and hafnium tantalum carbide; however, an unambiguous conclusion was impossible to draw because the produced powders were finely divided (the crystallite size was ~23–40 nm, and the particle size (as determined by scanning electron microscopy) was ~37–45 nm). The thermal behavior of the obtained finely divided Ta₄HfC₅ powders in an air flow at 20–1000°C was studied, and the effect of the crystallite and particle sizes in the samples on the positions of exothermic peaks related to oxidation was established, It was noted that a product of the oxidation of the produced Ta₄HfC₅ powders is not only the Ta₂O₅ phase, but also the complex oxide Hf₆Ta₂O₁₇.

Series of spinel solid solutions with a specified cation composition, Mg_{1 +x}MnO_{3 – δ} and, for the first time, MgLi_xMnO_{3 – δ}, potential materials of catalytic systems for oxidation reactions such as oxidative conversion of methane and chemical looping combustion process were prepared by solid-state syntheses from mechanocomposites obtained by milling of ultra-high purity precursors (MgO, Mn₂O₃, MnO₂, and Li₂CO₃). Their homogeneity region was found to be up to 1573 K at p(O₂) = 0.21 atm. For both series of solid solutions, the synthesis from Mn₂O₃ and MnO₂ in air was investigated by the TG-DSC method and the oxygen content in the resulting materials was determined (TG-DSC, titration). The products of extensive reduction of spinels Mg_{1 +x}MnO_{3 – δ} and MgLi_xMnO_3–δ with an Ar + 4.8% H₂ mixture were investigated. Parameters of conversion of the reduction products to the initial single-phase spinels on treatment with air were determined. The obtained materials showed good reproducibility of reversible oxygen capacity over 20 reduction–oxidation cycles.

The phosphate–sulfate synthesis approach preventing the elimination of sulfur in the process of synthesis has been tested for NaBa₆Zr(PO₄)₅SO₄ as an example. The phase formation and thermal stability of phosphate–sulfate have been studied by X-ray diffraction and DTA-TG. The NaBa₆Zr(PO₄)₅SO₄ structure (space group I\(\overline 4 \)3d, a = 10.5449(3) Å, V = 1172.54(5) ų, Z = 4) allied to the eulytite mineral has been refined by the Rietveld method. The structure is formed by wavy chains of edge-sharing (Na,Ba,Zr)O₆-octahedra and (P,S)O₄-tetrahedra sharing apices with the octahedra. Using thermal X-ray diffraction, it has been established that phosphate–sulfate is a strongly expanding material (α_а = α_b = α_c = 13.3 × 10^–6°C^–1).

A series of four new copper(II) complexes [Cu₂(2-BrC₆H₄CH₂COO)₄(Phen)₂] (1), [Cu(2-BrC₆H₄CH₂COO)₂(Bipy)] (2), [Cu₂(2-BrC₆H₄CH₂COO)₄(3-BrPy)₂] (3) and [Cu₂(2-BrC₆H₄CH₂COO)₄(3-MePy)₂] (4) where Phen = 1,10-phenenthroline, Bipy = 2,2′-bipyridine, BrPy = bromopyridine and MePy = methylpyridine have been successfully synthesized and analyzed by elemental analysis, FT-IR, UV-Visible, and single crystal XRD. Complexes 1, 3 and 4 are dimeric and crystallize in the monoclinic space groups p21/c and C2/c, respectively. Distorted square pyramidal geometry around each Cu(II) ion in 1 is formed by the two nitrogen atoms from phenenthroline lying equatorially and three oxygen atoms from three monodentately coordinated carboxylate ligands. Two out of three ligands bridged the two metal ions with Cu···Cu intra dimer distance of 3.62 Å. In 3 and 4, four bidentate carboxylate ligands coordinate to two metal atoms which bridge them equatorially to give rise paddlewheel conformation with square pyramidal geometry around each metal atom. The axial positions of a square pyramid and trigonal bipyramid are occupied by nitrogen donor substituted pyridines with Cu···Cu intra dimer distances of 2.66 and 2.69 Å, respectively. The complex 2 being monomeric, crystallizes in the monoclinic space group C2/c with distorted square planar geometry around metal atom. A wide range of hydrogen bonding and π‒π stacking interactions are present throughout the crystal lattice in all complexes. DNA binding study through spectroscopic technique suggested strong capacity of complexes 1–4 to bind with DNA strand preferably through intercalative and groove binding modes with K_b values 6.03 × 10³, 1.34 × 10⁴, 3.18 × 10⁴ and 3.14 × 10⁴ M^–1 respectively. The α-glucosidase and anticholinesterase enzyme inhibition assays were performed to investigate the potential of 1–4 as anti-diabetic and anti-alzheimer agents. The results revealed anti-diabetic nature of synthesized complexes with IC₅₀ values in following order 1 < 2 < 3 < 4 with acarbose as control in concentration dependent manner. All these complexes exhibited mild activities against anticholinesterases with galantamine hydrobromide as control. The manuscript reports structurally diverse, bio-active complexes.

Coordination compounds [Co(L¹)₃](Mal) · 4H₂O (I) and [Ni(L²)₃](Mal) · H₂O (II) (L¹ is benzohydrazide, L₂ is phenylacethydrazide, and H₂Mal is maleic acid) have been synthesized and characterized by IR spectroscopy and diffuse reflectance spectroscopy. Crystal structures of I and II have been determined by single-crystal X-ray diffraction. Structural units of crystals I and II are complex cations [Co(L¹)₃]²⁺ and [Ni(L²)₃]²⁺, respectively, maleate-ions Mal^2–, and crystallized water molecules bound by a branched system of hydrogen bonds. Metal atoms at the complex cations of crystals I and II have octahedral coordination (3O + 3N) formed by three bidentate chelate ligands Lⁿ (n = 1, 2).

The reactions of tris(5-bromo-2-methopxyphenyl)antimony with 2-, 3-nitrobenzaldoximes and 3-fluorophenylacetic acid in the presence of tert-butyl hydroperoxide with the formation of products with the general formula (2-MeO-5-Br-C₆H₃)₃SbХ₂, where Х = ONCHC₆H₄NO₂-2 (I), ONCHC₆H₄NO₂-3 (II), OC(O)CH₂C₆H₄F-3 (III), have been studied. According to X-ray diffraction data, complexes I and II crystallize in the form of solvates (with 0.5C₆H₆ and 2C₆H₆, respectively). The Sb atoms in molecules of complexes I–III have a trigonal bipyramidal coordination with the carbon atoms of aryl radicals in the equatorial plane and the oxygen atoms of oximate and carboxylate ligands in axial positions. The ОSbО axial angles are 173.47(18)° (I), 170.71(9)° (II), and 173.96(10)° (III), and the OSbC angles variate within 86.2(2)°–95.1(2)° (I), 81.31(13)°–94.35(12)° (II), and 83.12(12)°–96.50(13)° (III). The ranges of Sb–C band lengths are 2.097(6)–2.109(6) Å (I), 2.115(4)–2.137(4) Å (II), and 2.119(4)–2.122(3) Å (III), and the Sb–O bond are 2.050(5), 2.055(5) Å (I), 2.058(3), 2.093(3) Å (II), and 2.111(3), 2.110(3) Å (III).

The [CuLBr₂] complexes, where L is RRN–C(=S)–S–NHC₆H₁₁ and RR = (C₂H₅)₂, (CH₂)₅, or (CH₂)₂O(CH₂)₂, have been synthesized by reacting equimolar amounts of CuBr₂ in methanol and L in diethyl ether. The compounds have been studied by elemental analysis, IR spectroscopy, EPR, X-ray absorption spectroscopy, conductometry, magnetochemistry, and thermal analysis. According to IR spectroscopy data, the ligands in the complexes are bidentately coordinated to Cu(II) through the thione sulfur sulfenamide and nitrogen atoms. Exact structural parameters of the nearest environment of Cu(II) have been determined from analysis of Cu and Br K-edge EXAFS spectra. The Cu–N, Cu–S, and Cu–Br bond lengths are within 2.06–2.08, 2.24–2.49, and 2.33–2.38 Å, respectively. The EPR spectra of the complexes in a DMF solution at 293 K are described by the isotropic spin Hamiltonian with spin S = 1/2, including hyperfine coupling to the nuclear spin of the central copper atom and additional hyperfine coupling to the nuclear spins of two equivalent bromine atoms and one nitrogen atom.

The isobaric heat capacity of the pyrochlore lanthanum hafnate phase was measured by adiabatic calorimetry in the temperature range 0–346 K. Thermodynamic functions (the entropy, entropy increment, and reduced Gibbs energy) were calculated to be used for modeling physical and chemical processes where lanthanum hafnate is involved and for optimizing lanthanum hafnate preparation processes.

The melting and crystallization of the natural system Si–Al–Ti–Fe–Mg–Ca–Na–K–O, which represents andesite-basalt, an effusive medium rock that contains 35–95% glass, were studied by physicochemical modeling and experimentally. The presence of volcanic glass and the non-equilibration of phenocrystal minerals with the major andesite-basalt composition hamper the obtainment of data on the mineral compositions of such rocks and on the behavior of their melts. The methods described, based on chemical analysis data, make it possible to calculate the melt compositions obtainable in various atmospheres, thereby making it possible to select the most rational use of igneous rocks in the production of mineral fiber, stone ceramics, and cast-stone articles.

The calorimetric enthalpies of complexation of selected dipeptides, namely, glycyl-DL-alanine, glycyl-DL-leucine, and glycyl-DL-tyrosine (HL^±), with Nd³⁺ and Eu³⁺ ions at 298.15 K and an ionic strength of 0.1 (on the background of KNO₃) were determined. Thermodynamic characteristics of formation were calculated for the LnL²⁺ and LnHL³⁺ complexes of these dipeptides with Nd³⁺ and Eu³⁺ ions for various molar ratios [metal] : [ligand] in the pH range 1.6–7.5. The obtained thermodynamic parameters served to infer the structures of the complexes.

Functionally graded SiC–TiC composite materials are promising for using in the aerospace industry as relatively low-density materials. The production of such materials by the sol–gel synthesis of a finely divided titanium carbide matrix in the pore space of SiC frameworks was studied. It was demonstrated that the distribution of the TiC matrix in the space of the SiC framework can be changed by varying the composition of the coordination sphere of precursors. It was shown that, after eight cycles of hydrolysis of titanium-containing precursors in the presence of a phenol formaldehyde resin with subsequent carbonization and carbothermal synthesis (1400°C, dynamic vacuum, 2 h), the weight gains of the samples differed significantly: for the precursor [Ti(OC₄H₉)_2.05(O₂C₅H₇)_1.95], which is more sensitive to moisture, it was 23%, and for the complex [Ti(OC₄H₉)_1.95(O₂C₅H₇)_2.05], it was 37%. Moreover, in the former case, near-surface regions of the material were predominantly densified. It was noted that, with increasing content of the modifying phase TiC, the compressive strength increased, and the specific surface area decreased (as determined by low-temperature nitrogen sorption and mercury porosimetry). The obtained gradient of the composition of the SiC–TiC ceramics across the depth was confirmed by X-ray computed microtomography: the total porosity of the near-surface regions of the ceramics differed by a factor of 2.9.

CuInS₂ nanoparticles were synthesized by a solvothermal method using a 1:1 (v/v) water : ethylene glycol (EG) as a binary solvent mixture. The synthesized powder, characterized by XRD technique, was indexed as CuInS₂ with a tetragonal structure. FESEM and TEM images revealed that the CuInS₂ powder composed of spherical nanoparticles with diameters in the range of 15–30 nm. The CuInS₂ powder was also synthesized using water as a solvent for comparison. Particle size of the CuInS₂ nanoparticles synthesized using mixed solvent of water : EG was smaller with softer agglomeration behavior than those synthesized using water (50–75 nm) offering better photovoltaic properties, including open-circuit voltage (V_oc), short-circuit current density (J_sc), and conversion efficiency (η). The difference in these characteristics of the CuInS₂ nanoparticles was discussed based on some physicochemical properties of the solvents used.