Vol 64, No 8 (2019)

The current state of chemistry of 11-vertex polyhedral boron hydrides is considered. Their synthesis and interconversions, the substitution reactions of their terminal hydrogen atoms, and the insertion reactions with the closure of the icosahedral cage are discussed.

Using the Voronoi–Dirichlet polyhedra (VDPs), structures of 420 compounds containing 646 coordination polyhedra LnSe_n in the crystal structures have been analyzed, where Ln is any lanthanide from La to Lu. It is shown that the VDP parameters make it possible to determine the valence state of the Ln atoms. It has been determined that selenides contain Ln(II) and Ln(III) atoms which bond 4–10 selenium atoms existing in the form of Se^2– or Se^– ions. The VDPs of the Se atoms are studied; it is found that the Se–Se homoatomic bonds arise only when the electron donor metal atoms are deficient in the composition of crystalline compounds. By using VDP parameters, the dependence of the multiplicity of the Se–Se covalent bond on its length is detected, the efficiency of which is tested on a number of compounds, including Ln polyselenides. Some features of lanthanide compression in selenides are studied.

Phosphates Zn_xMg_0.5 + xE_2 – x(PO₄)₃ (E = Ti, Zr) have been synthesized by the sol-gel method with further thermal treatment and studied by X-ray diffraction, electron microprobe analysis, and IR spectroscopy. It has been established that the Zn_xMg_0.5 + xTi_2 – x(PO₄)₃ solid solution (0 ≤ х ≤ 0.5, space group R\(\bar {3}\)) crystallizes in the NaZr₂(PO₄)₃ structural type and is stable up to 1050°C. The structure of Zn_0.2Mg_0.7Ti_1.8(PO₄)₃ has been refined. It is based on the framework of PO₄ tetrahedra with shared apices and (Mg,Ti)O₆ octahedra. The framework cavities accommodate Mg²⁺ and Zn²⁺ cations with octahedral oxygen coordination. The Zn_xMg_0.5 + xZr_2 – x(PO₄)₃ solid solution (0 ≤ х ≤ 0.5, space group P2₁/n) crystallizing in the Sc₂(WO₄)₃ structural type is thermally unstable above 1000°C. The number of bands for the stretching and bending vibrations of the \({\text{PO}}_{4}^{{3 - }}\) ion in the IR spectra of these orthophosphates agrees with the group factor analysis for space groups R\(\bar {3}\) and P2₁/n. The thermal expansion of the Zn_xMg_0.5 + xE_2 – x(PO₄)₃ solid solutions has been studied within a temperature range of 25–800°C. The control over the composition of these moderately and highly expansive materials provides the possibility to change the thermal expansion characteristics in the desired direction.

The recrystallization of Zn(OOCPh)₂[O(H)Me]₄ (1) (chloroform diffusion to a methanolic solution, dissolution of the powder in boiling MeCN, and exposure of the methanolic solution at room temperature) is found to be accompanied with the formation of {Zn(µ-OOCPh)₃Zn(µ-OOCPh)}_n polymer single crystals. The diffusion of an MeOH solution of γ,γ'-bipyridyl to a methanolic solution of 1 (in the ratio 1 : 1) gives rise to the formation of {Zn(µ-dipy)(η²-OOCPh)(OOCPh)}_n polymer, and the same reaction in the ratio 2 : 1 under strong dilution gives rise to methanol deprotonation to yield {Zn[(µ-OMe)(µ-OOCPh)Zn(OOCPh)]₂(µ-dipy)₂}_n. The product compounds are characterized by chemical analysis, X-ray crystallography, and IR spectroscopy.

The structure and properties of two-dimensional monolayers composed of 1,6-carboranes have been studied by means of density functional theory calculations with periodic boundary conditions. Calculations of the phonon dispersion spectrum and band structure have shown that the 2D monolayers are dynamically stable and refer to indirect band gap semiconductors with a band gap of ~2.5 eV. Calculations of mechanical properties demonstrate that Young’s modulus for 2D 1,6-carborane nanosheets is lower than that for the monolayer of hexagonal boron nitride (h-BN) but exceeds that for the MoS₂ monolayer.

The isobaric heat capacity of neodymium orthotantalate M-NdTaO₄ was measured using adiabatic calorimetry in the temperature range 7–342 K. Smoothed heat capacity values were used to calculate the thermodynamic functions (entropy, enthalpy increment, and reduced Gibbs free energy) in the region 0–345 K with the contribution of low-temperature (<8 K) magnetic transformation being ignored.

Theoretical partition of the ternary reciprocal system Na,Ba||Br,MoO₄ into simplexes was performed, the stable diagonal of the system was determined, and the heat of the reaction at the conversion point was calculated. The chemical interaction in the system and the phase equilibria were described, and the crystallization fields of phases were delimited. The validity of the theoretical partition was confirmed by experimental investigation of the stable diagonal and two stable elements of the ternary reciprocal system Na,Ba||Br,MoO₄ by differential thermal analysis. It was found that the system Na,Ba||Br,MoO₄ is a singular irreversible reciprocal system with eutectic melting. The system is divided by the stable cutting diagonal NaBr–BaMoO₄ into two stable phase triangles, NaBr–BaBr₂–Na₂MoO₄ and NaBr–BaMoO₄–Na₂MoO₄. The results of the partition were corroborated by the X-ray powder diffraction analysis data. In the stable cutting diagonal, a saddle quasi-binary eutectic point, e 721°C, was revealed. The coordinates (melting point and composition) of two ternary eutectics, E₁ 586°C and E₂ 525°C, were found. The maximum crystallization field in the composition square corresponds to high-melting barium molybdate.

Extraction of lanthanum chloride and nitrate from neutral chloride and nitrate solutions with a binary extractant (R₃NHA) based on an equimolar mixture of diglycolic acid N,N-dioctylamide and tri-n-octylamine was studied. It was shown that the extraction of lanthanum chloride with R₃NHA proceeds by the mechanism of binary extraction of salts to give the LaA₃ extractable compound in the organic phase. In the case of lanthanum nitrate extraction, complexes of a different composition are formed in the organic phase, with the ratio of the metal concentration in the organic phase to the initial concentration of the binary extractant being 1 : 1. The extractability of lanthanides in the system with this binary extractant increased with increasing atomic number of the metal.

Cadmium sulfide (CdS) nanoparticles have been synthesized from CdX₂ (X = Cl^–, I^–) complexes of 4-chlorobenzaldehyde and benzophenone thiosemicarbazone. The complexes have been studied by thermogravimetric analysis (TGA), elemental analysis, FT-IR, and NMR spectroscopy. The solvothermal decomposition of the complexes has afforded oleylamine-capped CdS nanoparticles with a wurtzite hexagonal phase. The transmission electron microscopy (TEM) studies show different morphologies which are influenced by reaction temperature and the nature of the ligands on the precursor complexes. Particles in the form of irregular cubes, elongated cubes and nanodendrites have been observed. The UV-Vis spectroscopy measurements show temperature and nature of complex-dependant optical properties. Blue-shifted band gap energies have been observed at lower reaction temperatures.