Vol 63, No 12 (2018)

The thermal behavior of MgH₂ mechanocomposites with Mg₂NiH_{4 – δ} + Mg₂NiH_0.3 two-phase mixture and phase equilibria in the system Mg–Ni–H involving MgH₂ were studied by powder X-ray diffraction and TG–DSC. The graphic representation of phase equilibria involving MgH₂ and Mg₂NiH_{4 – δ} and Mg₂NiH_x (0 < x < 0.3) solid solutions in the practically important field with high magnesium content area was revised. The possibility of MgH₂ mechanocomposites with Mg₂NiH_{4 – δ} and Mg₂NiHx for use as magnesium intercalating agents and alternative intercalating agents—organomagnesium compounds were considered.

Calcium phosphate phase formation was studied under process conditions involving human blood plasma. Calcium phosphate was synthesized with variable supersaturation (S) and experimental time. It was found that a non-stoichiometric hydrated carbonated hydroxyapatite, identical in the composition to calcifications in humans, is formed under the experimental conditions. The highest amount of carbonate ions (5.54 wt %) in the solid phase corresponds to the apatite synthesized at S = 50 for 10 weeks. The dissolution rate of solid phases was determined by mathematical processing of the obtained kinetic curves; this can be used to find compounds able to stop the development of vascular calcinosis.

A two-stage scheme was proposed for the synthesis of alkoxy derivatives of the closo-decaborate anion [B₁₀H₉(OR)]^2–, where R = C₂H₅, iso-C₃H₇, C₄H₉. At the first stage, the oxonium derivatives with the general formula [B₁₀H₉(OR₂)]^– were synthesized by the reaction between the [B10H11]–anion and acyclic ethers. At the second stage, the synthesized oxonium derivatives reacted with hydrazine hydrate to form the alkoxy derivatives with the general formula [B₁₀H₉(OR)]^2–, where R = C₂H₅, iso-C₃H₇, C₄H₉. This approach appreciably increased the yield of target products and simplified their separation. The alkoxy derivatives were separated and characterized by IR and ¹H, ¹¹B, and ¹³C NMR spectroscopy.

The complexes [Ph₃PR]₂⁺[ZrCl₆]^2–, R = Et (I), CH₂Ph (II) (1: 1 solvate with acetonitrile), and CH₂C(O)OMe (III) have been synthesized by the reaction between zirconium tetrachloride and triphenylorganyl phosphonium chlorides in acetonitrile and structurally characterized. The phosphorus atoms in triphenylorganyl phosphonium cations have a distorted tetrahedral coordination: the CPC angles are 108.29(9)°–110.84(8)° (I), 106.91(8)°—112.21(8)° (II), and 107.26(9)°–112.83(9)° (III), and the P–C bond lengths are 1.793(2)–1.803(2) Å (I), 1.791(2)–1.824(2) Å (II), and 1.784(2)–1.811(2) Å (III). The Zr–Cl distances in the centrosymmetric octahedral anions [ZrCl₆]^2– of complex I are 2.4625(11)–2.4634(11) Å. The octahedral configuration of anions in complexes II and III is distorted: the trans-ClZrCl angles are 176.80(2)°, 177.12(2)°, 179.80(2)° (II) and 175.53(3)°, 175.97(2)°, 177.75(2)° (III), and the Zr–Cl bonds are 2.4489(11)–2.4953(15) Å (II) and 2.4510(8)−2.4864(9) Å (III).

Fundamental insights into the ethene protonation reaction was obtained over different cluster models of acidic CrO_x/SiO₂, MoO_x/SiO₂, and WO_x/SiO₂ catalysts at the M06/Def2-TZVP level of theory. The clusters varied from MSiO₄H₃ structures (all-fixed, H-optimized, and all-relaxed) to MSi₄O₄H₉ (saturated with H atoms) and further to MSi₄O₁₃H₉ (saturated with OH atoms). The formation of the ethene protonation adducts followed the order of WO_x/SiO₂ < MoO_x/SiO₂ < CrO_x/SiO₂ in terms of the thermodynamic favorability which agreed well with the partial charges and the global softness data. The natural bond orbital analysis revealed a partial flow of electrons from the bridging O atom to the hydrocarbon fragment than to the metal during the initiation. Although the interbond angles were comparably different in the largest cluster, the bond lengths and orbital energy levels did not change significantly from a cluster to another. Concerning the thermochemical properties, any of the cluster models would be utilized within a 2 kcal/mol confidence limit.

Structures, energies, and spectroscopic characteristics of the isomers of the family of doubly doped М₂Al₄₂ clusters with dopants M from the first two periods and H, Cu, and Zn atoms located in different positions at the surface and in the inner cavity of the aluminum cage have been calculated by the density functional theory method. The effect of the dopant nature on the relative energies of isomers and on the energies of their dissociation along the channels М₂Al₄₂ → 2М + Al₄₂ and М₂Al₄₂ + 2Al → 2М+ Al₄₄. The results are compared with the results of previous DFT calculations of endohedral (M@Al₁₂) and exohedral (Al@)MAl₁₁) isomers of the simpler doped clusters MAl₁₂ with the same dopants M. The influence of the aluminum cage size on the relative energy stability of the surface and and internal sopant positions is considered.

The isobaric heat capacity of samarium orthotantalate M-SmTaO₄ was measured by adiabatic and differential scanning calorimetry in the range 17–1115 K. Smoothed heat capacity values were used to calculate thermodynamic functions (entropy, enthalpy increment, and reduced Gibbs free energy) with the contribution from low-temperature (<17 K) magnetic transformations being ignored.

The electronic state and local surrounding of both iron ions and tin dopant ions in Lu_{1 – x}Ca_xFe_0.997Sn_0.003O₃ (x = 0.003; 0.1; 0.2) compounds were studied by ⁵⁷Fe and ¹¹⁹Sn Mössbauer spectroscopy. The analysis of ⁵⁷Fe spectra showed that in the Lu_0.8Ca_0.2Fe_0.997Sn_0.003O₃ sample, obtained by air annealing, the charge deficit created by the substitution of Lu³⁺ by Ca²⁺ was compensated by the partial transition of Fe³⁺ to the +5 oxidation state. With a further increase in the value of x (in the Lu_0.8Ca_0.2Fe_0.997Sn_0.003O₃ compound) a mixed compensation mechanism appeared, including the formation of oxygen vacancies VO in addition to Fe⁵⁺ ions. Annealing the sample with x = 0.1 in H₂ at 400°C led to the reduction of Fe⁵⁺ to Fe³⁺ and, accordingly, to the pure vacancy mechanism of the Ca²⁺ charge deficit compensation. The analysis of ¹¹⁹Sn spectra showed that the substitution of Lu³⁺ by Са²⁺ in the Lu_0.8Ca_0.2Fe_0.997Sn_0.003O₃ structure led to the increase in the value of the magnetic field H, probed by some Sn⁴⁺ ions, as compared to the value of H> observed in the case of Lu_0.997Ca_0.003Fe_0.997Sn_0.003O₃. This change can be explained by a local increase in the angle of the indirect exchange interaction in the chain Fe³⁺–О₂––Sn⁴⁺, reflecting the presence of Ca²⁺ cation, larger than that of Lu³⁺, in the vicinity of Sn⁴⁺ ion.

Phase equilibria were studied and a Т–х diagram of section BiB₃O₆–YbBO₃ was constructed using X-ray powder diffraction and differential thermal analysis (DTA). The diagram has a peritectic point lying near 95 mol % BiB₃O₆ at 810°С. A limited subsolidus solubility of the components is observed in α-BiB₃O₆ in the range 0 ≤ х ≤ 0.3 YbBO₃.

A general topologic transformation scheme of phase diagram is proposed for inorganic salt–oxyethylated surfactant–water systems that have a lower critical solution temperature (LCST) or where the surfactant–water binary subsystem is homogeneous over the entire range of liquid temperatures for the case where the salt has the salting-out, salting-in, or salting-in-and-salting-out effect. Examples are provided to illustrate the implementation of the suggested variants of the general scheme.

Lanthanum nitrate distribution in three-component aqueous-organic systems with D2EHPA from acetate or acetic acid–acetate solutions has been studied, it has been shown that variation in sodium acetate concentration or composition of CH₃COONa–CH₃COOH mixture can affect metal distribution ratios. It has been found that extraction in three-component mixture of 1: 1: 1 composition (aqueous solution Ln(NO₃)₃ + CH₃COONa + CH₃COOH–D2EHPA in hexane–isopropyl alcohol) can provide lanthanide separation, which is dependent on the ratio of sodium acetate and acetic acid in aqueous phase and on D2EHPA concentration in organic phase. Lanthanide–lanthanum separation factors have been calculated for the extraction of lanthanide nitrates from acetic acid–acetate solutions.

To study the complexing processes occurring in the extraction systems, the extraction of acetic, propionic (methylacetic), monochloroacetic, dichloroacetic and trichloroacetic acids using benzo-15- crown-5 as an extractant is considered. The extraction isotherms of acids with the pure solvent and 1 M benzo-15-crown-5 in chloroform are determined. The dependences of the distribution ratios of the considered acids on the extractant concentration in the organic phase are presented. Based on the experimental data and the “blank” extraction isotherm equations, the acid: benzo-15-crown-5 ratio in the complexes formed in the extract have been calculated (minus the contribution of extraction with the pure solvent). No complexation of methylacetic acid with benzo-15-crown-5 occurs, and the stability of the complexes of chloro-substituted acetic acids rises in the order acetic acid < monochloroacetic acid < dichloroacetic acid < trichloroacetic acid.

Extraction of rare earth element(III) (REE) ions from chloride solutions with picrolonic acid mixtures with phosphoryl-substituted aza podands in chloroform has been studied. A considerable synergetic effect observed has been caused by the formation of hydrophobic mixed-ligand complexes of REE. The stoichiometry of extracted complexes has been determined and extraction constants have been calculated. The effect of aqueous phase composition, organic solvent nature, and the structure of phosphoryl-substituted aza podands on the efficiency of REE(III) recovery into organic phase have been considered.

Silica coated iron oxide nanoparticles with controlled silica shell thickness were prepared by a modified Stöber method. Modification of the Stöber method consisted of changing the synthesis conditions to control the thickness of the SiO₂ shell. The core-shell nanoparticles were characterized by means of X-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectroscopy and vibrational sample magnetometry. It was found that the shell formed after 8 hours of stirring. An increase of the tetraethoxysilane- magnetite mass ratio from 12.5 to 25.1 led to an increase of the shell thickness, whereas further increase in the tetraethoxysilane-magnetite mass ratio (from 25.1 to 37.6) led to decrease shell thickness. The core size has only insignificant influence on the shell thickness. Magnetic properties of composite particles correlate well with properties of pure magnetite nanoparticles considering dilution of magnetic particles by silica. Obtained results can be used for fabrication of silica shell with controlled thickness on the surface of different sized magnetite nanoparticles.