Trends in the cation distribution in the structures of the compounds forming in the Ln<Subscript>2</Subscript>O<Subscript>3</Subscript>-GeO<Subscript>2</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> systems

The cationic networks in the structures of the initial oxides and all binary and ternary compounds forming in the Ln₂O₃-GeO₂-P₂O₅ systems have been studied. In the phase diagrams of the Nd₂O₃-GeO₂-P₂O₅ and Er2O₃-GeO₂-P₂O₅ systems, the regions of the structural influence of individual compounds with topologically identical cationic networks—anisotropic (A), combined (C), and isotropic (I)—are united into common areas. The A: C: I area ratio is 1: 1: 1 in the neodymium system and 1.7: 1: 3.4 in the erbium system.     

Conformation of cationic N,N‐di­methyl­glycine in di­methyl­glycinium tri­fluoro­acetate

In the title compound, C₄H₁₀NO₂⁺·C₂F₃O₂^?, the main N—C—COOH skeleton of the protonated amino acid is nearly planar. The C=O/C—N and C=O/O—H bonds are syn and the two methyl groups are gauche to the methyl­ene H atoms. The conformation of the cation in the crystal is compared to that given by ab initio calculations (Hartree–Fock, self‐consistent field molecular‐orbital theory). The tri­fluoro­acetate anion has the typical staggered conformation with usual bond distances and angles. The cation and anion form dimers through a strong O—H?O hydrogen bond which are further interconnected in infinite zigzag chains running parallel to the a axis by N—H?O bonds. Weaker C—H?O interactions involving the methyl groups and the carboxy O atoms of the cation occur between the chains.     

The reactivity of SbVO<Subscript>5</Subscript> with T-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> in solid state in air

The reactivity of SbVO₅, a compound known since a short time, with T-Nb₂O₅ in solid state in air has been investigated over the whole component concentration range of a system built by these two reacting substances. The investigation results have shown that an equimolar mixture of SbVO₅ and T-Nb₂O₅ reacts with a subsequent formation of a hitherto unknown compound of the formula Nb₂VSbO₁₀. This compound has been characterized by the methods XRD, DTA/TG, and SEM. Its orthorhombic unit cell parameters have been calculated, and its stability in air up to 880 ± 10 °C has been proved. At this temperature, the compound melts incongruently with an accompanying deposition of solid Nb₉VO₂₅, i.e., of a compound that crystallizes in the binary oxide system V₂O₅–Nb₂O₅.     

Kinetic Isotope Effect in the Photoreduction of <Emphasis Type="Italic">o</Emphasis>-Benzoquinones in the Presence of <Emphasis Type="Italic">N,N</Emphasis>-Dimethylaniline

The kinetics of photoinduced reduction of a series of 3,5- and 3,6-di-tert-butylbenzoquinones-1,2 was studied in the presence of N,N-dimethylaniline, its deuterated analog, and a series of para-substituted N, N-dimethylanilines. On passing from the endothermic to the exothermic range of the free energy of electron transfer ΔG _e , the effective rate constants k _H and k _D and the quantum yields ϕ_H and ϕ_D of the reaction varied nonmonotonically with a maximum at ΔG _e of approximately +0.1 eV. For the reactant pairs relevant to the ascending (left-hand) branch of the plot k _H = f(ΔG _e ), the H/D isotope effect takes place, varying from two to five in magnitude. For the reactant pairs at the maximum and in the descending (right-hand) branch of the plot k _H = f(ΔG _e ), there is no isotope effect or its value is insignificant.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 5, 2005, pp. 348–352.Original Russian Text Copyright © 2005 by Abakumov, Shurygina, Chesnokov, Druzhkov, Lopatin, Chechet, Cherkasov.     

Changes in the heat capacity of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> solid solutions near the point of antiferromagnetic phase transition in Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>

Al₂O₃-Cr₂O₃ solid solutions with 0, 4, 7, 10 and 20 mol% of corundum were synthesized using a high-pressure/high-temperature apparatus and characterized by X-ray powder diffraction. Calorimetric measurements were carried out using DSC-111 (Setaram). Heat capacity was measured by the enthalpy method in a temperature range of 260–340 K, near magnetic phase transition in pure Cr₂O₃ (305 K). Magnetic contribution into the heat capacity was derived and found to change irregularly with the composition.     

EPR of copper ions in Pb<Subscript>2</Subscript>MoO<Subscript>5</Subscript> crystals

The article presents the results of EPR studies of Pb₂MoO₅ crystals containing a copper impurity. Based on the analysis of angular dependences of the EPR spectra, it is found that copper ions incorporate into the structure of the Pb₂MoO₅ crystal in the Cu²⁺ state and occupy the molybdenum site with the formation of a linear extended Cu(II)–V(O)–Pb(IV) defect along the а axis of the crystal. An oxygen vacancy appears in the structure of the defect to compensate the charge and the lead ion acquires the Pb⁴⁺ charge state. According to the structure of this center, one magnetically non-equivalent position with the direction of main values of А and g of A(Cu)_zz and g_zz tensors parallel to the а axis is observed in the EPR spectra. Moreover, the EPR spectra exhibit an addition hyperfine structure from one lead atom on which the unpaired electron density is 0.061%. The obtained data on the structure of the defect formed when the copper impurity incorporates into the Pb₂MoO₅ crystal provided the assumption that the observed light scattering when the light beam is directed perpendicular to the а axis may be due to the cooperative effect of the presence of di- and tetravalent ions substituting for molybdenum in the linear configuration of Pb–O–Mo bonds.     

Solvent-specific reduction of Na<Subscript>2</Subscript>PtI<Subscript>6</Subscript> in acetone

Oxidation state of iodide complexes of Pt^II and Pt^IV in large excess of NaI with respect to platinum in water and acetone solution has been determined by means of ¹⁹⁵Pt NMR spectroscopy. In acetone, iodide complexes of Pt^IV are almost quantitatively reduced into Pt^II, and iodine is bound in a poorly soluble polymeric complex with sodium iodide and acetone. Iodometric titration has revealed the formation of equivalent amount of iodine. Reduction of platinum has not been observed in aqueous medium.     

Phase relations in the CaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system in the subsolidus region

Phase relations in the CaO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction and differential thermal analyses, and the isothermal section at 600°C has been constructed. The formation of ternary compounds at the component ratios 1CaO: 1Bi₂O₃: 1B₂O₃ (CaBi₂B₂O₇) and 1CaO: 1Bi₂O₃: 2B₂O₃ (CaBi₂B₄O₁₀) has been established X-ray diffraction characteristics of these phases are presented.     

Specific features of the thermodynamics of activation in the LaNi<Subscript>5</Subscript>-H<Subscript>2</Subscript> and CeNi<Subscript>5</Subscript>-H<Subscript>2</Subscript> systems

Using heat conducting Tian—Calvet calorimetry and volumetric measurements, the first hydrogen absorption—desorption cycles in the LaNi₅-H₂ and CeNi₅-H₂ systems were studied. The pressure—composition isotherms were plotted, the equilibrium pressures of hydrogen along the absorption and desorption branches and in the region of hysteresis for different activation steps were determined, and the enthalpies of phase transitions α → β and β → α were calculated. The profiles of the heat evolution curves were analyzed. It was concluded that the mechanism of the reactions studied changes upon activation.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 134–139, January, 2005.     

Electrochemical dissolution of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> in acidic solutions

The cyclic voltammetry method was used to study the regularities of the electrochemical behavior of cobalt cobaltite in an acidic medium. It is shown that cathodic reduction of Co₃O₄ in the studied range of potentials of +1.0 to −0.8 V is a multistage process occurring according to the scheme:      

Electrochemical dissolution of Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> in acid solutions

The present study deals with the electrochemical reductive dissolution of Mn₃O₄, which was added to carbon-paste electroactive electrodes (CPEEs) in acid solutions. It was found that in the experimental conditions the thermodynamically stable form of manganese was . Kinetic features of the electrochemical reductive dissolution of Mn₃O₄, which was realized under potential cycling conditions (+1.0 V→−0.7 V→+1.0 V), were determined by the electrode polarization direction. It was shown that the cathodic reduction of Mn₃O₄ was accomplished in three stages. Manganese was dissolved in the supporting solution only at the third stage. The first two stages involved solid-phase reactions. The anodic cycling stage included an active dissolution of Mn₃O₄ and the lower manganese oxide (MnO) accumulated on the electrode surface during the cathodic reduction.     

Synthesis of NH<Subscript>4</Subscript>TiOF<Subscript>3</Subscript> Crystals in the Presence of Polyoxyethylene Ethers

The effect of polyoxyethylene ethers as surfactants on the morphology of NH₄TiOF₃ crystals obtained by hydrolysis of (NH₄)₂TiF₆ in the presence of boric acid is analyzed. Depending on the molecular weight of the polyoxyethylene ether, the geometric dimensions (thickness and lateral size) of the crystals change. The obtained samples were characterized by X-ray and electron diffraction, Raman spectroscopy, and scanning electron microscopy. The heat treatment of NH₄TiOF₃ powders gives anatase mesocrystals retaining the initial particle morphology.     

Features of propane conversion in the presence of SmVO<Subscript>3</Subscript> and SmVO<Subscript>4</Subscript>

Features of propane conversion in the presence of samarium vanadite and samarium vanadate, both produced via solid-phase synthesis, are studied. It is shown that SmVO₃ catalyzes mainly the propane cracking process to form methane and ethylene, while SmVO₄ equally accelerates both cracking and the dehydrogenation of propane. Based on the results from catalytic experiments, energies of activation are calculated for the thermal cracking of propane (104 kJ/mol) and the conversion of propane in the presence of SmVO₃ (39 kJ/mol) and SmVO₄ (42 kJ/mol). The thermal stability of SmVO₄ in a hydrogen atmosphere is studied via temperature-programmed reduction, while SmVO₃ stability in an oxidizing environment is studied by DTA. Energies of activation for the reduction of SmVO₄ (75 kJ/mol) and the oxidation of SmVO₃ (244 kJ/mol) are calculated using the Kissinger method.     

A re‐examination of supra­molecular aggregation in two polymorphs of acetone 2,4‐dinitro­phenyl­hydrazone

The structure of the triclinic polymorph of acetone 2,4‐dinitrophenylhydrazone, C₉H₁₀N₄O₄, has been redetermined from diffraction data collected at 120 (2) K; the mol­ecules are linked by C—H⋯O hydrogen bonds into centrosymmetric R₂²(10) dimers which are themselves linked into a chain by an aromatic π–π stacking inter­action. In the monoclinic polymorph, which crystallizes with Z′ = 2 in the space group P2₁/n, one type of mol­ecule forms dimers exactly as in the triclinic polymorph, while the other forms C(6) chains.     

<Superscript>1</Superscript>H NMR spectra of water contained in solutions of poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone) and its modification products in CDCl<Subscript>3</Subscript>

¹H NMR spectra in CDCl₃ of poly(N-vinylpyrrolidone), epoxidized poly(N-vinyl-pyrrolidone), and products derived from the latter by modification with amino acids (glycine, β-alanine, γ-aminobutyric acid, and ε-aminocaproic acid) were examined. The ¹H NMR spectra of the modified polymers contain signals for water protons due to different centers of water sorption. These signals differ in chemical shift and integral intensity and indicate a changed spatial packing of the polymer as the result of its modification. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2377–2380, October, 2005.     

Assessment of <Superscript>210</Superscript>Po in foodstuffs consumed in Korea

²¹⁰Po in the daily diet in Korea was analyzed and the ingestion dose from an intake of ²¹⁰Po was estimated by considering the dietary habit of a Korean person. The ²¹⁰Po concentrations of a leafy vegetable (0.36 Bq·kg⁻¹ for lettuce) in the terrestrial food were higher than those of grain, whereas Chinese cabbage had a lesser ²¹⁰Po concentration (0.019 Bq·kg⁻¹). The ²¹⁰Po concentration of the animal product was similar to those detected in the grain and vegetable. The ²¹⁰Po concentrations in the shell and crustaceous were high from 19.1 to 33.0 Bq·kg⁻¹, however, its value fell in the overall range of the reported values. The effective dose from ²¹⁰Po for an adult from the Korean population was about 269.4 μSv·y⁻¹. Nearly 80% of the ingestion dose from the intake of ²¹⁰Po was attributed to the consumption of seafood. It suggests that the marine food ingestion is a critical pathway for natural ²¹⁰Po to the Korean population.     

A uniform and one‐dimensional stacking of 2,5‐di­chloro­tetra­cyano­quinodimethanide mol­ecules in the tetra­methyl­arsonium salt

In the tetra­methyl­arsonium salt of 2,5‐di­chloro‐7,7,8,8‐tetra­cyano­quinodimethanide [systematic name: tetra­methyl­arson­ium 2,2′‐(2,5‐dichlorocyclohexa‐2,5‐diene‐1,4‐diylidene)bis(propanedinitrile)], C₄H₁₂As⁺·C₁₂H₂Cl₂N₄^? or [As(CH₃)₄](C₁₂H₂Cl₂N₄), the cation lies disordered about a twofold axis and the radical ion lies about an inversion center forming a uniform [interplanar distance 3.35 (2) Å] and one‐dimensional stacking without any slip. The electrical conductivity of the single crystal at room temperature was less than 10^?9 S cm^?1, and the temperature dependence of para­magnetic susceptibility obeyed a one‐dimensional antiferromagnetic Heisenberg model with a spin‐exchange integral of 83 K in the temperature range 1.8–320.0 K.     

Forms of iron occurrence in a series of binary tellurides Fe<Subscript>x</Subscript>Ti<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>1.45</Subscript>

Nonstoichiometric tellurides Fe_xTi_1–x Te_1.45 synthesized at 850°C were studied by X-ray phase and X-ray fluorescence analysis and by ⁵⁷Fe Mössbauer spectroscopy. The mutual iron-titanium substitution is limited in this series. The system contains four individual phases in which iron is in three different states: Fe²⁺ in an asymmetric environment, Fe²⁺ in a symmetric environment, and Fe⁰. The distribution of various iron states in the system depends not only on the Fe : Ti ratio, but also on the structure of phases.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1761–1764.Original Russian Text Copyright © 2004 by Pankratova, Zabolotnaya, Panchuk, Semenov, Zvinchuk, Suvorov.This revised version was published online in April 2005 with a corrected cover date.     

Mass spectrometric investigation of vaporization in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The thermodynamics of vaporization in the Bi₂O₃-Fe₂O₃ quasibinary system was studied by high-temperature mass-spectrometry. The partial pressures of the constituents of a saturated vapor over the system at 1100 K were determined. Based on the experimental data, the following parameters were calculated: the activities of the components of the Bi₂O₃-Fe₂O₃ system condensed phase, the standard enthalpies of some heterogeneous reactions, and standard enthalpies of formation and enthalpies of formation for crystalline BiFeO₃ and Bi₂Fe₄O₉ from individual oxides. An optimal temperature for the solid-phase synthesis of bismuth ferrites from simple oxides is recommended.     

Electrochemical Synthesis of Co-intercalation Compounds in the Graphite-H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-H<Subscript>3</Subscript>PO<Subscript>4</Subscript>System

Anodic oxidation of highly oriented pyrolytic graphite in an electrolyte containing concentrated sulfuric and anhydrous phosphoric acids is studied for the first time. The synthesis was carried out under galvanostatic conditions at a current I = 0.5 mA and an elevated temperature (t = 80°C). Intercalation compounds of graphite (ICG) are shown to form at all concentration ratios of H₂SO₄ and H³PO⁴ acids. The intercalation compound of step I forms in solutions containing more than 80 wt % H₂SO₄, a mixture of compounds of intercalation steps I and II forms in 60% H²SO⁴, intercalation step II is realized in the sulfuric acid concentration range from 10 to 40%, and a mixture of compounds of intercalation steps III and II is formed in 5% H₂SO₄ solutions. The threshold concentration of H₂SO₄ intercalation is ∼2%. With the decrease in active intercalate (H₂SO₄) concentration, the charging curves are gradually smoothed, the intercalation step number increases, and the potentials of ICG formation also increase. As the sulfuric acid concentration in the electrolyte changes from 96 to 40 wt %, the filled-layer thickness d _i in ICG monotonously increases from 0.803 to 0.820 nm, which apparently is associated with the greater size of phosphoric acid molecules. With further increase in H₃PO₄ concentration in solution, d _i remains unchanged. According to the results of chemical analysis, both acids are simultaneously incorporated into the graphite interplanar spacing and their ratio in ICG is determined by the electrolyte composition.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 651–655.Original Russian Text Copyright © 2005 by Leshin, Sorokina, Avdeev.