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The antisymmetry of small water clusters of various configurations with three to five molecules, which are stable according to the ab initio calculated data, was analyzed. The antisymmetry operation was alteration of the direction of all hydrogen bonds including the direction of the external unrealized Н-bonds. It was found that most configurations of small clusters were antisymmetric. Other configurations form pairs of antipode configurations with very close energies.

The apparent molar volume of urea φ in aqueous solution in the range Т = 273-323 K and m = 1-10 (molality) depends linearly on m^1/2. An equation for φ(m, T) was derived. The partial molar characteristics of urea and water (volume, dilatability, and temperature coefficients of volumes) were calculated. The dependences have characteristic points (extrema, inflection points), shifted to the region of lower temperatures for dilute solutions. The dependences for 2m and 4m of the urea solution retain the characteristics of the Y₁(T) of pure water. In these solutions, the proper structure of water is preserved.

In equations for the partial volume, dilatability, heat capacity, and adiabatic compressibility of aqueous urea, the properties are "fitted" to the singular temperature T_s of overcooled water T_s = 227.15 K
(R. J. Speedy, J. Phys. Chem., 91, 3354 (1987)). The equations for the characteristics of D₂O-(ND₂)₂CO and Т₂O-(NТ₂)₂CO systems were obtained by scaling the temperature to 6 and 9.4 K, respectively. The properties of infinitely dilute solutions did not reveal the sign reversal of the isotope effect. The isoconcentrates of the partial volumes and dilatability form wagging lines in the region of low temperatures. The temperature dependences of the properties have extrema and inflection points, while the isotope effects in solutions of finite concentrations experience sign reversal. The maximum density temperature (MDT) of the solution decreases as the urea concentration increases, and also on passing from D₂O-(ND₂)₂CO to H₂O-(NH₂)₂CO. Thus, for the 8m solution, the MDT is 259.6 K (protium system) and 266.7 K (deuterium system). The difference is almost equal to the shift of the MDT after the H₂O → D₂O transition (7.2 K).

The concentration dependence of normalized absorbance (to the total number of moles of components in one liter) of HF solutions in acetonitrile (1:12-10:1) is analyzed. It is found that in the binary liquid system (BLS) under study molecular complexes with stoichiometric 1:1 and ~10:1 ratios of molecules occur along with the heteroassociates (HAs) found previously with the ratio HF:CH₃CN of 4:1. For each of the HAs the concentration range at which it is formed in BLS is evaluated, and the positions of HF stretching vibrational bands are found. Optimum configurations and vibrational frequencies of molecular complexes (HF)_m⋅(CH₃CN)_n (m = 1-6, n = 1-2) of various topology are calculated using the density functional method (B3LYP/6-31 ++ G (d, p)). Their relative stability and the structure peculiarities are studied; complexation tendencies in the HF-CH₃CN system are revealed. The structure of HAs with 1:1 and 4:1 stoichiometric ratios of molecules is determined by comparing the results of calculations and experiment.

Interaction and reorganization contributions to solvation enthalpies of nonelectrolytes in aqueous solutions of amides of carboxylic acids with different degree of N-substitution and N-methylpyrrolidone are calculated. The data are discussed using structurally thermodynamic characteristics of water-amide systems obtained by us previously. It is found that the type of concentration dependence of the solvation enthalpy of nonelectrolytes in all solutions investigated is determined by the type of reorganization component. It is shown that the highest solvation exothermicity of nonelectrolytes in water is due to the lowest value of the reorganization contribution in spite of that nonelectrolytes interact weaker with water than with non aqueous components.

Rubidium and cesium chlorites are prepared and studied by single crystal and powder X-ray diffraction. The compounds are isostructural; crystallize in the orthorhombic system; space group Cmcm, Z = 4. Unit cell parameters: a = 6.3464(8) Å, b = 6.4223(8) Å, c = 7.7493(9) Å for RbClO₂ and a = 6.5998(9) Å, b = 6.6116(9) Å, c = 8.3161(11) Å for CsClO₂. The structures can be represented as 3D frameworks formed by metal cations and chlorite anions acting as tetradentate bridging and bidentate chelating oxygen ligands.

The structure of Nb₂Mo₃O₁₄ double oxide is refined from powder data using synchrotron radiation and the anomalous scattering effect; space group P2₁m is found for the material. It is demonstrated that in the tetragonal unit cell with parameters а = 23.173 Å, с = 4.0027 Å Nb⁵⁺ and Мо⁶⁺ ions are stochastically distributed in МО₆ octahedra and МО₇ pentagonal bipyramids of the polygonal network structure of the Мо₅О₁₄ type.

Four structural models of volborthite Cu₃(OH)₂(V₂O₇)⋅2H₂O (a = 10.646(2) Å, b = 5.867(1) Å, c =
14.432(2) Å, β = 95.19(1)°, V = 897.7(5) ų, Z = 4, R/R_w = 0.038/0.046) calculated in the space groups determined from the systematic absences are compared. Based on the structure balance and the similarity of constituting polyhedra, values of the R factor, and isotropic thermal parameters, the space group Ia is found to be preferable, which is the only possible asymmetric and uniform variant. Hydrogen atoms of ОН-groups, oxygen atoms and, partially, hydrogen atoms of water are localized.

A polyhydrate of the tetraisoamylammonium salt of linear (uncrosslinked) polyacrylate (~25 monomeric units in the polyacrylate chain) is described and compared to polyhydrates of cross-linked tetraisoamylammonium polyacrylates (0.5-3% of cross-linking with divinylbenzene or divinylsulfide). Powder X-ray diffraction reveals that the polyhydrate containing a linear polyacrylate molecule has the same structure (hexagonal, a = 12.26 Å, c = 12.71 Å at 3°C) as polyhydrates of the cross-linked polyacrylate molecules. A single crystal of the polyhydrate obtained from an aqueous solution of linear tetraisoamylammonium polyacrylate is studied by X-ray diffraction at -173°C. The structure is hexagonal; space group P-6m2; the polyhydrate framework is a slightly distorted variant of the hexagonal structure-I of clathrate hydrates.

The complex Ru₄(μ₄-S)(μ,η³-C₃H₅)₂(CO)₁₂ is prepared and examined by IR and NMR spectroscopy; its crystal structure is determined (an automatic Bruker-Nonius X8 Apex four-circle diffractometer equipped with a 2-D CCD-detector, 100 K, graphite-monochromated molybdenum source, λ = 0.71073 Å). The crystal belongs to the orthorhombic crystal system with unit cell parameters a = 19.3781(9) Å, b = 12.2898(7) Å, c = 10.1726(4) Å, V = 2422.6(2) ų, space group Pnma, Z = 4, composition C₁₈H₁₀O₁₂Ru₄S, d_x = 2.343 g/cm³. The molecule of point symmetry C₁ is situated on the mirror plane of the space group Pnma, two carbonyl groups at Ru2 and Ru3 atoms overlapping with the allylic ligand with a weight of 50% so that carbon atoms coincide. Thus, we have a racemic structure with two overlapping enantiomers of the molecule of Ru₄(μ₄-S)(μ,η³-C₃H₅)₂(CO)₁₂.