Heat capacity and density of methylpyrrolidone solutions of sodium and potassium perchlorates at different concentrations and 298.15 K

The heat capacity and density of solutions of sodium and potassium perchlorates in N-methylpyrrolidone (MP) at 298.15 K were studied by calorimetry and densimetry. The standard partial molar heat capacities $ \bar C_{p2}^ \circ $ \bar C_{p2}^ \circ and volumes $ \bar V_2^ \circ $ \bar V_2^ \circ of NaClO₄ and KClO₄ in MP were calculated. The standard heat capacities $ \bar C_{pi}^ \circ $ \bar C_{pi}^ \circ and volumes $ \bar V_i^ \circ $ \bar V_i^ \circ of the perchlorate ion in an MP solution at 298.15 K were determined. The results are discussed with allowance for the specifics of solvation in the solutions of the salts under study. The coordination number of the ClO₄⁻ ion in an MP solution at 298.15 K was calculated.     

The compressibility of water-dimethyl sulfoxide mixtures over the temperature and pressure ranges 278–323.15 K and 1–1000 bar

The compressibility coefficients of water-dimethyl sulfoxide (DMSO) binary liquid mixtures were measured over the temperature range 278–323.15 K at pressures from atmospheric to 1000 bar. At these state parameters, the partial molar volumes and partial molar compressibility coefficients $ \bar k_1 $ \bar k_1 and $ \bar k_2 $ \bar k_2 of water and DMSO were calculated. The dependences of the compressibility coefficients of mixtures on mixture composition passed a minimum. The minimum shifted to lower DMSO concentrations as the temperature increased. The dependences contained the inversion region where the k value was independent of pressure. The limiting molar partial compressibility coefficient of DMSO $ \bar k_2 $ \bar k_2 was negative at 278.15 K and increased as the temperature grew.     

Volume properties of a ternary system: Water-urea-amino acid. Dilute and concentrated solutions

Partial molar volumes $ \bar V_U^0 $ \bar V_U^0 of amino acids in an aqueous urea solution are studied. For a saturated urea solution $ \bar V_U^0 $ \bar V_U^0 equals the molar volume of the amino acid, therefore, in the saturated solution, the amino acid dissolves without changing the system volume. Hydrophobic effects are manifested in the volumetric characteristics only in dilute (<1 mol/kg) urea solutions. Within a three-layer hydration model, the numbers of amino acid hydration are found. By the example of alanine and leucine, it is shown that their decrease with increasing urea concentration is determined by a zwitterionic moiety and does not depend on the size of the hydrocarbon radical of the amino acid.     

Oxygen nonstoichiometry and the thermodynamic properties of manganites Ca1 ? x ? ySrxLayMnO3 ? δ

The content of oxygen in Ca_{0.6 − y} Sr_0.4La _y MnO_{3 − δ}, where y = 0 and 0.05, was determined by coulometric titration over the temperature range 650–950°C at oxygen partial pressure in the gas phase varied from 10⁻⁴ to 1 atm. The results were used to calculate the partial molar enthalpy, Δ$ \bar H $ \bar H _O(δ), and entropy, Δ$ \bar S $ \bar S _O(δ), of oxygen in manganites. Changes in the Δ$ \bar H $ \bar H _O(δ) and Δ$ \bar S $ \bar S _O(δ) dependences caused by the introduction of lanthanum are evidence of the formation of local clusters of the double perovskite type in the Ca_0.6Sr_0.4MnO_{3 − δ} matrix.     

Dependence of molecular polarizability on the orientational order in nematic liquid crystals

The dispersion dependences of refractive indices in the visible range were used to obtain experimental values of the Lorentz tensor components L _j and the mean molecular polarizability $ \bar \gamma $ \bar \gamma for five nematic liquid crystals belonging to two homological series. The dependence of L _j components on the homologue number, mesophase temperature, birefringence value, and the orientational order of molecules in the nematic phase and upon a nematic-smectic A phase transition was revealed. The effect of the isotropization of the Lorentz tensors and the local field tensor with decreasing birefringence and molecular polarizability anisotropy Δγ was confirmed. The quadratic dependence $ \bar \gamma $ \bar \gamma (S) on the molecular orientational order parameter S in the nematic phase was found. It was invariant with respect to the nematic-smectic A transition. The dependences $ \bar \gamma $ \bar \gamma (S) and Δγ(S) are explained within molecular statistical theory as consequences of the correlation between orientational and conformational degrees of freedom of molecules. These conformational degrees of freedom are related to the internal rotation of molecular fragments, which affects the electronic conjugation of the fragments and the oscillator strengths of molecular transitions.     

Volumetric properties of the water-ethylene glycol mixtures in the temperature range 278–333.15 K at atmospheric pressure

Density of the water-ethylene glycol binary mixtures was measured in the entire range of compositions in the temperature range 278–333.15 K (6 values) at atmospheric pressure using a vibration densimeter. Mixtures with low concentrations of ethylene glycol were studied at 15 temperatures in the range of 274–333.15 K. Excess molar volumes V _m ^E , the partial molar volumes of water -V ₁ and ethylene glycol, -V ₂, the coefficients of thermal volume expansion α of the mixture, the partial molar volume coefficients of thermal expansion of water $ \bar V_1 $ \bar V_1 and ethylene $ \bar V_2 $ \bar V_2 were calculated. Excess molar volumes were described using the Redlich-Kister equation. The density ρ of the mixture was found to increase with the increasing ethylene glycol concentration at all temperatures, but at low content of ethylene glycol the dependence ρ = f(T) of the mixture at ∼276.5 K passed through a maximum. The coefficient α increases sharply in the composition range 0 < x < 0.2, in the range 0.5 < x <1 remains almost unchanged, and at T > 277 K is positive for all compositions. The dependences $ \bar \alpha _1 $ \bar \alpha _1 = f (x) and $ \bar \alpha _2 $ \bar \alpha _2 = f (x) are complex in whole temperature range and are characterized by the presence of an extremum. V _m ^E values are negative at all temperatures, and upon increase in the temperature the deviation from ideality decreases (x is the mole fraction of ethylene glycol).     

Formation of colloid solutions and gels during the radiation-chemical telomerization of tetrafluoroethylene in acetone

The polymerization of tetrafluoroethylene (TFE) is initiated by the radicals generated by the radiolysis of acetone. The oligomer chain length n increases with an increase in the initial monomer concentration C. The transition from the true to the colloid solution at C ≈ 0.07 mol/l takes place at an average telomer chain length of $ \bar n $ \bar n ≈ 5. The transition of the colloid solution into gel is observed at C ≈ 0.30–0.35 mol/l. The acetone/TFE ratio in the centrifugation sediment decreases with an increase in the centrifugal acceleration and C. Its minimal value of ∼4 is attained at C > 2 mol/l when $ \bar n $ \bar n ≈ 12–15. The mean particle diameter in the phase separation region is 0.6–0.8 μm. A scaling model of radical polymerization is proposed to explain the molecular-mass distribution of telomers.     

Concentration dependences of the heat capacity of solutions of alkali metal iodides in N-methylpyrrolidone-water mixed solvent at 298.15 K

Heat capacities of solutions of alkali metal iodides (MeI) in N-methylpyrrolidone (MP)-water mixed solvent were measured over the range of compositions. The influence of the composition of the mixed solvent on the heat capacity of MeI-MP-H₂O ternary systems is discussed. Standard partial molar heat capacities $ \bar C_{p_2 }^o $ \bar C_{p_2 }^o (MeI) in the MP-water mixed solvent at 298.15 K are calculated.     

Thermodynamic properties of Ni-Ga melts

The partial mixing enthalpies of the components (Δ_m $ \bar H $ \bar H _i ) of the Ni-Ga melts were measured using the high-temperature isoperibolic calorimetry at 1770 ± 5 K in wide concentration interval. The limiting partial mixing enthalpy of gallium in a liquid nickel (Δ_m $ \bar H $ \bar H _Ga^∞) is −95.5 ± 19.8 kJ mol⁻¹, and similar function of nickel in liquid gallium (Δ_m $ \bar H $ \bar H _Ni^∞) is −74.5 ± 16.4 kJ mol⁻¹. The integral mixing enthalpy of liquid alloys of this system was calculated from partial enthalpies for the whole concentration area (Δ_m H _min = −32.1 ± 2.7 kJ mol⁻¹ at x _Ni = 0.5). The Δ_m H value of liquid nickel-gallium alloys independence of the temperature is confirmed. Enthalpies of formation of liquid (Δ_m H) phases of Ni-Ga system were compared with ones for solid (Δ_f H) phases of this system. An analysis of d-metals influence on formation energy of Ga-d-Me melts was made using the values of Δ_f H for intermediate phases of these systems. The article was translated by the authors.     

Subsolidus phase relations in the Na2MoO4-CoMoO4-Cr2(MoO4)3 system

Triple molybdate NaCoCr(MoO₄)₃, a phase of variable composition Na₂MoO₄-CoMoO₄-Cr₂(MoO₄)₃ (0 ≤ x ≤ 0.5) having nasicon structure (space group R $ \bar 3 $ \bar 3 c), and triple molybdate NaCo₃Cr(MoO₄)₅ crystallizing in triclinic space group P $ \bar 1 $ \bar 1 were synthesized in the subsolidus region of the Na₂MoO₄-CoMoO₄-Cr₂(MoO₄)₃ ternary salt system. Crystal parameters were calculated for the newly synthesized molybdates and phases. The vibration spectra of Na_{1 − x} Co_{1 − x} Cr_{1 + x} (MoO₄)₃ and electrophysical properties were studied. Upon Na + Co → Cr(III) substitution, chromium cations are distributed to cobalt sites and additional vacancies are generated in the sodium sublattice.     

Theoretical investigation of some O-nitrosyl carboxylate biologic molecules �� A natural bond orbital study

Theoretical study of several O-nitrosyl carboxylate compounds have been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6-31G** basis set. Geometries obtained from DFT calculations were used to perform the natural bond orbital (NBO) analysis. It is noted that weakness in the O₃-N₂ bond is due to $ n_{O_1 } \to \sigma _{O_3 - N_2 }^* $ n_{O_1 } \to \sigma _{O_3 - N_2 }^* delocalization and is responsible for the longer O₃-N₂ bond lengths in O-nitrosyl carboxylate compounds. It is also noted that decreased occupancy of the localized $ \sigma _{O_3 - N_2 } $ \sigma _{O_3 - N_2 } orbital in the idealized Lewis structure, or increased occupancy of $ \sigma _{O_3 - N_2 }^* $ \sigma _{O_3 - N_2 }^* of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are related with the resulting p character of the corresponding sulfur natural hybrid orbital (NHO) of $ \sigma _{O_3 - N_2 } $ \sigma _{O_3 - N_2 } bond orbital. In addition, the charge transfer energy decreases with the increase of the Hammett constants of subsitutent groups.     

Synthesis and crystal structure of sodium isopolyvanadate [Na2(H2O)8]2H2[V10O28] · 4H2O

The sodium hydrogen oxovanadate [Na₂(H₂O)₈] ₂H₂[V₁₀O₂₈] · 4H₂O was synthesized and studied by TGA, X-ray diffraction, and NMR and IR spectroscopy. The crystals are triclinic, space group P $ \bar 1 $ \bar 1 , a = 8.545(7) ?, b = 10.827(2) ?, c = 11.627(2) ?, α = 105.48(3)°, β = 99.38(3)°, γ = 101.29(3)°, V = 989.9(3) ?³, ρ(calcd) = 2,381 g/cm³, Z= 1.     

Crystal structure of a new coordination polymer [LaAg(Pydc)(HPydc)(C2O4)0.5(H2O)2]n (H2Pydc = pyridine-3,5-dicarboxylic acid)

A new 3D coordination polymer, [LaAg(Pydc)(HPydc)(C₂O₄)_0.5(H₂O)₂] _n (I) (H₂Pydc = pyridine-3,5-dicarboxylic acid), has been hydrothermally synthesized and characterized by elemental analyses and single crystal X-ray diffraction. The X-ray diffraction analysis reveals that I (C₁₅H₁₁AgLaN₂O₁₂) crystallizes in triclinic space group P $ \bar 1 $ \bar 1 and features an interesting 3D framework constructed by 2D layers via strong Ag-Ag interactions. Unit cell parameters for I (n = 1): a = 7.749(2), b = 8.316(1), c = 14.239(3) ?, α = 97.64(2)°, β = 100.12(2)°, γ = 94.37(2)°, and Z = 2.     

Two octacyanomolybdate(IV)-M(II) (M = Mn,Co) bimetallic assemblies: Crystal structures and magnetic properties

Two cyano-bridged bimetallic complexes {[M₂(H₂O)₄Mo(CN)₈] · 4H₂O} _n [M = Mn (I) and Co (II)] have been synthesized and structurally characterized. The single-crystal X-ray analyses reveal that these two compounds have three-dimensional structures, and cell parameters are similar in a tetragonal system with space group I $ \bar 4 $ \bar 4 . In the both complexes, each [Mo(CN)₈]⁴⁻ building block is linked with M²⁺ [M = Mn and Co] ions through its eight CN ligands. Each M²⁺ center is connected to four Mo units forming a three-dimensional framework. In addition, magnetic studies of these complexes have been presented.     

Synthesis and study of the variable-composition phase Na1?xCo1?xFe1+x(MoO4)3, 0 ≤ x ≤ 0.4, with nasicon structure

The synthesis conditions for variable-composition phase Na_1−x Co_1−x Fe_1+x (MoO₄)₃, 0 ≤ x ≤ 0.4, crystallizing in the nasicon structure type (R $ \bar 3 $ \bar 3 c) were examined. For this phase, the crystallographic parameters were calculated, vibrational spectra were interpreted, and temperature dependence of electrical conductivity, dielectric constant, and dielectric loss tangent were examined.     

On the theory of oscillating flows in complex liquids

Experiments with highly concentrated suspensions and other complex liquids frequently demonstrate nonmonotonic N- or S-shaped dependences of viscous stress σ on shear rate $ \dot \gamma $ \dot \gamma and strong oscillations of the shear rate at a constant flow-inducing external stress, as well as oscillations of the viscous stress at a constant average shear rate. A phenomenological mathematical model is proposed for oscillating flows according to which oscillations arise when an applied stress (or the average shear rate, depending on the design of an experiment) is in the descending region of the σ-$ \dot \gamma $ \dot \gamma dependence and a complex liquid exhibits pronounced viscoelastic properties.     

New approximate formulae for the generalized temperature integral

The generalized temperature integral $ \int\limits_0^T {T^m } \exp ( - E/RT)dT $ \int\limits_0^T {T^m } \exp ( - E/RT)dT frequently occurs in non-isothermal kinetic analysis. Here E is the activation energy, R the universal gas constant and T the absolute temperature. The exponent m arises from the temperature dependence of the pre-exponential factor. This paper has proposed two new approximate formulae for the generalized temperature integral, which are in the following forms:

Subsolidus phase equilibrium in Cs2MoO4-Al2(MoO4)3-Zr(MoO4)2 system and crystal structure of new ternary molybdate Cs(AlZr0.5)(MoO4)3

The subsolidus area of Cs₂MoO₄-Al₂(MoO₄)₃-Zr(MoO₄)₂ system was studied by X-ray powder diffraction. Two new molybdates with component molar ratios of 1: 1: 1 (S₁) and 5:1:2 (S₂) were synthesized for the first time. The crystallographic parameters of the 5:1:2 compound were determined. Solution- melt crystallization and spontaneous nucleation yielded crystals of new 1:1:1 cesium aluminum zirconium molybdate Cs(AlZr_0.5)(MoO₄)₃. Its formula unit and crystal structure were refined by X-ray diffraction (1592 reflections, R=0.0249). Trigonal crystals: a=12.9441(2) ?, c=12.0457(4) ?, V=1747.86(7) ?³, Z = 6, space group R $ \bar 3 $ \bar 3 . The three-dimensional combined framework of this structure is formed by MoO₄ tetrahedrons linked through common vertices to (Al,Zr)O₆ octahedrons. Cesium atoms occupy large cavities of the framework. Crystallographic position M(1) is occupied by randomly distributed Al³⁺ and Zr⁴⁺ cations.     

Symmetry of (Na<Subscript>0.5</Subscript>R<Subscript>0.5</Subscript>)MO<Subscript>4</Subscript> crystals (R = Gd,La; M = W,Mo)

Kinetic order-disorder phase transitions (space group space group $ I\bar 4 $ I\bar 4 ↔ space group I4₁/a) have been considered for nonactivated and activated scheelite compounds (Na_0.5Gd_0.5)WO₄ (NGW), (Na_0.5Gd_0.5)MoO₄ (NGM), (Na_0.5La_0.5)WO₄(NLW), and (Na_0.5La_0.5)MoO₄ (NLM) synthesized by the Czochralski method and structural and growth sources of crystal dissymmetrization have been suggested. For NGW, it was shown that an increase in the difference between the content of Gd and Na in two positions of the structure with space group $ I\bar 4 $ I\bar 4 and their ratio leads to an increase in the deviation from centrosymmetry. On the basis of available literature data and our results, it was demonstrated that the degree of order depends on the initial composition of the reaction mixture, crystal growth and cooling rates, activator concentrations, and postgrowth treatment conditions. The inconsistency between X-ray diffraction data and asynchronous second harmonic generation studies was explained by the possibility of formation of centrosymmetric superstructures and/or local ordering of atoms.     

Coordination polymers based on [Re6Se8(CN)6]4? cluster anion, lanthanide cations, and tetraatomic alcohol erythritol

By the interaction of aqueous solutions of salts of the [Re₆Se₈(CN)₆]⁴⁻ cluster anion with salts of Nd(III), Tb(III), and Yb(III) lanthanides in the presence of tetraatomic alcohol erythritol (butane-1,2R,3S,4-tetraol) three new compounds are obtained: K[Nd(C₄H₁₀O₄)(H₂O)₄{Re₆Se₈(CN)₆}]·4H₂O (P $ \bar 1 $ \bar 1 space group, a = 11.544 ?, b = 13.643 ?, c = 13.838 ?, α = 111.97°, β = 108.08°, γ = 90.08°) (1); [{Yb₂(C₄H₉O₄)₂ × (H₂O)₂}{Re₆Se₈(CN)₆}]·5H₂O (P $ \bar 1 $ \bar 1 space group, a = 10.308 ?, b = 10.505 ?, c = 11.154 ?, α = 88.21°, β = 81.83°, γ = 78.50°) (2); [{Tb₂(C₄H₉O₄)₂(C₄H₁₀O₄)}{Re₆Se₈(CN)₆}]·4H₂O (P $ \bar 1 $ \bar 1 space group, a = 10.002 ?, b = 10.276 ?, c = 11.762 ?, α = 91.32°, β = 104.01°, γ = 106.02°) (3). The structures of these compounds are the coordination polymers (chain (2) and grids (1 and 3)) with different coordination modes of erythritol to the lanthanide cations.