A new approach to the structure of concentrated aqueous electrolyte solutions using pulsed NMR methods

It is shown that selective measurements of the magnetic dipole—dipole interactions between specific pairs of nuclear spins in glasses of concentrated aqueous electrolytes can provide detailed structural information of relevance to the liquid. The validity of the approach is demonstrated by selective measurements of the inter- and intra-molecular (H₂O) proton—proton interactions in LiCl and LiBr solutions at 100 K. For LiCl,4H₂O, these measurements are consistent with a short range (≈0.8 nm) distorted sodium chloride structure with Cl^? and Li(H₂O)⁺₄ as basic units: each Cl^? ion is octahedrally coordinated to six OH bonds. For LiCl,RH₂O solutions in the composition range 4 <R < 10, the excess H₂O is packed interstitially at the interfaces between clusters of LiCl,4H₂O. This structure is consistent with various properties of the solution at room temperature. LiBr solutions have similar structures.     

The heat of dehydration of concentrated sodium chloride and potassium chloride solutions

The molar heats of dehydration, ΔH¯_dehyd., of concentrated sodium chloride and potassium chloride solutions were measured with a differential scanning calorimeter in the scanning and isothermal modes. The overall ΔH¯_dehyd. was found to be 44.5 and 44.3 kJ mole^?1 H₂O for NaCl and KCl solutions respectively. There is an astonishing difference between concentrated NaCl and KCl solutions in the way water is lost. The number of fractions of heat dehydration were 2 for NaCl and 3 for KCl. The excess ΔH¯_dehyd. was about 10 kJ mole^?1 H₂O for fraction II of NaCl, and 17 and 55 kJ mole^?1 H₂O for fractions II and III, respectively, of KCl.     

Die Berechnung komplexer Absorptionsgleichgewichte ionogener Substanzen in wäßrigen Lösungsmitteln mit Hilfe eines Reaktionsmodells

The solubility of ionogen substances in water and aqueous ionic solutions is important for calculation of absorption processes. Aqueous solutions with complex reaction systems behave themselves extremely nonideal. In simple cases equilibria can be determined with the concept of nonideal thermodynamics. The model used in this work is based on ideal calculation of reaction equilibria and gas solubility. The model parameters (equilibrium constants andHenry constants) for the systems SO₂-H₂O,MEA-H₂S-H₂O,DEA-H₂S-H₂O andMEA-CO₂-H₂O are computed by regression of experimental data. Equilibrium reactions are selected according toBrinkley's method. The selection of the reacting species has decisive influence on the accuracy of the data fitting. Data regression is done numerically and leads to the formulation of nonlinear systems of equations, which have to be solved for each data point. This solutions are performed in an inner loop. By using the maximum-likelihood-principle the model parameters are optimized in the superior regression loop. Experimental data for the regression are the partial pressure and the total concentration of gas in the liquid phase. The used model is able to fit these data satisfactoryly. The model parameters, which are calculated from simultaneous data regression for different temperatures, ensure a simple correlation ofvan't Hoff. However, for similar reactions equilibria in different reaction systems, it is impossible to compute the same values for the equilibrium constants.     

Glass transition behaviour of ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate–H2O mixed solutions

Here, we have measured the glass transition temperature (T_g) of the ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate–H₂O mixed solutions as a function of H₂O concentration (x mol% H₂O). The glass-forming composition region was also determined. Contrary to the results of the quaternary ammonium type of ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate–H₂O mixed solutions, we did not observed the multiple glass transition behaviour. We also measured the glassy Raman spectra of the solutions at T = 77 K. We find that the “nearly free” hydrogen bonded Raman band of water molecules in the aqueous [bmim][BF₄] solution exists up to around x = 60 mol% H₂O, even at T = 77 K.     

Differential enthalpies of solution of LiCl·H2O,NaCl, KCl,MgCl2·6H2O,CaCl2·6H2O,and BaCl2·2H2O in water at 298.15 K,near the saturation concentration

The direct measurements of differential enthalpies of solution Δ_sol H ₂, of LiCl·H₂O, NaCl, KCl, MgCl₂·6H₂O, CaCl₂·6H₂O and BaCl₂·2H₂O, as the function of molality,m, in the region of concentrated solutions were performed. On this basis the enthalpies of crystallization, Δ_cryst H _m, were calculated and compared to the appropriate literature data.     

The influence of the supramolecular structure of water on the kinetics of vaporization

The kinetics of water vaporization was studied gravimetrically using a Q-1500 D derivatograph with an accuracy of ±5 × 10^?5 g under atmospheric conditions. Various supramolecular structures were created in liquid water using solutions of K, Na, Ba, and Zn chlorides with various concentrations. The kinetic dependences of weight P loss caused by the vaporization of solutions were compared with the data on pure water used to prepare the solutions. The dependence of the rate of vaporization V on the concentration of hydrated ions in solutions was used to show that the rate V is the sum of the rates of vaporization of particles of two types, (a) H₂O molecules and (b) supramolecular formations (H₂O clusters) with H-bonds. As a consequence, a nonlinear (piecewise linear) dependence of the kinetics of vaporization P = f(τ) of water and solutions is observed. The rate of vaporization (V ₁) along the initial P = f(τ) curve portions is substantially (by ～30%) higher than its stationary value (V).     

Specific F binding to phenyl ring of aromatic polymers

Most of the hydrogels deswell more remarkably in F⁻ containing solutions than in other monovalent anion containing solutions. However, significant deswelling followed by abnormal reswelling of polymer gel in KF solutions with increasing F⁻ concentration was observed in a series of polymer gels consisted of phenyl rings, for instance, poly(styrene sulfonic acid) (PSSA), hydroxypropyl methylcellulose phthalate (HPMCP) and poly(4-vinyl phenol) (P4VPh) gel. Driving force of this phenomenon was studied to reveal the specific interactions involved in the aqueous systems of aromatic polymers. Elemental analysis and XPS results suggest that F⁻ is embedded to the gel by the physical adsorption of KF, as well as the interactions between phenyl ring and F⁻. Further theoretical calculations revealed that the interaction may be (phenyl)CH?F⁻(H₂O)_n interaction, which is stronger than (phenyl)CH?(H₂O)_n hydrogen bond. This kind of interaction decreases with the increasing water number and it is invalid when the surrounding water number is more than 5 for the phenol-F⁻(H₂O)_n system. Therefore, we conclude that F⁻ could bind to phenyl ring via such (phenyl)CH?F⁻(H₂O)_n interaction in solutions with low hydrophilicity. The strong polarization effect of F⁻ and (phenyl)CH?F⁻(H₂O)_n interaction are two important driving forces for the reswelling of gels.     

New crystal forms of tris(2-aminoethanolato-O,N)cobalt(III): Structures and properties

Crystal forms of cobalt(III) tris(2-aminoethanolate) hydrates, i.e., red cubic crystals of the composition fac-[Co(NH₂CH₂CH₂O)₃] · 5.44H₂O (fac-I · 5.44H₂O) and blue prismatic crystals of the composition mer-[Co(NH₂CH₂CH₂O)₃] · 3H₂O (mer-I · 3H₂O) were studied by the ⁵⁹Co, ¹³C NMR and X-ray diffraction methods. It was found that mer-[Co(NH₂CH₂CH₂O)₃] · 3H₂O (mer-I · 3H₂O) is a new pseudopolymorphic modification of fac-[Co(NH₂CH₂CH₂O)₃] · 3H₂O (fac-I · 3H₂O), while fac-I · 3H₂O represents a new polymorphic modification of the complex mer-[Co(NH₂CH₂CH₂O)₃] · 3H₂O (mer-I · 3H₂O) described previously. The comparative analysis of the spectra revealed dynamic equilibrium between these geometric isomers; the fac-isomer is stable in aqueous solutions.     

Crystal structure of calcium dihydroethylenediaminetetraacetate(2-) dihydrate Ca(H2Edta)·2H2O

The crystals of Ca(H₂Edta)·2H₂O (orthorhombic system, a = 8.5919(7) Å, b = 17.807(2) Å, c = 18.941(2) Å; Z = 8, space group Pbca) precipitate from solutions of Na₂H₂Edta·2H₂O and CaCl₂. The Ca atom is surrounded by the oxygen atoms of the water molecule and the carboxyl groups of the five neighboring H₂Edta^2? anions with protonated nitrogen atoms (distorted octahedron). As a result, a three-dimensional framework of [Ca(H₂O)H₂Edta)] with built-in crystal water molecules is formed.     

Infrared study of magnesium–nickel hydroxide solid solutions

The IR spectra of the co-precipitated solid solutions Mg_xNi_1−x(OH)₂ were studied in the 4000–40 cm⁻¹ region. The spectra as a whole resemble those of Mg(OH)₂ and β-Ni(OH)₂, while certain differences are noted when compared with the spectra of the mechanically mixed samples Mg(OH)₂+β-Ni(OH)₂. Such a behavior may imply formations of mono-phase solid solutions which have a brucite-like crystal structure. The composition-dependent band shifts were observed for the fundamentals and this tendency is discussed in terms of polarization of the OH bond and partial covalency of the MO bonds. The gradual changes in band position of Mg_xNi_1−x(OH)₂ (1.00≥x≥0.00) were used to assign the IR active lattice modes of the solid solutions and to review the assignment of β-Ni(OH)₂.     

Experimentelle Bestimmung der Kristallkeimgröße bei übersättigten Natriumthiosulfatlösungen

The present work offers experimental results on the problem about the size of crystal nuclei of supersaturated solutions. Two supersaturated Na₂S₂O₃·5 H₂O solutions were separated by a porous membrane, whose average pore diameter was varied (from 120 μ to 10–15 mμ). The crystallization was called forth in one of the solutions. Experiments showed that with pore dimensions of the order of 10–15 mμ, the second supersaturated solution does not crystallize. The average pore diameter thus estimated coincides with the one found for supersaturated Na₂SO₄·10 H₂O solutions. It is of the order of theOstwald crystal nucleus (ca. 1 mμ), and that, calculated byGorbatschew andSchlikow (1,2–3,0 mμ), and similar to the size of crystal nuclei given byGopal (ca. 10 mμ).     

Density of N<Subscript>2</Subscript>O Solutions in Perfluorodecalin As a Function of Concentration

The dependence of density ρ of nitrogen oxide N₂O solutions in perfluorodecalin on the N₂O concentration is measured. At a constant temperature, this dependence has a linear character: ρ = аx + b. Coefficients a and b are tabulated for five temperatures: 293, 298, 303, 313, and 328 K. These data allow us to control the N₂O concentration in perfluorodecalin.     

Synthesis and study of solid solutions between cobalt and nickel phosphates with varied degree of anion protonation

Continuous substitutional solid solutions between cobalt and nickel phosphates with varied degree of anion protonation were obtained: Co_1?x Ni _x HPO₄·1.5H₂O and (Co_1?x Ni _x )₃(PO₄)₂·8H₂O, where 0 ≤ x ≤ 1.00. The thermolysis of the solid solutions was studied by the example of Co_1?x Ni _x HPO₄·1.5H₂O. The phases synthesized were compared with the previously described continuous solid solution Co_1?x Ni _x (H₂PO₄)₂·2H₂O.     

Kinetic isotope effects for oxidation reaction of olefins by p-quinones in water-acetonitrile solutions of cationic and chloride anionic palladium complexes

Kinetic isotope effects for oxidation reactions of ethylene and cyclohexene in solutions of cationic palladium(ii) complexes in MeCN-H₂O(D₂O) systems, were measured. It was established that the ratio of the initial reaction rates ${{R_0^{H_2 O} } \mathord{\left/ {\vphantom {{R_0^{H_2 O} } {R_0^{D_2 O} }}} \right. \kern-0em} {R_0^{D_2 O} }} $ is equal to 1 for both reactions with the use of cationic complexes of the type Pd(MeCN) _x (H₂O)_4?x ²⁺, which differs from oxidation reactions catalyzed by chloride palladium complexes in the same solutions, where the ratio ${{R_0^{H_2 O} } \mathord{\left/ {\vphantom {{R_0^{H_2 O} } {R_0^{D_2 O} }}} \right. \kern-0em} {R_0^{D_2 O} }} $ = 5.0±0.16 and 4.73±0.14 at H⁺ molar fraction of 0.48 and 0.16, respectively (H⁺ molar fraction was calculated based on the sum of [H⁺] and [D⁺]).     

Thermogravimetric investigation of the dehydration thermodynamics of amorphous silica after its hydrothermal and thermovaporous treatment

After hydrothermal and thermovaporous treatment of chemically pure amorphous aqueous silicic acid in solutions of NaOH and NH₄OH and in water vapour it is possible, using complex thermal analysis, to detect the weight loss and heat effects corresponding to evaporation of various forms of combined water, and to estimate the heats of evaporation of these forms. From the obtained data, the following water forms have been identified: (1) at 200–300° capillary-condensed water formations of the cluster type evaporate;ΔH _deh is about 8 kcal/mole H₂O; (2) at 250–400°, molecules of water linked by hydrogen bonds with hydroxyl groups on the surface and in the volume of the particles;ΔH _deh. is about 5 kcal/mole H₂O; (3) at 350 600°, molecules of water coordinated to silicon atoms in the volume of the particles;ΔH _deh is approximately 1 kcal/mole H₂O. The total evaporation heat changes from 10 kcal/mole H₂O when water of form 1 predominates, to 5 kcal/mole H₂O when forms 2 and 3 predominate.     

X-ray powder diffraction study of monoclinic V-ZrO2 solid solutions obtained from gels

Rietveld refinement of six monoclinic V_xZr_1−xO₂ solid solutions, with x=0, 0.01, 0.02, 0.05, 0.075 and 0.1, prepared by heating dried gel precursors at 1300°C in air atmosphere, has been characterized using X-ray powder diffractometer data. The present results confirm that crystal structure of these solid solutions contain V⁴⁺(Zr⁴⁺) cations surrounded by seven oxygens, four at a distance between 2.13 and 2.28 Å (referred as to O(2) in the tetrahedrally coordinated oxygens) and other three at a distance between 2.03 and 2.20 Å (denoted as O(1) in the triangularly coordinated oxygens). The trends in the lattice parameter variation of V_xZr_1−xO₂ solid solutions specimens with the nominal vanadium amount are in accordance with previous results obtained by experiments measured using an internal standard.     

Spectroelectrochemical behaviour of water bounded Chl a in the presence of various acceptors

The spectroelectrochemical behaviour of non-aqueous solutions containing (Chl a·H₂O)₂ and (Chl a·2 H₂O)_n, used as models for P 700 and P 680, respectively, is reported. The potential associated with the electron-transfer processes and the kind of electrode reactions in the presence of substances (benzylviologen and dichlorophenolindophenol) used as a specific acceptor for photosystems I and II were studied. To carry out the measurements, a thin-layer spectroelectrochemical cell with a platinum optically transparent electrode was used.     

Dependence of nanophase separated structure of epoxy hydrogels on swelling conditions investigated by SANS

A hydrophilic non-stoichiometric epoxy network was prepared by end-linking reaction of α,ω-diamino terminated poly(oxypropylene)-b-poly(oxyethylene)-b-poly(oxypropylene) (POP-POE-POP) and diglycidyl ether of Bisphenol A propoxylate (PDGEBA) at the excess of amino groups. Series of epoxy hydrogels swollen to various degrees was prepared by swelling of the epoxy network in D₂O and solutions of inorganic salt (KNO₃) in D₂O, respectively, and investigated by small-angle neutron scattering (SANS). Degree of swelling was controlled in two ways: by partial evaporation of the solvent and by KNO₃ concentration in the swelling solution. Nanophase separated structure of all hydrogels was confirmed by SANS. Scattering data were fitted to the Teubner-Strey model assuming bicontinuous locally lamellar structure of the hydrogels. Changes in SANS profiles induced by the presence of KNO₃ in swelling solutions reflect a refinement of the nanophase separated structure of hydrogels caused by improvement of POE-D₂O interaction by means of breakage of deuterium-bonded structure of D₂O by nitrate anions.     

Vanadotungstate isopolyanions with V: W = 4: 2 in aqueous solutions and in crystalline salts

Polycondensation in solutions containing HVO ₄ ^2? and WO ₄ ^2? ions in the 4: 2 ratio and the overall concentration c _v+w ⁰ = 5 × 10^?3 mol/l is studied. Speciation diagrams for individual and mixed vanadium(V) and tungsten(VI) polyanions are plotted based on the results of simulation for pHs 2–13 (Z = 0–3.50) on the nitrate ion background. The 6-isopolyvanadotungstate formed in the solutions retain the initial V: W ratio. The concentration formation constants for the vanadotungstate isopolyanions in aqueous solutions are determined. Compounds Tl₆V₄W₂O₁₉ · 5H₂O, Pr₂V₄W₂O₁₉ · 14H₂O, and Na₅HV₄W₂O₁₈ · 27H₂O are synthesized. Their formulas are identified using chemical analysis and IR spectroscopy.     

Diffusion and localization of o-Ps in D2O determined from positron annihilation in SDS micellar solutions

A microscopic diffusion model is presented for the determination of orthopositronium (o-Ps) lifetime in micellar solutions. Among other parameters, the lifetime density function depends on the o-Ps diffusion coefficient in the water phase. Orthopositronium diffusion coefficients are determined by fitting this lifetime density function to positron annihilation spectra obtained from 1 mol/dm³ solution of sodium dodecylsulphate (SDS) in D₂O at different temperatures. The activation energy of the o-Ps diffusion in D₂O obtained from an Arrhenius plot as E_a = 0.9₂₂ ± 0.1₀₃ eV indicates strong localization.