Temperature and Concentration Dependence of the Electrical Conductance,Diffusion, and Kinetics Parameters of the Ions in Aqueous Solutions of Sulfuric Acid,Selenic Acid,and Potassium Tellurate

The temperature and concentration dependences of the electrical conductance of aqueous solutions of sulfuric acid, selenic acid, and potassium tellurate were studied. The coefficients of the corresponding empirical equations were determined, and the values of equivalent conductances of the anions were evaluated at infinite dilution at the experimental temperatures. The values of the coefficients in the Fuoss and Onsager equation were evaluated for the three electrolytes at 298 K. The values of the molecular and ionic coefficients of self-diffusion at infinite dilution were calculated in the temperature range 288–318 K. The change of the translational energy Δ E∘_tr. of water molecules in the ionic hydration sphere was determined. The number of water molecules participating in the ionic hydration sphere at 298 K and the changes of Gibbs free energy, enthalpy, and entropy of activation of ionic conductance were calculated. The results obtained were interpreted according to the Samoylov’s theory of positive and negative hydration of ions. The differences observed in the temperature dependences of the mentioned parameters were explained in terms of the different radii and hydration numbers of the ions.     

A structural study of saturated aqueous solutions of some alkali halides by X-ray diffraction

The structure of nearly saturated or supersaturated aqueous solutions of NaCI [6.18 mol (kg H₂O)^–1], KCI [4.56 mol (kg H₂O)^–1], KF [16.15 mol (kg H₂O)^–1] and CsF [31.96 mol (kg H₂O)^–1] has been investigated by means of solution X-ray diffraction at 25°C. In the NaCI and KCI solutions about 30% and 60%, respectively, of the ions form ion pairs and the Na⁺–Cl^– and K⁺–Cl^– distances have been determined to be 282 and 315 pm, respectively. The average hydration numbers of Na⁺ and Cl^– ions are 4.6 and 5.3, respectively, in the NaCI solution and those of K⁺ and Cl^– ions in the KCI solution are both 5.8. In the KF solution, clusters containing some cations and anions, besides 1:1 (K⁺–F^–) ion pairs, are formed. The K⁺–F^– interatomic distance has been determined to be 269 pm, and nonbonding K⁺...K⁺ and F^–...F^– distances in the clusters are 388 and 432 pm, respectively, and the average coordination numbers n _KF , n _KK and n _FF have been estimated to be 2.3, 1.9, and 1.6, respectively. In the highly supersaturated CsF solution an appreciable amount of clusters containing several caesium and fluoride ions are formed. The Cs⁺–F^– distance in the cluster has been determined to be 312 pm, while the nonbonding Cs⁺...Cs⁺ and F^–...F^– distances are estimated to be 442 and 548 pm, respectively, the distances being about and times the Cs⁺–F^– distance, respectively. The coordination numbers n _CsF , n _CsCs , and n _FF in the first coordination sphere of each ion are 3.3, 2.3 and 5.3, respectively, and the result shows the formation of clusters of higher order than 1:1 and 2:2 ion pairs. These ion pairs and clusters may be regarded as embryos for the formation of nuclei of crystals and the results obtained in the present diffraction study support observations for the nucleation of the alkali halide crystals studied by molecular dynamics simulations previously examined.     

Spectrophotometric and potentiometric investigations of the H2PO 4 − -HPO 4 2− equilibrium at elevated pressure and temperature

The second dissociation reaction of phosphoric acid has been studied Raman spectrophotometrically and potentiometrically at pressures up to 100 MPa and temperatures up to 473.2 K in solutions with ionic strengths from 0.3 to about 1.0 mol-kg^–1. Molalities, of orthophosphate salts from 0.005 to 0.1 mol-kg^–1 have been used. The changes of the widths at half-height and the Raman shifts for both H₂PO ₄ ^– and HPO ₄ ^2– ions with changing variables of state are reported. Stoichiometric equilibrium constants for the second dissociation reaction are evaluated.     

Intradiffusion coefficients for perchlorate ions in zinc perchlorate and zinc chloride solutions at 25°C: Comparing transport properties of zinc chloride and zinc perchlorate systems

Intradiffusion coefficients for³⁶ClO ₄ ^– have been measured in solutions of zinc perchlorate of concentration 0.1 to 3 mol dm^–3 at 25°C by the diaphragm cell technique. In addition, intradiffusion coefficients for perchlorate ions in zinc chloride solutions have been measured over a concentration range at 25°C. The results confirm previous work on the effect of complexation on diffusion in zinc chloride solutions above a salt concentration of 0.1M. The present data, together with literature data for diffusion coefficients of the other species present in the zinc perchlorate electrolyte system, have enabled a simple analysis of the hydration around the zinc ions to be carried out. This indicates that the water diffusion data are consistent with the zinc ions having an effective hydration sphere of 11 (±2) water molecules. This is in keeping with values obtained for other simple divalent electrolytes using the same model. The model is extended here to allow analysis of water diffusion in zinc chloride solutions taking into account the presence of complexed chloro-zinc species. The experimental data are consistent with the effective hydration of the chloro-zinc complexes being independent of the number of chloride ligands and equal to 18±3 over a concentration range of 0 tol mol-dm^–3. This postulate is discussed in terms of its consequences on the water ligand dynamics for the complex equilibria.     

Partial Molar Volumes of Tetraalkylammonium Ions in N, N-Dimethylformamide

The densities of tetraalkylammonium bromide, R₄NBr (R = Et, Pr, Bu, Hex, Hep, Oct), solutions in dimethylformamide have been measured for the composition range (0.05–0.4) mol-kg⁻¹ at 25 ^∘C. Apparent molar V_φ and limiting partial molar volumes ⫫₂^o of the electrolytes have been evaluated. Using the extrapolation values, the limiting partial molar volumes of the tetraalkymammonium ions (⫫_i^o) have been calculated. Analysis of different contributions to the ionic ⫫_i^o indicated partial penetration of solvent molecules into the van der Waal’s volume of tetraalkylammonium (TAA) ions.     

The synergistic effect of cobalt-dicarbollide anions on the extraction of M lanthanide cations by Calix[4]arenes: a molecular dynamics study at the water–‘oil’ interface

We report molecular dynamics studies on the effect of CCD^– (chlorinated cobalt-dicarbollide) anions on the Eu³⁺ lanthanide cation extraction by a calix[4]arene-CMPO ligand L, focusing on the water–‘oil’ interface, where ‘oil’ is modelled by chloroform. The free L ligand and its EuL³⁺ complex are found to adsorb and to concentrate at the interface, but are too hydrophilic to be extracted. Addition of CCD^– anions in diluted conditions (either covalent linked to L or as separated CCD^– H₃O⁺ ions) also leads to adsorption of these species at the interface. However, at high concentrations, CCD^– anions saturate the interface and promote the extraction of EuL³⁺ to the oil phase. Another important feature concerns the uncomplexed Eu(CCD)₃ salt: accumulation of CCD^– anions at the interface creates a negative potential which attracts the hydrated Eu³⁺ ions, therefore facilitating their complexation by interfacial ligands. These features allow us to better understand the synergistic effect of lipophilic anions in the assisted liquid-liquid extraction of trivalent M³⁺ lanthanide or actinide cations. To cite this article: B. Coupez, G. Wipf, C. R. Chimie 7 (2004).

Résumé

Synergie due aux anions dicarbollides lors de l’extraction d’ions lanthanides M³⁺ par des calix[4]arènes : simulations de dynamique moléculaire à l’interface eau–« huile ». Nous étudions par simulations de dynamique moléculaire l’effet de synergie dû aux anions CCD^– (cobalt-dicarbollides) lors de l’extraction de Eu³⁺ par un calix [4]arène L, en se focalisant sur l’interface eau–« huile », l’huile étant modélisée par du chloroforme. On montre que le ligand L et son complexe EuL³⁺ s’adsorbent à l’interface, mais sont trop hydrophiles pour être extraits. L’addition d’anions CCD^– (qu’ils soient sous la forme d’ions CCD^– H₃O⁺ séparés ou greffés de façon covalente au calixarène) conduit aussi à l’adsorption de ces espèces à l’interface. Cependant, aux plus fortes concentrations, les anions CCD^– saturent l’interface et induisent l’extraction du complexe EuL³⁺ vers l’huile. Un autre résultat remarquable concerne les sels Eu(CCD)₃ : l’accumulation des anions CCD^– à l’interface y crée un potentiel négatif, ce qui attire les cations Eu³⁺ et facilite ainsi leur complexation par des ligands à l’interface. Ces résultats permettent de mieux comprendre l’effet de synergie dû aux anions CCD^– lors de l’extraction d’ions lanthanides ou actinides M³⁺ et, d’une manière générale, ce qui se passe à l’interface entre l’eau et des liquides non miscibles. Pour citer cet article : B. Coupez, G. Wipf, C. R. Chimie 7 (2004).     

Effects of inorganic salts on the properties of aqueous poly(vinylpyrrolidone) solutions

Cloud point curves and temperatures have been determined for aqueous solutions of poly(vinylpyrrolidone) at several concentrations for a variety of inorganic salts (phosphates, monohydrogen phosphates, sulfates, carbonates, dihydrogen phosphates and fluorides). The resulting dependency of the critical temperatures (mostly between 289 and 350 K) on the molar concentration can be expressed as sequences showing the decreasing effect of anion species or cation species in salting out the polymer. The decreasing order of effectiveness of the anions in reducing the temperatures is PO ₄ ^3– >HPO ₄ ^2– >SO ₄ ^2– CO ₃ ^2– >H₂PO ₄ ^– >F^–. The order for cation is Na⁺>K⁺. The changes brought about in temperatures by the salts were found to be the results of the changes taking place in the hydrophilic and hydrophobic interactions among polymer, solvent and additive salts and of the change of water structure by structure making or structure breaking ions, and of the influence of salts on the hydration sheath of the polymer.Deceased     

A B3LYP study on counterpoise-corrected geometry optimizations for hydrated complexes of [K(H2O)n] and [Na(H2O)n]

We report the basis set dependencies and the basis set superposition errors for the hydrated complexes of K⁺ and Na⁺ ions in relation to the recent studies of the KcsA potassium channel. The basis set superposition errors are estimated by the geometry optimizations at the counterpoise-corrected B3LYP level. The counterpoise optimizations alter the hydration distances by about 0.02–0.03 Å. The enthalpies and free energies for K⁺ + n(H₂O) → [K(H₂O)_n]⁺ and Na⁺ + n(H₂O) → [Na(H₂O)_n]⁺ (n = 1–6) are compared between the theoretical and experimental values. The results show that the addition of diffuse functions to K, Na, and O species are effective. However, it is also found that the counterpoise corrections using diffuse functions work so as to underestimate the free energies for the complexes with increasing the hydration number. The stabilization energies in aqueous solution are larger for a Na⁺ ion than for a K⁺ ion, suggesting the contributions of their dehydration processes to the ion selectivity of the KcsA potassium channel. The changes in coordination distance between the isolated [K(H₂O)₈]⁺ and the [K(H₂O)₈]⁺ in the KcsA potassium channel indicate the importance of hydrogen bondings between the first hydration shell and the outer hydration shells.     

Genesis of phase composition of supported Al?Fe?O catalysts

XPS, ESR and ESDR methods have been used for studying Al–Fe–O catalysts calcined at 620–1270 K. -Al₂O₃ interaction with impregnating solutions of iron oxalate complexes was shown to lead to the formation of isolated Fe³⁺ ions, and supported phases of solid solutions and associates at 620–820 K.     

Structural Characteristics of Hydrated Complexes of Aminoacids in Aqueous Solutions

Aqueous solutions of nine α-aminoacids were studied in a diluted range of concentrations (from 0. 01 m to 0.1 m) at 5°C, 15°C, 25°C, 35°C, and 45°C based on the model that uses molar adiabatic compressibility (β _s V _m ) as a measure of hydration of the solute. For the resulting hydrated complexes of aminoacids, structural characteristics have been determined. At increased concentrations of the acid, variation of its hydration number is the chief factor affecting the molar compressibility of the hydrated complex.Original Russian Text Copyright © 2004 by V. N. Afanasiev, E. Yu. Tyunina, and V. V. Ryabova__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 883–888, September–October, 2004.     

Specific Structural Features of Concentrated Aqueous Solutions of Potassium Iodide in a Wide Temperature Range

The structural characteristics of concentrated aqueous solutions of KI under the conditions of isobaric heating (P 20 MPa, T 298–623 K) were studied by the method of integral equations. As the temperature is increased, the continuous tetrahedral network of hydrogen bonds in the KI:15H₂O solution is destroyed (at 323 K); in the KI: 8H₂O solution, this network is not formed in the entire temperature range. The number of intermolecular H bonds in the systems appreciably decreases on heating. With increasing temperature, the influence exerted by the salt concentration on the intrinsic solvent structure becomes weaker. In both solutions, heating results in significant destruction of the first hydration shell of the K⁺ ion. At the same time, the nearest environment of the I⁻ ion becomes more structured on heating to 473–523 K. On further heating, however, the first hydration shell of the anion is destroyed. Heating exerts virtually no effect on the amount of contact ion pairs in the KI:15H₂O solution but decreases the content of contact associates in the KI:8H₂O solution.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 2, 2005, pp. 211–219.Original Russian Text Copyright © 2005 by Fedotova, Gribkov, Trostin.     

Ion association studies in aqueous NiSO4 solutions by positron lifetime spectroscopy

Ion association has been studied by positron lifetime spectroscopy in aqueous solutions containing the Ni²⁺ and SO ₄ ^2– ions at 294 K with the double aim of assessing the reliability of the method for quantitative determination of complex formation constants and of probing the validity of various expressions to calculate single-ion activity coefficients at high ionic strength. The existence of two complexes, identified as NiSO₄ and Ni₂SO ₄ ²⁺ , is shown by the data analysis. Considering the formation constant of the former, K_I=(196±10)M^–1, determined in previous works leads to discarding several of the expressions commonly used for activity corrections. Two possible values are retained for K_I, (193±20)M^–1 and (179±20)M^–1, while K_II related to Ni₂SO ₄ ²⁺ is better defined, as (2.57±0.14)M^–1.     

Isotope Effect on Fractional Dilatability of Solute Water as an Indicator of the H-Bonding Ability of an Aprotic Dipolar Solvent

Based on experimental data about the density of very dilute solutions of H₂O and D₂O in 1,4-dioxane, hexamethylphosphotriamide, and acetonitrile at 278.15 K-318.15 K we determined the limiting partial molar volume (error ±0.03 cm³·mol⁻¹) and dilatability of the water component. A correlation equation has been derived which relates the isotope effect (IE) in the limiting excess partial molar dilatability of water to the energy of the H₂O-solvent hydrogen bond. The stated IE may be used as a “structural indicator” for evaluating the ability of an aprotic dipolar solvent to undergo specific interactions through hydrogen bonding.Original Russian Text Copyright © 2004 by E. V. Ivanov, V. K. Abrosimov, and E. Yu. Lebedeva__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 1020–1026, November–December, 2004.     

Aqueous partial molar heat capacities and volumes for NaTcO4 and NaReO4

A flow microcalorimeter/densimeter system has been commissioned to measure heat capacities and densities of solutions containing radioactive species as a function of temperature. Measurements were made for NaTcO₄(aq) at six temperatures (189.15 K to 373.15 K for the heat capacities, 287.43 K to 396.67 K for the densities) over the molality range 0.01 to 0.29 mol-kg^–1. Measurements for NaReO₄(aq) (NaReO₄ is a common nonradioactive analogue for NaTcO₄) were made under similar conditions, but for eight temperatures and a more extensive range of molalities, 0.05 to 0.65 mol-kg^–1. Heat capacities of NaCl(aq) reference solutions were also measured from 293.15 K to 398.15 K.The heat capacity and density data are analysed using Pitzer's ioninteraction model. Equations for the apparent molar heat capacities and volumes are reported. Values of the NaReO₄(aq) partial molar heat capacities are compared to literature values based on integral heats of solution. The agreement between the two sets of NaReO₄ results is good below 330 K, but only fair at the higher temperatures. Values of the partial molar volumes have also been derived. Using literature values and the results of our experiments, it is calculated that the disproportionation of hydrated TcO₂(s) to form TcO ₄ ^– (aq) and Tc(cr) occurs more readily at high temperatures. The uncertainties introduced by using thermodynamic values for ReO ₄ ^– (aq), in the absence of values for TcO ₄ ^– (aq), are discussed.     

Intradiffusion coefficients of all species in aqueous gallium perchlorate solutions and solution viscosities at 25°C

Intradiffusion coefficients of all species (cation, anion and solvent) and viscosities have been measured for aqueous solutions of gallium perchlorate in the concentration range 0–2.3 mol-kg^–1 at 25°C. The perchlorate ion intradiffusion measurements were made using³⁶ClO ₄ ^– as the tracer species in diaphragm cell experiments. The development of a method to synthesize³⁶ClO ₄ ^– from³⁶Cl^– by electrolysis is described. The perchlorate intradiffusion coefficients results show a concentration dependence that is very similar to that for D(Cl^–) in corresponding trivalent metal chloride solutions. A simple hydration analysis based on all the transport results estimates a total (effective) cation hydration for gallium within a 0–2 mol-kg^–1 range of 10 (±1.5).     

Dissolution and extraction of actinide oxides in supercritical carbon dioxide containing the complex of tri-n-butylphosphate with nitric acid

Dissolution of individual actinide oxides (Th, U, Pu, Np), or their mechanical mixtures, as well as of solid solutions U–Pu, U–Np, U–Am and U-Pu-Eu oxides in supercritical fluid carbon dioxide (SF-CO₂) containing the complex of tri-n-butyl phosphate (TBP) with nitric acid (TBP–HNO₃) has been investigated. The effect of the calcination temperature of solid solutions of dioxides on the separation of actinides during supercritical fluid extraction (SFE) has been studied as well. It was shown for the first time that milligram amounts of uranium dioxide could be quantitatively dissolved in (SF-CO₂) containing the TBP–HNO₃ complex and efficiently separated from Pu, Np, and Th during SFE of mechanical mixture of these oxides. On the contrary, both U and Pu are quantitatively dissolved in SF-CO₂–TBP–HNO₃ during SFE from solid solutions of U–Pu dioxide. An increase of the calcination temperature of the mixed U(IV)–Pu(IV) dioxide from 850 to 1200 °C has no influence on the relative extraction yield of these actinides during SFE. To cite this article: T. Trofimov et al., C. R. Chimie 7 (2004).

Résumé

Dissolution d’oxides d'actinides et extraction d’éléments dans le dioxide de carbone supercritique contenant le complexe tri-n-butylphosphate–acide nitrique. La dissolution d’oxydes de Th, U, Pu et Np, de leurs mélanges et de solutions solides U–Pu, U–Np, U–Am et U–Pu–Eu dans le dioxyde de carbone supercritique (CO₂-SC) contenant le complexe tri-n-butyl phosphate–acide nitrique (TBP–HNO₃) a été étudiée, et notamment l’effet de la température de calcination des solutions solides. On montre que quelques milligrammes de UO₂ peuvent être dissous dans le système CO₂-SC–TBP–HNO₃ et être séparés de Pu, Np et Th en traitant un mélange d’oxydes. En revanche, U et Pu sont dissous dans la phase CO₂-SC–TBP–HNO₃ durant le traitement des solutions solides U(IV)–Pu(IV). Une augmentation de la température de calcination de 850 à 1200 °C de ces solutions solides n’a pas d’effet sur le rendement d’extraction des actinides. Pour citer cet article : T. Trofimov et al., C. R. Chimie 7 (2004).     

High-pressure synthesis and structures of lanthanide germanides of LnGe5 (Ln=Ce, Pr, Nd, and Sm) isotypic with LaGe5

A series of lanthanide penta-germanides LnGe₅ (Ln=Ce, Pr, Nd and Sm) has been prepared by high-pressure (5–13 GPa) and high-temperature (500–1200 °C) reaction. CeGe₅ crystallizes in an orthorhombic unit cell (S.G. Immm (71)) with a=4.000(5) Å, b=6.192(5) Å, c=9.86(1) Å, and V=244.1(5) Å³. The new germanides are isotypic with LaGe₅ consisting of a Ge covalent network with tunnels where guest ions Ln³⁺ are situated. The network is composed of sublayers with edge-sharing Ge six-membered rings with only boat conformation. The sublayers are connected by rare eight-coordinated Ge atoms. The cell volume of the compounds systematically decreases from La to Sm compounds, except for CeGe_5, owing to the lanthanide contraction. The lattice constants of CeGe₅ are smaller than those of the Pr compound because it contains Ce⁴⁺ ions. CeGe₅ is paramagnetic above 2 K, but does not obey the Curie–Weiss law. PrGe₅ and NdGe₅ are Curie–Weiss type paramagnets with Weiss temperatures of –3.3 and –18.4 K. SmGe₅ shows an antiferromagnetic transition at 10.4 K.     

Relationship between the Structural State of Water and the Character of Ion Hydration in Concentrated 1:1 Aqueous Solutions of Electrolytes in Extreme Conditions

It is suggested that the association parameter A be used as an indicator demonstrating the effect of extremal conditions on the structure of water in the series of solutions . Analysis of the diagrams A parameter–external conditions permitted us to establish that compression has a weak effect on association of water molecules in the systems, in which case the effect of the ion field on the mutual ordering of solvent molecules does not change. In conditions of strong compression in NaCl–H₂O, positive hydration of Na⁺ changes to negative. On the contrary, at elevated temperatures, the probability of association of bulk water molecules increases and the effect of ions on the structure of the solvent decreases. Positive hydration of Li⁺ and negative hydration of K⁺ become less pronounced, and Na⁺ has no ordering effect on the structure of the solvent any longer.     

Thermodynamics of Aqueous Diethylenetriaminepentaacetic Acid (DTPA) Systems: Apparent and Partial Molar Heat Capacities and Volumes of Aqueous H2DTPA3−, DTPA5−, CuDTPA3−, and Cu2DTPA− from 10 to 55°C

Apparent molar heat capacities and volumes have been determined for aqueous solutions of the mixed electrolytes Na₅DTPA + NaOH, Na₃CuDTPA + NaOH, and NaCu₂DTPA + NaOH, and the single electrolyte Na₃H₂DTPA (DTPA=diethylenetriaminepentaacetic acid) at temperatures from 10 to 55°C. The experimental results have been analyzed in terms of Young's rule with the Guggenheim form of the extended Debye–Hückel equation and the Pitzer ion-interaction model. These calculations led to standard partial molar heat capacities and volumes for the species H₂DTPA^3–(aq), DTPA^5–(aq), CuDTPA^3–(aq), and Cu₂DTPA^–(aq) at each temperature. The partial molar properties at 0.1 m ionic strength were also calculated. The standard partial molar properties were extrapolated to elevated temperatures with the revised Helgeson–Kirkham–Flowers (HKF) model. Values for the partial molar heat capacities from the HKF model have been combined with the literature data to estimate the ionization constants of H₂DTPA^3–(aq) and the formation constant of the CuDTPA^3–(aq) copper complex at temperatures up to 300°C.     

A single crystal EPR study of VO ions doped in Cs2Co(SO4)2.6H2O Tutton salt

EPR spectra of VO²⁺ ions doped in single crystals of Cs₂Co(SO₄)₂.6H₂O single crystals have been studied at various temperatures (390–103 K) on X-band frequency. The detailed EPR analysis shows three vanadyl complexes with differing intensities. The g and A tensors are found to be axially symmetric. The intense vanadyl complexes in the lattice are found to occupy the Co²⁺ substitutional sites, whereas the weak vanadyl complex at the interstitial sites. The optical absorption spectrum at room temperature shows three absorption bands characteristic of VO²⁺ ions in tetragonal symmetry. By correlating the EPR and optical data, the molecular bonding coefficients and the Fermi contact interaction terms have been evaluated and discussed. The line broadening of VO²⁺ spectra on cooling the crystal is explained on the basis of spin-lattice relaxation narrowing. The spin-lattice relaxation time for the host Co²⁺ ions has been estimated at various temperatures.