Showing papers on "Ionic radius published in 1976"

Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides

Abstract: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations. Revisions are based on new structural data, empirical bond strength-bond length relationships, and plots of (1) radii vs volume, (2) radii vs coordination number, and (3) radii vs oxidation state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In2+-X, pb2+-X, and TI+-X. Bonds with delocalized electrons and therefore metallic character, e.g. Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.

Solvent structure in aqueous mixtures. III. Ionic conductances in ethanol-water mixtures at 10 and 25°C

Abstract: Viscosities at 10 and 25°C and dielectric constants at 10°C are reported for ethanol-water mixtures. Precise transference numbers for KBr at 10°C were determined by the moving-boundary method for five solvent mixtures containing up to 20 mole % ethanol. Conductance measurements for the alkali halides and tetraalkylammonium bromides were carried out across the complete range of solvent composition at 25°C, but for the water-rich region only at 10°C. The resulting limiting ionic Walden products confirmed the conclusions arrived at from earlier measurements. The maxima occurring in the water-rich region cannot be attributed solely to a structure-breaking effect owing to the ionic size dependence which is in the wrong direction. The tetraalkylammonium ions in these mixtures do not exhibit an enhanced hydrophobic effect, nor do they appear to enhance structure of any kind. Rather, the addition of alcohol to an aqueous Bu4N+ solution merely reduces the magnitude of the hydrophobic effect, as illustrated by a steadily increasing Walden product in the water-rich region. A decrease in temperature has no effect on the Walden product for the Bu4N+ ion but increases the magnitude of the maxima for the alkali-metal and halide ions. These maxima are attributed to sorting of the solvent components by the ionic charge, due to an acid-base type interaction, so that the proportion of water in the ionic cospheres is greater than in the bulk solvents. The sorting effect is shown to be temperature independent. The oxyanions are shown to exhibit a behavior in these mixtures that cannot be identified at this time.

The effect of pressure on the physics and chemistry of potassium

Abstract: The equation of state and electronic structure of body-centered cubic potassium are investigated theoretically by the quantum-mechanical SAPW method. The results predict a series of pressure-induced electronic phase changes brought about by the sequential filling of initially unoccupied d-like electronic states. In addition to the discontinuous density changes that accompany these phase transitions, the presence of the d-like bands makes potassium extremely compressible. At pressures as low as 500 kb (0°K), the ionic radius of potassium becomes compatible with that of iron and its electronic structure becomes like that of a typical transition metal. These properties should greatly enhance the miscibility of potassium in iron or iron-sulfide melts.

Metal oxide catalytic compositions having perovskite crystal structures and containing metals of the platinum group

Abstract: Metal oxides of the type [A 1 1-x A 2 x ]B' 1-y Me y ]O 3 having perovskite-type crystal structures in which A 1 and A 2 are each one or more mono-, di-, or trivalent metals having ionic radii between about 0.8 and 1.65 Angstroms; B' is one or more metals having ionic radii between about 0.4 and 1.4 Angstroms; Me is one or more metals of the platinum group (ruthenium, osmium, rhodium, iridium, palladium, and platinum); x is between about 0.01 and 0.99; and y is between about 0.01 and 0.20 Are useful as catalysts for the oxidation of hydrocarbons and carbon monoxide and for the reduction of nitrogen oxides under conditions typical of those involved in the cleanup of the exhaust gases of internal combustion engines.

Molecular dynamics study of the effects of ions on water microclusters

Abstract: We report a molecular dynamics study of water ion microclusters. This study concerns clusters containing Na+, Rb+, Br−, and I− and up to eight water molecules, and larger clusters containing Cs+ and F− and up to 29 water molecules. For each cluster we calculated the total cluster energy, radial density functions, dipole orientations of water molecules around the ion, and effective ionic radii. The ion lowers the cluster energy by a considerable amount, depending to a great extent on the ionic radius. The ion strongly orients all of the water molecules in the cluster. The coordination numbers of the ions depend primarily on ion size and to a lesser extent on charge sign. Our calculated effective ionic radii are in reasonable agreement with the Pauling radii.

Salting out of alcohols by alkali halides at the freezing temperature

Abstract: The freezing-point depression of the ternary systems water-alkali halidesalcohols was measured with a precision Advanced Instrument osmometer. From the corresponding freezing-point depression of the binary systems the salting-out constantsk s were calculated. The effect of ionic size was investigated withtert-butanol, and the effect of alcohol chain length with NaCl. The trends ofk s with ionic size are similar to those of typical nonelectrolyte systems, andk s varies linearly with the volumes of the normal alcohols.

Crystal data for lanthanide orthophosphates

Abstract: Monoclinic unit-cell parameters for LnPO4 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy) have been redetermined from Guinier photographs, and are plotted against effective ionic radii of the lanthanides. Full powder-diffraction data are given for LaPO4 and GdPO4.

The structure of molten NaCl from a simulation model which allows for the polarization of both ions

Abstract: Two-ion-polarizable shell-model interionic potentials for NaCl are derived from solid-state data including ionic radii. Radial distribution functions for the melt are obtained from these potentials by a molecular dynamics simulation and the results are compared with recently reported measurements. Significant improvements over previous calculations based on rigid-ion potentials are found.

Electronic structure of some inorganic azides from x‐ray electron spectroscopy

Abstract: The electronic structure of some inorganic azides has been investigated by x‐ray electron spectroscopy for the purpose of contrasting the relative ionicities or degree of covalency of the alkali and heavy metal azides. Core and valence band electron spectra are presented along with deconvolutions of some of the overlapping bands. The splitting between the terminal N 1s band and the central N 1s band ΔEI for the inorganic azides has been found to be sensitive to the degree of ionicity of the respective compounds. This data when compared to some physical properties such as crystal structure, ionic radius, standard enthalpy of formation, lattice energy, and solubility provides evidence for a trend in ionicities. The observed trends indicate that the transition metal azides are considerably more covalent than the alkali or alkaline metal azides.

Studies of CeLnO/sub 3/ solid solutions and the perovskites CeLnO/sub 3/ and PrLnO/sub 3/(Ln = lanthanide elements)

Abstract: Interlanthanide perovskites CeTmO/sub 3/, CeYbO/sub 3/, CeLuO/sub 3/, PrYbO/sub 3/, PrLuO/sub 3/, and CeLnO/sub 3/ solid solutions have been prepared by cofusion techniques. Thermal stability and the optical properties of these materials have been investigated. A very important nephelauxetic effect (..delta..E = 3600 cm/sup -1/) is observed. The thermal stability of the compounds or of the solid solutions increases when the ionic radius of the Ln/sup 3 +/ decreases. The behavior of these compounds under oxidizing conditions is reported.

The crystal structure of Rb+, K+ and Na+ tetranactin complexes

Abstract: The molecular structures of several tetranactin complexes have been determined with X-ray reflexion data collected on a four-circle diffractometer. The structures of the form I crystals of the Rb + complex [space group P21/n, Z=4, a=15.927 (9), b=20.555 (14), c=15.495 (6) A~, fl=90.38 ° (3)] and K + complex were solved by the heavy-atom method, and refined by the block-diagonal matrix least-squares method: the R indices are 8.4 and 9"9 %, respectively, including H atoms. The structures of the form II crystals of the K + complex [space group C2/c, Z=8, a=27.455 (6), b= 12.420 (1), c= 30.211 (6) A, fl=97.15 ° (2)] and the Na + complex were determined by the symbolic addition procedure; the R indices were 11.1 and 11-9%, respectively, excluding hydrogen atoms. The molecular structures are approximately identical with those of the nonactin complexes in which all ethyl groups are replaced by methyl. Conformational energies of the complexes were calculated and the dependence of the cation selectivity on intra-ligand steric interactions was estimated. Strong attractive ion-dipole interactions were observed in an inverse proportion to ionic radii of the central cations. However, it was concluded that the ion selective behavior of the macrotetrolide must be closely related to the free energy of the hydration of cations in aqueous solutions.

Transference number and solvation studies in tetramethylurea

Abstract: Transference numbers of sodium and potassium thiocyanate, have been measured in tetramethylurea at 25°C by a modified Hittorf's method in the concentration range 1.5-9.4×10-2 M. A linear relationship is observed between the cation transference number and the square root of the concentration. Combining the limiting transference numbers and limiting equivalent conductances of these two salts, ionic mobilities of sodium, potassium, and thiocyanate ions have been found to be 16.08, 15.73, and 33.04 ohm-1 cm2 mol-1, respectively. From these values ionic mobilities of other univalent ions, effective ionic radii, and solvatlon numbers have been computed. Higher solvation of cations than of anions of comparable sizes is consistent with the aprotic nature of the solvent.

Growth‐Induced Anisotropy in Bubble Garnet Films Containing Calcium

Abstract: The growth‐induced anisotropy, Ku measured on (111) LPE films of Eu3−xCaxSix Fe5−xO12 grown on Sm3Ga5O12 substrates is large and positive (Ku = 4.0 to 8.1×104 ergs/cm3 for x = 0.5). Many experiments have shown that Ku in Eu3−xYxFe5−yGayO12 films is also positive. In films of compositions (YSmCa)3 (GeFe)5O12, the effects of Ca and of Y on the growth‐induced anisotropy are the same in sign and similar in magnitude. Since Ca2+ is larger in ionic radius than Eu3+ or Sm3+, whereas Y3+ is smaller, the simple site selectivity model of growth‐induced anisotropy would predict opposite signs of Ku for the Ca and Y additions. This contradiction shows that ionic radius is not the only relevant parameter which determines growth‐induced anisotropy in garnets, although size differences have been shown to account for the observed effects within the rare earth series. The charge difference between the Ca2+ ions and the rare earth ions, or the pairing of Ca2+ and Ge4+ or Si4+ ions during crystal growth may influence the si...

Effect of Counter-ions on the Thermodynamic Properties of Alkali Dodecyl Sulfates in Monomeric and Micellar Dispersions

Abstract: In order to elucidate the behavior of ionic portion as well as hydrophobic one of surfactant at solution and micelle formation with the view-point of enthalpy and heat capacity changes, the molar standard enthalpies of solution and micelle formation of lithium, sodium and potassium dodecyl sulfates (generically abr. as DMS), ΔsolH^- and ΔmH^- , were determined by calorimetry at various temperatures from 20° to 50°, and also their critical micelle concentrations, CMC's by electric conductivity measurement. The molar standard Gibbs free energy and entropy of micelle formation as well as the degree of counter-ion dissociation in micelle were calculated using thermodynamic relations from the values of CMC at various temperatures and ΔmH^- . On the basis of Born's theory, ΔsolH^- was expressed in the terms, explicitly containing the ionic radii of both dodecylsulfate anion and counter-cation, Li+, Na+, and K+, in MDS crystal and in water, and the terms, representing the hydrophobic contributions of MDS to lattice and hydration energies. The substitution of experimental and literary values into the above-mentioned expression gives, e.g. 2.2 A and 2.0 A as ionic radii of dodecylsulfate ion in crystal and in water, respectively. Also, ΔmH^- and its corresponding heat capacity, ΔmC^- , were analyzed with respect to the hydrophobic and ionic contributions to micelle formation.

Corresponding states theory for the fusion of ionic crystals

Abstract: Empirical deviations from a general thermodynamic-reduced equation of state for the orthobaric melting temperatures of alkali metal halide crystals are interpreted. A corresponding states analysis based upon reduced variables for the interaction potentials between ions shows that two limiting laws are obeyed. When the anion/cation radius ratio approaches unity the characteristic corresponding reduced length is proportional to the sum of ionic radii, but when this ratio is large, e.g. Li salts, the radius of the anion becomes the appropriate reduction parameter. The large difference in reduced melting temperatures between common-cation conformal groups can be understood by means of a first order perturbation treatment for the contribution of ion-induced dipole and short-range anion-anion iliteractions to the free energy difference between the crystalline and liquid phases of a reference salt in which these potentials are considered to be absent. Potential energy contributions due to nonconformable perturbations are found to be relatively small; this explains the observed phenomenological conformality among all the molten alkali metal halides, and many other ionic liquids, for both thermodynamic properties and linear transport coefficients.