Solvation of Ions. II. Use of a Variable Solvation Number for K+

Gibbs free energies of transfer of K(I) ion from water to water-dimethyl sulfoxide mixtures corrected to zero ionic strength have been used to deduce information concerning states of solvation of K+ ion in the purely aqueous phase and in the mixed solvent phase. It was found that the largest number of water molecules which needed to be assigned to the solvent cage of K+ was 11 in either phase. The partition equilibrium constant, /?0, for the distribution of K(H20)H+ between the two phases was found as a function of the mole fraction of dimethyl sulfoxide in the mixed solvent phase. The largest number of dimethyl sulfoxide molecules which needed to be assigned to the solvent cage was 10. The number of solvent molecules in the solvent cage was allowed to be variable and the overall formation constants of all K(H20)j((CH3)2S0)k+ ions contributing to the free energy of transfer were determined. The results are compared with the results from molecular dynamics computer simulations for K+ where possible

Solvation of Potassium Ion in Water and in Water-Dimethyl Sulfoxide Mixtures

A model has been obtained for the solvated K+ ion in the solvents named in the title using a modified Covington approach. The solvation number an this model was determined to be 14 of which 6 molecules were found to be unique and which were assigned to the inner solvation shell. These 6 inner solvent molecules were unique in that the stepwise formation constants for replacement of water by dimethyl sulfoxide were found to be given by the first stepwise formation constant Ki, and the statistical factors in the first six stepwise formation constants. The remaining eight solvent molecules were assigned to an outer solvation shell. Their stepwise formation constants for replacement of water by dimethyl sulfoxide were given by Ki, statistical factors and a power of a parameter k which determines changes in the free energy of the stepwise formation reaction exclusive of contributions from changing statistical factors. The stepwise formation constants (Ko to Ku inclusive) and the free energies of transfer of each of the 15 specie KWi4-iDi+ (i = 0,l,...,14) were used to compare the calculated free energies of transfer of K+ from water (W) to water (W) — dimethyl sulfoxide (D) mixtures with the experimental values. The agreement was satisfactory

Solvation of Chloropentaamminecobalt(III) Ion in Water-Dimethyl Sulfoxide Mixtures

The composition of the solvation shell of chloropentaamminecobalt(III) was investigated for water + dimethyl sulfoxide solvent mixtures using the Gibbs free energy of transfer and PMR solvent line broadening data. Strong evidence was found for the formation of solvated species with a unique dimethyl sulfoxide molecule in the solvation shell, which substantiates a previous conclusion concerning the existence of such species