Effect of preferential solvation on Gibbs energies of ionic transfer

Abstract

It is shown that the transfer potential of the Rb⁺ ion between water and 1,2-dichloroethane is strongly influenced by ion pairing in the organic phase. Ab initio calculations of the energy of the Rb⁺–TPB^– ion pair for different interionic distances leads to a contact ion-pair interionic distance of 0.36 nm. The very large differences in the transfer potential of Rb⁺ observed between organic solutions containing tetraphenylborate (TPB^–) and tetrakis(4-chlorophenyl)borate (TPBCl^–) are due to preferential solvation of the phenyl rings of the p-chloro derivative. These effects are likely to be present in systems where the size of the ionic components is greater than that of the solvent.