EFFECT OF PREFERENTIAL SOLVATION ON GIBBS ENERGIES OF IONIC TRANSFER

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.