Solvent coordination and free energies of transfer of cations in dipolar aprotic solvents

Abstract

The free energies of transfer of Li⁺, Na⁺ and Ag⁺ between dipolar aprotic solvents and their mixtures have been estimated from e.m.f. measurements using appropriate electrochemical cells. These are compared with values calculated from measured stability constants for coordination of the ions with the solvents involved, assuming that interaction energies outside the first coordination sphere are independent of the solvent. The values obtained by the two methods agree within experimental error over a range of free energies of transfer covering some 28 kcal mol^–1, and for a variety of solvents, including dimethylsulphoxide, dimethylacetamide, acetonitrile, propylene carbonate and dimethylthioformamide. The results support strongly an earlier suggestion that changes in the free energies of transfer of cations between dipolar aprotic solvents can be accounted for entirely by changes in the energy of coordination of the ions with the solvents.