Solvation of ions. XXII. Solvation of cations by hard N,N-dimethylformamide and soft N,N-dimethylthioformamide

Abstract

The free energies of transfer of some univalent cations from N,N-dimethylformamide to N,N- dimethylthioformamide at 25º are Li⁺, 64.0; Na⁺, 50.2; K⁺, 37.2; Cs⁺, 23.4; TI⁺, -4.2 and Ag⁺, - 87.0 kJ g-ion^-1. The values are based on the assumption of negligible liquid junction potential in an electrochemical cell. Certain ones of these values can be interpreted in terms of general interactions of hard and soft cations with hard and soft basic solvents. A linear free energy relationship, ΔG_tr(M⁺) = mΔG_tr(K⁺), is roughly obeyed by many cations for transfer to a variety of solvents. Deviations from this relationship, for example ΔG_tr(Ag²⁺) to acetonitrile, ΔG_tr (Ph₄As⁺) to water and ΔG_tr (Ag⁺) to N,N-dimethylthioformamide, allow specific solvation mechanisms to be detected.