Solvation of monatomic cations by polar solvents and the mean spherical approximation

The Gibbs solvation free energy ΔGisolv for monatomic cations of alkali metals and alkaline earth metals with a charge zi in six protic and ten aprotic dipolar solvents were analyzed in terms of the simplified Fawcett’s model based on the mean spherical approximation (MSA). Excellent linear relationships between −zi2/ΔGisolv and the ion radius ri were found resulting in the determination of fdd and δs correction terms from slopes and intercepts, respectively. It was shown that the fdd term increases with a dimensionless parameter describing dipole–dipole interactions and the δs term decreases with the empirical solvent parameter β describing the hydrogen-bond acceptor basicity. The role of these terms and their mutual relations are discussed.