Statistical Analysis of Gibbs Energies of Transfer of Cations and Soft Solvent Parameters

Gibbs energies of transfer of the cations Li+, Na+, K+, Rb+, Cs+, Ag+, Tl+, Ba2+, Cu2+, Cd2+, Pb2+ and Hg2+ from water as reference into up to 42 non-aqueous solvents were analyzed by a statistical procedure based on the spectral theorem. The data set had to be separated into three groups. The first group included the alkali metal cations and Ba2+, the second Tl+, Cd2+ and Pb2+ and the third group Ag+ and Hg2+. Analysis of the respective subgroups yielded classification schemes for solvents versus the individual groups of cations. The respective solvent parameters derived from statistical analysis for the subgroups did not depend on each other. Correlations with solvent parameters claiming to account for “solvent softness” were only found for the parameters derived from the subgroup consisting of Ag+ and Hg2+. A mere separation into “hard and soft solvents” was found to be insufficient to account for the experimental data.