CORRELATIONS BETWEEN EMPIRICAL LEWIS ACID-BASE SOLVENT PARAMETERS AND THE THERMODYNAMIC PARAMETERS OF ION SOLVATION .2. ACIDITY PARAMETERS OF CATIONS AND BASICITY PARAMETERS OF ANIONS

The parameters alpha, beta and gamma of the equation W-DELTA-SG(t)(MX) = alpha-B(KT) + beta-E(T) + gamma were calculated and analysed for different salts (MX) in pure solvents and in non-aqueous solvent-water mixtures (S). Among 109 different equations, only 64 were taken for the final analysis since in the case of 38 equations the parameters B(KT) and E(T) were highly correlated. After a statistical analysis and normalization, on the basis of the coefficients alpha and beta obtained, it was found that the ions analysed may be divided into three classes characterized by the different dependences of alpha on beta: class I, H+, Li+, Na+, Rb+, Cs+, Me4N+, Cl-, Br- and I-, where alpha-N = 1.074-beta-N + 1.639; class II, Ag+, Cl-, Br-, I-, OAc-, SCN- and N3- where alpha-N = 2.057-beta-N + 2.147; and class III, Ph4As+, BPh4-, Ph4C and Ph4Ge, where alpha-N is variable and beta-N is almost constant. Two main conclusions can be drawn out from the results obtained: the behaviour of ions considered as Lewis acids and bases reflects different hard-soft properties of the ions, and the behaviour of the Ph4As+ ions is different from that of BPh4-.