Scrutiny of the HSAB principle in some representative acid-base reactions

A thorough quantitative analysis of the HSAB principle is performed. Comple x formation reactions of a typical soft acid, Ag+, and typical hard acid, H F, with the bases XH3 (X = N, P, As) are studied using the DFT/B3LYP method with the 6-311G** basis set. For the molecules containing Ag+ and As, corr esponding pseudopotentials are used. Results of the calculations pertaining to the interactions of the hard acid, HF, are robust in comparison to thos e of Ag+. Correlation and nuclear relaxation effects are important in the c ase of the interactions of Ag+. Basis set superposition error changes the t rend, and the results vary drastically with the quality of the basis set. P seudopotentials do not introduce any error, and the zero-point energy repre sents at most 5% of the binding energy. The presence of the solvent, modele d as in Onsager's dipole method and in PCM, does not significantly change t he trend. In the exchange reactions, both HSAB and maximum hardness princip les are shown to be valid.