AN AB-INITIO STUDY RESULTING IN A GREATER UNDERSTANDING OF THE HSAB PRINCIPLE

The quantitative applicability of the hard-soft acid-base (HSAB) principle has been tested. Complexes of HF and Ag+ with several bases (HF, HCl, HBr, H2O, H2S, H2Se, NH3, PH3, and AsH3) have been studied at the HF, MP2, and QCISD(T) levels with 6-311+G** basis sets. Ab initio pseudopotential calculations have been performed for the molecules containing heavier elements, viz., Br, Sg, As, and Ag+. For the hard acid HF, the HSAB principle has been found to be valid even at the HF level. Correlation is important for soft-soft interactions. The maximum hardness principle has been found to be valid for reactions of HF. Reactions of hard acids like H+, Li+, and Na+ have also been studied at the MP2/6-311+G** level. Out of 45 reactions studied, there are only five reactions which are not in conformity with the HSAB principle.