Matching between Lewis acids and Lewis bases on the basis of quantitative softness values and their relation with the stability of the complexes—I

Abstract

The quantitative values of softness of Lewis bases, E m ‡ , and of Lewis acids, E n ‡ , have been calculated. The difference in the values of E n ‡ and E m ‡ , derived for a complex formed between a Lewis acid and base has been designated by ΔE nm ‡ . The stability of the complexes in terms of ΔE nm ‡ values has been expressed by “Matching Constant” which is represented by the following relations for different type of metal ions: |E n ‡E m ‡| fo non-transition metal ions, |E n ‡E m ‡| + CFSE for transition metal ions, |E n ‡E m ‡| + βY for metal ions having predominant covalent preference, and |E n ‡E m ‡|+( 1 10 )· CFSE for lanthanides. The matching con values have been found to be directly related to the thermodynamic stability (log k) of metal complexes.