An extension of the CNDO/2 formalism for the study of transition metal complexes

The electronic structure and the conformational analysis of some Ni(PX₃)₄ (X = F, OCH₃, Cl, CH₃, H) complexes are investigated within the framework of the previously described extended CNDO/2 method in order to interpret their magneto-optical behaviour and to propose a suitable scheme for the electronic content of a metal-ligand ( + ) dative bond. Chatt and Wilkinson's pattern, used up to now, is criticized and a new scheme is proposed which — taking accurately the role of electronegativity into account and abiding by Pauling's principle of electroneutrality — fits well the sets of available physico-chemical data and allows us to understand whyab initio bonds overlap populations as well as IR force constants are low for any metal-ligand ( + ) dative bond.