Theoretical CNDO molecular-orbital analysis of metal–ligand bonding as a function of ligand basicity in some purely σ-bonding systems

Abstract

A theoretical molecular-orbital (m.o.) analysis of the correlation of metal–ligand bond strength with the basicity of the ligands in a number of purely σ-bonding systems has been made at the CNDO level of approximation. An energy partitioning analysis consistent with the unrestricted Hartree–Fock (UHF) model at this level reveals the existence of linear correlations of the various energy contributions to metal–ligand interactions with ligand basicity. The diatomic ‘shared electron density’ and exchange interaction energy (E²_AB) are the most suitable parameters for assigning a covalency index to various metal–ligand bonds. An apparently irregular behaviour of the covalent interaction energy component (E¹_AB) computed at the CNDO level is critically examined.