Oxidation states, atomic charges and orbital populations in transition metal complexes

The differences and similarities between calculated atomic charge and formal oxidation state in transition metal complexes are discussed in the light of density functional theory calculations on a variety of four-coordinate complexes. It is shown that the oxidation state formalism provides a framework for the classification of families of compounds related by ligand substitution or redox processes, and can neither be replaced by nor deduced from net atomic charges.