A unified ligand field model comprising the effects of electrostatics and covalence on molecular electronic energies

The relevance of models describing molecular electronic energies including electrostatic as well as covalence effects is outlined and a summary of developments resulting in the present formulation is given. A simple, semi-empirical model based on a LCAO-MO approximation and comprising the point charge electrostatic model and angular overlap model is formulated. Although the present formulation is restricted to the antibonding effects of covalence it is applicable to p, d, f and g orbital energies. The mathematical and conceptual simplicity of the model derives from the application of a re-parameterized ionic model and the superposition principle for ligand contributions, the latter applied in the case of ionic as well as antibonding effects. A physical interpretation of the model, for diatomic as well as polyatomic molecules, is presented and the results of its application to the pentachlorovanadate(IV) ion are cited.