Exchange interaction in polynuclear complexes. Part 1.—Principles, model and application to the binuclear complexes of chromium(III)

Abstract

A model is proposed for exchange interaction taking into account the impact of the m.o. concept in inorganic chemistry. We define four principles that such a model should follow; invariance with respect to a unitary transformation between the orbital basis functions, validity of Heitler–London wavefunctions for the low lying terms, no difference in nature between direct and indirect exchange interactions, and the possible interpretation of the phenomenon by considering only the ground configuration (the coupling between ground and charge transfer configurations only leads to a small second order effect). Within this framework, we express the interaction hamiltonian as the sum of a one-electron operator coupling the magnetic orbitals in such a way that its eigenfunctions and eigenvalues are respectively the m.o.s. built from the magnetic orbitals and their energies, and a bielectronic operator. When the magnetic orbitals of similar symmetry are not orthogonal, the effect of the one electron operator on the energy differences between the low lying terms is largely predominant. The model is applied to the study of binuclear complexes of chromium(III).