Antiferromagnetism in transition metal complexes. Part 7.—Critique of the Heisenberg model and a re-examination of the system of three copper(II) ions in a linear array

Abstract

Methods which have been used to modify the basic Heisenberg–Dirac–Van Vleck treatment of magnetically concentrated systems are discussed. The electronic states arising from the interactions between three collinear copper(II) ions are investigated by a variety of methods using orthogonalised atomic or molecular orbital basis sets to examine the explicit form of the exchange integrals involved in the treatment of such systems. The complementary roles of chemical bonding and eletron-repulsion effects are illustrated and it is concluded that, in this system, a low-lying doublet state, unrecognised in the spin-exchange treatment, may be of magnetic importance.