The Double Exchange Phenomenon Revisited: The [Re2OCl10]3− Compound

Correlated ab initio calculations have been performed on the Re₂OCl₁₀]³⁻ anion. The calculated spectrum does not respect the intervals given by the usually accepted double exchange Hamiltonian. Surprisingly enough the ground-state happens to be of intermediate spin multiplicity (i.e. a quartet) at any level of correlation treatment. A model that combines the Anderson and Hasegawa method and the usually used double exchange one rationalizes the spectrum calculated both by a configuration interaction restricted to the open shell molecular orbitals and at a more correlated level of calculation. An alternative analysis of the double exchange phenomenon, based on a molecular orbital language, is presented. The specific effects of the electronic correlation brought by extended active space and by a difference dedicated configuration interaction are also analyzed.