MO model of electron delocalisation in mixed-valence biotahedral clusters

A simple extended Hückel type molecular orbital model is proposed for mixed-valence bioctahedral clusters. The model allows the study of the delocalisation of the excess electron in these systems as a function of the arrangement of octahedral units, metal-metal distances and electronic configurations. Fe(II)Fe(III) clusters with oxygen ligands are considered as examples. It is shown that the model provides information about the electronic structure of mixed-valence clusters which cannot be obtained from phenomenological vibronic theories.