MOLECULAR-ORBITAL MODEL OF ELECTRON DELOCALIZATION IN MIXED-VALENCE TRIMERIC CLUSTERS

A simple extended Huckel type molecular orbital model is used to study electronic distributions in mixed-valence iron-oxygen clusters contai ning three octahedral subunits. Two different structures were consider ed: one-atom bridged octahedra and octahedra with common faces. The st ability of symmetric structures relative to different non-totally symm etric distortions leading to the vibronic charge trapping was examined . It appears that the distribution of the excess electron cannot be de scribed by the simple alternative ''localization-delocalization''. The type of electronic distribution depends on the arrangement of octahed ral units, the metal-metal distances, and the electronic configuration s. The molecular orbital approach gives some insights into the peculia rities of the intramolecular electron delocalization in mixed-valence iron-oxygen trimers which are important for their catalytic activity.