ELECTRONIC-STRUCTURE AND BONDING IN TRINUCLEAR MOLYBDENUM AND TUNGSTEN CLUSTER COMPOUNDS OF M3X13 TYPE

This paper is concerned with some newly observed electronic properties of trinuclear cluster compounds belonging to the M3X13 structural type and particularly with the way in which the preferred number of electrons in the compounds of this type is influenced by the identity of the ligand intimately associated with the metal cluster. The ground-state electronic structures of a number of trinuclear molybdenum and tungsten cluster compounds have been studied by employing SCF-X-alpha-SW molecular orbital calculations. The calculations have been performed for the molybdenum and tungsten systems with six, eight, and nine metal d electrons. The results have been shown to give consistent and satisfactory explanations for the electron populations and related properties of these compounds. The M-M bonding in these cluster compounds has been examined in detail by employing the results of the present calculations and compared with a long-established bonding scheme of less rigorous origin. Comparative studies have also been carried out on the followed trimolybdenum systems: Mo3(mu-3-X)(mu-Y)3 (X = O, Y = O, X = O, Y = Cl, X = S, Y = S). It has been found that the preferred oxidation levels in these systems are directly related to the significant differences in their electronic structures caused by different interactions between the metal atoms and the intimate ligand atoms.