AB-INITIO STUDIES OF ELECTRONIC-STRUCTURES AND QUASI-AROMATICITY IN M(3)S(4-N)O(N)(4+) (M=MO, W N=0-4) CLUSTERS

Electronic structure calculations have been carried out on the incomplete cubane-type transition-metal cluster cores M(3)S(4-n)O(n)(4+) (M = Mo, W; n = 0-4, of which the cluster core Mo3S44+ has been previously shown to exhibit what has been referred to as quasi-aromaticity. All the clusters are theoretically viewed to exhibit so-called quasi-aromaticity, i.e. having benzene-like behaviour. The calculations were accomplished at the level of Hartree-Fock self-consistent field theory by using an ab initio quantum chemical method with relativistic effective core potentials. The nature of the quasi-aromaticity is elucidated by analysing the calculated canonical molecular orbitals and localised molecular orbitals by the Foster-Boys localisation technique. On the basis of canonical molecular orbital and localised molecular orbital calculations, as well as Mulliken population analysis and natural population analysis, the d-p pi bonding scheme in these clusters is established.