Ab initio studies of electronic structures and quasi-aromaticity in M3S4 –nO 4+n(M = Mo, W; n= 0–4) clusters

Abstract

Electronic structure calculations have been carried out on the incomplete cubane-type transition-metal cluster cores M₃ S_4–nO⁴⁺_n(M= Mo, W; n= 0–4, of which the cluster core Mo₃S⁴⁺₄ 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–pπ bonding scheme in these clusters is established.