Electronic structures and d pπ bonding of some M 3X 4+4 cluster compounds

Abstract

Using a quantum chemical ab initio method with relativistic effective core potentials, electronic structures of the group VI cluster cores M 3X 4+ 4 (M = Mo, W; X = O, S, Se, Te) and the oxoselenido cluster cores M 3O n Se 4+ 4− n (M = Mo, W; n = 0–4) in trinuclear incomplete cubane-type compounds have been calculated at the level of self-consistent field with inclusion of d-orbitals in the basis sets of oxygen, sulphur, selenium and tellurium atoms. By virtue of the calculated canonical molecular orbitals (CMO) and localized molecular orbitals (LMO), the nature of d pπ bonding and its effect on the stabilities and reactivities in substitution and addition reactions of the clusters are discussed. The clusters under consideration have been shown theoretically to exhibit what we have previously chosen to call “quasi-aromaticity”, i.e. having benzene-like behaviour. The influence of the d-orbitals of group VI atoms is considered.