Experimental and theoretical studies on inorganic magic clusters: M 4X 6 (M = W, Mo, X = O, S)

Abstract

Studies using ultraviolet photoelectron spectroscopy (UPS) and density functional theory (DFT) demonstrate that M 4X 6 (M = W, Mo and X = O, S) clusters show large gaps (about 2 eV) between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), indicative of their high stability and chemical inertness. In particular, W 4O 6 has a lower symmetry and a larger HOMO–LUMO gap than other hitherto discovered magic clusters. Although the similarity between the electronic structures of W 4O 6 and Mo 4S 6 may be regarded as an indication that both clusters have similar geometric structures, our detailed DFT-calculations reveal otherwise. This result implies that synergetic approach using theoretical and experimental methods are essential to shed light on cluster geometries.