An ab initio study on the chemical bond and the mechanism of cluster formation of the tungsten-sulfur clusters

Using ab initio method and natural bond analyses, the electronic structures of dinuclear tungsten cluster [Et4N](2)[W2S4(TDT)(2)] and the cubane-like tetranuclear mixed-metal clusters W2MM'S-4(TDT)(2)(PPh3)(2) (M,M' = Cu,Ag) have been studied. It is shown that the tungsten clusters are similar with the molybdenum clusters. Besides the metal-metal and metal-sulfur direct bonding, the metal-sulfur-metal interactions can be discerned by the multi-center d-p pi bondings, which exist among the metal and bridging(or terminal) sulfur atoms. The research results discover that the 3c pi(W-S-b-W) and pi(W-S-t) bonds in the dinuclear cluster built some 'active centers'. The nature of multi-centered d-p pi bondings and their effects on the stability and reactivities in [2+1+1] addition reactions of the tetranuclear clusters are discussed. (C) 1998 Elsevier Science B.V.