A Theoretical Investigation of Bonding and Electron Counting in Compounds Structurally Related to Ti5Te4

Extended Hückel tight-binding calculations indicate that the valence electron count (VEC) of compounds adopting the Ti5Te4-type structure is imposed by metal-metal bonding. The average metal-metal overlap population is almost constant and maximum in the VEC range 44-50, which corresponds exactly to the VEC range of the characterized compounds. Related phases deriving from the Ti5Te4 structure through insertion of extra metal atoms or metal clusters between the chains have very similar bonding and VEC count. Calculations on V3As2 and Cu4Nb5Si4 indicate that the inserted atoms provide Ti5Te4-type substructure with an electron number, which tends to maximize the metal-metal bonding.