SOLID-STATE ELECTRONIC-STRUCTURE OF TRAMETHYLTETRASELENAFULVALENE)-HEXAFLUOROPHOSPHATE

The band structure and solid-state electronic properties of tramethylt etraselenafulvalene)-hexafluorophosphate (TMTF)(2)PF6 are investigated by a crystal orbital (CO) approach of the complete neglect of differe ntial overlap (CNDO) type. (TMTSF)(2)PF6 crystallizes in the triclinic space group <P(1)over bar> with TMTSF molecules that ale almost perpe ndicular io the crystallographic a axis. We analyze the atomic net cha rges q(i), so-called Wiberg bond indices W-ij, two-center energies E-i j of bonded atomic pairs in the organic donor unit, as well as the dis persion curves epsilon(i)(k) and the electronic density of states (DOS ) distribution. We predict a change transfer (CT) of 1.237e to the hex afluorophosphate unit. In the organic pi system a pronounced bond orde r alternation occurs. The CC bonds within each pentagon exhibit almost perfect double bond character while the CC bridge between both pentag ons is of partial double-bond character only. The SeC bonds are essent ially of the single-bond type. Electrostatic Madelung contributions sh ould St important for the stabilization of the crystal. The band struc ture is characteristic for a molecular crystal with weak covalent inte rmolecular interactions. The CO data suggest the possibility of a dime nsionality crossover of (TMTSF)(2)PF6 as a function of temperature. (C ) 1998 Elsevier Science S.A. All rights Reserved.