CONCERNING THE BAND-STRUCTURE OF D(M(DMIT)2)2 (D=TTF,CS, NME4-M=NI,PD) MOLECULAR CONDUCTORS AND SUPERCONDUCTORS - ROLE OF THE M(DMIT)2 HOMO AND LUMO

We report tight-binding band structure calculations showing that the partially filled band of D[M(dmit)2]2 molecular conductors containing dimeric building blocks can originate either from the LUMO (lowest unoccupied molecular orbital) or the HOMO (highest occupied molecular orbital) of the M(dmit)2 acceptor, depending upon the strength of the intra-dimer transfer integrals (tHOMO and tLUMO) with respect to the HOMO-LUMO splitting. The first situation is found for D=Me4N and M=Ni whereas the second one is found for D=Cs or TTF (δ phase) and M=Pd. Both the HOMO and LUMO bands are partially filled in the TTF[Ni(dmit)2]2 and α′-TTF[Pd(dmit)2]2 salts which contain M(dmit)2 stacks with uniform chains. The structural reasons behind these surprising results are explained. © 1990.