Crystal and electronic structure of (BPDT-TSeF)-Ni(dmit)2 system BPDT-TSeF = bis(propylenedithio)tetraselenafulvalene

Three donor-acceptor type molecular conductors in the (BPDT-TSeF)-Ni(dmit)2 system have been electrochemically obtained. α-1:2 salt (semiconductor) is very similar to sulfur analogue α-(BPDT-TTF)[Ni(dmit)2]2. β-1:2 salt is an insulator. 1:1 salt shows a novel (semi)metal-insulator transition at 162K. In the crystal structure of the 1:1 salt, BPDT-TSeF and Ni(dmit)2 molecules form separated uniform one-dimensional arrays. This structure is almost the same at R.T. and at 110K except the slight tilting of the donor and acceptor molecules. Simple band structure calculation explains the energy gap formation and the phase transition at 162K.