Structure and properties of BETS salts: kappa-(BETS)(8)(Cu2Cl6)(CuCl4), theta-(BETS)(2)(CuCl2) and (BETS)(2)(CuCl4)

kappa-(BETS)(8)(Cu2Cl6)(CuCl4) (1), theta-(BETS)(2)(CuCl2) (2). (BETS)(2)(C uCl4) (3) (BETS = bis(ethylenedithio) tetraselenafulvalene), have been prep ared by diffusion-electrocrystallisation of BETS and (AsPh4)(2)(Cu2Cl0) sol utions in chlorobenzene-ethanol. 2 has also, been obtained by simple diffus ion of BETS and (AsPh4)(2)(Cu2Cl0) solutions. 1 and 2 exhibit metal-like be haviour, down to 40 for 1 and 4K for 2. 3 behaves as an insulator. The crys tal structures of 1, 2. and 3 are determined by X-ray diffraction methods. The structures of 1 (at 140 and 25 K) and 2 are characterised by a strong d isorder of their respective anions. The cn stal structure of 3 shows an unu sual packing of the BETS molecules, consisting of slipped stacked (BETS)(2) dimers. leading to insulating properties. Based on the structures of 1 (at 140 and 25 K). 2 and 3. molecular and band structure calculations are carr ied out for the interpretation of the physical behaviours of these phases. (C) 2001 Academie des sciences / Editions scientifiques et medicales Elsevi er SAS.