SEMICONDUCTING CHARGE-TRANSFER SALTS OF BEDT-TTF [BIS(ETHYLENEDITHIO)TETRATHIAFULVALENE] WITH HEXACHLOROMETALLATE(IV) ANIONS

Two new crystalline charge-transfer salts of BEDT-TTF [bis(ethylenedit hio)tetrathiafuivalene] containing hexachlorometallate anions of 5d el ements have been synthesised, characterised structurally and their mag netic and conducting behaviour investigated. alpha-(BEDT-TTF)(4)[ReCl6 ]. C6H5CN is triclinic [P (1) over bar; a = 9.455(2), b = 11,306(3), c = 18.193(5) Angstrom; alpha = 101.85(2), beta = 92.74(2), gamma = 110 .52(2)degrees; Z = 1]. Its structure consists of alternate layers of B EDT-TTF and of [ReCl6](2-). C6H5CN, the former consisting of two cryst allographically independent stacks, in one oi which the molecules carr y a charge close to +1 while in the other they are approximately neutr al. The cations lie between the [ReCl6](2-) moieties while the neutral molecules are closest to the C6H5CN species showing that the structur e is determined by electrostatic interactions. (BEDT-TTF)(2)[IrCl6] is likewise triclinic [P (1) over bar; a=8.721(1), b=10.257(2), c=11.086 (2) Angstrom; alpha = 111.00(1), beta= 98.31(1), gamma = 103,32(1)degr ees; Z = 1]. Its packing motif is new among BEDT-TTF salts, containing no discrete layers of anions and cations. Face-to-face BEDT-TTF dimer s form an infinite three-dimensional network. Both compounds are semic onducting and their magnetic properties are dominated by the Curie-Wei ss behaviour of the anions.