IODINE CHARGE-TRANSFER SALTS OF BIS(1,2,3,5-DISELENADIAZOLYL) DIRADICALS - SOLID-STATE CHARACTERIZATION OF THE THIOPHENE-BRIDGED DERIVATIVE[(SE2N2C)C4H2S(CN2SE2)][I]

Electroreduction of the 2,5-thiophene-bridged bis(1,2,3,5-diselenadiaz olylium) salt [T-2,5-Se][SbF6](2) in acetonitrile, at a Pt wire and in the presence of iodine, affords a highly conductive (sigma = 10(2) S cm(-1) at 293 K) 1:1 charge-transfer (CT) salt [T-2,5-Se] [I], the cry stal structure of which has been determined by single-crystal X-ray di ffraction. The crystals belong to the orthorhombic space group Fm2m, a = 3.544(2), b = 10.9808(16), c = 31.464(5) Angstrom, V= 1224.5(7) Ang strom(3). The structure consists of perfectly superimposed pi-stacks o f molecular units bridged by columns of disordered iodines. This packi ng motif is similar to that of the related 1,3-benzene-bridged derivat ive [1,3-Se] [I], but the lateral intermolecular Se ... Se interaction s linking adjacent pi-stacks are considerably shorter, indicative of a more isotropic electronic structure for [T-2,5-Se][I]. Magnetic susce ptibility measurements on [T-2,5-Se][I] nonetheless indicate a phase t ransition to a diamagnetic state near 200 K, behaviour similar to that observed for [1,3-Se][I]. The electronic structures and transport pro perties of the two compounds are discussed in the light of extended Hu ckel band-structure calculations.