Synthesis, structures and electrical properties of the charge-transfer salts of 4,5-ethylenedithio-4′,5′-(2-oxatrimethylenedithio)diselenadithiafulvalene (EOST) with linear anions [I–3, IBr–2, ICl–2, I2Br–, AuBr–2, Au(CN)–2]

An unsymmetrical donor 4,5-ethylenedithio-4′,5′-(2-oxatrimethylenedithio)-diselenadithiafulvalene (EOST)† has been synthesized. Single crystals of some charge-transfer salts of EOST have been prepared electrochemically. The crystal structures of EOST and its charge-transfer salts were analysed by X-ray crystallography. The dc resistivities were measured on the single crystals. Eight of the salts with linear anions [(EOST)2I3, α-(EOST)2IBr2, β-type IBr2 salt, (EOST)2ICl2, (EOST)2I2Br, α- and β-type AuBr2 salts and Au(CN)2 salt] retained their metallic conductivity down to low temperatures (⩽ 35 K) and some were found to be isostructural. The overlap integrals of some salts and the tight-binding band was examined for (EOST)2I3. The result suggested that it has a quasi-one-dimensional electronic structure and that EOST molecules interact most strongly in a side-by-side direction. The crystal and electronic structures of (EOST)2I3 are discussed by comparison with the isostructural compound (EOTT)2IBr2[EOTT: 4,5-ethylenedithio-4′,5′-(2-oxatrimethylenedithio) tetrathiafulvalene].