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]

Abstract

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].