Crystal structures and electrical properties of the radical salts of the unsymmetrical donor EOTT [4,5-ethylenedithio-4′,5′-(2-oxatrimethylenedithio)tetrathiafulvalene]

The crystal structures and/or electrical properties of EOTT2X [X = AuCl2, AuBr2, Aul2, Au(CN)2, Ag(CN)2, ICl2, IBr2, I2Br, l3, Br3 and MnCl4, FeCl4, CoCl4, NiCl4] are reported. Concerning the linear anion salts seven (X = AuBr2, Aul2, ICl2, I2Br, I3, Br3) of them were found to be isostructural. Although they apparently have columnar structures, there are many sulfur–sulfur short contacts, which lead to a two-dimensional network in the donor sheet. Their Fermi surfaces were calculated to be closed and elliptical by the tight-binding band approximation. EOTT2FeCl4 is disordered at the anion site and has a dimeric columnar structure along the a axis. The Aul2 salt is metallic down to low temperatures. The IBr2 salt also exhibited decreased resistivity with an inflexion at ca. 110 K and a sample-dependent minimum around 25 K. The metal–insulator (M–I) transitions occurred in AuBr2, ICl2 and Br3 salts at temperatures >100 K. The other salts [I3, I2Br, AuCl2, Au(CN)2, Ag(CN)2, FeCl4, NiCl4, MnCl4 and CoCl4] are semiconductors. EOTT2ICl2 is polymorphic: the α-type is isostructural with the other linear anion salts with an M–I transition around 145 K. The β-type is semiconducting and has a dimeric structure. The M–I transition of α-EOTT2ICl2 might be explained by a structural transition to a similar insulating state to the β-type.