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

Abstract

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.