A novel metal–insulator transition in (EDO-TTF) 2X (X=PF 6, AsF 6)

Abstract

Single crystals of cation radical salts of ethylenedioxy-tetrathiafulvalene (EDO), (EDO) 2X (X=PF 6, AsF 6, ClO 4) were prepared by electrocrystallization. Metal–insulator (MI) transitions with big molecular deformation were observed in (EDO) 2PF 6 at 280 K and in (EDO) 2AsF 6 at 268 K. Their crystal structures are almost the same at room temperature (RT), and in both cases, the calculated band structures show quasi-one-dimensional electronic nature. The magnetic susceptibility of (EDO) 2PF 6 and (EDO) 2AsF 6 showed the thermal hysteresis around 280 and 268 K, respectively, indicating the MI transition being the first-order. Their crystal structures in the insulating phase are isostructural to each other and to that of (EDO) 2ClO 4 at RT. The structural analysis of these salts revealed that the mechanisms of the MI transitions observed in PF 6 and AsF 6 salts are the same, which show the cooperative nature of Peierls, charge-ordering (CO), and order–disorder (OD) one.