Phase transition of γ-(BEDT-TTF)3(HSO4)2

The structural properties and the metal-insulator (MI) transition of γ-ET3(HSO4)2 (1) are discussed, in comparison with those of γ-ET3(ClO4)2 (2). Transition of 1 is related to a structural change, as in the case of 2. The substitution of hydrogen of the anion with deuterium lengthens the O···O distance of intermolecular hydrogen bonds between the two anions, although an MI transition temperature is not changed appreciably. The hydrogen bonds between the two anions make the rotation of the anion molecules strongly hindered and shift their positions close to each other, which enables the puckering motion of the ethylene bridge of ET molecules easily.