Crystal Structure and Physical Properties of {Bis(ethylenedithio)tetrathiafulvalene}2dicyano-Silver and -Gold

Abstract

Abstract We report the crystal and electronic band structures and the electrical, magnetic, and optical properties of {bis(ethylenedithio)tetrathiafulvalene}2dicyano-silver and -gold, η-(BEDT–TTF)2M(CN)2, M = Ag or Au. The compounds belong to the monoclinic system; space group C2/c, a = 36.28(8), b = 4.286(2), c = 22.02(6) Å, β = 110.62(9)° and V = 3205 Å3, and a = 36.44(8), b = 4.256(2), c = 22.16(6) Å, β = 111.3(1)° and V = 3201 Å3, respectively. The structure consists of pairs of stacks with parallel BEDT–TTF molecules along b. Molecules in neighboring pairs of stacks are tilted by 55.3°. There are several short S···S contacts between stacks to form layers, which are separated by the anions along a. The transfer integrals suggest a highly dimerized system. The band structure calculation, however, predicts metallic behavior contrary to the semiconducting properties observed (σRT ≈ 10−1—10 S cm−1 and EA = 0.15(2) eV). The static (SQUID magnetometry) and spin (EPR) susceptibilities are modelled to a singlet–triplet system with an energy gap of 315(5) K (39(1) meV). This is one of two phases in the BEDT–TTF family to exhibit an activated susceptibility for a spin dimer model.