Synthesis, structure and conductivity of molecular conductor β-(BEDT-TTF)(HSO4)

A new BEDT-TTF-based radical salt, β-(BEDT-TTF)(HSO4) [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene], has been synthesized by oxidative electrocrystallization. The crystal structure was determined by four-circle X-ray diffraction. The crystal belongs to monoclinic system, C2/c space group with the unit cell parameters of: a = 1.5996(2) nm, b = 1.06173(10) nm, c = 1.15083(11) nm, β = 120.534(8)°, V = 1.6834(3) nm3, and R = 0.0611. In the title crystal, the BEDT-TTF radicals are stacked to form columns along the [1 0 1] axis and the molecular planes of BEDT-TTFs in adjacent columns are parallel to each other. The inter-stack side-by-side S…S short contacts along the b-axis help to form a kind of cationic conducting sheet parallel to (1 0 1) plane. The room temperature conductivity at certain direction on (1 0 1) plane of β-(BEDT-TTF)(HSO4) single crystal was measured to be 11.7 S cm−1. From 100 K to 290 K, the resistivity–temperature curve demonstrates its typical semiconductivity with an excitation energy of 0.26 eV.