Synthesis and properties of ethylenethiotetraselenafulvalene (ET-TSF) and its conductive radical cation salts

The title heterocycle-fused tetraselenafulvalene derivative, ET-TSF (ethylenethiotetraselenafulvalene) has been synthesized as a novel electron donor. Electrocrystallization of ET-TSF gave highly conductive radical cation salts with I 3 - , Cl - , Br - , and AuI 2 - counter anions. Among them, the AuI 2 salt isostructural with the organic superconductor (MDT-TSF)-AuI 2 (MDT-TSF = methylenedithiotetraselenafulvalene) was highly conductive (1600 S cm -1 ) and metallic down to 1.8 K with no superconducting transition.