Synthesis and properties of conductive radical cation salts of MDT-TSF (methylenedithiotetraselenafulvalene)

Abstract Electrocrystallizaion of MDT-TSF (methylenedithiotetraselenafulvalene) in the presence of ( n -Bu 4 N)AuI 2 , ( n -Bu 4 N)PF 6 , or a mixture of Cu(SCN), KSCN, and 18-crown-6-ether as a supporting electrolyte gave (MDT-TSF)-X salts (X=AuI 2 , PF 6 , or Cu(NCS) 2 ). X-ray structural analyses revealed that the salts adopt various types of crystal structures depending on the counter anion involved; the AuI 2 salt takes a characteristic uniform stacking structure, the PF 6 salt θ-type, and the Cu(NCS) 2 salt κ-type structure. Regardless of the structure type, all the salts are highly conductive at room temperature (>10 2 S cm −1 ) and retain metallic down to low temperature. Of them, the AuI 2 salt having a high conductivity of 2000 S cm −1 at room temperature showed a superconducting transition at 4.5 K.