Highly Conductive 1 : 1 Radical Cation Salts of Anthra[1,9-cd : 4,10-c′d′]bis[1,2]dichalcogenoles

Abstract

Abstract Various radical cation salts of 2,3-dimethyl-tetrathioanthracene (DMTTA) and -tetraselenoanthracene (DMTSA) with NO3−, BF4−, ClO4−, PF6−, AsF6−, and Br− counter anions were prepared by an electrocrystallization technique. It has been found that these salts have either 1 : 1 or 2 : 1 stoichiometry depending on the volumes of the anions, but all are electrically conductive regardless of the stoichiometries. In particular, the NO3 and BF4 salts of DMTSA, in spite of 1 : 1 stoichiometry, recorded unusually high room temperature conductivities of 440 and 450 S cm−1, respectively, and had metallic behaviors down to around 200 K. In addition, the other salts were semiconductors with very low activation energies. X-Ray crystallographic analyses showed that the crystal structures of all the salts consist of one-dimensional stacking columns of the donor molecules, but the two metallic salts have more favorable uniform stacking columns in which there are not only effective π electronic interactions but also strong heteroatomic interactions. Furthermore, solid electronic spectra indicated that these 1 : 1 radical cation salts have the advantage of marked reduction of on-site Coulombic repulsion in the donor molecules, which serves to suppress a Mott transition.