In the presence of [NBu(4)][PF(6)] as the electrolyte, thianthrene (TA) is transformed by electrochemical oxidation to thianthrenium hexafluorophosphate containing the TA(center dot+) radical cation. The reactions were performed in CH(2)Cl(2), H(3)CCN, and liquid SO(2) as solvents. In CH(2)Cl(2), TA[PF(6)] is sparingly soluble and is deposited directly in crystalline form on the platinum electrode. In H(3)CCN and liquid SO(2), TA[PF(6)] is highly soluble and gives dark blue solutions from which it can be crystallized upon concentration of the solutions. The air sensitive crystals are black with bronze metallic luster. They belong to the monoclinic system (C2/m, a = 12.4345(8), b = 10.5318(6), c = 11. 1303(7) angstrom. beta = 112.565(3)degrees) and are built up of almost planar TA(center dot+) cations and octahedral [PF(6)](-) anions. The F atoms of the anions are disordered over two positions. The radical cations are associated to form dimeric units (TA(center dot+))(2) with the planar molecules stacked with two weak S center dot center dot center dot S bonds (3.06 angstrom). In the crystal these dimers are separated by the [PF(6)](-) anions. Electrical conductivity measurements show TA[PF(6)] to be a small-gap semiconductor. Conductivity is low at r. t. but reaches 2.5 (.) 10(-5) S m(-1) at 110 degrees C. the activation energy in the high-temperature region amounts to 1.2 eV. Periodic quantum-chemical calculations at hybrid density-functional level predict it strong Coupling between neighboring (TA(center dot+)) spin centers, resulting in it singlet ground state. The calculated hand gaps of both sin let (1.5 eV) and triplet (0.9 eV) states are small, consistent with the measured conductivity.
