Electrochemical evidence for the existence of three stable oxidation states for heterocycles of the type X?C6H4?CN2E2 (E = S,Se). X-ray crystal structure of the dimer with X = Cl,E = S

The preparation and isolation in the solid state of five aryl 1,2,3,5-dithia- and diselenadiazolyls is reported. The structure of the dimer of 4-Cl? C₆H₄? CN₂S₂ in the solid state was obtained: monoclinic, C2/c with Z = 8, a = 20.982(10), b = 10.058(3), c = 15.867(6) Å, β = 93.34(4)°, R = 0.066, R_w = 0.053 for 1 099 data. Cyclic voltammetry shows reversible oxidation to a 6π cation for all 10 compounds in both CH₂Cl₂ and CH₃CN; reversible reduction to an 8π anion is observed in CH₂Cl₂ for all except X = CF₃, E = S. The reductions are only quasi-reversible in CH₃CN for E = Se. The oxidation process is independent of chalcogen type; the reduction process is found to be about 0.2 V more negative for E = S vs E = Se.