Isolation and X-ray Structural Characterization of a Dicationic Homotrimer of 2,3,6,7-tetramethoxy-9,10-dimethylanthracene cation radical

Electrochemical oxidation of 2,3,6,7-tetramethoxy-9,10-dimethylanthracene (1) showed that it undergoes a highly reversible electrochemical oxidation (Eox = 0.81 V vs SCE) and forms a modestly stable cation-radical salt in solution. X-ray crystallography established that 1+SbCl6- crystallizes as a (centrosymmetric) dicationic homotrimer via a close cofacial association of a pair of cationic and one neutral molecule of 1 with an interplanar separation of ∼3.2 Å. The structure of the dicationic homotrimer was also reproduced by DFT calculations. Furthermore, the structure of a dicationic spiro adduct, formed by a slow decomposition of a solution of 1+SbCl6- was also established by X-ray crystallography