A zwitterionic viologen disulfonate-hydroquinone charge-transfer crystal: 2,2'-(4,4'-bipyridinium-1,1'-diyl)di(ethanesulfonate)-hydroquinone (1/2).

The structure of the title compound, C(14)H(16)N(2)O(6)S(2).2C(6)H(6)O(2), consists of 2,2'-(4,4'-bipyridinium-1,1'-diyl)di(ethanesulfonate) molecules (with crystallographically imposed twofold symmetry) that are hydrogen bonded to each other, as well as to hydroquinone molecules, in a complex three-dimensional motif. The orange color of the crystals is indicative of the donor-acceptor interaction between the electron-rich hydroquinone pi-donor and the electron-deficient bipyridinium pi-acceptor. The dihedral angle between the bipyridyl planes is 38.31 (11) degrees. The distance from the centroid of one of the hydroquinone molecules to the center of the bipyridinium group is 3.653 (3) A, which is within the range typically observed for molecular complexes exhibiting charge-transfer characteristics.