A Photochromic Zwitterionic Viologen: 4,4'-Bipyridinium-1,1'-bis(2-ethylsulfonate) Monohydrate

The structual analysis of the title compound, C₁₄H₁₆N₂O₆S₂.H₂O, shows that the packing of the zwitterionic molecule in the crystal is such that the anionic sulfonate groups are located between the dicationic bipyridinium groups of adjacent molecules. Hydrogen bonds between a water molecule and the sulfonate groups link adjacent molecules into infinite molecular chains. The bipyridinium portions of adjacent molecules are not parallel, but form an angle of 58.0 (1)° with respect to one another, forming a wedge within which the anionic groups are located.

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