4,4′-([4,4′-bipyridine]-1,1′-diium-1,1′-diyl)dibenzoate dihydrate

We report here the synthesis of a neutral viologen derivative, C24H16N2O4·2H2O. The non-solvent portion of the structure (Z-Lig) is a zwitterion, consisting of two positively charged pyridinium cations and two negatively charged carboxylate anions. The carboxylate group is almost coplanar [dihedral angle = 2.04 (11)°] with the benzene ring, whereas the dihedral angle between pyridine and benzene rings is 46.28 (5)°. The Z-Lig molecule is positioned on a center of inversion (Fig. 1). The presence of the twofold axis perpendicular to the c-glide plane in space group C2/c generates a screw-axis parallel to the b axis that is shifted from the origin by 1/4 in the a and c directions. This screw-axis replicates the molecule (and solvent water molecules) through space. The Z-Lig molecule links to adjacent molecules via O—H...O hydrogen bonds involving solvent water molecules as well as intermolecular C—H...O interactions. There are also π–π interactions between benzene rings on adjacent molecules.