Hydrogen-bonding patterns in 4,4′-bipyridinium bis(3-carboxy-4-hydroxybenzenesulfonate) dihydrate

In the title compound, C10H10N22+·2C7H5O6S−·2H2O, 4,4′-bi­pyridine is centrosymmetric and protonated at both N atoms. The inversion-related hydrogen-bonded supramol­ecular chains (made up of water mol­ecules and sulfonate motifs arranged in an alternating manner) are cross-linked by 4,4′-bipyridinium cations via N—H⋯O (sulfonate) hydrogen bonds.