4-Nitro­anilinium 3-carb­oxy-4-hy­droxy­benzene­sulfonate monohydrate

In the title hydrated salt, C₆H₇N₂O₂⁺·C₇H₅O₆S⁻·H₂O, the benzene ring of the cation makes a dihedral angle of 1.32 (19)° with the attached nitro group. In the anion, an intra­molecular O—H...O hydrogen bond with an S(6) ring motif is formed between the carb­oxyl and hy­droxy groups; the dihedral angle between the carb­oxyl group and the benzene ring is 8.76 (8)°. The crystal structure exhibits inter­molecular N—H...O, O—H...O, C—H...O, and π–π [centroid–centroid distances = 3.6634 (9) and 3.7426 (9) Å] inter­actions to form a three-dimensional network.

Uronium 3-carb­oxy-4-hy­droxy­benzene­sulfonate

In the title compound, CH₅N₂O⁺·C₇H₅O₆S⁻, the dihedral angle between the benzene ring and the mean plane of the uronium cation is 76.02 (8)°. The carboxyl group in the anion is twisted by 1.47 (9)° from the benzene ring. In the crystal, the cation is linked to the anion by weak O—H...O and N—H...O hydrogen bonds and π–π inter­actions [centroid–centroid distance = 3.8859 (8) Å], forming a three-dimensional network.