4-Carb­oxy­pyridin-1-ium 2,4,5-tri­carb­oxy­benzoate monohydrate

The title hydrated salt, C₆H₆NO₂⁺·C₁₀H₅O₈⁻·H₂O, was isolated from the 1:1 cocrystallization of benzene-1,2,4,5-tetra­carb­oxy­lic acid and isonicotinic acid in ethanol solution. In the crystal, the cation is close to planar [r.m.s. deviation = 0.085 Å for the nine fitted atoms; the C—C—C—O(carbon­yl) torsion angle = −8.7 (4)°], but twists are evident in the anion, with all but the carb­oxy­lic acid group diagonally opposite the carboxyl­ate group being significantly twisted out of the plane of the benzene ring [C—C—C—O(carbon­yl) torsion angles = −118.1 (2), −157.6 (2), 4.3 (3) and 77.3 (3)°]. In the crystal, the ions and water mol­ecules are consolidated into a three-dimensional architecture by O—H...O and N—H...O hydrogen bonding along with C—H...O inter­actions.