Piperazine-1,4-diium bis­(2,4,5-tricarb­oxy­benzoate) dihydrate

In the title hydrated salt, C₄H₁₂N₂²⁺·2C₁₀H₅O₈⁻·2H₂O, the piperazinediium cation, lying about an inversion center, adopts a chair conformation. The benzene ring of the anion makes dihedral angles of 25.17 (8)° with the carboxyl­ate group and angles of 8.50 (7), 20.07 (7) and 80.86 (8)° with the three carb­oxy­lic acid groups. In the crystal, the cations, anions and water mol­ecules are connected by O—H...O and N—H...O hydrogen bonds into double layers parallel to (110).