Experimental Crystal data

R factor = 0.030; wR factor = 0.085; data-to-parameter ratio = 10.0. In the title hydrated salt, C4H12N2 2+2C10H5O82H2O, 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). Related literature For supramolecular architectures involving benzene-1,2,4,5-tetracarboxylic acid and its anions, see: Aghabozorg et al. (2006, 2008); Chiwei et al. (2005); Pasban et al. (2012); Pasda