Tetra-imidazolium piperazinediium bis-(benzene-1,3,5-tricarboxyl-ate) dihydrate.

During the crystallization of the title compound, 4C(3)H(5)N(2) (+)·C(4)H(12)N(2) (+)·2C(9)H(3)O(6) (3-)·2H(2)O, the acidic protons were transferred to the imidazole and piperazine N atoms, forming the final 4:1:2:2 hydrated mixed salt. The mean planes of the three carboxyl-ate groups in the anion are twisted with respect to the the central benzene ring, making dihedral angles of 13.5 (1), 14.5 (1) and 16.9 (1)°. In the crystal, the component ions are linked into a three-dimensional network by a combination of inter-molecular N-H⋯O, O-H⋯O and weak C-H⋯O hydrogen bonds. Further stabilization is provided by π-π stacking inter-actions with centroid-centroid distances of 3.393 (2) Å and weak C=O⋯π inter-actions [O-centroid = 3.363 (2) Å].