monohydrate

R factor = 0.043; wR factor = 0.120; data-to-parameter ratio = 14.3. In the title hydrated salt [systematic name: 1-(1,3-benzo-dioxol-5-ylmethyl)piperazin-1-ium 4-nitrobenzoate monohy-drate], C12H17N2O2 +C7H4NO4H2O, the piperazinium ring of the cation adopts a slightly distorted chair conformation. The piperonyl and piperazine rings are rotated with respect to each other with an N—C—C—C torsion angle of 45.6 (2). In the anion, the nitro group is almost coplanar with the adjacent benzene ring, forming a dihedral angle of only 3.9 (4). In the crystal, the cations, anions and water molecules are linked through N—H O and O—H O hydrogen bonds into chains along the a axis. In addition, weaker intermolecular C— H O interactions are also observed within the chains. The anions form centrosymmetric couples through -stackin