catena-Poly[piperazindiium[zincate(II)-bis(μ-pyridine-2,3-dicarboxylato)-κ3N,O2:O3;κ3O3:N,O2] tetrahydrate]

The centrosymmetric title compound, {(C4H12N 2)[Zn(C14H6N2O8)2] ·4H2O} n or {(pipzH2)[Zn(py-2,3-dc)2] ·4H2O} n , where py-2,3-dcH2 is pyridine-2,3-dicarboxylic acid and pipz is piperazine, was obtained by the reaction of zinc(II) nitrate tetra-hydrate with (pipzH2)(py-2,3-dc) as a proton-transfer compound in aqueous solution. Each ZnII (site symmetry ) is coordinated in a distorted octa-hedral geometry by four O atoms and two N atoms from two bidentate (py-2,3-dc)2- ligands, which also act as bridging ligands between ZnII atoms. The four donor atoms of the two coplanar (py-2,3-dc)2- anions form a square-planar arrangement around the ZnII centre. In the crystal structure, extensive O - H⋯O, N - H⋯O and C - H⋯O hydrogen bonds, as well as ion pairing and π-π stacking [with a distance of 3.8693 (8) Å between two aromatic rings] between different fragments, play an important role in the stabilization of the supra-molecular structure. © International Union of Crystallography 2007.