Poly[piperazinediium [aquabis(μ-pyridine-2,5-dicarboxylato)zincate] dihydrate]

The polymeric title compound, {(C4H12N2)[Zn(C7H3NO4)(2)-( H2O)]center dot 2H(2)O}(n), was obtained by the reaction of zinc(II) nitrate hexahydrate with the proton-transfer compound (pipzH(2))(py-2,5-dc) (where pipz is piperazine and py-2,5-dcH(2) is pyridine-2,5-dicarboxylic acid) in aqueous solution. Each Zn II atom is coordinated in a distorted octahedral geometry by four O atoms and two N atoms from one water molecule and two (py-2,5-dc)(2-) ligands, which also act as bridging ligands between Zn II atoms. pi-pi Stacking interactions between two aromatic rings of (py-2,5-dc)(2-) fragments, with centroid-centroid distances of 3.4747 (7) and 3.7081 (7) angstrom are observed. The crystal structure is stabilized by O-H center dot center dot center dot O and N-H center dot center dot center dot O hydrogen bonds.