The title compound, (C4H12N2)[Co(H2O)6][Co(C7H3O4)2]2- 8H2O, was obtained by the reaction of cobalt(II) nitrate hexahydrate with the proton-transfer compound piperazinediium pyridine-2,6-dicarboxylate or (pipzH2)(pydc) (where pipz is piperazine and pydcH2 is pyridine-2,6-dicarboxylic acid) in aqueous solution. The anionic complex, [Co(pydc)2]2 , features six-coordinate CoII with a distorted octahedral geometry. The structure also contains hexaaquacobalt( II) cations (site symmetry 1), and piperazinium (site symmetry 1) as counter-ions and eight uncoordinated water molecules. The torsion angles indicate that the (pydc)2 units are almost perpendicular to each other. In the crystal structure, extensive O—H O, N—H O and C—H O hydrogen bonds, as well as ion pairing and distances for – interactions between anion fragments, play an important role in stabilizing the structure.
