The reaction of cadmium(II) nitrate tetrahydrate with the proton-transfer compound piperazinium pyridine-2,5- dicarboxylate, or (pipzH2)(py-2,5-dc)2H2O (in which pipz is piperazine and py-2,5-dcH2 is pyridine-2,5-dicarboxylic acid), in aqueous solution (molar ratio 1:2) leads to the formation of the title compound, (C4H12N2)1.5[Cd(C7H3NO4)2(C7H4- NO4)]3H2O or (pipzH2)1.5[Cd(py-2,5-dc)2(py-2,5-dcH)]- 3H2O. The anion is a six-coordinate complex with a distorted octahedral geometry around CdII. Extensive intermolecular O—H O, N—H O and C—H O hydrogen bonds involving the (py-2,5-dc)2 ligand, (pipzH2)2+ as counter-ion and the uncoordinated water molecules connect the various components into a supramolecular structure.
