The reaction of cadmium(II) nitrate hexahydrate with the proton-transfer compound (pipzH₂)(ox) (where pipz=piperazine and oxH₂=oxalic acid), in aqueous solution leads to the formation of the title polymeric compound (C₂H₆CdO₇)_n. This compound crystallizes in the triclinic system, space group Pī with two formula in the unit cell. The unit cell parameters are: a = 5.998 (4) Å, b = 6.634 (5) Å, c = 8.482 (6) Å,
α = 74.679 (10)°, β = 74.348 (11)° and γ = 81.112(11)°. The final R value was 0.087 for 1309 measured reflections. The Cd^II ion is seven-coordinated by five O atoms of oxalate ions as tetradentate bridging ligands and two O atoms of coordinated water molecules with distorted pentagonal bipyramid geometry around the central atom. The asymmetric unit also contains one water molecule. The crystal structure is stabilized by O–H···O hydrogen bonds, linking the molecules into a three-dimensional framework, which results in the formation of a supramolecular structure.