catena-Poly[[[tetra-aqua-cadmium(II)]-μ-3,3'-[p-phenyl-enebis(oxymethyl-ene)]bis-(1-pyridinioacetate)] dinitrate hemihydrate].

In the title polymeric coordination complex, {[Cd(C(22)H(20)N(2)O(6))(H(2)O)(4)](NO(3))(2)·0.5H(2)O}(n), obtained from the self-assembly of the flexible double betaine 3,3'-[p-phenyl-enebis(oxymethyl-ene)]bis-(1-pyridinioacetate) with cadmium nitrate, both the octa-hedrally coordinated Cd(II) cation and the substituted betaine ligand lie on inversion centres. The chains constructed through the trans-related acetate groups of the ligand are inter-connected via O-H⋯O hydrogen bonds involving coordinated aqua ligands, the nitrate anions and the partial-occupancy (0.25) water mol-ecule of solvation, forming a three-dimensional structure.