catena-Poly[[[tetra­aqua­cadmium(II)]-μ-3,3′-[p-phenyl­enebis(oxymethyl­ene)]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-phenyl­enebis(oxymethyl­ene)]bis­(1-pyridinioacetate) with cadmium nitrate, both the octa­hedrally 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 mol­ecule of solvation, forming a three-dimensional structure.