Poly[[hexa-aqua-(μ(3)-2,2'-bipyridine-4,4',6,6'-tetra-carboxyl-ato-κ(6)O(4):N,O(6),O(6'),N':O(4'))dinickel(II)] dihydrate].

In the title complex, {[Ni(2)(C(14)H(4)N(2)O(8))(H(2)O)(6)]·2H(2)O}(n), the two Ni(II) atoms are located in different special positions (one on a twofold rotation axis and the second on a centre of symmetry) and have different distorted octa-hedral environments (one by two N atoms from a bipyridine unit, two O atoms from two water mol-ecules and two O atoms from two carboxyl-ate groups, and the second by four O atoms from four water mol-ecules and two O atoms from two carboxyl-ate groups). Thus, the environments of the Ni(II) atoms may be denoted as NiN(2)O(4) and NiO(6). In the crystal, there exists an extensive network of classical O-H⋯O hydrogen bonds.