Poly[diaqua­di-μ (4)-citrato-trizinc(II)]

The title compound, [Zn(3)(C(6)H(5)O(7))(2)(H(2)O)(2)](n), is a polymer in which the repeating unit contains three zinc atoms, two hepta-dentate Hcit ligands (Hcit = citric acid trianion) and two coordinated water mol­ecules, only half of which are independent due to one of the metal atoms lying on a centre of symmetry. The two independent cations both exhibit an octa­hedral geometry, but the way in which they are coordinate are different; while the Zn atom in a general position is bound to three Hcit ligands and one water mol­ecule, the one at the centre of symmetry is coordinated by six O atoms from two symmetry-related Hcit ligands through the (protonated) hydroxyl and carboxyl­ate groups. The three carboxyl­ate groups coordinate to the Zn centres in three different ways, viz. chelating, bridging and a mixture of both, in an unusual coordination mode for citrate. The result is a two-dimensional structure parallel to (010), built up by a square-grid motif. Intermolecular O—H⋯O hydrogen bonds are present in the crystal structure