Monoclinic polymorph of poly[aqua(μ4-hydrogen tartrato)sodium]

A monoclinic polymorph of the title compound, [Na(C4H5O6)(H2O)]n, is reported and complements an orthorhombic form [Kubozono, Hirano, Nagasawa, Maeda & Kashino (1993). Bull. Chem. Soc. Jpn, 66, 2166–2173]. The asymmetric unit contains a hydrogen tartrate anion, an Na+ cation and a water molecule. The Na+ ion is surrounded by seven O atoms derived from one independent and three symmetry-related hydrogen tartrate anions, and a water molecule, forming a distorted pentagonal–bipyramidal geometry. Independent units are linked via a pair of intermolecular bifurcated O—H...O acceptor bonds, generating an R21(6) ring motif to form polymeric two-dimensional arrays parallel to the (100) plane. In the crystal packing, the arrays are linked by adjacent ring motifs, together with additional intermolecular O—H...O interactions, into a three-dimensional network