A new polymorph of magnesium oxalate dihydrate

In the asymmetric unit of the title compound, catenapoly[[ diaquamagnesium( II)]- mu-oxalato], [ Mg(C2O4)(H2O)2](n), there is one Mg atom in an octahedral coordination with site symmetry 222, a unique C atom of the oxalate anion lying on a twofold axis, an O atom of the anion in a general position and a water O atom at a site with imposed twofold rotation symmetry. The Mg2+ ions are ligated by water molecules and bridged by the anions to form chains that are held together by O-H center dot center dot center dot O hydrogen bonds. The structure of the title compound has already been reported in a different space group [ Lagier, Pezerat & Dubernat ( 1969). Rev. Chim. Miner. 6, 1081 - 1093; Levy, Perrotey & Visser ( 1971). Bull. Soc. Chim. Fr. pp. 757 - 761].