Experimental

R factor = 0.029; wR factor = 0.086; data-to-parameter ratio = 11.7. In the title hydrated molecular salt, (C3H5N2)[Cr(C2O4)2-(H2O)2]2H2O, the complete cation is generated by a crystal-lographic twofold rotation axis, with one C atom lying on the rotation axis. The complete anion is generated by crystal-lographic inversion symmetry (CrIII site symmetry 1), to generate a slightly distorted CrO6 octahedron with trans water molecules and chelating oxalate dianions. The oxalate ion is almost planar (r.m.s. deviation = 0.017 Å) and the five-membered chelate ring is a shallow envelope with the metal ion displaced by 0.126 (1) A ̊ from the ligand atoms. The crystal structure features O—H O, N—H O and C—H O hydrogen bonds, which link the components into a three-dimensional network. Related literature For a related structure and background to oxalate complexes, see: Chérif et al. (2012). For the structures of salts containing the [Cr(C2O4)2(H2O)2] anion with various cations, see: Bélombe ́ et al. (2009); Nenwa et al. (2010); Chérif et al. (2011); Kahlenberg et al. (2011). For geometric parameters of th