(Dimethylphosphoryl) methanaminium hydrogen oxalate-oxalic acid (2/1)

The reaction of (dimethylphosphoryl) methanamine (dpma) with oxalic acid in ethanol yielded the title solvated salt, C3H11NOP (+)center dot C2HO4 center dot 0.5C(2)H(2)O(4). Its asymmetric unit consists of one dpmaH(+) cation, one hydrogen oxalate anion and a halfmolecule of oxalic acid located around a twofold rotation axis. The H atom of the hydrogen oxalate anion is statistically disordered over two positions that are trans to each other. The hydrogen oxalate monoanion is not planar (bend angle similar to 16 degrees) whereas the oxalic acid molecule shows a significantly smaller bend angle (similar to 7 degrees). In the crystal, the components are connected by strong O-H center dot center dot center dot O and much weaker N-H center dot center dot center dot O hydrogen bonds, leading to the formation of layers extending parallel to (001). The structure was refined from a racemically twinned crystal with twin components in an approximate 1: 1 ratio.