Crystal structure of di­methyl­ammonium hydrogen oxalate hemi(oxalic acid)

Single crystals of the title salt, Me(2)NH(2) (+)·HC(2)O(4) (−)·0.5H(2)C(2)O(4), were isolated as a side product from the reaction involving Me(2)NH, H(2)C(2)O(4) and Sn(n-Bu)(3)Cl in a 1:2 ratio in methanol or by the reaction of the (Me(2)NH(2))(2)C(2)O(4) salt and Sn(CH(3))(3)Cl in a 2:1 ratio in ethanol. The asymmetric unit comprises a di­methyl­ammonium cation (Me(2)NH(2) (+)), an hydrogenoxalate anion (HC(2)O(4) (−)), and half a mol­ecule of oxalic acid (H(2)C(2)O(4)) situated about an inversion center. From a supra­molecular point of view, the three components inter­act together via hydrogen bonding. The Me(2)NH(2) (+) cations and the HC(2)O(4) (−) anions are in close proximity through bifurcated N—H⋯(O,O) hydrogen bonds, while the HC(2)O(4) (−) anions are organized into infinite chains via O—H⋯O hydrogen bonds, propagating along the a-axis direction. In addition, the oxalic acid (H(2)C(2)O(4)) mol­ecules play the role of connectors between these chains. Both the carbonyl and hydroxyl groups of each diacid are involved in four inter­molecular inter­actions with two Me(2)NH(2) (+) and two HC(2)O(4) (−) ions of four distinct polymeric chains, via two N—H⋯O and two O—H⋯O hydrogen bonds, respectively. The resulting mol­ecular assembly can be viewed as a two-dimensional bilayer-like arrangement lying parallel to (010), and reinforced by a C—H⋯O hydrogen bond.