Crystal structure of dimethylammonium hydrogen oxalate hemi(oxalic acid)

Single crystals of the title salt, Me2NH2+center dot HC2O4-center dot 0.5H(2)C(2)O(4), were isolated as a side product from the reaction involving Me2NH, H2C2O4 and Sn(n-Bu)(3)Cl in a 1: 2 ratio in methanol or by the reaction of the (Me2NH2)(2)C2O4 salt and Sn(CH3)(3)Cl in a 2: 1 ratio in ethanol. The asymmetric unit comprises a dimethylammonium cation (Me2NH2+), an hydrogenoxalate anion (HC2O4-), and half a molecule of oxalic acid (H2C2O4) situated about an inversion center. From a supramolecular point of view, the three components interact together via hydrogen bonding. The Me2NH2+ cations and the HC2O4- anions are in close proximity through bifurcated N-H center dot center dot center dot(O, O) hydrogen bonds, while the HC2O4- anions are organized into infinite chains via O-H center dot center dot center dot O hydrogen bonds, propagating along the a-axis direction. In addition, the oxalic acid (H2C2O4) 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 Me2NH2+ and two HC2O4- ions of four distinct polymeric chains, via two N-H center dot center dot center dot O and two O-H center dot center dot center dot 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 center dot center dot center dot O hydrogen bond.