Crystal structure of bis­(allyl­ammonium) oxalate

The title salt, 2C(3)H(8)N(+)·C(2)O(4) (2−), crystallized with six independent allyl­ammonium cations and three independent oxalate dianions in the asymmetric unit. One of the oxalate dianions is nearly planar [dihedral angle between CO(2) planes = 1.91 (19)°], while the other two are twisted with angles of 11.3 (3) and 26.09 (13)°. One cation has a synperiplanar (cis) conformation with an N—C—C—C torsion angle of 0.9 (3)°, whereas the five remaining cations are characterized by gauche arrangements, with the N—C—C—C torsion angles ranging from 115.9 (12) to 128.8 (3)°. One of the allyl­ammonium cations is positionally disordered (fixed occupancy ratio = 0.45:0.55). In the crystal, the cations and anions are connected by a number of strong N—H⋯O and N—H⋯(O,O) hydrogen bonds, forming layers parallel to (001), with the vinyl groups protruding into the space between the layers.