The title salt, 2C3H8N(+)·C2O4 (2-), crystallized with six independent allyl-ammonium cations and three independent oxalate dianions in the asymmetric unit. One of the oxalate dianions is nearly planar [dihedral angle between CO2 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 allyl-ammonium 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.
Keywords: allylammonium; crystal structure; dication; hydrogen bonding; oxalate.