Betaine betainium hydrogen oxalate

The title compound, C5H12NO2+·C2HO4−·C5H11NO2 or HC2O4−·(HBET·BET)+ [BET is tri­methyl­glycine (betaine); IUPAC name: 1-carboxy-N,N,N-tri­methyl­methanaminium hydro­xide inner salt], contains pairs of betaine mol­ecules bridged by an H atom, forming dimers linked by a strong hydrogen bond. The hydrogen oxalate anions have a rather unusual star conformation, with an internal torsion angle of 70.1 (4)°. The betaine–betainium dimers are anchored between two zigzag chains of hydrogen oxalate mol­ecules hydrogen bonded head-to-tail running parallel to the b axis. An extended network of C—H⋯O interactions links the anionic chains to the cationic dimers.