title: Allyl-ammonium hydrogen oxalate hemihydrate.
abstract: In the title hydrated mol-ecular salt, C3H8N(+)·C2HO4 (-)·0.5H2O, the water O atom lies on a crystallographic twofold axis. The C=C-C-N torsion angle in the cation is 2.8 (3)° and the dihedral angle between the CO2 and CO2H planes in the anion is 1.0 (4)°. In the crystal, the hydrogen oxalate ions are linked by O-H⋯O hydrogen bonds, generating [010] chains. The allyl-ammonium cations bond to the chains through N-H⋯O and N-H⋯(O,O) hydrogen bonds. The water mol-ecule accepts two N-H⋯O hydrogen bonds and makes two O-H⋯O hydrogen bonds. Together, the hydrogen bonds generate (100) sheets.
authors.affiliation: Faculty of Chemistry, University of Opole, Oleska 48, 45-052 Opole, Poland.
authors.forename: Błażej
authors.initials: B
authors.lastname: Dziuk
authors.affiliation: Faculty of Chemistry, University of Opole, Oleska 48, 45-052 Opole, Poland.
authors.forename: Bartosz
authors.initials: B
authors.lastname: Zarychta
authors.affiliation: Faculty of Chemistry, University of Opole, Oleska 48, 45-052 Opole, Poland.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Ejsmont
keywords: crystal structure