4-Methoxybenzamidinium hydrogen oxalate monohydrate

The title hydrated salt, C8H11N2O+·C2HO4 -·H2O, was synthesized by a reaction of 4-methoxybenzamidine (4-amidinoanisole) and oxalic acid in water solution. In the cation, the amidinium group forms a dihedral angle of 15.60 (6)°with the mean plane of the benzene ring. In the crystal, each amidinium unit is bound to three acetate anions and one water molecule by six distinct N-H⋯O hydrogen bonds. The ion pairs of the asymmetric unit are joined by two N-H⋯O hydrogen bonds into ionic dimers in which the carbonyl O atom of the semi-oxalate anion acts as a bifurcated acceptor, thus generating an R 1 2(6) motif. These subunits are then joined through the remaining N-H⋯O hydrogen bonds to adjacent semi-oxalate anions into linear tetrameric chains running approximately along the b axis. The structure is stabilized by N-H⋯O and O-H⋯O intermolecular hydrogen bonds. The water molecule plays an important role in the cohesion and the stability of the crystal structure being involved in three hydrogen bonds connecting two semi-oxalate anions as donor and a benzamidinium cation as acceptor.