4-Meth­oxy­benzamidinium hydrogen oxalate monohydrate

The title hydrated salt, C(8)H(11)N(2)O(+)·C(2)HO(4) (−)·H(2)O, 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.