2-Amino-5-nitro-pyridinium hydrogen oxalate.

In the cation of the title mol-ecular salt, C5H6N3O2 (+)·C2HO4 (-), the dihedral angle between the aromatic ring and the nitro group is 3.5†(3)°; in the anion, the dihedral angle between the CO2 and CO2H planes is 10.5†(2)°. In the crystal, the anions are linked into [100] chains by O-H⋯O hydrogen bonds. The cations cross-link the chains by way of N-H⋯O hydrogen bonds and the structure is consolidated by C-H⋯O inter-actions.