The title compound, C7H8N2O4, crystallizes as a zwitterion, with molecules organized into molecular sheets via carboxyl–carboxylate and N+—H⋯carboxylate contacts. These sheets are constructed from translationally related molecules that further link to neighboring motifs via π-stacking [centroid–centroid distance 3.504 (3) Å] and weak C—H⋯O contacts.
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