2-Aminopyridinium-fumarate-fumaric acid (2/1/1).

The title complex, 2C5H7N2+.C4H2O42-.C4H4O4, contains cyclic eight-membered hydrogen-bonded rings involving 2-aminopyridinium and fumarate ions. The fumaric acid molecules and fumarate ions lie on inversion centers and are linked into zigzag chains by O-H...O hydrogen bonds. The dihedral angle between the pyridinium ring and the hydrogen-bonded fumarate ion is 7.60 (4) degrees. The fumarate anion is linked to the pyridinium cations by intermolecular N-H...O hydrogen bonds. The heterocycle is fully protonated, thus enabling amine-imine tautomerization.