Bis(2-aminopyridinium) maleate.

Two cyclic eight-membered hydrogen-bonded rings exist in the title compound, 2C(5)H(7)N(2)(+) x C(4)H(2)O(4)(2-), involving the 2-aminopyridinium and maleate ions. The dihedral angle between the two pyridinium rings hydrogen bonded to the maleate ion is 74.80 (4) degrees. The maleate anion lies on a twofold axis and is linked to the pyridinium cations by intermolecular N-H.O hydrogen bonds. The heterocycle is fully protonated, which enables amino-imino tautomerization.