2-Amino-4-methyl-pyridinium 6-carb-oxy-pyridine-2-carboxyl-ate sesquihydrate.

In the title compound, C(6)H(9)N(2) (+)·C(7)H(4)NO(4) (-)·1.5H(2)O, extensive O-H⋯O, O-H⋯N, N-H⋯O and C-H⋯O hydrogen bonds, as well as ion pairing, π-π stacking inter-actions [centroid-centroid distances = 3.4690 (8) and 3.6932 (8) Å between aromatic rings] occur in the crystal. There are hydrogen-bonding inter-actions between water mol-ecules, which result in cyclic tetra-meric water clusters. One of the water O molecules has half occupancy. In the anion molecules, the -CO(2) and -CO(2)H groups make torsion angles of 1.73 (18) and -12.14 (18)° with respect to the ring.