4,4′-Bipyridinium bis­(2-carboxy­pyridine-3-carboxyl­ate)

The title salt, C(10)H(10)N(2) (2+)·2C(7)H(4)NO(4) (−) or (4,4′-bpyH(2))(py-2,3-dcH)(2), prepared by the reaction between pyridine-2,3-dicarboxylic acid (py-2,3-dcH(2)) and 4,4′-bipyridine (4,4′-bpy), consists of two anions and one centrosymmetric dication. In the crystal, there are two strong O—H⋯O hydrogen bonds involving the two carboxyl­ate groups, with an O⋯O distance of 2.478 (1) Å, and an N—H⋯N hydrogen bond between the anion and cation, with an N⋯N distance of 2.743 (1) Å. These inter­actions, along with other O—H⋯O and C—H⋯O hydrogen bonds, π–π stacking [centroid–centroid distances 3.621 (7) and 3.612 (7) Å] and ion pairing, lead to the formation of the three-dimensional structure.