2′,6′-Bis(4-carb­oxy­phen­yl)-4,4′-bipyridin-1-ium nitrate 0.25-hydrate

In the title compound, C₂₄H₁₇N₂O₄⁺·NO₃⁻·0.25H₂O, the central pyridine ring of the 2′,6′-bis­(4-carb­oxy­phen­yl)-4,4′-bipyridin-1-ium cation is almost coplanar with one benzene ring [dihedral angle = 1.03 (5)°], while it makes dihedral angles of 9.59 (5)° with the other benzene ring and 13.66 (6)° with the pyridinium ring. In the crystal, N—H...O and O—H...O hydrogen bonds link the cations and nitrate anions into a sheet in the (302) plane. The crystal structure also exhibits π–π inter­actions between the central pyridine ring and the benzene rings of neighboring mol­ecules [centroid–centroid distance = 3.6756 (13) Å].