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) ].