2-Carb­oxy-6-(quinolin-1-ium-8-yl­oxy)benzoate

In the zwitterionic title compound, C(17)H(11)NO(5), the dihedral angle between the two aromatic rings is 76.90 (7)°. The dihedral angles between the carboxyl groups and the benzene ring are 64.02 (9) and 21.67 (9)°, the larger angle being associated with an intra­molecular N—H⋯O(carbox­yl) hydrogen bond, resulting from proton transfer from the carb­oxy­lic acid group to the quinoline N atom and giving an S(9) ring motif. In the crystal, mol­ecules are connected by O—H⋯O hydrogen bonds into chains extending along the b-axis direction. An overall two-dimensional network structure is formed through π–π inter­actions between the quinoline rings [minimum ring-centroid separation = 3.6068 (6) Å].