2-Hydroxy-5-{[(E)-4-methoxybenzylidene]azaniumyl}benzoate

In the title zwitterion, C15H13NO4, obtained from the condensation of 5-aminosalicylic acid and 4-methoxybenzaldehyde, the 4-hydoxyanilinic group of the 5-aminosalicylic acid moiety and the 4-methoxybenzaldehyde moiety are twisted with respect to one another, making a dihedral angle of 10.37 (7)°. The carboxylate group makes a dihedral angle of 5.7 (2)° with the parent 4-hydoxyanilinic group. An intramolecular O—H⋯O hydrogen bond forms an S(6) ring motif. In the crystal, intermolecular C—H⋯O and N—H⋯O hydrogen bonds with R 2 1(7) ring motifs link the molecules into infinite chains extending along the c axis. The occurence of slipped π–π stacking between symmetry-related aromatic rings reinforces the packing.