2-Hy­droxy-5-[(E)-(1H-indol-3-yl­methyl­idene)aza­nium­yl]benzoate

The zwitterionic title compound, C(16)H(12)N(2)O(3), was obtained as a result of the condensation of 5-amino­salicylic acid and 1H-indole-3-carbaldehyde. The whole mol­ecule is roughly planar: the 4-hy­droxy­anilinic group and the 1H-indole-3-carbaldehyde moieties are only slightly twisted, making a dihedral angle of 7.77 (11)°, whereas, the carboxyl­ate group makes a dihedral angle of 3.34 (45)° with the parent 4-hy­droxy­anilinic group. S(6) ring motifs are formed due to intra­molecular O—H⋯O hydrogen bonding. In the crystal, inter­molecular N—H⋯O and C—H⋯O hydrogen bonds build up pseudo-rings with R (1) (2)(4), R (2) (1)(7) and R (2) (2)(14) ring motifs. These pseudo-dimers are further linked by N—H⋯O hydrogen bonds into a chain extending along [101]. C—H⋯π inter­actions also occur, along with offset π–π inter­actions between the anilinic phenyl and the heterocyclic five-membered rings with a centroid–centroid distance of 3.5716 (19) Å.