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The title Schiff base compound, C17H13N3O3, crystallizes in a zwitterionic form and exists in a trans configuration about the C=N bond. The mol­ecule is slightly twisted, the dihedral angle between the benzene ring and naphthalene ring system being 10.80 (9)°. The nitro group is twisted relative to the plane of the benzene ring [dihedral angle = 8.88 (12)°]. Bifurcated intra­molecular N—H⋯N and N—H⋯O hydrogen bonds formed between iminium groups and amine N atoms and naphthalen-2-olate O atoms generate S(5) and S(6) ring motifs, respectively. In the crystal, neighbouring zwitterions are linked through weak C—H⋯O inter­actions, giving rise to screw chains along [010]. Mol­ecules in these chains are linked to those of an adjacent chains through N—H⋯O hydrogen bonds and weak C—H⋯O inter­actions, forming sheets parallel to the ac plane. O⋯C [2.895 (3) Å] short contacts and π–π inter­actions [centroid–centroid distance = 3.8249 (19) Å] are also observed.

The title compound, C7H6ClNO2, is almost planar, with an r.m.s. deviation of 0.040 Å. An intra­molecular N—H⋯O hydrogen bond generates an S(6) ring motif. In the crystal, mol­ecules are linked into centrosymmetric dimers by pairs of O—H⋯O hydrogen bonds. These dimers are stacked along [010].

The title Schiff base compound, C18H13NO2, is a zwitterion, with the naphthol hy­droxy group deprotonated and the imine N atom protonated. It adopts an E configuration about the central C=N double bond. The dihedral angle between the naphthyl ring system and the benzene ring is 1.73 (11)°. An intra­molecular N—H⋯O hydrogen bond generates an S(6) ring motif. In the crystal, adjacent mol­ecules are connected by inter­molecular C—H⋯O hydrogen bonds, forming a supra­molecular ribbon along the b axis.

Key indicators: single-crystal X-ray study; T = 100 K; mean (C-C) = 0.002 Å; R factor = 0.038; wR factor = 0.111; data-to-parameter ratio = 18.8.The title Schiff base compound, C 14 H 10 ClNO 4 , has been synthesized by the reaction of 5-amino-2-hydroxybenzoic acid and 5-chloro-2-hydroxybenzaldehyde. The molecule is a zwitterion in the crystal, with the phenolic hydroxy group deprotonated and the imine N atom protonated. It adopts an E configuration about the central C N double bond. The dihedral angle between the two benzene rings is 3.83 (7) . Intramolecular N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonding generates S(6) ring motifs. In the crystal, molecules are connected by intermolecular O-HÁ Á ÁO and C-HÁ Á ÁCl hydrogen bonds, forming a supramolecular chain. Related literature