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.

In the title zwitterion, C 15 H 13 NO 4 , 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-HÁ Á ÁO hydrogen bond forms an S(6) ring motif. In the crystal, intermolecular C-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds with R 2 1 (7) ring motifs link the molecules into infinite chains extending along the c axis. The occurence of slippedstacking between symmetry-related aromatic rings reinforces the packing.
The occurence of slippest π-π stacking (Janiak, 2000) between symmetry related aromatic rings play an important role in stabilizing the packing.

Experimental
Equimolar quantities of 5-aminosalicylic acid and 4-anisaldehyde were refluxed in methanol for 30 min resulting in clear brown solution. The solution was kept at room temperature which affoarded light brown prisms after 72 h.

Refinement
All H atoms attached to C atoms and N atom were fixed geometrically and treated as riding with C-H = 0.95 Å (methyl) or 0.93 Å (aromatic) and N-H = 0.86 Å with U iso (H) = 1.2U eq (C aromatic or N) or U iso (H) = 1.5U eq (C methyl ). H atoms of the hydroxyl group was located in difference Fourier maps and included in the subsequent refinement using restraints

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.