(E)-1-[(2-Amino-5-nitrophenyl)iminiomethyl]naphthalen-2-olate

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.


Comment
Schiff base ligands are members of an important class of compounds, possessing a wide spectrum of biological and pharmacological activities such as antibacterial and antifungal (Karthikeyan et al., 2006), anticancer (Dao et al., 2000), anti-HIV (Sriram et al., 2006), activities. Apart of these activities they have also been used as ligands to study coordination chemistry (Kagkelari et al., 2009). As part of our ongoing research on the synthesis of Schiff base ligands and their complexes (Eltayeb et al., 2007;2008;2010), the title compound (I) was synthesized and its crystal structure was determined. The title Schiff base ligand in neutral form was tested for anti-inflammatory, analgesic and kinase inhibition activities and showed moderate anti-inflammatory and analgesic activities (Sondhi et al., 2006).
The molecule of (I) ( between the NH + and amino N atom and to the naphthalen-2-olate Ogenerates an S(5) and S(6) ring motifs, respectively (Bernstein et al., 1995). The bond distances are in normal ranges (Allen et al., 1987) and comparable with the related structures (Eltayeb et al., 2009;2010).
In the crystal packing, neighbouring zwitterions are linked through weak C-H···O interactions (Table 1)  Å are also observed.

Experimental
The title compound was synthesized by adding 2-hydroxy-1-naphthaldehyde (0.688 g, 4 mmol) to the solution of 4-nitrobenzene-1,2-diamine (0.306 g, 2 mmol) in ethanol (30 ml). The mixture was refluxed with stirring for 3 hrs. The resultant solid was obtained and then filtered and washed with ethanol. Red plate-shaped single crystals of the title compound suitable for x-ray structure determination were obtained from acetone by slow evaporation at room temperature after several days.

Refinement
Amine and iminium H atoms were located from the difference maps and were refined isotropically. The remaining H atoms were placed in calculated positions with d(C-H) = 0.93 Å for aromatic and CH atoms and the U iso values were constrained supplementary materials sup-2 to be 1.2U eq of the carrier atoms. The highest residual electron density peak is located at 0.70 Å from H4A and the deepest hole is located at 0.65 Å from C4. Fig. 1. The molecular structure of the title compound, with 50° probability displacement ellipsoids and the atom-numbering scheme. Intramolecular hydrogen bonds are shown as dashed lines." is correct.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
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.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O1 0.82332 (14