(E)-4-Bromo-2-[(2-hydroxyphenyl)iminiomethyl]phenolate

The title compound, C13H10BrNO2, crystallizes in a zwitterionic form. The zwitterion exists in a trans configuration about the C=N bond and is almost planar, the dihedral angle between the two benzene rings being 2.29 (9)°. An intramolecular N—H⋯O hydrogen bond formed between the iminium NH+ and the phenolate O− atoms generates an S(6) ring motif. In the crystal, the zwitterions are linked through O—H⋯O hydrogen bonds into chains along [101] and these chains are further connected through C—H⋯Br interactions into a two-dimensional network perpendicular to (101). C⋯C [3.572 (3)–3.592 (3) Å] and C⋯Br [3.5633 (19)–3.7339 (18) Å] short contacts are observed. The crystal studied was a twin with twin law 00, 00, 001 with a domain ratio of 0.09919 (2):0.90081 (2).


Comment
Much attention has been given to Schiff base ligands due to their applications such as in coordination chemistry (Kagkelari et al., 2009), chelated boron catalyst (Wei & Atwood, 1998), pharmacological activities, anticancer (Dao et al., 2000), anti-HIV (Sriram et al., 2006), antibacterial and antifungal (Karthikeyan et al., 2006) activities. We have reported the crystal structures of Schiff base ligands which existed in a zwitterionic form i. (Eltayeb et al., 2009) (Eltayeb et al., 2010). Herein we report the crystal structure of the title zwitterionic Schiff base ligand (I).
The molecule is almost planar with the dihedral angle between the two benzene rings of 2.31 (9)°. The hydroxy group is co-planar with the attached C8-C13 benzene ring with the r.m.s. of 0.0102 (2) Å for the seven non H atoms. Intramolecular N-H···O hydrogen bond between the NH + and the phenolate Ogenerates an S(6) ring motif ( Fig. 1; Table 1) which help to stabilize the planarity of the molecule (Bernstein et al., 1995). The bond distances are in normal ranges (Allen et al., 1987) and comparable with those found in related structures (Eltayeb et al., 2009(Eltayeb et al., , 2010Tan & Liu, 2009).
In the crystal packing (Fig. 2), the zwitterions are linked through O2-H1O2···O1 hydrogen bonds into chains along the

Experimental
The title compound was synthesized by adding 5-bromo-2-hydroxybenzaldehyde (0.402 g, 2 mmol) to a solution of 2aminophenol (0.218 g, 2 mmol) in ethanol (30 ml). The mixture was refluxed with stirring for half an hour. The resultant yellow solution was filtered and the filtrate was evaporated to give a yellow solid product. Yellow needle-shaped single crystals of the title compound suitable for x-ray structure determination were obtained from ethanol by slow evaporation at room temperature after nine days.

Refinement
Hydroxyl H atom was placed in calculated positions with d(O-H) = 0.82 Å and the U iso values was constrained to be 1.5U eq of the carrier atom. The remaining H atoms were located from the difference map and isotropically refined. The highest residual electron density peak is located at 0.80 Å from Br1 and the deepest hole is located at 0.99 Å from Br1.
supplementary materials sup-2 The crystal studied was a twin with twin law 1 0 0, 0 1 0, 0 0 1, leading to a distribution (refined BASF parameter) of 0.09919/0.90081 (2). Fig. 1. The molecular structure of the title compound, with 50% probability displacement ellipsoids and the atom-numbering scheme. Hydrogen bond is shown as dashed lines.

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.