(E)-3-{[(2-Bromo-3-methylphenyl)imino]methyl}benzene-1,2-diol: crystal structure and Hirshfeld surface analysis

In the title Schiff base derivative carrying a 2-bromo-3-methylphenyl group, the conformation about the C=N bond is E. In the crystal, O—H⋯O hydrogen-bond interactions consolidate the crystal packing. A Hirshfeld surface analysis and fingerprint plots were used to further investigate the intermolecular interactions in the solid state.


Chemical context
Schiff bases containing an azomethine or imine (-C N-) unit are condensation products of primary amines and carbonyl compounds that were first reported by Hugo Schiff (1864). Schiff bases have a wide variety of applications in many areas of biological, organic and inorganic chemistry. The medicinal uses and applications of Schiff bases and their metal complexes are of increasing clinical and commercial importance and are increasingly significant in the medicinal and pharmaceutical fields because of their extensive range of biological activities (Karthikeyan et al., 2006).

Structural commentary
The structure of the title compound is shown in Fig. 1. It crystallizes in the centrosymmetric P1 space group with Z = 4 (Z 0 = 2). The two crystallographically independent molecules have nearly the same geometrical parameters and the primary difference between them is the rotational orientation of H2 and H4A. The discussion will therefore be limited to that of the molecule containing O1. The molecular structure is constructed from two individually planar rings. The whole molecule is approximately planar, with a maximum deviation of 0.117 (3) Å from planarity for the hydroxyl O1 atom of the catechol ring. The dihedral angle between the two benzene ring planes is 2.80 (17) . The methyl C1 atom deviates from the plane of the C2-C7 benzene ring by 0.039 (2) Å while C9 deviates from the plane of the C9-C14 benzene ring by 0.024 (3) Å . The C8-N1-C7-C6 and C14-C9-C8-N1 torsion angles are À1.6 (5) and À1.1 (5) , respectively. The planar molecular conformation of each molecule is stabilized by an intramolecular O-HÁ Á ÁN hydrogen bond (Table 1).

Figure 2
A partial view of the crystal packing of the title compound. Intra-and intermolecular hydrogen bonds are shown as dotted lines while thestacking interactions are depicted by dashed lines.

Figure 1
The molecular structure of the title compound with the atomic numbering scheme. The dashed lines indicate the intramolecular O-HÁ Á ÁN hydrogen bonds. Displacement ellipsoids are drawn at the 30% probability level.
imine N atom acts as an hydrogen-bond acceptor, is an important prerequisite for the tautomeric shift toward the phenol-imine form. In fact, in all eight structures of the phenol-imine tautomers, hydrogen bonds of this type are observed.

Hirshfeld surface analysis
Hirshfeld surface analysis of the title compound was performed utilizing the CrystalExplorer program (Turner et al., 2017). The three-dimensional d norm surface is a useful tool for analysing and visualizing the intermolecular interactions and utilizes the function of the normalized distances d e and d i , where d e and d i are the distances from a given point on the surface to the nearest atom outside and inside, respectively. The blue, white and red colour convention used for the d normmapped Hirshfeld surfaces indicates the interatomic contacts longer, equal to or shorter than the van der Waals separations. The standard-resolution molecular three-dimensional (d norm ) plot with d e and d i for the title compound is shown in Fig. 3. The bright-red spots near the oxygen and hydrogen atoms indicate donors and acceptors of a potential O-HÁ Á ÁO interaction. As can be seen from the two-dimensional fingerprint plots (scattering points spread up to d e = d i = 1.5 Å ; Fig. 4), the dominant interaction in the title compound originates from HÁ Á ÁH contacts, which are the major contributor (42.4%) to the total Hirshfeld surface. The contribution from the OÁ Á ÁH/HÁ Á ÁO contacts (13.5%) is represented by a pair of sharp spikes that are characteristic of hydrogen-bonding interactions (Fig. 4). Other significant interactions are BrÁ Á ÁH/ HÁ Á ÁBr (12.9%) and CÁ Á ÁH/HÁ Á ÁC (15.3%). While it is likely there are other identifiable points of contact that can be highlighted in the crystal, these may be of limited significance and do not require detailed discussion nor illustration. The interactions are visualized in Fig. 5.

Synthesis and crystallization
A mixture of 2,3-dihydroxybenzaldehyde (34.5 mg, 0.25 mmol) and 2-bromo-3-methylaniline (46.5 mg, 0.25 mmol) was stirred with ethanol (30 mL) at 377 K for 5 h, View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm , d e and d i .

Figure 4
Two-dimensional fingerprint plots of the crystal with the relative contributions of the atom pairs to the Hirshfeld surface.

Figure 5
Hirshfeld surface mapped over d norm to visualize the intermolecular interactions.
affording the title compound (49.73 mg, yield 65% m.p. 410-412 K). Single crystals suitable for X-ray measurements were obtained by recrystallization from ethanol at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The hydroxy H atom was located in a difference-Fourier map, and the hydroxy group was allowed to rotate during the refinement procedure (AFIX 147); O-H = 0.82 Å with U iso (H) = 1.5U eq (O). The C-bound H atoms were positioned geometrically and refined using a riding model: C-H = 0.93 Å with U iso (H) = 1.2U eq (C) for aromatic H atoms and C-H = 0.96 Å with U iso (H) = 1.5U eq (C) for methyl H atoms.  SHELXT2018 (Sheldrick, 2015a), SHELXL2018 (Sheldrick, 2015b); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: Mercury (Macrae et al., 2006), WinGX (Farrugia, 2012) and PLATON (Spek, 2009). 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.