Crystal structure of (E)-2-{[(4-anilinophenyl)imino]methyl}phenol

The title compound crystallized with two independent molecules (A and B) in the asymmetric unit, which differ essentially in the orientation of the terminal aminophenyl ring with respect to the central benzene ring. In the crystal, molecules are linked via N—H⋯O hydrogen bonds forming –A-B–A–B– zigzag chains propagating along [010].


Chemical context
Schiff bases often exhibit various biological activities and in many cases have been shown to have antibacterial, anticancer, anti-inflammatory and antitoxic properties (Lozier et al., 1975). They are used as anion sensors (Dalapati et al., 2011), as non-linear optics compounds (Sun et al., 2012) and as versatile polynuclear ligands for multinuclear magnetic exchange clusters (Moroz et al., 2012). Schiff bases have also been used to prepare metal complexes (Faizi & Sen, 2014;Faizi & Hussain, 2014;Penkova et al., 2010). We report herein on the crystal structure of the title compound synthesized by the condensation reaction of salicyladehyde and N-phenyl-pphenylenediamine.
The conformation of the two molecules differs essentially in the orientation of the terminal aminophenyl rings (C14-C19 and C33-C38) with respect to the central benzene rings (C8-C13 and C27-C32); this dihedral angle is 50.51 (4) in molecule A and 54.61 (14) in molecule B. The two outer aromatic rings (C1-C6 and C14-C19 in A, and C20-C25 and C33-C38 in B) are inclined to one another by 51.39 (14) and 49.88 (14) in molecules A and B, respectively. The C-N, C N and C-C bond lengths are normal and close to the values observed in related structures (Sliva et al., 1997;Petrusenko et al., 1997).

Supramolecular features
In the crystal, molecules are connected by N-HÁ Á ÁO hydrogen bonds, generating -A-B-A-B-zigzag chains extending along [010]; Table 1 and Fig. 2. The chains are linked via C-HÁ Á Á interactions involving neighbouring A molecules, forming slabs lying parallel to (100); see Table 1

Database survey
There are very few examples of similar compounds in the literature although some metal complexes of similar ligands have been reported on (Xie et al., 2013;Safin et al., 2012). A search of the Cambridge Structural Database (Version 5.35, May 2014;Groom & Allen, 2014) revealed the structure of one very similar compound, viz. N-[(E)-4-chlorobenzylidene]-N 0 -phenylbenzene-1,4-diamine (II) (Nor Hashim et al., 2010), in which the 2-phenol ring in the title compound is replaced by a 4-chlorobenzene ring. In (II), the central six-membered ring makes a dihedral angle of 12.26 (10) with the 4-chlorophenyl ring. The same dihedral angle is smaller in the title compound, 4.93 (14) in molecule A and 7.12 (14) in molecule B, owing to the presence of the intramolecular O-HÁ Á ÁN hydrogen bond. The outer phenyl ring is inclined to the central sixmembered ring by 44.18 (11) in (II), compared to 50.51 (4) and 54.61 (14) in molecules A and B, respectively, of the title compound.

Synthesis and crystallization
100 mg (1 mmol) of N-phenyl-p-phenylenediamine were dissolved in 10 ml of absolute ethanol. To this solution, 66 mg (1 mmol) of salicyladehyde in 5 ml of absolute ethanol was added dropwise with stirring. The mixture was stirred for 10 min, two drops of glacial acetic acid were then added and the mixture was further refluxed for 2 h. The resulting reddish yellow precipitate was recovered by filtration, washed several times with a small portions of EtOH and then with diethyl ether to give 120 mg (75%) of the title compound. Crystals suitable for X-ray analysis was obtained within 3 days by slow evaporation of a solution in methanol. The molecular structure of the two independent molecules (A and B) of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 40% probability level. Intramolecular O-HÁ Á ÁN hydrogen bonds are shown as dashed lines (see Table 1 for details). Table 1 Hydrogen-bond geometry (Å , ).  Symmetry codes: (i) x; y; z À 1; (ii) x; y þ 1; z þ 1; (iii) Àx; y þ 1 2 ; Àz þ 1.

Figure 3
A view along the c axis of the crystal packing of the title compound. The hydrogen bonds and C-HÁ Á Á interactions are shown as dashed lines (see Table 1 for details; for the latter interactions the atoms involved are shown as light and dark grey balls).

Figure 2
A view of the -A-B-A-B-zigzag hydrogen-bonded chain in the crystal of the title compound, extending along the b axis (hydrogen bonds are shown as dashed lines; see Table 1 for details).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The N-H and O-H H atoms were located from a difference Fourier map and constrained to ride on their parent atoms, with N-H = 0.86 and O-H = 0.82 Å and with U iso (H) = 1.2U eq (N) and = 1.5U eq (O). All Cbound H atoms were positioned geometrically and refined using a riding model with C-H = 0.93 Å and with U iso (H) = 1.2U eq (C).

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