2-{[4-(Phenyldiazenyl)phenyl]iminomethyl}phenol

The molecule of the title compound, C19H15N3O, is approximately planar and displays a trans configuration with respect to the C=N and N=N double bonds. An intramolecular O—H⋯N hydrogen bond generates an S(6) ring motif. The dihedral angles between the hydroxyphenyl ring and the phenyl and benzene rings are 4.31 (8) and 6.60 (8)°, respectively. The dihedral angle between the phenyl and benzene rings linked by the azo group is 2.70 (8)°. The imino group is coplanar with the hydroxyphenyl ring, as shown by the C—C—C—N torsion angle of −1.8 (2)°. The azo group is disordered over two position with refined site-occupancy factors of ca 0.87/0.13. In the crystal structure, molecules are linked together by intermolecular C—H⋯O interactions along the c axis and also are packed as one-dimensional extended chains down the b axis.

The molecule of the title compound, C 19 H 15 N 3 O, is approximately planar and displays a trans configuration with respect to the C N and N N double bonds. An intramolecular O-HÁ Á ÁN hydrogen bond generates an S(6) ring motif. The dihedral angles between the hydroxyphenyl ring and the phenyl and benzene rings are 4.31 (8) and 6.60 (8) , respectively. The dihedral angle between the phenyl and benzene rings linked by the azo group is 2.70 (8) . The imino group is coplanar with the hydroxyphenyl ring, as shown by the C-C-C-N torsion angle of À1.8 (2) . The azo group is disordered over two position with refined site-occupancy factors of ca 0.87/0.13. In the crystal structure, molecules are linked together by intermolecular C-HÁ Á ÁO interactions along the c axis and also are packed as one-dimensional extended chains down the b axis.

Comment
Azobenzene and its derivatives have attracted much attention for their high potential in industrial applications, such as liquid crystals, light-driven switches and image-storage devices (Liu et al., 1990;Ikeda & Tsutsumi, 1995). In addition, azo compounds represent the dominant class of synthetic colourant employed in the textile, printing, agrochemical and pharmaceutical industries. As a result of the presence of the stable chromophoric azo group (N═N) which is capabale of linking different aromatic systems with electron-donating and/or electron-withdrawing groups, dyes can be designed to resist chemical or photochemical degradation processes (Evans et al., 1980;Griffiths & Allen, 1980;Leaver et al., 1980;Flamingi & Monti, 1985).
In the title compound (I) (Fig. 1), the molecule adopts a trans configuration with respect to the C═N and N═N double bonds. The bond lengths and angles are within the normal ranges (Allen et al., 1987). An intramolecular O-H···N hydrogen bond generates a S(6) ring motif (Bernstein et al., 1995). The dihedral angles between the hydroxyphenyl ring and the two phenyl rings are 4.31 (8) and 6.60 (8)°, respectively. The dihedral angle between the two phenyl rings joined by the azo group is 2.70 (8)°. The azo group is disordered over two position and the refined site-occupancy factors of the disordered parts are 0.869 (3)/0.131 (3). The imino group is coplanar with the hydroxyohenyl ring as it can be shown by the C1-C6-C7-N1 torsion angle of -1.8 (2)°. In the crystal structure, molecules are linked together by intermolecular C-H···O interactions (Table 1) along the c axis and also are packed as 1-D extended chains down the b axis (Fig. 2).

Experimental
The title compound was synthesized by mixing equimolar amount of the p-phenylazo aniline and salicylaldehyde in ethanol under reflux condition for 1 h. Single crystals suitable for X-ray diffraction were obtained by evaporation of an ethanol solution at room temperature.

Refinement
The H atom bound to the oxygen atom was located from the difference Fourier map and refined freely with the parent atom.
The rest of the hydrogen atoms were positioned geometrically and refined as riding model with C-H = 0.93 Å and U iso (H) = 1.2U eq (C). The highest peak is located 0.73 Å from C11 and the deepest hole is located 0.66 Å from C19.   (7) 0.0062 (7) Geometric parameters (Å, °)