4-Phenyldiazenyl-2-[(R)-(1-phenylethyl)iminomethyl]phenol

The title chiral photochromic Schiff base compound, C21H19N3O, was synthesized from (R)-1-phenylethylamine and the salicylaldehyde of an azobenzene derivative. The molecule corresponds to the phenol–imine tautomer, the C=N and N—C bond distances being 1.279 (3) and 1.477 (3) Å, respectively. An intramolecular O—H⋯N hydrogen bond occurs. The diazenyl group adopts a trans form with an N=N distance of 1.243 (3) Å.

The title chiral photochromic Schiff base compound, C 21 H 19 N 3 O, was synthesized from (R)-1-phenylethylamine and the salicylaldehyde of an azobenzene derivative. The molecule corresponds to the phenol-imine tautomer, the C N and N-C bond distances being 1.279 (3) and 1.477 (3) Å , respectively. An intramolecular O-HÁ Á ÁN hydrogen bond occurs. The diazenyl group adopts a trans form with an N N distance of 1.243 (3) Å .
The crystal structure of (I) is similar to that of the analogous Schiff base ligands (Akitsu et al., 2006b;Miura et al., 2009).
The molecule of (I) (Fig. 1) adopts an E configuration with respect to the imine C=N double bond with C6-C7-N1-C8 torsion angle of 179.21 (16)°. Thus, the π-conjugated system around the imine group is essentially planar. The C1-O1 bond distance of 1.337 (3) Å suggests that it is in the phenol-imine tautomer. The contraction of the C7=N1 bond is also in agreement with the phenol-imine tautomer. As for the azobenzene moiety, the azo N=N double bond adopts an E configuration with the N=N distance of 1.243 (3) Å. Beside them, geometric parameters reported agree with the corresponding values for analogous azobenzene derivatives (Aslantaş et al., 2007;Khandar & Rezvani,1999).
The planarity of (I) is stabilized by an intramolecular O-H···N hydrogen bond (Table 1). However, there is no intermolecular hydrogen bonds in the crystal structure.

Experimental
Treatment of aniline (6.24 g, 67.0 mmol) in 30 ml of 6M HCl and NaNO 2 (4.69 g, 68.0 mmol) in 30 ml of H 2 O for 30 min at 278 K gave rise to the yellow precursor. Treatment of the precursor and salicylaldehyde (8.18 g, 67.0 mmol) in 30 ml of 10 % NaOH aqueous solution for 1 hour at 278 K, and the resulting brown precipitates were filtrated and washed with water and ethanol, and dried in a desiccator for several days. Treatment of the brown precipitates (0.226 g, 1.00 mmol) and (R)-1-phenylethylamine (0.121 g, 1.00 mmol) for 2 hours at 313 K gave rise to redish violet crystals after evaporation (yield 0.21 g, 64 %).

Refinement
All H atoms were placed at the calculated positions (C-H = 0.95-1.00 Å) and were included in the refinement in the riding mode with U iso (H) = 1.2-1.5U eq (C). The OH hydrogen atom was located in a difference Fourier map, and was freely refined.
Friedel pairs were merged.  Fig. 1. The molecular structure of (I), showing the atom labeling scheme. Displacement ellipsoids are drawn at the 50% probability level.

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.
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 Rfactors(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.