4-(4-Ethylphenyldiazenyl)phenol

The crystal structure of the title compound, C14H14N2O, determined at 100 K, shows that the molecules are not planar in the solid state, in contrast to other diazene (azobenzene) derivatives. The dihedral angle between the planes of the two aromatic rings is 42.32 (7)°. The molecules are linked by intermolecular O—H⋯N hydrogen bonds, forming an infinite one-dimensional chain.


Comment
Azobenzenes are widely used as dyes, but also as photochemical switch using photo-isomerization by UV light to induce a conformational change from trans to cis and back. This principle has been explored extensively in order to exploit the isomerization for several applications. (Shibaev et al., 2003) The presence of the phenolic moiety makes it possible to form complexes with e.g. poly (4-vinylpyridine) homopolymer or with poly (4-vinylpyridine) containing block copolymers. These supramolecular comb-like polymeric structures give rise to hierarchical structure-in-structure morphologies comparable with the systems with poly (4-vinylpyridine) containing block co-polymers complexed with nona-or pentadecylphenol. (Ruokolainen et al., 1998(Ruokolainen et al., , 1999 The molecular geometry of (I) and the adopted atom-numbering scheme are shown in the perspective view in Figure 1. The crystal structure is similar to several other azo compounds, (Kocaokutgen et al. 2003;Soylu et al. 2004;Zhang et al., 1998) The -N1=N2-bond length is 1.2636 (16) Å, indicating a double-bond character.
Regarding the azo double bond the rings are in a trans configuration. In contrast to many other azocompounds the benzene rings of EPAP are not coplanar.

Experimental
To a vigorously stirred solution of 1.21 g of ethylaniline (0.01 mol) in 3 ml of water and 3 ml of concentrated hydrochloric acid, a solution of 2.8 g sodiumnitrite in 20 ml water was added drop wise while maintaining the temperature during the reaction at 0 °C. The resulting pale yellow mixture was added drop wise to a phenolate ion solution which was prepared by dissolving 0.94 g phenol (0.01 mol) and 0.84 g potassium hydroxide (0.015 mol) in 20 ml of methanol. Dichloromethane was used to extract the product from the aquatic reaction mixture, followed by 5 times washing with water. The solvent was then removed by evaporation. Subsequently the crude product was purified over a silica gel column using a dichloromethane / n-hexane mixture (3:1 v/v). The final solution was evaporated to dryness and dried further overnight in vacuum at 40°C.
The yield of the bright orange crystalline solid was 61%. Single crystals of (I) suitable for the x-ray analysis were grown by slow evaporation from a dichloromethane solution at room temperature in air.

Refinement
All hydrogen atoms were located in a difference Fourier map and refined with isotropic displacement parameters.

Special details
Experimental. The final unit cell was obtained from the xyz centroids of 3059 reflections after integration using the SAINTPLUS software package (Bruker, 2007).
Reduced cell calculations did not indicate any higher metric lattice symmetry and examination of the final atomic coordinates of the structure did not yield extra symmetry elements (Spek, 1988;Le Page 1987, 1988 Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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.