3-Phenyldiazenyl-1,2-dimethyl-1H-indole

In the title molecule, C16H15N3, the indole ring system is planar within 0.021 (3) Å and the phenyl ring is inclined to this plane by 17.32 (14)°. π–π contacts involving the pyrrole rings of inversion-related indole units [centroid–centroid distance = 3.5187 (17) Å] stabilize the crystal structure.

In the title molecule, C 16 H 15 N 3 , the indole ring system is planar within 0.021 (3) Å and the phenyl ring is inclined to this plane by 17.32 (14) .contacts involving the pyrrole rings of inversion-related indole units [centroid-centroid distance = 3.5187 (17) Å ] stabilize the crystal structure.

Comment
Azo compounds are very important in the field of dyes, pigments and advanced materials (Hunger, 2003). It has been known for many years that the azo compounds are the most widely used class of dyes, due to their versatile applications in various fields such as the dyeing of textile fibers, the coloring of different materials, colored plastics and polymers, biological-medical studies and advanced applications in organic syntheses (Catino & Farris, 1985;Zollinger, 2003;Bahatti & Seshadri, 2004;Taniike et al., 1996;Fadda et al., 1994). They are also used in the fields of nonlinear optics and optical data storage (Taniike et al., 1996;Bach et al., 1996;Clark & Hester, 1993). Their optical properties depend on not only the spectroscopic properties of the molecules but also their crystallographic arrangements (Biswas & Umapathy, 2000;Willner & Rubin, 1996). Previously, the syntheses, crystal structures, spectroscopic and tautomeric properties of novel azo indole dyes have been reported in solution and solid state (Hökelek et al., 2007a,b;Seferoğlu et al., 2008;Seferoğlu et al., 2007;Seferoğlu et al., 2006). We report herein on the synthesis and crystal structure of the title compound.

Experimental
For the preparation of the title compound, aniline (190 mg, 2 mmol) was dissolved in HCl (1.5 ml) and water (4.0 ml).
The solution was cooled in an ice-salt bath and a cold solution of NaNO 2 (150 mg, 2 mmol) in water (3.0 ml) was added dropwise with stirring. The resulting diazonium salt was cooled in an ice-salt bath and then added dropwise with stirring to 1,2-dimethylindole (300 mg, 2 mmol) in an acetic acid/propionic acid mixture (2:1, 8.0 ml). The solution was stirred at 273-278 K for 1 h and the pH of the reaction mixture was maintained at 4-6 by the simultaneous addition of a sodium hydroxide solution (40-50 ml). The mixture was stirred for a further 1 h. The resulting solid was filtered, washed with cold water and crystallized from ethanol (yield; 440 mg, 92%, m.p. 398 K).

Refinement
The C9 methyl H-atoms were included in calculated positions and treated as riding atoms: C-H = 0.96 Å, with U iso (H) = 1.5U eq (C). The remaining H-atoms were located in a difference Fourier map and were refined freely.  Fig. 1. The molecular structure of the title molecule with the atom-numbering 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 > 2sigma(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.