N,N-Diethyl-4-[(E)-(pyridin-3-yl)diazenyl]aniline

The molecule of the title compound, C15H18N4, adopts a trans conformation with respect to the diazo N=N bond. The dihedral angle between the benzene and pyridine rings in the molecule is 8.03 (5)°. In the crystal, a weak C—H⋯π interaction arranges the molecules into a corrugated ribbon, with an antiparallel orientation of neighboring molecules propagating in the [100] direction.

Cg is the centroid of C6-C11 ring.

Comment
This molecule as a donor-acceptor substituted stilbene-like derivative supposed to show nonlinear optical response (Forrest et al., 1996). According to experimental data, such a response for molecules with a CH═CH bridge is higher than for molecules with an N═N bridge (Chemla & Zyss, 1987). On the other hand, theoretical calculations have predicted that azobenzenes can exhibit larger hyperpolarizabilities than stilbene analogues (Morley, 1995). The title compound has a noncentrosymmetric packing and therefore crystals of this material might demonstrate SHG. Usually because of antiparallel dipole positions in the P2 1 2 1 2 1 space group the SHG is weak or undetectable. However there are some exceptions from such regularity, for instance, for molecules of coordination compounds described with two dipole moments (Rivera et al., 2006) SHG was experimentally observed. We tried to experimentally evaluate SHG of this crystal. SHG experiment on a single crystal was done; laser power was increased step by step without appearance of visible SHG. At the maximal laser power crystals were melted under femtosecond laser beam. The absence of SHG for tested sample is not surprising since orientation of neighboring molecules in crystal is antiparallel that prevents SHG.
The molecular structure of the title compound (I) (Fig. 1) shows the presence of an N═N [1.2856 (2) A] double bond; the molecule adopts almost planar Z-configuration with the dihedral angle between the two aromatic rings equal to 8.03 (5)°. The endocyclic angles of pyridine ring cover the range 116.64 (5)-124.09 (5)°. The endocyclic angles at the C1 and C5 atoms adjacent to the N1 heteroatom are larger than 120°, and those at the other atoms of the ring are smaller than 120°. Same distribution of endocyclic angles was observed in the other pyridine compounds reported by us earlier (Draguta et al., 2012). The C9-N4, C6-N3 and C4-N2 bond lengths are 1.3666 (15), 1.4213 (17) and 1.4284 (17) Å, respectively, consistent with the single and double bonds between related C and N atoms.
In the absence of hydrogen bonds and stacking, crystal packing of title compound is determined by weak C-H···π (Table 1, Fig. 2) interactions which stabilize herringbone motif into antiparallel molecular orientation, with the angle between molecular vectors connecting C1 and N4 atoms equal to 178.00 (2)°.

Experimental
Title compound was synthesized according to the published procedure (Peor et al., 2008). After purification red plate-like crystals with melting point of 114°C were obtained from slow evaporation from ethanol solution. Second harmonic generation (SHG) in single-crystal of the compound under investigation was tested using irradiation by laser beam with diameter 2 mm, wavelength 1.04 µm, power 700 mW, duration 150 fs at 75 MHz repetition. Initial power density was 2 × 10 6 W cm -2 ; it was increased step by step up to melting of the sample. UV-Vis: 385 nm; fluorescence: 480 nm.

Refinement
H atoms attached to C atoms were found in difference Fourier maps and subsequently placed at calculated positions with C-H = 0.95 Å (aromatic) or 0.98-0.99 Å (sp 3 C atom). Isotropic displacement parameters for these H atoms were supplementary materials sup-2 Acta Cryst. (2013). E69, o1280 calculated as Uiso(H) = 1.5Ueq(carrier C) in the case of the methyl group, and Uiso(H) = 1.2Ueq(carrier C) otherwise.
Since this is a light-atom structure determined with Mo Kα radiation, there is no anomalous signal with which to refine a meaningful Flack parameter. For this reason, 895 Friedel pairs were merged for the final rounds of refinement.

Computing details
Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).   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.