4-[4-(4-Nitrophenyldiazenyl)phenyl]hexanenitrile

In the molecule of the title compound, C18H18N4O2, the aromatic rings are oriented at a dihedral angle of 3.72 (3)°. In the crystal structure, intermolecular C—H⋯O hydrogen bonds link the molecules into centrosymmetric dimers. There are also C—H⋯π interactions.

In the molecule of the title compound, C 18 H 18 N 4 O 2 , the aromatic rings are oriented at a dihedral angle of 3.72 (3) . In the crystal structure, intermolecular C-HÁ Á ÁO hydrogen bonds link the molecules into centrosymmetric dimers. There are also C-HÁ Á Á interactions.

4-[4-(4-Nitrophenyldiazenyl)phenyl]hexanenitrile
Ran-zhe Lu, Lu-na Han, Min Zhang, Bin Wang and Hai-bo Wang S1. Comment The photophysical properties of azo compounds are of large interest in the development of nonlinear optical and optical data storage materials (Bach et al., 1996;Taniike et al., 1996;Clark & Hester, 1991). As part of our studies in this area, we report herein the synthesis and crystal structure of the title compound.
In the molecule of the title compound (Fig 1), the bond lengths (Allen et al., 1987) and angles are within normal ranges.
In the crystal structure, intermolecular C-H···O hydrogen bonds (Table 1) link the molecules into centrosymmetric dimers ( Fig. 2), in which they may be effective in the stabilization of the structure. There also exist C-H···π interactions (Table 1).

S2. Experimental
The title compound has been synthesized according to a literature method (Zhao et al., 2002). Crystals suitable for X-ray analysis were obtained by slow evaporation of an ethanol solution.

S3. Refinement
H atoms were positioned geometrically, with C-H = 0.93, 0.97 and 0.96 Å for aromatic, methylene and methyl H, respectively, and constrained to ride on their parent atoms, with U iso (H) = xU eq (C), where x = 1.5 for methyl H and x = 1.2 for all other H atoms.

Figure 1
The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% 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.