1H-Benzotriazol-1-yl 4-{(E)-[4-(dimethylamino)phenyl]diazenyl}benzoate

The title compound, C21H18N6O2, was obtained as a by-product of a reaction between (E)-4-(4-dimethylaminophenylazo)benzoic acid and 2-amino-4-(2-pyridyl)-6-(6-pyridyl)-1,3,5-triazine, which has a very low solubility, under peptidic coupling conditions, using THF as solvent. The condensation reaction occurred between 1-hydroxybenzotriazole and (E)-4-(4-dimethylaminophenylazo)benzoic acid. The dihedral angle between the benzene rings in the (E)-diphenyldiazene fragment is 10.92 (13)° and that between the benzotriazole mean plane and the central benzene ring is 80.57 (7)°. In the crystal, π–π stacking [centroid–centroid distances = 3.823 (2) and 3.863 (2) Å] of similar fragments generates molecular layers parallel to (0-12). The crystal packing also features weak C—H⋯N hydrogen bonds involving N atoms of the benzotriazole ring.

Recently 1-hydroxybenzotriazole was used in the preparation of one-dimensional coordination polymers (Papaefstathiou et al., 2002).
The molecular structure of the title compound is shown in Fig. 1. The diphenyldiazene fragment of the molecule is not planar (its benzene rings form a dihedral angle of 10.92 (13) °) and adopts an E conformation about the N2═N3 bond.

Refinement
Hydrogen atoms were located in a difference electron density map and refined in a riding model (including free rotation for methyl groups), with U iso (H) = 1.2 (1.5 for methyl groups) times U eq (C).  The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
Packing diagram of the title compound viewed along the a-axis. Hydrogen C-H···N bonds are shown as dashed lines.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 > 2σ(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.