N,N′-Bis[(E)-4-cyanobenzylidene]urea

The molecule of the title compound, C17H10N4O, has crystallographically imposed C 2 symmetry. The urea group and the benzene ring are nearly coplanar, the dihedral angle between them being 4.15 (7)°. The crystal packing is stabilized by aromatic π–π stacking interactions, with a centroid-to-centroid separation of 3.833 (4) Å.

The molecule of the title compound, C 17 H 10 N 4 O, has crystallographically imposed C 2 symmetry. The urea group and the benzene ring are nearly coplanar, the dihedral angle between them being 4.15 (7) . The crystal packing is stabilized by aromaticstacking interactions, with a centroid-tocentroid separation of 3.833 (4) Å .

Related literature
For a general background on the use of nitriles as starting materials, see: Íkizler & Sancak (1992). For the products of the condensation of urea with alkynes, see: Martínez-García et al.

N,N′-Bis[(E)-4-cyanobenzylidene]urea
De-Hong Wu and Ling Hu S1. Comment Nitriles are parent compounds for the preparation of various functional organic materials having imidazole, triazole, or thidiazole functionalities (Íkizler & Sancak, 1992). The Schiff-base compounds derived from the condensation of urea with alkynes are very few (Martínez-García et al., 2004) because of the low reactivity of the NH 2 group of urea. Here we report the crystal structure of the title compound, which was obtained by the reaction of urea with 4-cyanobenzaldehyde in acetic acid with ammonium chloride as a catalyzer.
The molecule of the title compound ( Fig. 1) possesses a crystallographically imposed C 2 symmetry, with atoms C1 and O1 located on a two-fold axis. The urea group and the aromatic rings are nearly coplanar, forming a dihedral angle of 4.15 (7)°. In the crystal packing, molecules are linked along the a axis by aromatic π-π stacking interactions, with centroid-to-centroid separations of 3.833 (4) Å, perpendicular interplanar distances of 3.474 (4) Å and centroid-centroid offsets of 1.620 (3) Å.

S2. Experimental
A mixture of 4-cyanobenzaldehyde (0.53 g, 4 mmol), urea (0.36 g, 6 mmol) and NH 4 Cl (0.10 g, 1.6 mmol) was heated with stirring at 100°C in 5 ml acetic acid for 5 h. After cooling, the reaction mixture was washed with cold water (3 × 50 ml) and the residue recrystallized from ethyl acetate/n-hexane (1:2 v/v) to afford the title compound (0.57 g, 50%). Single crystals suitable for X-ray structure analysis were obtained by the slow evaporation of an ethyl acetate solution in air.

S3. Refinement
All H atoms were placed in calculated positions and refined using a riding model aproximation, with C-H = 0.93 Å and with U iso (H) = 1.2U eq (C).

Figure 1
The molecular structure of the title compound, showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Unlabelled atoms are related to the labelled atoms by (-x, y, 1/2 -z).  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.43 e Å −3 Δρ min = −0.27 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 > 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1 0.0000 0.1727 (