4-[(E)-2-(2,4,6-Trinitrophenyl)ethylidene]benzonitrile

In the crystal of the title compound, C15H8N4O6, the molecules are organized in layers due to their linkage by weak C—H⋯N hydrogen bonds. The layers are themselves interconnected by weak C—H⋯O hydrogen bonds and π–π interactions [centroid–centroid distances = 3.8690 (15) and 3.9017 (16) Å]. The dihedral angle between the rings is 31.9 (1)°.

In the crystal of the title compound, C 15 H 8 N 4 O 6 , the molecules are organized in layers due to their linkage by weak C-HÁ Á ÁN hydrogen bonds. The layers are themselves interconnected by weak C-HÁ Á ÁO hydrogen bonds andinteractions [centroid-centroid distances = 3.8690 (15) and 3.9017 (16) Å ]. The dihedral angle between the rings is 31.9 (1) .

Comment
The title compound was synthesized as a new ligand for iron-phosphine complexes for use in non-linear optical (NLO) applications [Wenseleers et al. (1998), Garcia et al. (2001), Robalo et al. (2006), Garcia et al. (2007)]. The molecular structure of the title compound ( Fig. 1) is mainly determined by steric factors involving the nitro groups, which force the nitro-substituted ring out of the plane of the CH=CH fragment by 54.0 (3)°. In addition, the nitro group in the 6-position is twisted by 56.6 (3)° out of the plane of the benzene ring, whereas the nitro groups in the 2-and 4-positions remain almost in the latter plane, with torsion angles of 6.2 (3)° and 3.6 (4)°, respectively. A similar conformation of the nitro-substituted ring can be seen in other trinitrostilbenes, such as MALZOP [Hanson et al. (2005)], PIGBAJ [Oehlke et al. (2007)] and GIMBOT [Gérard & Hardy (1988)]. In the case of the latter, the two rings are parallel to each other, but the ethenylic link is rotated by approximately 90° with respect to both rings.
The fact that the nitro group in the 6-position is twisted so much more than the other two may be linked to the weak intermolecular hydrogen bond involving O32 of the nitro group and H3 of the neighbouring molecule (Table 1). As a consequence of this twist, the second oxygen atom of this nitro group, O31, comes quite close to O12 of a neighbouring molecule within the layer depicted in Fig. 2 [O31···O12 iv , 2.821 (3) Å, symm. code iv = x, 1+y, z], but this should not be seen as a stabilizing contact. In fact, these layers are rather formed by the weak hydrogen bond involving H5A and the nitrogen atom N1C of the nitrile group (Table 1). The layers display a typical herringbone structure and extend along the [-1 0 2] plane.
Ten drops of piperidine were added, and the mixture was refluxed overnight. After cooling, the precipitate was collected by filtration. The crude product was refluxed for 4 h in p-xylene (25 ml) in the presence of a catalytic amount of iodine.
After cooling, a mixture of yellow powder and orange-red crystals was collected, and both powder and crystals turned out to be the desired product. All the H atoms have been observed in the difference electron density map and were left to refine freely. Fig. 1. Molecular structure of the title compound showing the numbering scheme. Displacement ellipsoids are drawn at the 50% probability level; hydrogen atoms are represented by spheres with an arbitrary radius.