Crystal structure of (Z)-2-[(E)-2-benzylidenehydrazin-1-ylidene]-1,2-diphenylethanone

The title compound has an almost planar 1,2-dibenzylidenehydrazine backbone with an approximately orthogonal planar phenyl ethanone substituent on one of the imine C atoms. In the crystal, molecules are linked via C—H⋯O hydrogen bonds and C—H⋯π interactions, forming a three-dimensional structure.

The title compound, C 21 H 16 N 2 O, has an almost planar (r.m.s. deviation = 0.0074 Å ) 1,2-dibenzylidenehydrazine backbone with an approximately orthogonal almost planar (r.m.s. deviation = 0.0368 Å ) phenylethanone substituent on one of the imine C atoms. The dihedral angle between the two mean planes is 76.99 (4) . In the crystal, molecules are linked via C-HÁ Á ÁO hydrogen bonds and C-HÁ Á Á contacts, forming a three-dimensional structure with molecules stacked along the a-axis direction.

Chemical context
Aromatic carbonyl compounds react easily with hydrazines to form hydrazones, which can condense with a second molecule of a carbonyl compound to yield an azine. As a result of their fascinating physical and chemical properties, azines and their derivatives have been utilized extensively in areas such as dyes (Kim et al., 2010) and non-linear fluorophores (Facchetti et al., 2002). They are also noted for their biological and pharmaceutical applications (Wadher et al., 2009;Pandeya et al., 1999). Furthermore, there are many reports of polyazines as highly conjugated polymers functioning in electronic, optoelectronic and photonic applications (Dudis et al., 1993). As part of our studies of Schiff base azines, the title compound was synthesized and its molecular and crystal structure are reported on herein.

Structural commentary
The molecule of the title compound, Fig. 1, comprises a 1,2dibenzylidenehydrazine backbone with a phenyl ethanone substituent on atom C2. Both the hydrazine and ethanone fragments are approximately planar with r.m.s. deviations of 0.0074 Å from the O1/C1/C11-C16 mean plane and 0.0368 Å from the plane through the 16 atoms of the dibenzyl-idenehydrazine unit. The two mean planes are almost orthogonal with a dihedral angle of 76.99 (4) . The molecule adopts a Z conformation with respect to the C2 N1 bond and an E conformation with respect to the C3 N2 bond, with the carbonyl atom O1 and the C11-C16 phenyl ring located on opposite sides of the dibenzylidenehydrazine plane. The bond lengths and angles in the title molecule agree reasonably well with those found in closely related structures (Abbasi et al., 2007;Wieland et al., 2011).

Supramolecular features
In the crystal, a pair of C35-H35Á Á ÁO1 hydrogen bonds link adjacent molecules into dimers with R 2 2 (20) ring motifs (Fig. 2  and Table 1). Atom O1 is also involved in two further C-HÁ Á ÁO hydrogen bonds, C3-H3Á Á ÁO1 and C32-H32Á Á ÁO1 that generate R 1 2 (6) ring motifs. These contacts link the dimers into stacks parallel to (011); see Table 1   The molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
A view of the dimers formed via C-HÁ Á ÁO contacts (blue dashed lines; see Table 1 for details) and linked into stacks running parallel to (011) in the crystal of the title compound. Table 1 Hydrogen-bond geometry (Å , ).

Figure 3
A view of the chains along the c-axis direction formed by C-HÁ Á Á contacts in the crystal of the title compound (shown as green dotted lines with the ring centroids displayed as coloured spheres, see Table 1 for details).

Figure 4
A view along the a-axis direction of the crystal packing of the title compound. Hydrogen bonds are drawn as blue dashed lines with a representative C-HÁ Á Á contact shown as a green dotted line (see Table 1 for details).
interaction (Table 1). These interactions link molecules in a head-to-tail fashion, forming chains along c, as shown in Fig. 3. With 16 molecules in the orthorhombic unit cell, these various contacts combine to form a three dimensional structure with molecules stacked along the a-axis direction, as shown in Fig. 4.  (Abbasi et al., 2007), with an hydroxy substituent in the p position on the equivalent of the benzene ring, and 1,2-diphenyl-2-[4-(4pyridyl)benzylidenehydrazono]ethan-1-one, with a pyridyl ring in the same position (Patra & Ng, 2009). Two reports of polymorphs of the symmetrical 2,2 0 -(1,2-hydrazinediylidene)bis(diphenylethanone) have also appeared (Patra et al., 2009;Wieland et al., 2011)