Crystal structure of (E)-N-(3,3-diphenylallylidene)-9-ethyl-9H-carbazol-3-amine

In the title compound, the carbazole ring system is essentially planar (maximum deviation = 0.025 Å). The crystal packing is stabilized by intermolecular C—H⋯π interactions, forming a three-dimensional supramolecular network.


Chemical context
Carbazole and its derivatives have become quite attractive compounds owing to their applications in pharmacy and molecular electronics. It has been reported that carbazole derivatives possess various biological activities, such as antitumor (Itoigawa et al., 2000), anti-oxidative (Tachibana et al., 2001), anti-inflammatory and antimutagenic (Ramsewak et al., 1999). Carbazole derivatives also exhibit electroactivity and luminescence properties and are considered to be potential candidates for electronic devices such as colour displays, organic semiconductor lasers and solar cells (Friend et al., 1999). These compounds are thermally and photochemically stable, which makes them useful materials for technological applications. For instance, the carbazole ring is easily funtionalized and covalently linked to other molecules (Díaz et al., 2002). This enables its use as a convenient building block for the design and synthesis of molecular glasses, which are widely studied as components of electroactive and photoactive materials (Zhang et al., 2004). Against this background, and in order to obtain detailed information on molecular conformations in the solid state, X-ray studies of the title compound have been carried out.

Structural commentary
The molecular structure of the title compound is illustrated in Fig. 1. The C15 N2 bond of the central imine group adopts an E conformation. The carbazole ring system (N1/C1-C12) is ISSN 2056-9890 essentially planar [maximum deviation = 0.039 (2) Å for atom C9]. The phenyl rings C18-C23 and C24-C29 of the (3,3-diphenylallylidene) unit are oriented at dihedral angles of 75.9 (1) and 64.6 (1) , respectively, to the mean plane of the carbazole ring system. The dihedral angle between the two phenyl rings is 76.1 (1) . The sum of the bond angles around atom N1 (359.7 ) of the pyrrole ring is in accordance with sp 2 hybridization. The geometric parameters of the title molecule agree well with those reported for similar structures (Murugavel et al., 2009;Archana et al., 2011).

Supramolecular features
In the crystal, molecules are linked by six intermolecular C-HÁ Á Á interactions, forming a three-dimensional supramolecular network (Table 1 and Fig. 2). Four of these interactions involves a benzene H atom of the carbazole ring system and a benzene ring of an adjacent molecule, viz. C7-H7Á Á ÁCg1 i , C11-H11Á Á ÁCg3 ii , C20-H20Á Á ÁCg4 iv , and C29-H29Á Á ÁCg3 v . The other two involve a benzene H atom of the carbazole ring system and the pyrrole ring of an adjacent molecule (C8-H8Á Á ÁCg2 i ), and a methylene H atom of the ethyl group and a benzene ring of an adjacent molecule (C13-H13AÁ Á ÁCg1 iii ); see Table 1 and Fig. 2 for full details.

Synthesis and crystallization
A 25 ml round-bottom flask was charged with 9-ethyl-9Hcarbazol-3-amine (1 mmol), 3,3-diphenylacrylaldehyde (1 mmol) and sulfated SnO 2 -Bi 2 O 3 -fly ash catalyst (20 mg) in water (15 ml) and the mixture was refluxed at 363 K for 1h. On completion of the reaction (monitored by TLC with ethyl acetate and hexane as an eluent 20%) the mixture was cooled to ambient temperature. Dichloromethane (20 ml) was then added to separate the organic and aqueous layers. The organic  Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A partial view along the b axis of the crystal packing of the title compound, showing the intermolecular C-HÁ Á Á interactions (see Table 1 for details), forming a three-dimensional supramolecular network. H atoms not involved in these interactions have been omitted for clarity.

Figure 1
Molecular structure of the title compound with the atom labelling. Displacement ellipsoids are drawn at the 30% probability level. layer was filtered, dried on anhydrous Na 2 SO 4 and the solvent removed using a rotary evaporator. The crude product obtained was purified by column chromatography on silica gel (200 mesh) with hexane and ethyl acetate (4:1) as eluent, to afford the title compound in good yield (93%). Red crystals suitable for X-ray diffraction analysis were obtained after recrystallization in CH 2 Cl 2 .

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were positioned geometrically and constrained to ride on their parent atom with C-H = 0.93-0.97 Å and with U iso (H) = 1.5U eq for methyl H atoms and 1.2U eq (C) for other H atoms.

sup-1
Acta Cryst. program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia (2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009). 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.