9-(4-Bromophenyl)-9H-carbazole

In the title molecule, C18H12BrN, the 4-bromophenyl ring is inclined to the mean plane of the carbazole moiety (r.m.s. devation = 0.027 Å) by 49.87 (5)°. In the crystal, molecules stack along [001] and are linked by C—H⋯π interactions forming a corrugated two-dimensional network lying parallel to (100).

In the title molecule, C 18 H 12 BrN, the 4-bromophenyl ring is inclined to the mean plane of the carbazole moiety (r.m.s. devation = 0.027 Å ) by 49.87 (5) . In the crystal, molecules stack along [001] and are linked by C-HÁ Á Á interactions forming a corrugated two-dimensional network lying parallel to (100).
(I) crystallizes in the space group P2 1 /c with one molecule (Fig. 1) in the asymmetric unit. The molecules are arranged in distinct crystallo-chemical layers parallel to (010). The layers contact via the carbazoles ( Fig. 2 (a,b)). The contacting carbazoles are strongly inclined to each other [angle between least squares (l.s.) plane 59.08°], thus π-π interactions can be ruled out. The phenyl rings inside the layers are related by inversion and therefore coplanar. Nevertheless, the rings do not overlap, excluding π-π interactions ( Fig. 2(b)).
Two structures that can be considered as isostructural (Kálmán et al., 1999) with (I) have been described, viz. the analogues with Br substituted by the pseudo-halogenide CN (Saha and Samanta, 1999) or by a NO 2 group (Chen et al., 2005). A second polymorph of the CN analogue is structurally unrelated (Xie et al., 2012). In all three isostructural crystals the benzene ring is strongly inclined with respect to the carbazole moiety [angles between l.s. planes of both aromatic systems: (I): 49.87 (5)°; CN: 47.89 (6)°; NO 2 : 53.08 (6)°]. The inclination of the carbazole and phenyl moieties is of particular interest, since it determines the overall degree of conjugation and therefore greatly influences the electrochemical and photo-physical properties of bipolar materials (Tao et al., 2011).
Several structures with distinctly more bulky substituents on the para-position of the phenyl ring have been described which nevertheless feature a virtually identical arrangement of the carbazole rings as observed in (I). Thus, it is useful to ,,slice′′ the crystal structure of (I) into two kinds of slabs parallel to (010) which do not correspond to layers in the crystallo-chemical sense as depicted in Fig. 1. The slabs designated as A are made up of the carbazole rings of two adjacent crystallo-chemical layers ( Fig. 3(a)), whereas the B slabs are composed of the 4-bromophenyl moieties ( Fig.   3(b)). The A and B slabs feature p1(c)1 (the parentheses mark the direction missing translational symmetry) and p1 layer symmetry, respectively. Examples of structures which feature isostructural A slabs and structurally unrelated B slabs are 2-(4-(9H-carbazol-9-yl)benzylidene)indan-1-one ( Fig. 4(a)) (Kim et al., 2011), 9-(4-((4-methylphenyl)ethynyl)phenyl)-9H-carbazole ( Fig. 4(b)) and the isostructural 4-bromophenyl analogue (Fig. 4(c)) (Liu et al., 2010), the mono-toluene solvate of 3-(4-(9H-carbazol-9-yl)phenyl)acrylic acid (Fig. 4(d)) (Wu et al., 2007) and 9-(4-(2-(4-(2,1,3benzothiadiazol-4-ylethynyl)phenyl)vinyl)phenyl)-9H-carbazole ( Fig. 4(e)) (Chen, et al., 2012). The crystal structure of the latter is depicted in Fig. 5 and a comparison of the A slabs to those in (I) is given in Fig. 3(c). Despite being structurally unrelated, the B slabs in all these structures feature, like the corresponding slab in (I), p1 symmetry. Therefore, these structures possess likewise overall P2 1 /c space group symmetry. In the crystal chemistry of inorganic compounds, the A and B slabs are called modules and the structures given above can be considered as members of a supplementary materials sup-2 Acta Cryst. (2014). E70, o330-o331 merotypic series (Ferraris et al., 2004). Whereas describing crystal structures of organic molecules in terms of modular materials is uncommon, we have recently applied these concepts to the solvatomorphs of a carbazole based organic molecule related to (I) (Stöger et al., 2012).

Experimental
The synthesis of (I) was performed according to the procedure described by Xu et al. (2007). A fused silica ampoule was charged with 9H-carbazole (5.35 g, 32.0 mmol, 1.00 eq.), 1,4-dibromobenzene (9.06 g, 38.4 mmol, 1.20 eq.), CuSO 4 ·5H 2 O (400 mg, 1.6 mmol, 0.05 eq.) and K 2 CO 3 (4.42 g, 32.0 mmol, 1.00 eq.) The sealed ampoule was heated to 250 °C for 68 h. After cooling, the tube was carefully opened with a diamond blade, releasing a small amount of gas. The solid residue was partitioned between toluene and water and the aqueous phase was extracted with toluene. The combined organic layers were washed with water, dried over anhydrous Na 2 SO 4 and concentrated under reduced pressure. Purification was performed by column chromatography (light petroleum:DCM 75:25) yielding 9-(4-bromophenyl)-9H-carbazole (4.22 g, 13.1 mmol, 41%) as white solid. Large single crystals of (I) were grown by slow evaporation of a CDCl 3 solution.

Refinement
The structure was refined against F values using the Jana2006 software package (Petříček et al., 2006). The non-H atoms were located in the electron density map obtained by charge-flipping implemented in SUPERFLIP (Palatinus & Chapuis, 2007) and refined with anisotropic displacement parameters. The H atoms were placed at calculated positions and refined as riding on the parent C atoms.  The molecular structure of (I). C, N and Br are represented by grey, blue and green ellipsoids drawn at the 75% probability levels, H atoms by white spheres of arbitrary radius.