2,7-Dibromo-9-octyl-9H-carbazole

In the crystal structure of the title compound, C20H23Br2N, the octyl chains are extended in an anti conformation and form a segregating bilayer, isolating rows of carbazole units. The carbazole moieties are engaged in offset π–π interactions; the smallest centroid-to-centroid distance is 4.2822 (11) Å. This offset packing motif allows the methylene group attached directly to the N atom to be involved in two short C—H⋯π interactions (H⋯centroid distances = 2.96 and 2.99 Å) with an adjacent carbazole. One of the Br atoms also participates in a short contact [3.5475 (3) Å] with a symmetry-related (−x, 1 − y, −z) Br atom. This value is significantly smaller than the sum of the van der Waals radii for bromine (3.70 Å).

In the crystal structure of the title compound, C 20 H 23 Br 2 N, the octyl chains are extended in an anti conformation and form a segregating bilayer, isolating rows of carbazole units. The carbazole moieties are engaged in offsetinteractions; the smallest centroid-to-centroid distance is 4.2822 (11) Å . This offset packing motif allows the methylene group attached directly to the N atom to be involved in two short C-HÁ Á Á interactions (HÁ Á Ácentroid distances = 2.96 and 2.99 Å ) with an adjacent carbazole. One of the Br atoms also participates in a short contact [3.5475 (3) Å ] with a symmetry-related (Àx, 1 À y, Àz) Br atom. This value is significantly smaller than the sum of the van der Waals radii for bromine (3.70 Å ).

D-HÁ
In such compounds, an alkyl group is useful because it increases the solubility and helps control molecular packing, which are important parameters in preparing devices such as organic light-emitting diodes and solar cells (Blouin & Leclerc, 2008).
Crystals of 2,7-dibromo-9-octyl-9H-carbazole belonging to the space group P2 1 /c were grown by slowly cooling a saturated hot solution in hexanes. The octyl chain adopts a fully extended conformation, with torsion angles ranging from 174.47 (17)° to 179.9 (2)° (Fig. 1). The octyl groups are parallel and packed tightly, leading to the formation of a bilayered structure (Fig. 2).

Experimental
The title compound was obtained by a two-step synthesis starting from 4,4'-dibromo-2-nitrobiphenyl. A reductive Cadogan ring-closure reaction was performed according to Dierschke et al. (2003) to afford 2,7-dibromocarbazole, which was alkylated with 1-bromooctane following a procedure reported by Bouchard et al. (2004). Crystallization of the title compound from hexanes afforded needles which were used in this study. Spectroscopic data proved to be consistent with the reported values.

Refinement
H atoms were placed in idealized positions and allowed to ride on their parent atoms, with C-H distances of 0.99 Å (methylene), 0.98 Å (methyl) and 0.95 Å (aromatic C-H), and with U iso (H) of 1.2U eq (C) for aromatic and methylene H atoms and 1.5U eq (C) for terminal methyl groups.

Special details
Experimental. X-ray crystallographic data for the title compound were collected from a single-crystal sample, which was mounted on a loop fiber. Data were collected using a Bruker Microstar diffractometer equipped with a Platinum 135 CCD Detector, Helios optics and a Kappa goniometer. The crystal-to-detector distance was 4.0 cm, and the data collection was carried out in 512 x 512 pixel mode.
The initial unit-cell parameters were determined by a least-squares fit of the angular setting of strong reflections, collected by a 10.0 degree scan in 33 frames over three different parts of the reciprocal space (99 frames total).
Due to geometrical constraints of the instrument and the use of copper radiation, we consistently obtain a data completeness lower than 100% depending on the crystal system and the orientation of the mounted crystal, even with appropriate data collection routines.
Typical values for data completeness range from 83-92% for triclinic, 85-97% for monoclinic and 85-98% for all other crystal systems.