Crystal structure of 4-bromo-N-[(3,6-di-tert-butyl-9H-carbazol-1-yl)methylidene]aniline

In the title compound, C27H29BrN2, an intramolecular N—H⋯N hydrogen bond forms an S(6) ring motif. In the crystal, two molecules are associated into an inversion dimer via a pair of C—H⋯π interactions. The dimers are linked by another pair of C—H⋯π interactions, forming a ribbon along the c-axis direction.


Chemical context
Carbazole derivatives have been widely applied in various fields such as pharmaceuticals (Obora, 2018), electroluminescent materials (Krucaite & Grigalevicius, 2019;Taneda, et al., 2015) and dyes (Zhao et al., 2019). As a result of the high acidity of the N-H bond, 9H-carbazoles have also attracted much attention as hydrogen donors in hydrogenbonding systems (Rubio et al., 2015;Wiosna-Sałyga et al., 2006). Substitution of the 1 position of 9H-carbazole with a hydrogen acceptor can afford an intramolecular hydrogenbonding system in the molecules. In this work, a Schiff base including carbazole, N-(3,6-di-tert-butyl-9H-calbazol-1-ylmethylidene)-4-bromoaniline, is newly synthesized. 3,6-Ditert-butyl-9H-carbazole is useful in order to substitute the 1-position of the 9H-carbazole moiety because the substitution reaction would only occur at its 1-and 8-positions. Thus, the title compound has two tert-butyl groups on the carbazole moiety. The title compound is a suitable model to investigate an intramolecular hydrogen bond between the heteroaromatic N-H and the N atom of the imino group. We report herein on its molecular and crystal structures.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The molecule adopts an E configuration with respect to the C N double bond. The carbazole ring is almost planar with a maximum deviation of 0.0781 (16) Å at atom C8. There is an intramolecular N-HÁ Á ÁN hydrogen bond involving the amino group (N3-H3) in the carbazole ring and an imine N atom (N2), generating an S(6) ring motif (Table 1). The dihedral angle between the mean planes of the carbazole ring system and the benzene C25-C30 ring is 42.72 (7) . The bond lengths and angles of the title compound are normal and agree with those values in other carbazole imine compounds (Gibson et al., 2003;Nolla-Saltiel et al., 2018). One of the tertbutyl substituents shows rotational disorder around the C13-C20 bond axis over two sites with occupancies of 0.592 (3) and 0.408 (3).

Supramolecular features
In the crystal, two molecules are associated through a pair of C-HÁ Á Á interactions (C22A-H22CÁ Á ÁCg1 i in the major disorder component or C21B-H21EÁ Á ÁCg1 i in the minor disorder component; Cg1 is the centroid of the C25-C30 ring; symmetry code as in Table 1), forming a centrosymmetric dimer. The dimers are linked by another pair of C-HÁ Á Á interactions (C29-H29Á Á ÁCg2 ii ; Cg2 is the centroid of the C4-C9 ring; symmetry code as in Table 1), forming a ribbon along the c-axis direction (Fig. 2). These ribbons are linked via a C-HÁ Á Á interaction involving the minor disorder component  Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
The molecular structure of the title compound, with atom labelling. Only the major disordered component is shown. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented by spheres of arbitrary radius. The intramolecular N-HÁ Á ÁN hydrogen bond is shown as a dashed line.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The H atom attached to atom N3 was located in a difference-Fourier map and freely refined. The C-bound H atoms were positioned geometrically (C-H = 0.93-0.96 Å ) and refined using a riding model with U iso (H) = 1.2U eq (C). Orientational disorder of the tert-butyl substituent (C20-C23) around the C13-C20 bond axis is observed and the occupancies refined to 0.592 (3) and 0.408 (3).   (Rigaku OD, 2018); cell refinement: CrysAlis PRO (Rigaku OD, 2018); data reduction: CrysAlis PRO (Rigaku OD, 2018); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: CrystalStructure (Rigaku, 2016). 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 was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 sigma(F 2 ) is used only for calculating Rfactor (gt).