1-Nitro-9H-carbazole

In the title molecule, C12H8N2O2, the nitro group is tilted slightly with respect to the carbazole moiety [angle between the least-squares planes = 4.43 (9)°]. In the crystal, the molecules are connected via pairs of N—H⋯O hydrogen bonds into dimers with -1 symmetry. The dimers in turn are arranged into layers parallel to (10-1).

In the title molecule, C 12 H 8 N 2 O 2 , the nitro group is tilted slightly with respect to the carbazole moiety [angle between the least-squares planes = 4. 43 (9) ]. In the crystal, the molecules are connected via pairs of N-HÁ Á ÁO hydrogen bonds into dimers with 1 symmetry. The dimers in turn are arranged into layers parallel to (101).

Comment
In the last years, arylamines have been widely employed as electron donors in materials for organo-electronic applications as for example organic light emitting diodes (OLEDs) (Shirota and Kageyama, 2007;Tao et al., 2011;Yook and Lee, 2012). In the course of systematic investigations of the impact of planarized arylamine moieties on the photophysical and electro-chemical properties of bipolar host materials for phosphorescent OLEDs (Kautny, et al., 2013), we synthesized the title compound 1-nitro-9H-carbazole (I) starting from 2-bromo-N-(2-nitrophenyl)benzenamine. Single crystals of (I) grown from CDCl 3 were subjected to X-ray diffraction for structure elucidation. To our knowledge, (I) is the first structurally characterized nitrocarbazole.
(I) crystallizes in the space group P2 1 /n with one molecule in the asymmetric unit. As expected, due to the conjugated πelectron system, the molecule is virtually flat. The largest distance from the least-squares (LS) plane defined by the atoms of the carbazole ring (N1, C1-C12) is only 0.1420 (10) Å, as observed for the O1 atom of the nitro group. The N2 atom of the nitro group is located at 0.0512 (10) Å from the plane, all other atoms are closer than 0.04 Å. The plane defined by the three atoms of the nitro group (N2, O1, O2) is inclined to the LS plane of the carbazole ring by 4.43 (9)°.
The molecules are connected via medium-strength N-H···O hydrogen bonds (N···O: 2.9940 (10) Å) to dimers with 1 symmetry (Fig. 1). The packing of the dimers, on the other hand, is solely controlled by van-der-Waals interactions. The dimers are arranged into distinct crystallo-chemical layers parallel to (101), whereby adjacent dimers are related by the nglide (Fig. 2).

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 and refined with anisotropic displacement parameters. The H atoms were located in difference Fourier maps and freely refined.