Crystal structures of two new carbazole derivatives: 12-(4-nitrophenyl)-7-phenylsulfonyl-7H-benzofuro[2,3-b]carbazole and 2-methyl-4-(4-nitrophenyl)-9-phenylsulfonyl-9H-thieno[2,3-b]carbazole

The title compounds are carbazole derivatives, with a benzofuran ring system in (I) and a methylthiophene ring in (II) fused with the respective carbazole moiety. In the crystals of both compounds, molecules are linked via C—H⋯O hydrogen bonds, forming sheets lying parallel to (10).

The title compounds, C 30 H 18 N 2 O 5 S, (I), and C 27 H 18 N 2 O 4 S 2 , (II), are carbazole derivatives with a phenylsulfonyl group and a nitrophenyl group attached to the carbazole moiety in identical positions in both molecules. A benzofuran ring system in (I) and a methylthiophene ring in (II) are fused with the respective carbazole moieties on the same sides. The mean plane of the carbazole ring system makes a dihedral angle of 3.17 (7) with the benzofuran ring system in (I) and a dihedral angle of 3.39 (11) with the methylthiophene ring in (II), implying that both fused units are essentially planar. The mean planes of the carbazole ring systems in both the compounds are almost orthogonal to the respective nitro-substituted phenyl rings, making dihedral angles of 75.64 (10) and 77.63 (12) in compounds (I) and (II), respectively. In (I), the phenylsulfonyl ring system is positionally disordered with a refined occupancy ratio of 0.63 (2):0.37 (2). In both compounds, the molecular structures are stabilized by intramolecular C-HÁ Á ÁO hydrogen bonds, generating S(6) ring motifs with the sulfone group O atoms. In the crystal of compound (I), molecules are linked by pairs of C-HÁ Á ÁO hydrogen bonds, which generate R 2 2 (18) inversion dimers, and interconnected by C(14) chains running along the c-axis direction, whereas in compound (II), the C-HÁ Á ÁO hydrogen bonds generate R 4 3 (37) ring motifs. In the crystals of both compounds, C-HÁ Á ÁO hydrogen-bonded sheets are formed lying parallel to (101). In addition, C-HÁ Á Á and offsetinteractions [intercentroid distance = 3.7158 (14) Å in (I) and 3.9040 (15) Å in (II)] are also present in the crystals of both compounds.

Chemical context
Carbazole and its derivatives are interesting compounds owing to their applications in pharmacy and molecular electronics. Carbazole derivatives exhibit various biological activities such as antitumor (Itoigawa et al., 2000), antioxidative (Tachibana et al., 2001), anti-inflammatory and antimutagenic (Ramsewak et al., 1999). They also exhibit electroactivity and luminescence and are considered to be potential candidates for electronic applications, such as colour displays, organic semiconductors, laser and solar cells (Friend, et al. 1999). Tetrahydrocarbazole systems are present in the framework of a number of indole-type alkaloids of biological interest (Saxton, 1983). Carbazole-based heterocyclic polymer systems can be chemically or electrochemically polymerized to give products with a number of applications, such as rechargeable batteries (Sacak, 1999) and electrochromic displays (Santhanam & Sundaresan, 1986). This enables their ISSN 2056-9890 use as suitable building blocks 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, the X-ray structure determination of the title compounds, (I) and (II), has been carried out to study their structural aspects and the results are presented here.
The mean planes of the carbazole ring systems make dihedral angles of 3.17 (7) and 3.39 (11) , respectively, with the benzofuran ring in (I) and the methylthiophene ring in (II), indicating that the ring systems they are essentially coplanar. The nitrophenyl rings in compounds (I) and (II) are inclined to the carbazole ring system by 75.64 (10) and 77.63 (12) , respectively. The NO 2 groups are inclined to the benzene ring (C19-C24) to which they are attached by 9.8 (4) in (I) and 9.3 (3) in (II). The phenylsulfonyl ring (C13-C18) is almost normal to the nitro-substituted phenyl ring (C19-C24) with a dihedral angle of 84.7 (2) in (I) and 83.98 (17) in (II).
In both compounds, as a result of the electron-withdrawing character of the phenylsulfonyl group, the N-Csp 2 bond lengths are longer than the mean value of 1.355 (14) Å for N-C bond lengths (CSD; Groom et al., 2016). Atom S1 has a distorted tetrahedral geometry. The widening of the O1 S1 O2 angle and narrowing of the N1-S1-C13 angle from the ideal tetrahedral values are attributed to the Thorpe-Ingold effect (Bassindale, 1984). The widening of the angles may be due to the repulsive interaction between the two short S O bonds. The molecular structure of compound (I), showing the atom labelling. Displacement ellipsoids are drawn at the 30% probability level. Intramolecular C2-H2Á Á ÁO1 and C9-H9Á Á ÁO2 hydrogen bonds, which generate two S(6) ring motifs, are shown as dashed lines (see Table 1). For the sake of clarity, the minor component of the disordered phenylsulfonyl ring has been omitted.

Figure 2
The molecular structure of compound (II), showing the atom labelling. Displacement ellipsoids are drawn at the 30% probability level. Intramolecular C2-H2Á Á ÁO1 and C9-H9Á Á ÁO2 hydrogen bonds, which generate two S(6) ring motifs, are shown as dashed lines (see Table 2). hybridization. In both compounds, the molecular structure is stabilized by intramolecular C-HÁ Á ÁO hydrogen bonds, which generate S(6) ring motifs with the sulfone oxygen atoms (Tables 1 and 2).

Figure 4
The crystal packing of compound (II), viewed along the ac diagonal, showing the intermolecular C-HÁ Á ÁO hydrogen bonds (see Table 2), which generate R 3 4 (37) ring motifs and form sheets lying parallel to the (101) plane. H atoms not involved in hydrogen bonding have been excluded for clarity. Table 1 Hydrogen-bond geometry (Å , ) for (I).

Figure 5
The crystal packing of compound (II), viewed along the c axis, showing the C-HÁ Á ÁO intermolecular hydrogen bonds which generate R 2 2 (18) inversion dimers (see Table 2). H atoms not involved in hydrogen bonding have been excluded for clarity.

Refinement
Crystal data, data collection and structure refinement details for compounds (I) and (II) are summarized in Table 3. The positions of the hydrogen atoms were localized from the difference electron-density maps. The C-bound H atoms were treated as riding atoms: C-H = 0.93-0.96 Å with U iso (H)= 1.5U eq (C-methyl) and 1.2U eq (C) for other H atoms. In compound (I), the phenylsulfonyl ring (C13-C18) is positionally disordered with a refined occupancy ratio of 0.63 (2): 0.37 (2). The bond distances of the disordered components were restrained using standard similarity restraint SADI [SHELXL97; Sheldrick, 2008] with s.u. of 0.01Å . Ellipsoid displacement (SIMU and DELU) restraints were also applied to the disordered ring. The methyl groups were allowed to rotate, but not to tip, to best fit the electron density.

Computing details
For both compounds, data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); 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) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 0.28 e Å −3 Δρ min = −0.21 e Å −3 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.

Hydrogen-bond geometry (Å, º)
Cg1 is the centroid of the furan ring O5/C10/C11/C25/C30 and Cg3 is the centroid of the benzene ring C1-C6. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.44 e Å −3 Δρ min = −0.36 e Å −3 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.