Crystal structures of three carbazole derivatives: 12-ethyl-7-phenylsulfonyl-7H-benzofuro[2,3-b]carbazole, (1), 2-(4,5-dimethoxy-2-nitrophenyl)-4-hydroxy-9-phenylsulfonyl-9H-carbazole-3-carbaldehyde, (2), and 12-phenyl-7-phenylsulfonyl-7H-benzofuro[2,3-b]carbazole, (3)

The title compounds are carbazole derivatives. In all three compounds, the carbazole skeleton is essentially planar. In two of the compounds, a benzofuran moiety is fused with a carbazole unit. Intermolecular C—H⋯O hydrogen bonds give rise to (12) inversion dimers in one compound, and to (40) ring motifs and (24) inversion dimers in a second compound. In the crystal of the third compound, C—H⋯O hydrogen bonds link the molecules to form chains running parallel to the a axis.

The three title compounds, C 26 H 19 NO 3 S, (1), C 27 H 20 N 2 O 8 S, (2), and C 30 H 19 NO 3 S, (3), are carbazole derivatives, where (1) and (3) are heterocyclecontaining carbazoles with a benzofuran moiety fused to a carbazole unit. In (2), a dimethoxynitrophenyl ring is attached to the carbazole moiety. In the three derivatives, a phenylsulfonyl group is attached to the N atom of the carbazole unit. Compound (1) crystallizes with two independent molecules in the asymmetric unit (A and B). The carbazole skeleton in the three compounds is essentially planar. In compound (1), the benzene ring of the phenylsulfonyl moiety is almost orthogonal to the carbazole moiety, with dihedral angles of 85.42 (9) and 84.52 (9) in molecules A and B, respectively. The benzene ring of the phenylsulfonyl group in compounds (2) and (3) are inclined to the carbazole moiety, making dihedral angles of 70.73 (13) and 81.73 (12) , respectively. The S atom has a distorted tetrahedral configuration in all three compounds. In the crystals, C-HÁ Á ÁO hydrogen bonds give rise to R 2 2 (12) inversion dimers for compound (1), and to R 2 2 (24) inversion dimers and R 4 4 (40) ring motifs for compound (2). The crystal packing in (1) also features C-HÁ Á Á andinteractions [shortest intercentroid distance = 3.684 (1) Å ], leading to supramolecular three-dimensional aggregation. In the crystal of compound (2), the combination of the various C-HÁ Á ÁO hydrogen bonds leads to the formation of a three-dimensional network. In the crystal of compound (3), molecules are linked by C-HÁ Á ÁO hydrogen bonds, forming chains running parallel to the a axis, and the chains are linked by C-HÁ Á Á interactions, forming corrugated sheets parallel to the ab plane.

Chemical context
Carbazoles are widely used as building blocks for new organic materials and play an important role in electroactive and photoactive devices. Carbazole derivatives have also been used as luminescent and hole-transporting materials (Dijken et al., 2004). These compounds are also thermally and phytochemically stable which makes them useful materials for technological applications (Diaz et al., 2002).
Heterocycle-containing carbazole derivatives are embodied in many natural products (Itoigawa et al., 2000) and display a broad spectrum of useful biological activities, such as antitumour, antimitotic and antioxidative activities (Prudhomme, 2003;Tachibana et al., 2003;Hu et al., 2006). A number of ISSN 2056-9890 benzo-annulated carbazole ring systems containing an aromatic ring fused to the carbazole nucleus are potential candidates for cancer treatment as a result of their DNA intercalative binding properties. They have been shown to bind to estrogen receptors and exhibit a pronounced antitumor activity against leukemia, renal tumor, colon cancer and malignant melanoma tumor cell lines (Pindur & Lemster, 1997).
Most heterocycle-containing carbazoles reported in the literature comprise a common heterocyclic ring moiety fused with a carbazole ring system, such as pyridocarbazoles and indolocarbazoles. In this context, we discuss here three carbazole derivatives, two of which have benzofuran moieties fused with the carbazole unit.

Structural commentary
The three title compounds C 26 H 19 NO 3 S, (1), C 27 H 20 N 2 O 8 S, (2), and C 30 H 19 NO 3 S, (3), are carbazole derivatives, where (1) and (3) are heterocycle-containing carbazoles with a benzofuran fused to the carbazole skeleton (Figs. 1 and 3, respectively). In (2), a dimethoxynitrophenyl ring is attached to the carbazole moiety (Fig. 2). In the three derivatives, a phenylsulfonyl group is attached to the N atom of the carbazole unit. Compound (1) crystallizes with two independent molecules (A and B) in the asymmetric unit, as shown in Fig. 1. The carbazole skeleton in the three compounds is essentially planar [maximum deviations of 0.052 (2) Å for atom C12 in molecule A and 0.080 (2) Å for atom C12 0 in molecule B of (1), À0.034 (2) Å for atom C10 in (2), and À0.042 (4) Å for atom C3 in (3)]. The carbazole benzofuran fused pentacyclic unit is almost planar in (1) and (3), with dihedral angles between the benzofuran and carbazole units being 2.48 (6) and 4.16 (6) in molecules A and B, respectively of (1), and 2.33 (8) in compound (3). In compound (1), the benzene ring of the phenylsulfonyl group is almost orthogonal to the carbazole moiety, with the dihedral angles between their mean planes being 85.42 (9) and 84.52 (9) in molecules A and B, respectively. The benzene ring of the phenylsulfonyl group in compounds (2) and (3) are inclined to the carbazole moiety making dihedral angles of 70.73 (12) and 81.73 (12) , respectively.
In compound (3), the phenyl ring attached at C12 is oriented at a dihedral angle of 78.39 (11) to the carbazole unit.

Figure 2
The molecular structure of compound (2), showing the atom-numbering scheme and displacement ellipsoids are drawn at the 30% probability level. The intramolecular O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, which generate three S(6) ring motifs, are shown as dashed lines (see Table 2).

Figure 3
The molecular structure of compound (3), showing the atom-numbering scheme and displacement ellipsoids drawn at the 30% probability level. The intramolecular C-HÁ Á ÁO hydrogen bonds, which generate two S(6) ring motifs, are shown as dashed lines (see Table 3).
are also linked via C2-H2Á Á ÁO5 i hydrogen bonds which form R 2 2 (24) inversion dimers. These dimers are further crosslinked by C17-H17Á Á ÁO8 ii hydrogen bonds (Table 2), forming sheets parallel to plane (102); as shown in Fig. 6. The sum of these interactions is the formation of a three-dimensional hydrogenbonded framework.
In the crystal of compound (3), molecules are linked through C2-H2Á Á ÁO3 i hydrogen bonds (Table 3), that generate infinite one-dimensional C(9) chains running parallel to the a axis (Fig. 7). The chains are further crosslinked by C17-H17Á Á ÁCg4 ii and C22-H22Á Á ÁCg3 iii interactions (Table 3), which results in the formation corrugated sheets parallel to the ab plane.

Database survey
A search of the CSD (Groom et al., 2016) revealed two closely related structures including the parent compound 7H-1benzofuro[2,3-b]carbazole (Panchatcharam et al., 2011a). This carbazole-benzofuran fused pentacyclic unit crystallizes in the space group Pca2 1 . However, compound 7-phenylsufonyl-7Hbenzofuran[2,3-b]carbazole (Panchatcharam et al., 2011b) is the closest analogue to the title compounds (1) and (3), and crystallizes in the space group P2 1 /c. The presence of an ethyl or phenyl substituent attached to the carbazole unit does not cause much variation in the structural parameters. The packing of the title compounds are consolidated by C-HÁ Á ÁO The crystal packing of compound (1), viewed along the a-axis, showing the formation of centrosymmetric A-A dimers, with descriptor R 2 2 (12). The dashed lines indicate the intermolecular C-HÁ Á ÁO hydrogen bonds (Table 1) and H atoms not involved in hydrogen bonding, and the phenyl ring of the phenylsulfonate groups, have been excluded for clarity.

Figure 5
The crystal packing of compound (2), viewed along the a axis, showing the formation of R 4 4 (40) graph-set ring motifs, resulting in the formation of sheets parallel to the bc plane. The dashed lines indicate the C-HÁ Á ÁO hydrogen bonds (Table 2), and H atoms not involved in the hydrogen bonding have been excluded for clarity. Table 4 Experimental details.

Figure 6
The crystal packing of compound (2), viewed normal to plane (204), showing the formation of R 2 2 (24) graph-set ring motifs, resulting in the formation of sheets parallel to plane (204). The dashed lines indicate the intermolecular C-HÁ Á ÁO hydrogen bonds (Table 2), and H atoms not involved in the hydrogen bonding have been excluded for clarity.
For the preparation of compound (2), to a solution of 4methoxycarbazole-3-carbaldehydes (0.82 g, 1.5 mmol) in dry DCM (20 ml), 1 M solution of BBr 3 (1.65 ml, 1.65 mmol) in DCM was added at 273 K. After completion of the reaction (monitored by TLC), it was poured into ice water (50 ml) containing HCl (5 ml). The organic layer was separated and the aqueous layer was then extracted with DCM (2 Â 10 ml). The combined organic layer was washed water (2 Â 30 ml) and dried (Na 2 SO 4 ). Removal of the solvent followed by tritura-tion of the crude product with MeOH (10 ml) gave compound (2) as a pale-yellow solid (yield 0.73 g, 92%; m.p. 467-469 K).

Refinement
Crystal data, data collection and structure refinement details for compounds (1), (2) and (3) are summarized in Table 4. The H atoms were included in calculated positions and treated as riding atoms: O-H = 0.82 Å , C-H = 0.93-0.97 Å , with U iso (H)= 1.5U eq (hydroxy O and methyl C) and 1.2U eq (C) for other H atoms. The methyl groups were allowed to rotate, but not to tip, to best fit the electron density.

(1) 12-Ethyl-7-phenylsulfonyl-7H-benzofuro[2,3-b]carbazole
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.