1-{2-[(E)-2-(2-Nitrophenyl)ethenyl]-1-phenylsulfonyl-1H-indol-3-yl}ethanone

In the title compound, C24H18N2O5S, the S atom has a distorted tetrahedral configuration, with bond angles varying from 105.11 (7) to 119.98 (8)°. As a result of the electron-withdrawing character of the phenylsulfonyl group, the N—Csp 2 bond lengths [1.414 (2) and 1.413 (2) Å] are slightly longer than the reported value of 1.355 (14) Å for N atoms with a planar configuration. The indole moiety is essentially planar, with a maximum deviation of 0.0177 (14) Å for the N atom. The phenyl ring of the sulfonyl substituent makes a dihedral angle of 85.70 (7)° with the mean plane of the indole moiety. The molecular structure features intramolecular C—H⋯O hydrogen bonds, which generate S(6) and S(12) ring motifs. In the crystal, adjacent molecules are linked via C—H⋯O hydrogen bonds, forming infinite C(7) chains running along the a-axis direction. The crystal packing also features C—H⋯π interactions, which form a three-dimensional structure.


Comment
The indole ring system is present in a number of natural products, many of which are found to possess pharmacological properties like anti-microbial, anti-inflammatory and anti-implantation activities (Rodriguez et al., 1985). Indole derivatives are also known to exhibit anti-oxidant activities (Olgen & Coban, 2003) and antihepatitis B virus activities (Chai et al., 2006).
In the title compound, Fig. 1, the indole ring is essentially planar with a maximum deviation of 0.0177 (14) Å for atom N1. The indole moiety is perpendicular to the phenylsulfonyl ring with a dihedral angle 85.70 (7)°. The nitro-group is inclined at an angle of 7.59 (9)° to the benzene ring to which it is attached. The nitro-phenyl ring makes a dihedral angle of 76.41 (7)° with the indole moiety mean plane. Short intramolecular C2-H2···O1 and C18-H18···O3 hyrogen bonds result in S(6) and S(12) ring motifs (Table 1 and Fig. 1). The molecular dimensions in the title compound are in excellent agreement with those reported for a closely related compound (Karthikeyan et al., 2012).
The expansion of the ispo angles at C1, C3 and C4 [122.34 (16), 121.59 (18) and 121.13 (18)°, respectively] and contraction of the apical angles at C2, C5 and C6 [117.12 (19), 118.54 (18) and 119.28 (16)°, respectively] are caused by the fusion of the smaller pyrrole ring to the six-membered benzene ring and the strain is taken up by the angular distortion rather than by bond-length distortions (Allen, 1981). As a result of the electron withdrawing character of the phenylsulfonyl group, the N-Csp 2 bond lengths, viz, N1-C1 [1.414 (2) Å] and N1-C8 [1.413 (2) Å], are longer than the mean value of 1.355 (14) Å reported for N atoms with planar configurations (Allen et al., 1987). Atom S1 has a distorted tetrahedral configuration. The widening of the angle O2═S1═O1 [119.98 (8)°] and the narrowing of the angle N1-S1-C17 [105.11 (7)°] from the ideal tetrahedral value are attributed to the Thorpe-Ingold effect (Bassindale, 1984). The widening of the angles may be due to the repulsive interactions between the two short S═O bonds, similar to what is observed in a related structure (Karthikeyan et al., 2011).
The crystal packing is stabilized by C-H···O hydrogen bonds ( Fig. 2 and Table 1) resulting in C(7) infinite chains of molecules running along the a axis direction (Bernstein et al., 1995). The crystal packing is further stabilized by C-H···π interactions forming a three-dimensional structure (Table 1 and Fig. 3).

Refinement
The hydrogen atoms were localized from the difference electron density maps and were refined as riding atoms: C-H = 0.93 and 0.96 Å for CH(aromatic) and methyl H atoms, respectively, with U iso (H) = 1.5 U eq (C-methyl) and = 1.2U eq (C) for other H atoms. The rotation angles for the methyl groups were optimized by least squares.

Figure 1
The molecular structure of the title molecule, with the atom labelling. Displacement ellipsoids are drawn at 30% probability level. The intramolecular C-H···O hydrogen bonds are shown as dashed lines (see Table 1 for details).  The crystal packing of the title compound viewed along the a axis, showing the formation of infinite C(7) chains. The dashed lines indicate C-H···O hydrogen bonds (see Table 1 for details).  The crystal packing of the title compound, showing the intermolecular C-H···π interactions as dashed lines (centroid = red sphere; see Table 1 for details). 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 > σ(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.