3-(1H-Indol-3-yl)-2-(2-nitrobenzenesulfonamido)propanoic acid including an unknown solvate

In the title compound, C17H15N3O6S, which crystallized with highly disordered methanol and/or water solvent molecules, the dihedral angle between the the indole and benzene ring systems is 5.3 (2)°, which allows for the formation of intramolecular π–π stacking interactions [centroid–centroid separations = 3.641 (3) and 3.694 (3) Å] and an approximate overall U-shape for the molecule. In the crystal, dimers linked by pairs of Ns—H⋯Oc (s = sulfonamide and c = carboxylate) hydrogen bonds generate R 2 2(10) loops, whereas Ni—H⋯π (i = indole) interactions lead to chains propagating in [100] or [010]. Together, these lead to a three-dimensional network in which the solvent voids are present as intersecting (two-dimensional) systems of [100] and [010] channels. The title compound was found to contain a heavily disordered solvent molecule, which could be methanol or water or a mixture of the two. Due to its uncertain nature and the unresolvable disorder, the data were processed with the SQUEEZE option in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155], which revealed 877.8 Å3 of solvent-accessible volume per unit cell and 126 electron-units of scattering density or 109.7 Å3 (16 electron units) per organic molecule.. This was not included in the calculations of overall formula weight, density and absorption coefficient.

In the title compound, C 17 H 15 N 3 O 6 S, which crystallized with highly disordered methanol and/or water solvent molecules, the dihedral angle between the the indole and benzene ring systems is 5.3 (2) , which allows for the formation of intramolecularstacking interactions [centroid-centroid separations = 3.641 (3) and 3.694 (3) Å ] and an approximate overall U-shape for the molecule. In the crystal, dimers linked by pairs of N s -HÁ Á ÁO c (s = sulfonamide and c = carboxylate) hydrogen bonds generate R 2 2 (10) loops, whereas N i -HÁ Á Á (i = indole) interactions lead to chains propagating in [100] or [010]. Together, these lead to a three-dimensional network in which the solvent voids are present as intersecting (twodimensional) systems of [100] and [010] channels. The title compound was found to contain a heavily disordered solvent molecule, which could be methanol or water or a mixture of the two. Due to its uncertain nature and the unresolvable disorder, the data were processed with the SQUEEZE option in PLATON [Spek (2009). Acta Cryst. D65,[148][149][150][151][152][153][154][155], which revealed 877.8 Å 3 of solvent-accessible volume per unit cell and 126 electron-units of scattering density or 109.7 Å 3 (16 electron units) per organic molecule.. This was not included in the calculations of overall formula weight, density and absorption coefficient.

Related literature
For related structures and background references to the biological activity of sulfonamides, see: Khan et al. (2011a,b  report the structure of the title compound, (I). Compound (I) was found to contain a heavily disordered solvent molecule, which could be methanol or water or a mixture of the two. Due to its uncertain nature and the unresolvable disorder, the data were processed with the SQUEEZE option in PLATON (Spek, 2009), to remove the solvent contribution to the scattering.
This allows intramolecular aromatic π-π stacking to occur: the separations of the centroid of the C12-C17 benzene ring with those of the C1-C6 and C1/C6/C7/C8/N1 rings are 3.641 (3) Å and 3.694 (3) Å, respectively. The N3/O5/O6 nitro group is twisted out of the plane of its atttached ring by 48.9 (4)°. The configuration of the stereogenic carbon atom (C10) in (I) is S, which is consistent with that of the equivalent atom in the starting material.
In the crystal, the molecules are linked into dimers via pairs of N s -H···O c (s = sulfonamide, c = carboxylate) hydrogen bonds ( Fig. 2, Table 1), which result in R 2 2 (10) loops. A crystallographic twofold axis directed along [110] generates the second molecule from the asymmetric molecule. In addition, weak N i -H···π (i = indole) interactions occur: these lead to [100] chains for the asymmetric molecule and [010] chains for symmetry-generated molecules in other locations in the unit-cell (Fig. 3). The carboxylic acid O-H group is directed towards the solvent void and probably forms a hydrogen bond to the solvent.
Together, the N-H···O and N-H···π bonds generate a three-dimensional network of molecules within the distinctive "tall" tetragonal unit-cell (Fig. 3). The solvent voids are apparent as square grids of intersecting [100] and [010] pseudo channels lying at z = 0, z = 1/4 and symmetry equivalent locations.
The molcular conformation and crystal structure (Khan et al., 2011a) of the closely related compound 3-(1H-indol-3yl)-2-(toluene-4-sulfonylamino)-propionic acid monohydrate, (II), are completely different to (I). In (II), where a paratoluene substituent has replaced the 2-nitrobebzene substituent in (I), the organic molecule adopts an extended Z-shaped conformation and no intramolecular π-π stacking can occur. In the crystal of (II), in which the solvent water molecule was located, N s -H···O s hydrogen bonds and O c -H···O w (s = sulfonamide, c = carboxylic acid, w = water) hydrogen bonds generate chains and the crystal symmetry is monoclinic. Another feature of (II) not seen in (I) is the presence of a short intermolecular C-H···O interaction arising from the α (chiral) C atom (Khan et al., 2011b). However, it is interesting to note that (I) and (II) both feature an unusual N i -H···π (i = indole) interaction.

Experimental
The title compound was prepared following the literature method (Deng & Mani, 2006) and recrystalized from methanol by slow evaporation to yield yellow blocks of (I).

Refinement
Due to the disordered solvent molecule and its uncertain identity, the data were processed with SQUEEZE in PLATON (Spek, 2009). This revealed 877.8 Å 3 of solvent accessible volume per unit cell and 126 electron-units of scattering density or 109.7 Å 3 (16 electron units) per organic molecule. This was not included in the calculations of overall formula weight, density and absorption coefficient. The original data set consisted of 31099 measured reflections (-11 ≤ h ≤ 11, -11 ≤ k ≤ 11, -54 ≤ l ≤ 54), for which R int was 0.068.
The C-and N-bound H-atoms were geometrically placed (C-H = 0.93-0.98 Å, N-H = 0.86 Å) and refined as riding with U iso (H) = 1.2U eq (carrier). The O-bound H was located in a difference map and refined as riding in its as-found relative position with U iso (H) = 1.5U eq (O).  The molecular structure of (I) with displacement ellipsoids drawn at the 40% probability level and the intramolecular π-π stacking interactions shown as double-dashed lines betweent the ring centroids.  Detail of the structure of (I) showing the formation of dimers linked by pairs of N-H···O hydrogen bonds, thus generating R 2 2 (10) loops. All C-bonded H atoms omitted for clarity. Symmetry code: (ii) y, x, 1 -z.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > 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.