Crystal structure and Hirshfeld analysis of 2-[bis(1-methyl-1H-indol-3-yl)methyl]benzoic acid

In the title compound, the dihedral angles between the 1-methyl indole units (A and B) and the benzoic acid moiety (C) are A/B = 64.87 (7), A/C = 80.92 (8) and B/C = 75.05 (8)°. An intramolecular C—H⋯O interaction arising from the methyne group helps to establish the conformation. In the crystal, (8) carboxylic acid inversion dimers linked by pairs of O—H⋯O hydrogen bonds are observed.


Chemical context
Bisindolyl methane and its derivatives are relatively easy to synthesize and show a broad spectrum of potential biological activities: for example, bis(indolyl)imidazole shows antiplasmodial activity towards plasmodium falciparum (Alvarado et al., 2013). Furthermore, they also have good potential as antibacterial (Imran et al., 2014;Challa et al., 2017), antileishmanial (Bharate et al., 2013), antitumor (Carbone et al., 2013), antiplatelet (Grumel et al., 2002) and anticancer (Guo et al., 2010;Jamsheena et al., 2016) agents. Oxidized bis(indolyl)methanes containing an acidic hydrogenbond-donor group and a basic hydrogen-bond-acceptor group can act as selective colorimetric sensors for either F À or HSO 4 À in an aprotic solvent (He et al., 2006). Arylfuryl-bis(indolyl)methanes have selective chromogenic and fluorogenic ratiometric receptors for the mercury ion in aqueous solution (Batista et al., 2014). As part of our studies in this area, we now report the acid-catalysed condensation reaction between carboxy benzaldehyde and indole to generate the title compound. ISSN 2056-9890

Supramolecular features
In the crystal of the title compound, neighbouring molecules are connected into dimers with an R 2 2 (8) graph-set motif via pairwise O3-H3OÁ Á ÁO1 hydrogen bonds (Table 1, Fig. 2).

Hirshfeld surface analysis
The Hirshfeld surface and fingerprint (FP) plots for the title compound were generated using CrystalExplorer17 (McKinnon et al., 2007). A view of the Hirshfeld surface mapped over d norm is shown in Fig. 3. The intense red spots near the O1-carbonyl and H30-benzoic acid atoms indicate the short interatomic OÁ Á ÁH/HÁ Á ÁO contacts relating to the hydrogen bond given in

Figure 3
View of the Hirshfeld surface of the title compound mapped over d norm in the range À0.68 to +1.45 au.

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level.

Synthesis and crystallization
Equimolar amounts of 2-carboxybenzaldehyde (3.0 mmol) and 1-methylindole (3.0 mmol) was mixed in a reaction vessel. A few drops of anhydrous acetic acid was added and the mixture was then irradiated in a domestic microwave oven at 100 W for 5 min. The crude product obtained was purified by recrystallization from an acetone-EtOH solvent mixture (v:v = 1:2) to give the pure product in 13.3% yield. IR (

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The hydroxy H atom was freely refined. C-bound H atoms were positioned geometrically and refined using a riding model with C-H = 0.93-0.96 and U iso (H) = 1.2-1.5U eq (C).    and publCIF (Westrip, 2010).

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 > 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.