Dimethyl 3,3′-[(4-nitrophenyl)methylene]bis(1H-indole-2-carboxylate) ethanol hemisolvate

There are two main molecules in the asymmetric unit of the title compound in which the two indole ring systems are approximately perpendicular to one another, at dihedral angles of 69.3 (5) and 82.8 (4)°.

There are two main molecules in asymmetric unit of the title compound, C 27 H 21 N 3 O 6 Á0.5C 2 H 5 OH. In both, the indole ring systems are approximately perpendicular to each other, at dihedral angles of 69.3 (5) and 82.8(4) . In the crystal, molecules are linked by N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds into a three-dimensional supramolecular architecture. The solvent ethanol molecule acts as a donor, forming an O-HÁ Á ÁO hydrogen bond, reinforcing the structure.

Structure description
There are abundant bis(indolyl)methane derivatives in various terrestrial and marine natural resources (Sundberg, 1996). They can be used as precursors for MRI necrosis avid contrast agents (Ni, 2008). As part of our ongoing studies of bis(indoyl)methane compounds, we now report the synthesis and crystal structure of the title bis-(indoly)methane compound.
The molecular structure of the title compound is shown in Fig. 1. In the first bisindole molhe two indole ring systems are nearly perpendicular to one another [dihedral angle = 69.3 (5) ] while the benzene ring (C2-C7) is twisted to the N2/C8-C15 and N3/C18-C25 indole ring systems by dihedral angles of 44.3 (3) and 77.6 (4) , respectively. The carboxyl groups are approximately co-planar with the attached indole ring systems, the dihedral angles between the carboxyl groups and the mean plane of the N2/C8-C15 and N3/C18-C25 indole ring systems being 20.7 (4) and 3.8 (5) , respectively. For the second bisindole molecule, the two indole ring systems are also nearly perpendicular to one another [dihedral angle = 82.8 (4) ] while the benzene ring (C29-C34) is twisted to the N5/C35-C42 and N6/C45-C52 indole ring systems with dihedral angles of 88.5 (5) and 81.8 (4) , respectively.

data reports
In the crystal, molecules are linked by N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds into a three-dimensional supramolecular architecture. The solvent ethanol molecule acts as a donor, forming an O-HÁ Á ÁO hydrogen bond, reinforcing the structure (  et al., 2020). In these structures, the indole ring systems are also nearly perpendicular to one another, making dihedral angles of 82.0 (5), 89.3 (5), 89.7 (5) and 88.3 (4) , respectively.

Synthesis and crystallization
Methyl indole-2-carboxylate (1.75 g, 10 mmol) was dissolved in 20 ml of ethanol, and 4-nitrobenzaldehyde (0.76 g, 5 mmol) and concentrated HCl (0.5 ml) were added and the mixture was heated to reflux temperature for 2 h. After cooling, the white product was filtered off and washed thoroughly with ethanol. The reaction was monitored by TLC (AcOEt: hexane = 1:3). Yield 90%. Single crystals of the title compound suitable for X-ray analysis were obtained by slow evaporation of an ethanol solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

Figure 1
The molecular structure of the title molecule with the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.

data-1
IUCrData ( where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.36 e Å −3 Δρ min = −0.28 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.

data-2
IUCrData (2021). 6, x210057 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.