Dimethyl 3,3′-(phenylmethylene)bis(1H-indole-2-carboxylate)

In the title compound, C27H22N2O4, the two indole ring systems are approximately perpendicular to each other, with a dihedral angle of 84.5 (5)° between their planes; the benzene ring is twisted with respect to the two indole ring systems at angles of 78.5 (5) and 86.5 (3)°. In the crystal, molecules are linked by N—H⋯O hydrogen bonds, weak C—H⋯O and C—H⋯N hydrogen bonds, and C—H⋯π interactions into a three-dimensional supramolecular architecture.

In the title compound, C 27 H 22 N 2 O 4 , the two indole ring systems are approximately perpendicular to each other, with a dihedral angle of 84.5 (5) between their planes; the benzene ring is twisted with respect to the two indole ring systems at angles of 78.5 (5) and 86.5 (3) . In the crystal, molecules are linked by N-HÁ Á ÁO hydrogen bonds, weak C-HÁ Á ÁO and C-HÁ Á ÁN hydrogen bonds, and C-HÁ Á Á interactions into a three-dimensional supramolecular architecture.  Table 1 Hydrogen-bond geometry (Å , ).

Comment
Indole derivatives are found abundantly in a variety of natural plants and exhibit various physiological properties (Poter et al., 1977;Sundberg, 1996). Among them, bis-indolymethane derivatives are found to be kinds of potentially bioactive compounds (Chang et al., 1999;Ge et al., 1999). In recent years, the synthesis and application of bis-indolymethane derivatives have been widely studied. The title compound is one of bis-indolymethane derivatives as a precursor for MRI Contrast Agents (Ni, 2008). We report here its crystal structure.
The molecular structure of the title compound is shown in Fig. 1. The benzene ring is twisted to the two indole rings with the dihedral angles of 101.5 (5) and 93.5 (3)°, respectively. Two indole rings make a dihedral angle of 84.5 (5)° to each other.
As shown in Figure 2, the molecules are linked by N-H···O and C-H···O and C-H···N hydrogen bonds into dimers in the crystal lattice. The structural parameters for the intermolecular hydrogen bonds resulting in the formation of dimers are given in Table 1.

Experimental
Methyl indole-2-carboxylate (17.5 g, 100 mmol) was dissolved in 200 ml methanol; commercially available benzaldehyde (5.3 g, 50 mmol) was added and the mixture was heated to reflux temperature. Concentrated HCl (3.7 ml) was added and the reaction was left for 1 h. After cooling the white product was filtered off and washed thoroughly with methanol. The reaction can be followed by TLC (CHCl 3 :hexane = 1:1). Yield was 93%. Crystals of the title compound suitable for X-ray analysis were obtained by slow evaporation of an ethanol solution.

Refinement
H atoms were positioned geometrically, with N-H = 0.86 Å and C-H = 0.93, 0.96, and 0.98 Å for aromatic, methyl, and methine H, respectively, and constrained to ride on their parent atoms, with U iso (H) = xU eq (C,N), where x = 1.5 for methyl H, and x = 1.2 for all other H atoms.  The molecular structure of (I), showing the atom-numbering scheme and displacement ellipsoids at the 30% probability level.   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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O1 0.52156 (18