4,4′-Dibromo-2,2′-{[(3aS,7aS)-2,3,3a,4,5,6,7,7a-octahydro-1H-1,3-benzimidazole-1,3-diyl]bis(methylidene)}diphenol

The cyclohexane ring in the title compound, C21H24Br2N2O2, adopts a chair conformation and the five-membered ring to which it is fused has a twisted envelope conformation. The asymmetric unit contains one half-molecule, which is related to the other half by a twofold rotation axis. The two N atoms of the five-membered ring are linked to the hydroxy groups by intramolecular O—H⋯N hydrogen bonds. In the crystal, intermolecular C—H⋯O and C—H⋯π interactions occur.

The cyclohexane ring in the title compound, C 21 H 24 Br 2 N 2 O 2 , adopts a chair conformation and the five-membered ring to which it is fused has a twisted envelope conformation. The asymmetric unit contains one half-molecule, which is related to the other half by a twofold rotation axis. The two N atoms of the five-membered ring are linked to the hydroxy groups by intramolecular O-HÁ Á ÁN hydrogen bonds. In the crystal, intermolecular C-HÁ Á ÁO and C-HÁ Á Á interactions occur.
Data collection: CrysAlis CCD (Oxford Diffraction, 2009); cell refinement: CrysAlis RED (Oxford Diffraction, 2009); data reduction: CrysAlis RED; program(s) used to solve structure: SIR2002 (Burla et al., 2003); program(s) used to refine structure: JANA2006 (Petříček et al., 2006); molecular graphics: DIAMOND (Brandenburg & Putz, 2005); software used to prepare material for publication: JANA2006.  Table 1. Its X-ray structure confirms the presence of intramolecular hydrogen bonds between the phenolic hydroxyl groups and nitrogen atoms [N-H, 1.903 (18) Å] that is however by 0.13 Å longer in comparison with related structure (Rivera et al., 2010), whereas the N···O distance In the title compound, C 21 H 24 Br 2 N 2 O 2 , the asymmetric unit contains one-half of the molecule, which is related to the other half by a twofold rotation axis [symmetry code: -x, y, -z] passing through C1. The orthorhombic unit cell contains two molecules. Instead, the molecules have identical (S,S)-molecular configuration and its absolute structure was determined with a Flack parameter of 0.01 (2) (Flack, 1983).

Physical Measurements
The melting point was determined with an Electrothermal apparatus, and it has not been corrected. IR spectrum was recorded as KBr pellets at 292 K on a Perkin-Elmer Paragon FT-IR instrument. NMR spectra were performed in CDCl 3 at room temperature on a Bruker AMX 400 Advance spectrometer.

Refinement
All hydrogen atoms were discernible in difference Fourier maps and could be refined to reasonable geometry. According to common practice H atoms attached to C atoms were nevertheless kept in ideal positions during the refinement. The isotropic atomic displacement parameters of hydrogen atoms were evaluated as 1.2*U eq of the parent atom.

Special details
Refinement. The refinement was carried out against all reflections. The conventional R-factor is always based on F. The goodness of fit as well as the weighted R-factor are based on F and F 2 for refinement carried out on F and F 2 , respectively. The threshold expression is used only for calculating R-factors etc. and it is not relevant to the choice of reflections for refinement.