4,4′-Dibromo-7,7′-dimethoxy-1,1′-spirobiindane

In the title compound, C19H18Br2O2, the dihedral angle between the two benzene rings of the spirobiindane molecule is 70.44 (8)°. In the crystal, molecules are interconnected along the c axis by C—H⋯O hydrogen bonds and π–π stacking [centroid–centroid distance = 3.893 (2) Å] interactions, forming an infinite chain structure. The chains are further interconnected through another set of C—H⋯O hydrogen bonds, forming layers approximately parallel to the bc plane.

In the title compound, C 19 H 18 Br 2 O 2 , the dihedral angle between the two benzene rings of the spirobiindane molecule is 70.44 (8) . In the crystal, molecules are interconnected along the c axis by C-HÁ Á ÁO hydrogen bonds andstacking [centroid-centroid distance = 3.893 (2) Å ] interactions, forming an infinite chain structure. The chains are further interconnected through another set of C-HÁ Á ÁO hydrogen bonds, forming layers approximately parallel to the bc plane.
The crude compound was purified by column chromatography on silica gel (hexane/EtOAc = 9:1 v.v), yield 65%. The orange crystals of the title compound having an average 0.40 × 0.16 × 0.10 mm dimension were obtained by slow evaporation from its solution of hexane.

Refinement
The H atoms were placed in idealized positions and allowed to ride on the relevant carbon atoms, with C-H = 0.93 and 0.97 Å for aryl and methylene H atoms, respectively, and U iso (H) = 1.2U eq (C).

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 > 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.

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