9,10-Dibromophenanthrene

The molecule of the title compound, C14H8Br2, is almost planar [maximum deviation 0.0355 (7) Å] and possesses crystallographic twofold (C2) symmetry. In the crystal, the molecules form face-to-face slipped antiparallel π–π stacking interactions along the c axis with an interplanar distance 3.471 (7) Å, centroid–centroid distances of 3.617 (5)–3.803 (6) Å.

However, the method involved relatively vigorous reaction conditions, and the title compound was not easily accessible.
Therefore, the development of milder methods was pursued. Recently, we established a new method for the preparation of the title compound. Thus, treatment of 2,2′-bis(dibromomethyl)biphenyl (Bacon & Bankhead, 1963) with potassium tbutoxide yielded the title compound in a high yield. Securement of the title compound let to obtain single crystals suitable for X-ray analysis. We report herein the crystal structure of the title compound.
The molecular structure of the title compound is shown in Fig. 1. The molecule possesses C 2 symmetry, and half of the formula unit is crystallographically independent. The molecule is almost planar with the maximum deviation of 0.0355 (7) Å for Br1. The bonds lengths and angles are in good agreement with the standard values. As shown in Fig. 2, the molecules form face-to-face slipped antiparrallel π-π stacking along the direction of the c axis. The interplanar distance is 3.471 (7) Å and controid-centroid distances of 3.617 (5)-3.803 (6) Å. Recently, we have reported the crystal structure of 3,6-dibromophenanthrene (Yokota et al., 2012), whose feature was a herrinbone-like arrangement, indicating the difference in packing arrangement depending on the positions of bromo substituents.
The resulting solid was extracted with toluene, washed with brine, and dried over Na 2 SO 4 . After evaporation, column chromatography on silica gel (hexane-CH 2 Cl 2 ) produced the title compound (161 mg, 79%) as a pale yellow solid. Single crystals suitable for X-ray analysis were obtained by slow evaporation from a toluene solution.

Refinement
All the aromatic H atoms were positioned geometrically and refined using a riding model with C-H = 0.94 Å and U iso (H) = 1.2U eq (C).

Figure 2
Packing diagram of the title compound viewed along the b axis. Hydrogen atoms are omitted for clarity. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.67 e Å −3 Δρ min = −1.49 e Å −3 Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 > 2σ(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.