2,2′-Dimethoxy-6,6′-dinitrobiphenyl

In the title compound, C14H12N2O6, the half molecule in the asymmetric unit of the cell is completed by a crystallographic twofold rotation axis, and the two benzene rings of the complete molecule make a dihedral angle of 60.5 (3)°. Furthermore, intermolecular weak C—H⋯O hydrogen bonds link adjacent molecules, forming a two-dimensional sheet. These sheets are stablized by face-to-face weak π–π contacts [centroid–centroid distance = 3.682 (1) Å] between the nearly parallel [dihedral angle = 0.12 (7)°] benzene rings of the neighboring molecules, resulting in a three-dimensional network.

In the title compound, C 14 H 12 N 2 O 6 , the half molecule in the asymmetric unit of the cell is completed by a crystallographic twofold rotation axis, and the two benzene rings of the complete molecule make a dihedral angle of 60.5 (3) . Furthermore, intermolecular weak C-HÁ Á ÁO hydrogen bonds link adjacent molecules, forming a two-dimensional sheet. These sheets are stablized by face-to-face weakcontacts [centroid-centroid distance = 3.682 (1) Å ] between the nearly parallel [dihedral angle = 0.12 (7) ] benzene rings of the neighboring molecules, resulting in a three-dimensional network.
Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 and PLATON.  (Jiang et al. 2001;García et al. 2002). Design and synthesis of such compounds play a very important role in the development of highly enantioselective asymmetric reactions. Thus, it is not surprising that a lot of methods have been developed to obtain these chiral compounds (Brunel 2005;Kočovský et al. 2003). In this paper, we report the synthesis and crystal structure of the title compound with C 2 -symmetry.

Structure Reports Online
A view of the molecular structure of the title compound is given in Fig.1. All bond lengths and angles are in the expected range and in good agreement with those reported previously (Yang et al. 2005). The dihedral angle between two benzene rings is 60.5 (3)°, which is considerable larger than those found in other biphenyls (Fischer et al. 2007), possibly due to the concomitant effects of the steric hindrance of adjacent methoxy and nitro groups.
In the crystal structure, each molecule is connected by four adjacent molecules through intermolecular C-H···O hydrogen bonds (Table 1), between methoxy groups and O atoms of the adjacent nitro groups, leading to the formation of a two-dimensional sheet in the ac plane. The sheets are further connected into a three-dimensional network (Fig.2) by the face-to-face weak π-π contacts between nearly parallel benzene rings of the neighboring title molecules. The Cg1···Cg1 iii distance is 3.6823 (11) Å, the perpendicular distance between the rings is 3.410 Å, and the slippage between the rings is 1.389 Å. Cg1 is the centroid of the benzene ring C1 -C6, the symmetry code iii = 1 -x, -y, 1 -z.

Experimental
The title compound was synthesized by a reported method (Chen, et al. 2001),namely, a mixture of 2-iodo-3-nitroanisol (14 g, 0.05 mol) and activated copper brone (9.5 g, 0.15 mol), 50 ml of dimethylformamide was stirried at 140°C for 4 h under nitrogen atmosphere. Yellow crystals suitable for X-ray diffraction study were obtained from a solution in acetic ester.

Refinement
All of the non-hydrogen atoms were refined anisotropically. The hydrogen atoms were assigned with common isotropic displacement factors U iso (H) = 1.2 times U eq (C,N) and 1.5 times U eq (O), respectively, and included in the final refinement by using geometrical restraints, with C-H distances of 0.93 Å.  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 Rfactors(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.