Bis(2-nitrophenyl)methane

In the title compound, C13H10N2O4, the nitro groups are twisted significantly relative to the benzene rings [dihedral angles = 16.64 (18) and 28.02 (11)°]. The benzene groups are nearly perpendicular to each other [dihedral angle = 87.72 (6)°]. Short intermolecular N⋯O and C⋯O [2.981 (2) and 3.060 (2) Å, respectively] contacts suggest possible weak π-interactions between nitro groups and between benzene and nitro groups. In addition, there are π–π interactions between one benzene group and an inversion-related equivalent [interplanar separation = 3.494 (2) Å].


Related literature
The synthesis of the title compound has been previously reported (Allinger & Youngdale, 1962), although by different methods from the preparation of the sample used for this study [a modification of the method given by Lu et al. (2006)]. For related structures, see: Barnes et al. (1981); Brito et al. (2007); Cousson et al. (1993);Housty (1961

Comment
4,4′-Methylene dianiline (4,4′-MDA) is principally used to produce 4,4′-methylene dianiline diisocyanate and other polymeric isocyanates, which are used to manufacture polyurethane foams. 4,4′-MDA is also used as a curing agent for epoxy resins and urethane elastomers, as a corrosion preventative for iron, as an antioxidant for lubricating oils, as a rubber processing chemical, and as an intermediate in the manufacture of elastomeric fibers. In the manufacturing process of 4,4′-MDA, by-products including 2,2′-methylene dianiline (2,2′-MDA) are produced. 2,2′-MDA can have hazardous health effects such as irritation to the skin and eyes, liver damage through acute oral or dermal exposure, and is a possible human carcinogen. In an effort to access 2,2′-MDA for use as a standard to measure the by-products created in the manufacturing process to synthesize 4,4′-MDA, we have developed a new synthesis of the intermediate 2,2′-dinitrodiphenylmethane and determined its crystal structure.
The molecular structure of bis(2-nitrophenyl)methane ( Fig. 1) is composed of an asymmetric unit containing one whole molecule. The N-O bond lengths (range 1.227 (2)-1.233 (2) Å) are consistent with a high degree of resonance in the nitro groups. Each nitro group is twisted from the bonded benzene moiety with angles between least-squares planes (N1, O1, O2 and C1-C6; N2, O3, O4 and C8-C13) of 16.64 (18)° and 28.02 (11)°, respectively. The benzene groups are nearly perpendicular with angles between least-squares planes of 87.72 (6)°. The orientation of the nitro groups allows for close intramolecular contacts between the oxygen atoms and methylene H atoms.

Experimental
Compound (I) was prepared by a modification of the method used by Lu et al. (2006).

Refinement
Hydrogen atoms were placed at calculated positions and refined in the riding model approximation with distances of C-H = 0.95 and 0.99 Å for the benzene and methylene groups, respectively, and with U iso (H) = 1.2×U eq (C).

Figure 1
A thermal ellipsoid plot (50% probability ellipsoids for non-H atoms) of the structure of (I).