4-Bromo-N-(4-bromophenyl)aniline

In the title compound, C12H9Br2N, the dihedral angle between the benzene rings is 47.32 (5)°, whereas the pitch angles, or the angles between the mean plane of each aryl group ‘propeller blade’ and the plane defined by the aryl bridging C—N—C angle, are 18.1 (2) and 31.7 (2)°. No intermolecular N—H hydrogen bonding is present in the crystal; however, there is a short intermolecular Br⋯Br contact of 3.568 (1) Å.

In the title compound, C 12 H 9 Br 2 N, the dihedral angle between the benzene rings is 47.32 (5) , whereas the pitch angles, or the angles between the mean plane of each aryl group 'propeller blade' and the plane defined by the aryl bridging C-N-C angle, are 18.1 (2) and 31.7 (2) . No intermolecular N-H hydrogen bonding is present in the crystal; however, there is a short intermolecular BrÁ Á ÁBr contact of 3.568 (1) Å .

Comment
The title compound, 4-bromo-N-(4-bromophenyl)aniline, C 12 H 9 Br 2 N (I), was first synthesized by Galatis & Megaloikonomos (1934) via the direct bromination of diphenylamine, and the structure was corroborated by Crounse & Raiford (1945) in their study of the hydrolysis of the benzoyl derivative. More recently, halogenated diphenylamines have been prepared by copper catalyzed coupling reactions (He et al., 2008). The crystal structure of the chloride analogue is known (Plieth & Ruban, 1961), and an analogous structure with an oxygen bridge has also been reported (Eriksson et al., 2004).
The title compound is an amine analogues of a class of brominated diphenyl ether materials (de Wit, 2002). Polybrominated diphenyl ethers are commonly used as flame retardants (Eriksson et al., 2004) in consumer products and electronics and have been found in humans (Lunder et al., 2010).
Compound (I) is a dibrominated diphenyl amine derivative with a "propeller blade" disposition of the benzene rings about the bridging nitrogen atom. The structure reveals that there is no intermolecular hydrogen bonding, although there are significant intermolecular Br···Br contacts (Medlycott et al. , 2007) at a distance of 3.568 (1) Å, which is shorter than the sum of the van der Waals radius of bromine, 1.85Å (Bondi, 1964), at 3.7 Å. The aryl-bridging C4-N-C7 angle in (I) is 128.5 (2)°, somewhat smaller than the C-N-C bond angle of 133.8° found in the isomorphous dichloro analog (Plieth & Ruban, 1961), but similar to the C-N-C bond angle of 128.1° in another similar structure, N-4-(bromophenyl)-4-nitroaniline, which contains one bromo and one nitro group (Li et al., 2010).
The dihedral angle in (I) is found to be 47.32 (5)°, whereas the pitch angles are 18.1 (2)° and 31.7 (2)°. The pitch angles are the angles between the mean plane of each aryl group "propeller blade" and the plane defined by the aryl bridging C4-N-C7 angle. The pitch angles are metrical parameters that describe the dispostion of the benzene rings about the bridging atom with greater detail than the dihedral angle; structures with equivalent dihedral angles may exhibit dramatically different orientations of the benzene rings about the bridging group (Lim & Tanski, 2007). In the isomorphous dichloro analog to the title compound, the dihedral angle is found to be significantly larger, 56.5°, as are the pitch angles of 22.1° and 39.1°. In another similar bromo compound, N-4-(bromophenyl)-4-nitroaniline, where the dihedral angle of 44.8° is more similar to that of the title compound, the pitch angles are found to be 12.6° and 35.1°.

Refinement
All non-hydrogen atoms were refined anisotropically. The hydrogen atoms on carbon were included in calculated positions and were refined using a riding model at C-H = 0.95Å and U iso (H) = 1.2 × U eq (C) of the aryl C-atoms. T hydrogen atom on nitrogen was refined semifreely with the help of a distance restraint, d(N-H) = 0.835 (16) Å and U iso (H) = 1.2 × U eq (N).
The extinction parameter (EXTI) refined to zero and was removed from the refinement.  Fig. 1. A view of compound (I), with displacement ellipsoids shown at the 50% probability level.

Experimental. A suitable crystal was mounted in a nylon loop with Paratone-N cryoprotectant oil and data was collected on a Bruker
APEX 2 CCD platform diffractometer. The structure was solved using direct methods and standard difference map techniques, and was refined by full-matrix least-squares procedures on F 2 with SHELXTL Version 6.14 (Sheldrick, 2008). 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.