2,4-Dichloro-1-iodo-6-nitrobenzene

In the crystal structure of the title compound, C6H2Cl2INO2, there are weak C—H⋯Cl interactions and I⋯O [3.387 (4) Å] close contacts. These interactions form sheets in the ac plane, with the closest contact between adjacent planes occurring between inversion-related nitro O atoms [3.025 (8) Å]. The molecule possesses mirror symmetry, with the halogen, N and C atoms all lying in the mirror plane. Hence, the dihedral angle between the benzene ring and the nitro group is 90°.

In the crystal structure of the title compound, C 6 H 2 Cl 2 INO 2 , there are weak C-HÁ Á ÁCl interactions and IÁ Á ÁO [3.387 (4) Å ] close contacts. These interactions form sheets in the ac plane, with the closest contact between adjacent planes occurring between inversion-related nitro O atoms [3.025 (8) Å ]. The molecule possesses mirror symmetry, with the halogen, N and C atoms all lying in the mirror plane. Hence, the dihedral angle between the benzene ring and the nitro group is 90 .

Comment
The title compound was synthesized as a precursor for the preparation of chiral polychlorinated biphenyl (PCB) derivatives (Lehmler et al., 2010) using the Suzuki-coupling reaction (Joshi et al., 2011;Lehmler & Robertson, 2001).
There are C3-H3···Cl2 (x -0.5, y, 0.5 -z) interactions [C3···Cl2 = 3.718 (7) Å] that link the molecules into flat ribbons along the a axis. Between adjacent ribbons there are close contacts between iodine atoms and the nitro group O atoms, with I···O distances of 3.387 (4) Å. Each iodine atom is the same distance from both oxygen atoms because they are equivalent by virtue of the mirror plane. The linking of adjacent ribbons in the crystal structure give sheets in the ac plane (since the mirror plane is perpendicular to b). The closest contact between adjacent planes occurs between inversion (1 - The distance between layers is simply half the b axis length. Viewed along the b axis, molecules appear to stack in an alternating fashion about a 2 1 screw (-x, 0.5 + y,-z), which places Cl1 of one molecule directly over the benzene ring of its screw-related counterpart.
As a result of the symmetrical interaction between the iodines and both nitro group O atoms, the molecular structure of the title compound displayed a 90° dihedral angle between the plane of the nitro group and the plane of the benzene ring (which lies on the mirror plane). Only a few solid state structures of structurally related molecules with a 1-iodo-2-nitrobenzene moiety have been reported previously. The molecular structures of 4-chloro-1-iodo-2-nitrobenzene, a structurally related halogenated nitrobenzene with one iodo substituent ortho to the nitro group, display smaller dihedral angles between benzene ring and nitro group [51.0 (3)° and 29.0 (2)°] in the solid state (Tahir et al., 2009). In contrast, 2,4-diiodo-3-nitroanisole, a nitrobenzene with two iodo substituents ortho to the nitro group, displayed dihedral angle of 88.0 (3)° (Li et al., 2012), probably due to the steric demand of the two ortho iodo substituents. These differences demonstrate that packing effects can make significant contributions to the molecular structure (i.e. the dihedral angle between benzene ring and nitro group) in the solid state.

Experimental
The title compound was synthesized from 2,4-dichloro-6-nitroaniline by sequential diazotization and iodonization with NaNO 2 -HCl-KI system (Sohn et al., 2003). Crystals of the title compound suitable for crystal structure analysis were obtained by slow evaporation of a solution of the title compound in hexane-ethyl acetate (10:1).

Refinement
H atoms were found in difference Fourier maps, but subsequently included in the refinement using riding models, with constrained distances set to 0.95Å (C sp2 H). U iso (H) values were set to 1.2U eq of the attached atom.  The molecular structure of the title compound, showing displacement ellipsoids drawn at the 50% probability level.

Special details
Experimental. Diffraction data were collected with the crystal at 90 K, which is standard practice in this laboratory for the majority of flash-cooled crystals. A correction for radiation damage was included in the SADABS (Sheldrick, 2008b) run. This seems to have resulted in all the atomic displacement parameter ellipsoids looking more spherical than usual.