Cyclohexa-2,5-diene-1,4-dione–1,2,4,5-tetrafluoro-3,6-diiodobenzene (1/1)

The asymmetric unit of the title co-crystal adduct, C6H4O2·C6F4I2, comprises a half-molecule each of cyclohexa-2,5-diene-1,4-dione and 1,2,4,5-tetrafluoro-3,6-diiodobenzene. The C6F4I2 molecule is almost planar (r.m.s. deviation = 0.0062 Å). In the crystal, the components are connected through O⋯I halogen bonds [3.017 (11) Å], leading to the formation of wavelike chains along the a axis. The crystal packing also features C—H⋯F interactions.


Comment
The title co-crystal is part of a study on the halogen bond, which is a powerful intermolecular interaction we and others have used extensively to produce a variety of structures involving perfuorinated compounds (Ji et al. 2011;Arman et al. 2010;Cardillo et al. 2000), usually very diffcult to crystallize.
In addition, the molecules are further stabilized in the crystal packing via a combination of C-H···F contacts (Table. 1), as shown in Fig. 2.

Experimental
The starting materials were commercial obtained from Aldrich. The 1:1 adduct was obtained by dissolving in chloroform, at room temperature and in a vial, equimolecular amounts of cyclohexa-2,5-diene-1,4-dione and 1,2,4,5-tetrafluoro-3,6diiodobenzene. The open vial was closed in a cylindrical bottle containing vaseline oil. Volatile solvents were allowed to diffuse at room temperature and, after one day, the yellow block crystals were obtained.

Refinement
All H atoms were positioned geometrically and treated as riding, with C-H bond lengths constrained to 0.93 Å (aromatic CH), and with Uĩso~(H) = 1.2Ueq(C).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 > σ(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.