2,9-Bis(trichloromethyl)-1,10-phenanthroline

The asymmetric unit of the title compound, C14H6Cl6N2, contains two crystallographically independent molecules, each of which is slightly twisted from planarity. The dihedral angles between the central ring and the two outer rings are 3.81 (7) and 4.30 (7)° in one molecule, and 4.13 (8) and 4.10 (7)° in the other. In the crystal structure, molecules are interlinked by C—Cl⋯Cl interactions into sheets parallel to the ac plane. These sheets are stacked along the b axis in such a way that the molecules are antiparallel; they are further connected into a supramolecular network. There are no classical hydrogen bonds. C⋯Cl [3.637 (2) Å], Cl⋯Cl [3.5639 (5)–3.6807 (8) Å] and Cl⋯N [3.3802 (15)–3.4093 (15) Å] short contacts and π–π interactions, with centroid–centroid distances in the range 3.5868 (9)–3.7844 (9) Å, are observed.


Comment
Trichloromethyl-substituted heterocyclic compounds are of great importance due to their broad spectrum of biological activities. 2,9-Bis(trichloromethyl)-1,10-phenanthroline is used as a potentially robust ligand for metal oxidation catalysts (Beer et al., 1993). 1,10-phenanthroline derivatives also show antitumor (Wesselinova et al., 2009) as well as luminescence properties (Armaroli et al., 1992). Recently a series of trichloromethyl-substituted heterocyclic compounds has been synthesized (Goswami et al., 2007) in good yield using N-chlorosuccinimide (NCS) and triphenylphosphine (PPh 3 ) in carbon tetrachloride. In supramolecular chemistry it is known that the self-association of individual molecules can lead to the formation of highly complex and fascinating supramolecular aggregates if halogen···π interactions contribute to the formation of specific motifs (Emmerling et al., 2007). The title compound was synthesized in order to study its supramolecular structure.
The asymmetric unit ( Fig. 1) contains two molecules, A and B, having slight differences in bond lengths and angles. The 1,10-phenanthroline unit is not strictly planar, with dihedral angles between the central ring and the C1-C4/C12/N1 and C7-C11/N2 rings of 3.81 (7) and 4.30 (7)°, respectively, for molecule A [the corresponding values for molecule B are 4.13 (8) and 4.10 (7)° ]. In both molecules, A and B, none of the Cl atoms of the trichloromethyl substitutent is coplanar with the 1,10-phenanthroline ring system. The bond distances adopt normal values (Allen et al., 1987).
In the crystal structure (Fig. 2), non-covalent interactions play a significant role in the three-dimensional supramolecular architecture, in which the molecules are interlinked into sheets parallel to the ac plane. These sheets are stacked along the b axis in such a way that the molecules are antiparallel. These sheets are further connected into a supramolecular network.

Experimental
A mixture of N-chlorosuccinimide (500 mg, 4.5 mmol) and triphenylphosphine (500 mg, 4.2 mmol) was moistened with CCl 4 (60 ml) in a round bottom flask and stirred at room temperature for 25 min. A solution of 2,9-dimethyl-1,10-phenanthroline (1 g, 5.2 mmol) was added to the suspension and the reaction mixture was stirred and heated under reflux for 7 h. The solution was cooled and filtered. The evaporated filtrate was washed with saturated aqueous Na 2 CO 3 and extracted repeatedly with CHCl 3 . Drying over anhydrous Na 2 SO 4 was carried out, and the solvent was removed under reduced pressure. The crude product was purified with SiO 2 chromatography (eluted with 1% ethyl acetate in petroleum ether) to give supplementary materials sup-2 the title compound as a white crystalline solid. Colorless plate-shaped single crystals suitable for X-ray structure determination were recrystalized from CH 2 Cl 2 :hexane (1:10, v/v) by slow evaporation of the solvent at room temperature over the course of a week.

Refinement
All H atoms were placed in calculated positions, with C-H = 0.93 Å, U iso (H) = 1.2U eq (C).
Figures Fig. 1. The molecular structure of the asymmetric unit of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme. Hydrogen atoms are shown as spheres of arbitrary radius. 2,9-Bis(trichloromethyl)-1,10-phenanthroline

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 120.0 (1) K. 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.