5,5′-Bis[(2,2,2-trifluoroethoxy)methyl]-2,2′-bipyridine

The complete molecule of the title compound, C16H14F6N2O2, is generated by crystallographic inversion symmetry, which results in two short intramolecular C—H⋯N hydrogen-bond contacts per molecule. In the crystal, aromatic π–π stacking [centroid–centroid distance = 3.457 (2) Å] and weak C—H⋯π interactions occur. A short H⋯H [2.32 (3) Å] contact is present.

However, the X-ray crystal structure of poly-fluorinated bpy ligands still remains elusive until recent elucidation of the structure on simplest 4,4'-bis(CF 3 CH 2 OCH 2 )-2,2'-bpy (Lu, Tu, Wu et al., 2010). Reported here is the significantly different crystal structure on its 5,5'-isomer. They vary only on the positions of two identical substituents, yet features of packing in the solid state show little in similarity.
The title compound I is centro-symmetric and crystallizes in the space group of P-1, one half of the molecule being crystallographically independent. Two structural features of the title compound I are the planarity and the anti conformation of connected pyridyl units. The bpy exhibits a planar core and the N-C3-C3 i -N i torsion angle is 180°, similar to the values in its 4,4'-isomer (Lu, Tu, Wu et al., 2010). Also noticed is the intramolecular weak hydrogen bonding interaction on C4-H4···N i , as suggested by the short H4···N i distance of 2.46 (2) Å and the C4-H4···N i angle of 102 (1)° (see Fig. 1).
Instead of intermolecular C-H···N and C-H···F interactions, stabilization of the structure of I is likely due to effective intermolecular C-H..π and F···F interactions. The π-π stacking is the driving force towards crystallization, with two adjacent bpy layers at a distance of 3.512 (2) Å. On top of this, the C6-H6A..π hydrogen bonding interaction has been observed between the methylene H atom and one of the adjacent bpy rings on the a-translation related direction. As shown in Table   1, the distance of H6A to bpy plane is 2.57 (2) Å, making less than 10° with the vector of H6A to centroid of the bpy ring.
Experimental 5,5'-bis(CF 3 CH 2 OCH 2 )-2,2'-bpy, (I), was prepared according to the general procedure described in Lu et al., (2007). The crude product was further purified by vacuum sublimation or chromatography to obtain the title compound as a colorless solid. Full characterization data are listed below.
Analytical data of (  Recrystallization proceeded with dissolution of I in DMSO to form a saturated solution, to which the water overlayer (5 cm 3 ) was added. Solvent diffusion over a period of ten days at 298 K afforded needle shaped crystals.

Refinement
The diffraction data were collected at 100K employing a Bruker CCD diffractometer; the structure was solved by successive Fourier maps. All H atoms were located at the end of anisotropic refinements and refined isotropically to convergence.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.