Wen-Han Tu

The intramolecular blue-shifting C–H⋯F–C hydrogen bond: crystal structure of [4,4′-bis(HCF2CF2CF2CF2CH2OCH2)-2,2′-bpy]MCl2 where M = Pt, Pd

In the solid state, the two fluorous ponytails in [4,4′-bis(HCF2CF2CF2CF2CH2OCH2)-2,2′-bpy]MCl2 (M = Pt 2; Pd 3) reveal one with a transoidal HCF2CF2CF2CF2CH2– chain on carbon backbone, similar to that with a normal fluorous alkyl group, and the other with a cisoidal HCF2CF2CF2CF2CH2– chain on a carbon backbone, exhibiting an intramolecular blue-shifting C–H⋯F–C hydrogen-bond. With the contraction of C–H bond, the increase in C–H stretch and the short H⋯F distance, these two examples are among the blue-shifting hydrogen bonds as defined by Hobza et al. The calculated C–H stretches using periodic density functional theory (DFT) are in good agreement with IR observations.

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.

4,4'-Bis(2,2,2-trifluoroethoxymethyl)-2,2'-bipyridine.

As part of a homologous series of novel polyfluorinated bipyridyl (bpy) ligands, the title compound, C(16)H(14)F(6)N(2)O(2), contains the smallest fluorinated group, viz. CF(3). The molecule resides on a crystallographic inversion centre at the mid-point of the pyridine C(ipso)-C(ipso) bond. Therefore, the bpy skeleton lies in an anti conformation to avoid repulsion between the two pyridyl N atoms. Weak intramolecular C-H...N and C-H...O interactions are observed, similar to those in related polyfluorinated bpy-metal complexes. A pi-pi interaction is observed between the bpy rings of adjacent molecules and this is probably a primary driving force in crystallization. Weak intermolecular C-H...N hydrogen bonding is present between one of the CF(3)CH(2)- methylene H atoms and a pyridyl N atom related by translation along the [010] direction, in addition to weak benzyl-type C-H...F interactions to atoms of the terminal CF(3) group. It is of note that the O-CH(2)CF(3) bond is almost perpendicular to the bpy plane.