The C−F⋅⋅⋅Cation Interaction: An Ammonium Complex of a Hexafluoro Macrocyclic Cage Compound

An ammonium complex of the hexafluoro cage compound 1 was isolated and its structure was elucidated by X-ray crystallographic analysis. The C−F bonds are elongated by the complexation, which is clear evidence of C−F⋅⋅⋅cation interaction. The driving force of NH4+ inclusion is the C−F⋅⋅⋅cation interaction, but the C−F⋅⋅⋅HN+ hydrogen bond does not contribute to this complexation. The crystal structure of the NH4+⊂1 shows short C−F⋅⋅⋅HN+ contacts (2.286–2.662 Å). Furthermore, it shows that closer F⋅⋅⋅H+(−N) distances give a larger F⋅⋅⋅H+−N angle. Although such structural features seem to indicate the existence of C−F⋅⋅⋅HN+ hydrogen bonds, the spectral data (1H NMR, 19F VT-NMR, and IR spectroscopy) did not support the existence of hydrogen bonds. Thermodynamic parameters, log Ks (4.6±0.1, 298 K), ΔH (−5.3±0.1 kcal mol−1), and ΔS (3.2±0.3 cal mol−1 K−1), of the complexation were obtained in CDCl3/CD3CN mixture.