The C-F center dot center dot center dot 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)C-ray crystallographic analysis. The C-F bonds are elongated by the complexation, which is clear evidence of C-F ... catio n interaction. The driving force of NH4+ inclusion is the C-F ... cation in teraction, but the C-F ... HN+ hydrogen bond does not contribute to this co mplexation. The crystal structure of the NH(4)(+)subset of 1 shows short C- FC-F ... HN+ contacts (2.286-2.662 Angstrom). Furthermore, it shows that cl oser F ... H+(-N) distances give a larger F ... H+-N angle. Although such s tructural features seem to indicate the existence of C-F ... HN+ hydrogen b onds, the spectral data (H-1 NMR, F-19 VT-NMR, and IR spectroscopy) did not support the existence of hydrogen bonds. Thermodynamic parameters, log K-s (4.6+/-0.1, 298K), Delta H (-5.3+/-0.1 kcal mol(-1)), and as (3.2+/-0.3 ca l mol(-1) K-1), of the complexation were obtained in CDCl3/CD3CN mixture.