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

• Published in: Chemistry : a European journal Vol. 6; no. 13; pp. 2334 - 2337
• Main Authors: Takemura, Hiroyuki, Kon, Noriyoshi, Yasutake, Mikio, Nakashima, Sachiko, Shinmyozu, Teruo, Inazu, Takahiko
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 03.07.2000; WILEY‐VCH Verlag
• Subjects: cryptands; cyclophanes; fluorine; host-guest chemistry; macrocyclic ligands
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/1521-3765(20000703)6:13<2334::AID-CHEM2334>3.0.CO;2-A

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.