Hydrogen bonding: Part 27. Amine/hydrogen fluoride molecular complexes

Abstract

N,N-Dimethyl-1-adamantamine·4HF and triethylenediamine·4HF are very stable crystalline solids in which C 3v F(HF) 3 moieties are bound through hydrogen to amine nitrogen in a manner previously observed for liquid alkylamine·4HF species. IR spectra demonstrate that these compounds are not ammonium salts, and consideration of theoretical studies and comparison with matrix-isolation IR spectra of ammonia and amine/hydrogen fluoride species strongly suggest that they are molecular complexes bound by three-center NHF bonds. Quinuclidine·3HF and 1-adamantamine·3HF contain similar NHF bonds between amine nitrogen and C 2v F(HF) 2 moieties. The different stoichiometric patterns observed for the formation of hydrogen fluoride complexes by various amines, as well as the balance between formation of molecular complexes or ionic salts, may be related to the ability of the system to form extended networks of hydrogen bonds. The preparation and IR study of F(HF) − n salts of the tetraethylammonium and N,N,N-trimethyl-1-adamantyl-ammonium cations are also reported.