Hydrogen bonding.: Part 73.: IR, NMR, and ab initio molecular orbital study of N,N-dimethyl-1-adamantamine-hydrogen fluoride, a crystalline, H2O stable compound with a three-center N-H-F bond

N,N-dimethyl-1-adamantamine-hydrogen fluoride is not a tertiary ammonium salt. It is a highly crystalline molecular complex whose infrared spectrum demonstrates the presence of covalent type three-center N-H-F bonds. The compound is obtained from ethanol-water solution, and FT-NMR spectra indicate that it is stable in aqueous solution. An ab initio molecular orbital study of this and potentially similar tertiary amine-hydrogen fluoride complexes suggests a value of about -18 kcal mol(-1) for the formation of N-H-F bond, and in addition predicts that secondary C-H ... F hydrogens bonding by beta-hydrogens of the amine may be present in such compounds. (C) 2000 Elsevier Science B.V. All rights reserved.