Fluorinated Aminopyridines: Synthesis, Structure, and Rare Liquid-Liquid Cocrystal Formation Driven by Unusually Short N-H•••F-C Hydrogen Bonding

The role of hydrogen bonding in the crystal packing of a series of 4-aminoperfluoropyridines was studied using single-crystal X-ray crystallography. The aminoperfluoropyridines were synthesized using only excess amine to serve as both nucleophile and base. Instead of addition to the perfluoropyridine ring, a strong N-H center dot center dot center dot F-C hydrogen bond led to cocrystal formation of perfluoropyridine with sterically hindered amines dicyclohexylamine as well as 2-methylpiperdine. This formation is, to our knowledge, the first report of two nonreacting liquids, consisting of only discrete small molecules, combining to form a cocrystalline solid stable under ambient conditions. Perfluoropyridine is stabilized in the crystal lattice approximately 100 degrees C above its normal boiling point.