Observation of aliphatic C-H•••X hydrogen bonds in imidazolium ionic liquids

Measurement of H/D isotope effects on the F-19 resonances of sequentially deuterated 1-n-butyl-3-methylimidazolium hexafluorophosphate and tetrafluoroborate isotopologues reveals the formation of aliphatic C-H center dot center dot center dot X hydrogen bonds between the fluorinated anions and protons along the N-alkyl sidechains of the cations.