Solvation of the Fluoride Anion by Methanol^†

Solvation of the fluoride anion by methanol was investigated through vibrational predissociation spectroscopy of small cluster ions. The strong hydrogen-bond interaction between the anion and the hydroxyl group of methanol led to a shift of some O−H stretching frequencies into the C−H stretch region. The use of deuterated methanol (d₁ and d₃) was essential in isolating and identifying the C−H and O−H stretching modes. Ab initio calculations were used to determine infrared frequencies/intensities and optimized geometries. When the theoretical results were combined with the experimental observations, the fluoride anion was found to exhibit surface solvation. Evidence for methanol−methanol hydrogen-bond interactions appears when the fluoride anion is solvated by four or more methanol molecules. These results are consistent with previous studies, which show surface hydration of the chloride, bromide, and iodide anions and solvation of the chloride and iodide anions with methanol. However, these results contrast with the hydration of the fluoride anion, where the ion was found to undergo interior solvation with up to five water molecules.