Fluoride Ion Interactions in Alkali-Metal Fluoride-Diol Complexes.

The activity of F is an important factor in the design of both inorganic and organic reactions involving fluorine compounds. The present study investigates interactions of F with diols in alkali-metal fluoride-diol complexes. Increases in the reactivities of alkali-metal fluorides and their solubilities in alcohols is observed with increasing cation size. The difference in alkali-metal ion size produces different structural motifs for F-diol complex salts. The CsF complex salt with ethylene glycol (EG), CsF-EG, has a layered structure, whereas the Rb and K complex salts, (RbF)-(EG) and (KF)-(EG), form columnar structures. Comparison of the CsF complex salts with three different diols- EG, 1,3-propylene glycol (PG), and 1,4-butylene glycol (PG)-revealed that the diol chain length affects the bridging mode in their layered structures. EG bridges two OH oxygen atoms within the same CsF layer in CsF-EG, whereas PG and BG bridge two OH oxygen atoms in different CsF layers in (CsF)-PG and CsF-BG, respectively. The F ion coordination environment involves interactions between alkali-metal ions and H atom(s) in the diol OH groups, where the FH interactions are more dominant than the FM interaction, based on Hirshfeld surface analyses. The O-H bond weakening observed by infrared spectroscopy also reflects the strengths of the FH interactions in these complex salts.