A Raman spectroscopic study of noble-gas fluoride adduct formation with bismuth pentafluoride

The fluoride-ion acceptor properties of BiF5 have been assessed by the preparation of several new adducts of the binary noble-gas fluroides with BiF5. The adducts XeF4·BiF5, XeF4·2BiF5, XeF2·BiF5, XeF2·2BiF5, 2XeF2·BiF5, KrF2·BiF5, and Cs[Bi2F11] have been prepared and characterized by low-temperature Raman spectroscopy. Although the compounds may be described as ionic to a first approximation, there are rather strong fluoride-bridge interactions between the respective cation and the anion which suggest substantial covalent contributions to the bonding. The present study complements previous studies of adducts between the noble-gas fluorides and AsF5 and SbF5. The strength of the cation–anion interactions can be taken as a measure of the acidity of the pentafluoride. It is shown that BiF5 is a much weaker Lewis acid than SbF5.