Formation Mechanism of NF4+ Salts and Extraordinary Enhancement of the Oxidizing Power of Fluorine by Strong Lewis Acids

Although the existence of the NF₄⁺ cation has been known for 51 years, and its formation mechanism from NF₃ , F₂ , and a strong Lewis acid in the presence of an activation energy source had been studied extensively, the mechanism had not been established. Experimental evidence had shown that the first step involves the generation of F atoms from F₂ , and also that the NF₃⁺ cation is a key intermediate. However, it was not possible to establish whether the second step involved the reaction of a F atom with either NF₃ or the Lewis acid (LA). To distinguish between these two alternatives, a computational study of the NF₄ , SbF₆ , AsF₆ , and BF₄ radicals was carried out. Whereas the heats of reaction are small and similar for the NF₄ and LAF radicals, at the reaction temperatures, only the LAF radicals possess sufficient thermal stability to be viable species. Most importantly, the ability of the LAF radicals to oxidize NF₃ to NF₃⁺ demonstrates that they are extraordinary oxidizers. This extraordinary enhancement of the oxidizing power of fluorine with strong Lewis acids had previously not been fully recognized.