3 years ago

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

Formation Mechanism of NF4+ Salts and Extraordinary Enhancement of the Oxidizing Power of Fluorine by Strong Lewis Acids
Monica Vasiliu, Karl O. Christe, Ralf Haiges, David A. Dixon
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. The presence of strong Lewis acids (LAs) enhances the oxidizing power of elemental fluorine (3.08 eV) by as much as 6.7 eV, making the resulting LAF radicals the strongest known neutral one-electron oxidizers. When combined with the lattice energy of about 6 eV of the solid product, LAF can easily oxidize compounds, such as NF3 to NF3+.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201701784

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