Metastable fluorides and potent oxidizers : Their preparation in liquid anhydrous HF, at room and lower temperatures

The low electronegativity of an oxidation state in an anion enables high oxidation states, e.g. Ni-IV, Au-V, and Ag-III, to be easily attained in liquid anhydrous HF (aHF), made basic with fluoride-ion donors. The oxidation state can be enhanced if elemental fluorine is photo-dissociated. Teflon valves and lines, especially transparent and kinetically stable fluorocarbon containers for the aHF solutions, provide for this. Binary fluorides, that are of low solubility in aHF, can be displaced by stronger F acceptors from their high oxidation-state anions. NiF4, NiF3, and AgF3, which can be made in this manner, are thermodynamically unstable with respect to loss of fluorine. The electronegativity of the oxidation state in the binary fluoride is higher than in the anion (hence the metastability) and when a strong F acceptor converts the binary fluoride into a cationic species, the electronegativity is further enhanced. Thus cationic Ag-III and Ni-IV are superior to KrF+, as one-electron oxidizers. They are able to remove the electron from all platinum-metal hexafluoro-anions, MF6-, to liberate the hexafluorides. All of this chemistry can be achieved at or below room temperature.