Because electronegativity of an oxidation state is low in an anion, salts of the high oxidation-state species [AgF 4 ] − and [NiF 6 ] 2− can be easily made, at 0°C, in liquid anhydrous HF (aHF) made basic with alkali fluorides. The containers are transparent fluorocarbon, and the F 2 is photo-dissociated. The [NiF 6 ] 2− salts, and the metastable binary fluorides NiF 4 and NiF 3 , derived from them, are efficient fluorinating agents for the conversion of hydrido compounds to their fully fluorinated relatives. With F 2 in aHF made acidic with fluoride-ion acceptors (e.g. MF 5 , M=As, Sb, Bi) attained oxidation-states are often lower (e.g. Ag II , Au II ) because of the higher electronegativity in cations. Cationic Ag III and Ni IV species (derived from the anions) are sufficiently long-lived, and potent, to generate the most powerfully oxidizing hexafluorides of the second and third transition series (i.e. [MF 6 ], M=Pt, Ru, Rh). This synthesis is especially valuable for RhF 6 , and has provided for the reinvestigation of the interaction of it with O 2 . It is proposed that the unexpectedly large unit cell of O 2 RhF 6 is a result of the presence of neutral O 2 and neutral RhF 6 as well as O 2 + and RhF 6 − in the lattice.