Silver(III) fluoride, AgF3, is an unstable, bright-red, diamagnetic compound containing silver in the unusual +3 oxidation state. Its crystal structure is very similar to that of Gold(III) fluoride: it is a polymer consisting of rectangular AgF4 units linked into chains by fluoro bridges.
Preparation
AgF3 can be prepared by treating a solution containing tetrafluoroargentate ions in anhydrous hydrogen fluoride with boron trifluoride. In anhydrous-HF solution, it decomposes spontaneously to Ag3F8 overnight at room temperature.
Earlier preparations were more heroic, involving the use of krypton difluoride as fluorinating agent, and tended to produce the mixed-valence Ag3F8.
References
Silver(III) fluoride Wikipedia(Text) CC BY-SA