Silver(III) fluoride

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(III) ions in anhydrous hydrogen fluoride with boron trifluoride; the potassium tetrafluoroargentate(III) was prepared by heating a stoichiometric mix of potassium and silver nitrate in a sealed container filled with pressurised fluorine gas at 400 °C for 24 hours, twice. When dissolved in anhydrous HF, it decomposes spontaneously to Ag₃F₈ overnight at room temperature. The high-valence silver compounds described in the thesis are notable for their variety of colours: KAgF₄ is bright orange, AgF₃ bright red, AgFAsF₆ is deep blue, Ag₃F₈ deep red-brown, and Pd(AgF₄)₂ is lime-green.

Earlier preparations used krypton difluoride as fluorinating agent, and tended to produce the mixed-valence Ag₃F₈ which may be thought of as silver(II) tetrafluoroargentate(III); Ag₂F₅, which is (AgF)⁺AgF₄^−, is formed by reacting AgF₃ with AgFAsF₆.

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