Syntheses and some properties of binary fluorides of silver, copper and nickel

Abstract

Thermally unstable highest-oxidation-state transition metal polymeric fluorides (e.g. AgF 3, NiF 4) are precipitated from anhydrous hydrogen fluoride (AHF) solutions of their salts by addition of fluoroacids (A) such as BF 3, PF 5 or AsF 5 [1]: MF x y− + yA → MF (x−y) + yAF −. Red, diamagnetic AgF 3 precipitated by AsF 5 from AHF solutions of AgF 4 − salts is reduced with excess of AsF 5 by following equation: AgF 3 + AsF 5 → AgFAsF 6 + 1/2F 2. While such reduction does not occur with BF 3 this acid is therefore preferred for the preparation of stoichiometric AgF 3. Silver trifluoride is thermodinamically unstable and loses F 2 in contact with AHF according to the equation: 3AgF 3 → Ag 3F 8 + 1/2F 2. The formation of Ag 3F 8 by the interaction of one mole of Ag(II) and two moles of Ag(III) confirmed that the material formed in the degradation of AgF 3 is a mixed valence material Ag(II)Ag(III) 2F 8. Interaction of AgF + with AuF 4 − (1:1) in AHF yields maroon Ag(II)Ag(III)F 5. Silver trifluoride is isostructural with AuF 3. Its powerful oxidizing properties are in accord with the tight binding of its valence shell d orbital electrons. CuF 6 3− salts interact quantitavely with liquid AHF already at −60° yielding bright red CuF 3: CuF 6 3− + 3xHF → CuF 3 + 3F(HF) x −. The oxidizing properties of above-mentioned fluorides will be discussed.