Direct synthesis of hexafluoroferrates(III) and reaction of thiocyanate and fluoride with iron(III) and hydrogen peroxide as an access to fluoro(sulfato)ferrates(III)

Abstract

The reaction of iron(II1) hydroxide with alkali-metal or ammonium fluoride and 48% hydrofluoric acid in the presence of hydrogen peroxide, followed by the addition of ethanol, directly gives alkali-metal or ammonium hexafluoroferrates(III), A₃FeF₆ (A = Na, K, or NH₄), in very high yields. An investigation of the reaction of ammonium or potassium thiocyanate and 48% HF with iron(II1) hydroxide in the presence of hydrogen peroxide has been carried out. Sulfate has been obtained as the oxidation product of SCN^-, without involving reduction of iron(II1) and providing an access to fluoro(sulfato)ferrates(III) of the types (NH₄)₂[Fe(SO₄)F₃J and K₃[Fe(SO₄)F₄]. Similar reactions with sulfates in lieu of thiocyanates, either in the presence of or in the absence of H₂0₂, do not afford fluoro(sulfato)ferrates(III), however. IR spectroscopy and laser Raman spectroscopy provide evidence for a chelated sulfate in each of the fluoro(sulfato)ferrates(III).