Ferrate

A ferrate is a salt of the extremely unstable ferric acid H₂FeO₄, a compound of hexavalent iron. The anion FeO₄^2- is a very strong oxidizer that readily reacts with organic compounds, ammonium and cations of metals that aren't in their highest state of oxidation. It is colored purple-red.

The existence of ferrates

The Russian amateur chemist "Odin" experimented with ferrates a lot, and his research sheds much light on various salts of the ferrate ion. According to him, the following ferrates exist:

• Lithium ferrate Li₂FeO₄ (stable, soluble)
• Sodium ferrate Na₂FeO₄ (stable, soluble)
• Potassium ferrate K₂FeO₄ (stable, soluble)
• Rubidium ferrate Rb₂FeO₄ (stable, low solubility)
• Cesium ferrate Cs₂FeO₄ (stable, soluble)
• Magnesium ferrate MgFeO₄ (unstable, low solubility)
• Calcium ferrate CaFeO₄ (stable, low solubility)
• Barium ferrate BaFeO₄ (stable, almost insoluble)

Odin also tried to synthesize ferrates of rare earth metals, but the results aren't unambiguous. His research suggests that rare earth ferrates likely exist, are insoluble and unstable.

The following ferrates do not exist:

• Ammonium ferrate (undergoes reduction of ferrate by ammonium upon formation);
• Ferrate salts of transition metal hydroxides (the ferrate ion oxidizes them to non-basic states of oxidation)

The possibility of organic esters of ferric acid is unknown but, most likely, only the most oxidation-resistant organic radicals such as perfluorocarbon radicals are capable of forming these esters.

Relevant Sciencemadness threads

• Overlooked ferrates