Barium ferrate, preparation

The best known oxoanion of iron is the ferrate(VI) prepared by oxidizing a suspension of hydrous iron(III) oxide in concentrated alkah with potassium hypochlorite or by anodic oxidation of iron in concentrated alkah. Crystals of potassium ferrate [13718-66-6], K FeO, are deep purple, orthorhombic, and contain discrete tetrahedral [FeOJ anions. Barium ferrate [13773-23A] can be precipitated from solutions of soluble ferrate salts. 

A brief review of ferrates(VI) Coord.Chem.Rev. l 91A) 5 ) gives the magnetic moment of the barium ferrate as 3. IS pg. This confirms the d configuration of the tetrahedral ion. This is also indicated by the three spin-allowed d-d bands at 786, 510 and 226 nm. If the solution obtained in the preparation is quickly transferred to a vacuum uv cell the spectrum can be recorded. DTA of the barium salt and other ferrates are also referred to in the above reference. 

To prepare potassium trioxalatoferrate(III), put 1.25 g of iron(III) sulphate, the prepared barium oxalate, 1.5 g of potassium oxalate, and 30 ml of water into a 500-ml beaker. Heat the mixture for several hours in a water bath, maintaining a constant volume. After separation of the barium sulphate precipitate, evaporate the filtrate to a volume of 5 ml and cool it. Filter off the potassium trioxalato-ferrate(III) crystals, rinse them with a small amount of water and then with ethanol, and dry them in a vacuum-desiccator over sulphuric acid. Write the equations of the reactions. 

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