Manganate
In inorganic nomenclature, a manganate is any negatively charged moelcular entity with manganese as the central atom. However, the name is usually used to refer to the tetraoxidomanganate(2−) anion, MnO2−4, also known as manganate(VI) because it contains manganese in the +6 oxidation state. Manganates are the only known manganese(VI) compounds.[1]
Manganate(VI)
The manganate(VI) ion is tetrahedral, similar to sulfate or chromate: indeed, manganates are often isostructural with sulfates and chromates. As a d1 ion, it is paramagnetic.
Preparation
Sodium and potassium manganates are usually prepared in the laboratory by stirring the equivalent permanganate in a concentrated solution (5–10 M) of the hydroxide for 24 hours.[2]
- 4 MnO−4 + 4 OH− → {{nowrap|4 MnO2−4 + 2 H2O + O2
Potassium manganate is prepared industrially, as an intermediate to potassium permanganate, by dissolving manganese dioxide in molten potassium hydroxide with potassium nitrate or air as the oxidizing agent.[1]
- 2 MnO2 + 4 OH− + O2 → 2 MnO2−4 + 2 H2O
Disproportionation
Manganates are unstable towards disproportionation in all but the most alkaline of aqueous solutions.[1] The ultimate products are permanganate and manganese dioxide, but the kinetics are complex and the mechanism may involved protonated and/or manganese(V) species.[3]
References
- ↑ 1.0 1.1 1.2 Cotton, F. Albert; Wilkinson, Geoffrey Advanced Inorganic Chemistry, 4th ed.; Wiley: New York, 1980; p 746. ISBN 0-471-02775-8.
- ↑ Carrington, A.; Symons, M. C. R. Structure and reactivity of the oxy-anions of transition metals. Part I. The manganese oxy-anions. J. Chem. Soc. 1956, 3373–80. DOI: 10.1039/JR9560003373.
- ↑ Sutter, Joan H.; Colquitt, Kevin; Sutter, John R. Kinetics of the disproportionation of manganate in acid solution. Inorg. Chem. 1974, 13 (6), 1444–46. DOI: 10.1021/ic50136a037.
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