Manganese(III) oxide
Template:Chembox Manganese(III) oxide is a chemical compound with the formula Mn2O3. It occurs in nature as the mineral bixbyite (recently changed to bixbyite-(Mn)[1][2]) and is used in the production of ferrites and thermistors.
Preparation and chemistry
Heating MnO2 in air at below 800 °C produces α-Mn2O3 (higher temperatures produce Mn3O4).[3] γ-Mn2O3 can be produced by oxidation followed by dehydration of manganese(II) hydroxide.[3] Many preparations of nano-crystalline Mn2O3 have been reported, for example syntheses involving oxidation of MnII salts or reduction of MnO2.[4][5][6]
Manganese(III) oxide is formed by the redox reaction in an alkaline cell:
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Manganese(III) oxide Mn2O3 must not be confused with MnOOH manganese(III) oxyhydroxide. Contrary to Mn2O3, MnOOH is a compound that decomposes at about 300 °C to form MnO2.[7]
Structure
Mn2O3 is unlike many other transition metal oxides in that it does not adopt the corundum (Al2O3) structure.[3] Two forms are generally recognized, α-Mn2O3 and γ-Mn2O3,[8] although a high pressure form with the CaIrO3 structure has been reported too.[9]
α-Mn2O3 has the cubic bixbyite structure, which is an example of a C-type rare earth sesquioxide (Pearson symbol cI80, space group Ia3, #206). The bixbyite structure has been found to be stabilised by the presence of small amounts of Fe3+, pure Mn2O3 has an orthorhombic structure (Pearson symbol oP24, space group Pbca, #61).[10] α-Mn2O3 undergoes antiferromagnetic transition at 80 K. [11]
γ-Mn2O3 has a structure related to the spinel structure of Mn3O4 where the oxide ions are cubic close packed. This is similar to the relationship between γ-Fe2O3 and Fe3O4.[8] γ-Mn2O3 is ferrimagnetic with a Néel temperature of 39 K.[12]
ε-Mn2O3 takes on a rhombohedral ilmenite structure (the first binary compound known to do so), wherein the manganese cations divided equally into oxidation states 2+ and 4+. ε-Mn2O3 is antiferromagnetic with a Néel temperature of 210 K.[13]
References
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- ↑ IMA 21-H: Redefinition of bixbyite and definition of bixbyite-(Fe) and bixbyite-(Mn). CNMNC Newsletter, 64, 2021; Mineralogical Magazine, 85, 2021).
- ↑ a b c Template:Greenwood&Earnshaw
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- ↑ a b Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications Template:ISBN
- ↑ High Pressure Phase transition in Mn2O3 to the CaIrO3-type Phase Santillan, J.; Shim, S. American Geophysical Union, Fall Meeting 2005, abstract #MR23B-0050
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