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Manganese(III) oxide

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Title: Manganese(III) oxide  
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Manganese(III) oxide

Manganese(III) oxide
Other names
dimanganese trioxide, manganese sesquioxide, manganic oxide
Jmol-3D images Image
RTECS number OP915000
Molar mass 157.8743 g/mol
Appearance brown or black crystalline
Density 4.5 g/cm3
Melting point 888 °C (1,630 °F; 1,161 K) (alpha form)
940 °C, decomposes (beta form)
0.00504 g/100 mL (alpha form)
0.01065 g/100 mL (beta form)
Solubility insoluble in alcohol, acetone
soluble in acid, ammonium chloride
Cubic, cI80[1]
Ia-3, No. 206
110 J·mol−1·K−1[2]
−971 kJ·mol−1[2]
NFPA 704
Related compounds
Other anions
manganese trifluoride, manganese(III) acetate
Other cations
chromium(III) oxide, iron(III) oxide
Related compounds
manganese(II) oxide, manganese dioxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
 N  (: YesY/N?)

Manganese(III) oxide is a chemical compound with the formula Mn2O3.

Preparation and chemistry

Heating MnO2 in air at below 800 °C α-Mn2O3 is produced (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:

2 MnO2 + Zn → Mn2O3 + ZnO

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]


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]

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 Neel temperature of 39 K.[11]


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  8. ^ a b Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
  9. ^ 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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