Chemistry:Manganese(III) oxide

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Manganese(III) oxide
Other names
dimanganese trioxide, manganese sesquioxide, manganic oxide, manganous oxide
3D model (JSmol)
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 ethanol, acetone
soluble in acid, ammonium chloride
+14,100·10−6 cm3/mol
Bixbyite, cI80
Ia3 (No. 206)
a = 942 pm
110 J·mol−1·K−1[2]
−971 kJ·mol−1[2]
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
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).
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Infobox references

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

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:

2 MnO2 + Zn → Mn2O3 + ZnO(citation?)

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] 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]


  1. Chandiran, Kalaiselvi; Murugesan, Ramesh Aravind; Balaji, Revathi; Andrews, Nirmala Grace; Pitchaimuthu, Sudhagar; Nagamuthu Raja, Krishna Chandar (2020-07-03). "Long single crystalline α-Mn2O3 nanorods: facile synthesis and photocatalytic application". Materials Research Express (IOP Publishing) 7 (7): 074001. doi:10.1088/2053-1591/ab9fbd. ISSN 2053-1591. 
  2. 2.0 2.1 Zumdahl, Steven S. (2009). Chemical Principles 6th Ed.. Houghton Mifflin Company. p. A22. ISBN 0-618-94690-X. 
  3. 3.0 3.1 3.2 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1049. ISBN 978-0-08-037941-8. 
  4. Shuijin Lei; Kaibin Tang; Zhen Fang; Qiangchun Liu; Huagui Zheng (2006). "Preparation of α-Mn2O3 and MnO from thermal decomposition of MnCO3 and control of morphology". Materials Letters 60: 53. doi:10.1016/j.matlet.2005.07.070. 
  5. Zhong-Yong Yuan; Tie-Zhen Ren; Gaohui Du; Bao-Lian Su (2004). "A facile preparation of single-crystalline α-Mn2O3 nanorods by ammonia-hydrothermal treatment of MnO2". Chemical Physics Letters 389: 83. doi:10.1016/j.cplett.2004.03.064. 
  6. Navin Chandra; Sanjeev Bhasin; Meenakshi Sharma; Deepti Pal (2007). "A room temperature process for making Mn2O3 nano-particles and γ-MnOOH nano-rods". Materials Letters 61 (17): 3728. doi:10.1016/j.matlet.2006.12.024. 
  7. Thomas Kohler; Thomas Armbruster; Eugen Libowitzky (1997). "Hydrogen Bonding and Jahn-Teller Distortion in Groutite,α-MnOOH, and Manganite,γ-MnOOH, and Their Relations to the Manganese Dioxides Ramsdellite and Pyrolusite". Journal of Solid State Chemistry 133 (2): 486–500. doi:10.1006/jssc.1997.7516. 
  8. 8.0 8.1 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
  10. Geller S. (1971). "Structure of α-Mn2O3, (Mn0.983Fe0.017)2O3 and (Mn0.37Fe0.63)2O3 and relation to magnetic ordering". Acta Crystallogr B 27 (4): 821. doi:10.1107/S0567740871002966. 
  11. Geller S. (1970). "Magnetic and Crystallographic Transitions in Sc+, Cr+, and Ga+ Substituted Mn2O3". Physical Review B 1: 3763. doi:10.1103/physrevb.1.3763. 
  12. Kim S. H; Choi B. J; Lee G.H.; Oh S. J.; Kim B.; Choi H. C.; Park J; Chang Y. (2005). "Ferrimagnetism in γ-Manganese Sesquioxide (γ−Mn2O3) Nanoparticles". Journal of the Korean Physical Society 46 (4): 941.