Manganese(III) oxide explained

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). γ-Mn2O3 can be produced by oxidation followed by dehydration of manganese(II) hydroxide. Many preparations of nano-crystalline Mn2O3 have been reported, for example syntheses involving oxidation of MnII salts or reduction of MnO2.[3] [4] [5]

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.[6]

Structure

Mn2O3 is unlike many other transition metal oxides in that it does not adopt the corundum (Al2O3) structure. Two forms are generally recognized, α-Mn2O3 and γ-Mn2O3,[7] although a high pressure form with the CaIrO3 structure has been reported too.[8]

α-Mn2O3 has the cubic bixbyite structure, which is an example of a C-type rare earth sesquioxide (Pearson symbol cI80, space group Ia, #206). The bixbyite structure has been found to be stabilised by the presence ofsmall amounts of Fe3+, pure Mn2O3 has an orthorhombic structure (Pearson symbol oP24, space group Pbca, #61).[9] α-Mn2O3 undergoes antiferromagnetic transition at 80 K. [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.[7] γ-Mn2O3 is ferrimagnetic with a Néel temperature of 39 K.[11]

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.[12]

Notes and References

  1. Web site: Bixbyite-(Mn) .
  2. IMA 21-H: Redefinition of bixbyite and definition of bixbyite-(Fe) and bixbyite-(Mn). CNMNC Newsletter, 64, 2021; Mineralogical Magazine, 85, 2021).
  3. Preparation of α-Mn2O3 and MnO from thermal decomposition of MnCO3 and control of morphology. Shuijin Lei . Kaibin Tang . Zhen Fang . Qiangchun Liu . Huagui Zheng . Materials Letters. 60. 2006. 53. 10.1016/j.matlet.2005.07.070.
  4. A facile preparation of single-crystalline α-Mn2O3 nanorods by ammonia-hydrothermal treatment of MnO2. Zhong-Yong Yuan . Tie-Zhen Ren . Gaohui Du . Bao-Lian Su . Chemical Physics Letters. 389. 2004. 1–3 . 83. 10.1016/j.cplett.2004.03.064.
  5. A room temperature process for making Mn2O3 nano-particles and γ-MnOOH nano-rods. Navin Chandra . Sanjeev Bhasin . Meenakshi Sharma . Deepti Pal . Materials Letters. 61. 2007. 3728. 10.1016/j.matlet.2006.12.024. 17.
  6. Hydrogen Bonding and Jahn-Teller Distortion in Groutite,α-MnOOH, and Manganite,γ-MnOOH, and Their Relations to the Manganese Dioxides Ramsdellite and Pyrolusite. Thomas Kohler . Thomas Armbruster . Eugen Libowitzky . Journal of Solid State Chemistry. 133. 1997. 486–500. 10.1006/jssc.1997.7516. 2.
  7. Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications
  8. High Pressure Phase transition in Mn2O3 to the CaIrO3-type Phase Santillan, J.; Shim, S. American Geophysical Union, Fall Meeting 2005, abstract #MR23B-0050
  9. Structure of α-Mn2O3, (Mn0.983Fe0.017)2O3 and (Mn0.37Fe0.63)2O3 and relation to magnetic ordering. Geller S.. Acta Crystallogr B. 1971. 27. 821. 10.1107/S0567740871002966. 4.
  10. Magnetic and Crystallographic Transitions in Sc+, Cr+, and Ga+ Substituted Mn2O3. Geller S.. Physical Review B. 1970. 1. 9 . 3763. 10.1103/physrevb.1.3763.
  11. Ferrimagnetism in γ-Manganese Sesquioxide (γ−Mn2O3) Nanoparticles. Kim S. H . Choi B. J . Lee G.H. . Oh S. J. . Kim B. . Choi H. C. . Park J . Chang Y. . Journal of the Korean Physical Society. 46. 4. 2005. 941.
  12. Ovsyannikov . Sergey V. . Tsirlin . Alexander A. . Korobeynikov . Igor V. . Morozova . Natalia V. . Aslandukova . Alena A. . Steinle-Neumann . Gerd . Chariton . Stella . Khandarkhaeva . Saiana . Glazyrin . Konstantin . Wilhelm . Fabrice . Rogalev . Andrei . Dubrovinsky . Leonid . 2021-09-06 . Synthesis of Ilmenite-type ε-Mn 2 O 3 and Its Properties . Inorganic Chemistry . en . 60 . 17 . 13348–13358 . 10.1021/acs.inorgchem.1c01666 . 34415155 . 237242460 . 0020-1669.

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