manganese(III) oxide

Heating MnO₂ in air at below 800 °C produces α-Mn₂O₃ (higher temperatures produce Mn₃O₄).{{Greenwood&Earnshaw|page=1049}} 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 Mn^II salts or reduction of MnO₂.{{cite journal|title=Preparation of α-Mn₂O₃ and MnO from thermal decomposition of MnCO₃ and control of morphology|author1=Shuijin Lei |author2=Kaibin Tang |author3=Zhen Fang |author4=Qiangchun Liu |author5=Huagui Zheng |journal=Materials Letters|volume=60|year=2006|page=53|doi=10.1016/j.matlet.2005.07.070}}{{cite journal|title=A facile preparation of single-crystalline α-Mn₂O₃ nanorods by ammonia-hydrothermal treatment of MnO₂|author1=Zhong-Yong Yuan |author2=Tie-Zhen Ren |author3=Gaohui Du |author4=Bao-Lian Su |journal=Chemical Physics Letters|volume=389|year=2004|issue=1–3 |page=83|doi=10.1016/j.cplett.2004.03.064}}{{cite journal|title=A room temperature process for making Mn₂O₃ nano-particles and γ-MnOOH nano-rods|author1=Navin Chandra |author2=Sanjeev Bhasin |author3=Meenakshi Sharma |author4=Deepti Pal |journal=Materials Letters|volume=61|year=2007|page=3728|doi=10.1016/j.matlet.2006.12.024|issue=17}}

Manganese(III) oxide is formed by the redox reaction in an alkaline cell:

: 2 MnO₂ + Zn → Mn₂O₃ + ZnO{{citation needed|date=August 2015}}

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.{{cite journal|title=Hydrogen Bonding and Jahn-Teller Distortion in Groutite,α-MnOOH, and Manganite,γ-MnOOH, and Their Relations to the Manganese Dioxides Ramsdellite and Pyrolusite|author1=Thomas Kohler |author2=Thomas Armbruster |author3=Eugen Libowitzky |journal=Journal of Solid State Chemistry|volume=133|year=1997|pages=486–500|doi=10.1006/jssc.1997.7516|issue=2}}

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,Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications {{ISBN|0-19-855370-6}} although a high pressure form with the CaIrO₃ structure has been reported too.High Pressure Phase transition in Mn₂O₃ to the CaIrO₃-type Phase Santillan, J.; Shim, S. American Geophysical Union, Fall Meeting 2005, abstract #MR23B-0050

α-Mn₂O₃ has the cubic bixbyite structure, which is an example of a C-type rare earth sesquioxide (Pearson symbol cI80, space group Ia{{overline|3}}, #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).{{cite journal|title=Structure of α-Mn₂O₃, (Mn_0.983Fe_0.017)₂O₃ and (Mn_0.37Fe_0.63)₂O₃ and relation to magnetic ordering|author=Geller S.|journal=Acta Crystallogr B|year=1971|volume=27|page=821|doi=10.1107/S0567740871002966|issue=4}} α-Mn₂O₃ undergoes antiferromagnetic transition at 80 K. {{cite journal|title = Magnetic and Crystallographic Transitions in Sc+, Cr+, and Ga+ Substituted Mn2O3|author = Geller S.|journal = Physical Review B|year=1970|volume=1| issue=9 |page=3763|doi=10.1103/physrevb.1.3763}}

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. γ-Mn₂O₃ is ferrimagnetic with a Néel temperature of 39 K.{{cite journal|title=Ferrimagnetism in γ-Manganese Sesquioxide (γ−Mn₂O₃) Nanoparticles|author1=Kim S. H |author2=Choi B. J |author3=Lee G.H. |author4=Oh S. J. |author5=Kim B. |author6=Choi H. C. |author7=Park J |author8=Chang Y. |journal=Journal of the Korean Physical Society|volume=46|issue=4|year=2005|page=941}}

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.{{Cite journal |last1=Ovsyannikov |first1=Sergey V. |last2=Tsirlin |first2=Alexander A. |last3=Korobeynikov |first3=Igor V. |last4=Morozova |first4=Natalia V. |last5=Aslandukova |first5=Alena A. |last6=Steinle-Neumann |first6=Gerd |last7=Chariton |first7=Stella |last8=Khandarkhaeva |first8=Saiana |last9=Glazyrin |first9=Konstantin |last10=Wilhelm |first10=Fabrice |last11=Rogalev |first11=Andrei |last12=Dubrovinsky |first12=Leonid |date=2021-09-06 |title=Synthesis of Ilmenite-type ε-Mn 2 O 3 and Its Properties |url=https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c01666 |journal=Inorganic Chemistry |language=en |volume=60 |issue=17 |pages=13348–13358 |doi=10.1021/acs.inorgchem.1c01666 |pmid=34415155 |s2cid=237242460 |issn=0020-1669|url-access=subscription }}

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{{Manganese compounds}}

{{oxides}}

Category:Manganese(III) minerals

Category:Sesquioxides

Category:Transition metal oxides