Manganese(III) oxide


Manganese oxide is a chemical compound with the formula Mn2O3.

Preparation and chemistry

Heating MnO2 in air at below 800 °C produces α-Mn2O3. γ-Mn2O3 can be produced by oxidation followed by dehydration of manganese hydroxide. Many preparations of nano-crystalline Mn2O3 have been reported, for example syntheses involving oxidation of MnII salts or reduction of MnO2.
Manganese oxide is formed by the redox reaction in an alkaline cell:
Manganese oxide Mn2O3 must not be confused with MnOOH manganese oxyhydroxide. Contrary to Mn2O3, MnOOH is a compound that decomposes at about 300 °C to form MnO2.

Structure

Mn2O3 is unlike many other transition metal oxides in that it does not adopt the corundum structure. Two forms are generally recognized, α-Mn2O3 and γ-Mn2O3, although a high pressure form with the CaIrO3 structure has been reported too.
α-Mn2O3 has the cubic bixbyite structure, which is an example of a C-type rare earth sesquioxide. The bixbyite structure has been found to be stabilised by the presence of
small amounts of Fe3+, pure Mn2O3 has an orthorhombic structure. α-Mn2O3 undergoes antiferromagnetic transition at 80 K.
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.