Manganese oxide is the chemical compound of formula Mn₂O₃.

Preparation and chemistry

Heating MnO₂ in air at below 800°C α-Mn₂O₃ is produced (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 Mn^II salts or reduction of MnO₂.

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) oxohydroxide. 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

Corundum

Corundum is a crystalline form of aluminium oxide with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red...

 (Al₂O₃

Aluminium oxide

Aluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...

) 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

Bixbyite

Bixbyite is a manganese iron oxide mineral with formula: 2O3. The iron:manganese ratio is quite variable and many specimens have almost no iron. It is a metallic dark black with a Mohs hardness of 6.0 - 6.5...

 structure, which is an example of a C-type rare earth sesquioxide (Pearson symbol

Pearson symbol

The Pearson symbol, or Pearson notation, is used in crystallography as a means of describing a crystal structure, and was originated by W.B. Pearson. The symbol is made up of two letters followed by a number. For example:* Diamond structure, cF8...

 cI80, space group Ia3, #206). The bixbyite

Bixbyite

Bixbyite is a manganese iron oxide mineral with formula: 2O3. The iron:manganese ratio is quite variable and many specimens have almost no iron. It is a metallic dark black with a Mohs hardness of 6.0 - 6.5...

 structure has been found to be stabilised by the presence of
small amounts of Fe³⁺, pure Mn₂O₃ has an orthorhombic structure (Pearson symbol

Pearson symbol

The Pearson symbol, or Pearson notation, is used in crystallography as a means of describing a crystal structure, and was originated by W.B. Pearson. The symbol is made up of two letters followed by a number. For example:* Diamond structure, cF8...

 oP24,space group Pbca, #61).

γ-Mn₂O₃ has a structure related to the spinel structure of Mn₃O₄

Manganese(II,III) oxide

Manganese oxide is the chemical compound with formula Mn3O4. Manganese is present in two oxidation states +2 and +3 and the formula is sometimes written as MnO.Mn2O3. Mn3O4 is found in nature as the mineral hausmannite.-Preparation:...

 where the oxide ions are cubic close packed. This is similar to the relationship between γ-Fe₂O₃

Iron(III) oxide

Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron oxide , which is rare, and iron oxide , which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main...

 and Fe₃O₄

Iron(II,III) oxide

Iron oxide is the chemical compound with formula Fe3O4. It is one of a number of iron oxides, the others being iron oxide , which is rare, and iron oxide also known as hematite. It occurs in nature as the mineral magnetite. It contains both Fe2+ and Fe3+ ions and is sometimes formulated as FeO ∙...

. γ-Mn₂O₃ is ferrimagnetic with a Neel temperature of 39 K.