Manganese(III) oxide

Manganese(III) oxide is a chemical compound with the formula Mn₂O₃. It occurs in nature as the mineral bixbyite (recently changed to bixbyite-(Mn)^[3][4]) and is used in the production of ferrites and thermistors.

Manganese(III) oxide

Names
Other names dimanganese trioxide, manganese sesquioxide, manganic oxide, manganous oxide
Identifiers
CAS Number	1317-34-6 Y
3D model (JSmol)	Interactive image
ChemSpider	14139 N
ECHA InfoCard	100.013.878
PubChem CID	14824
RTECS number	OP915000
UNII	XQ8YIG4A7C Y
CompTox Dashboard (EPA)	DTXSID90893847
InChI InChI=1S/2Mn.3O N Key: GEYXPJBPASPPLI-UHFFFAOYSA-N N InChI=1/2Mn.3O/rMn2O3/c3-1-5-2-4 Key: GEYXPJBPASPPLI-YNHMASKPAU
SMILES O=[Mn]O[Mn]=O
Properties
Chemical formula	Mn2O3
Molar mass	157.8743 g/mol
Appearance	brown or black crystalline
Density	4.50 g/cm3
Melting point	888 °C (1,630 °F; 1,161 K) (alpha form) 940 °C, decomposes (beta form)
Solubility in water	0.00504 g/100 mL (alpha form) 0.01065 g/100 mL (beta form)
Solubility	insoluble in ethanol, acetone soluble in acid, ammonium chloride
Magnetic susceptibility (χ)	+14,100·10−6 cm3/mol
Structure[1]
Crystal structure	Bixbyite, cI80
Space group	Ia3 (No. 206)
Lattice constant	a = 942 pm
Thermochemistry
Std molar entropy (S⦵298)	110 J·mol−1·K−1[2]
Std enthalpy of formation (ΔfH⦵298)	−971 kJ·mol−1[2]
Hazards
NFPA 704 (fire diamond)	1 0 0
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). N verify (what is YN ?) Infobox references

Preparation and chemistry

Heating MnO₂ in air at below 800 °C produces α-Mn₂O₃ (higher temperatures produce Mn₃O₄).^[5] γ-Mn₂O₃ can be produced by oxidation followed by dehydration of manganese(II) hydroxide.^[5] Many preparations of nano-crystalline Mn₂O₃ have been reported, for example syntheses involving oxidation of Mn^II salts or reduction of MnO₂.^[6][7][8]

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

2 MnO₂ + Zn → Mn₂O₃ + ZnO^{[citation needed]}

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.^[9]

Structure

Mn₂O₃ is unlike many other transition metal oxides in that it does not adopt the corundum (Al₂O₃) structure.^[5] Two forms are generally recognized, α-Mn₂O₃ and γ-Mn₂O₃,^[10] although a high pressure form with the CaIrO₃ structure has been reported too.^[11]

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).^[12] α-Mn₂O₃ undergoes antiferromagnetic transition at 80 K. ^[13]

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.^[10] γ-Mn₂O₃ is ferrimagnetic with a Néel temperature of 39 K.^[14]

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.^[15]