Manganese(II) oxide is an inorganic compound with chemical formula MnO.Arno H. Reidies "Manganese Compounds" Ullmann's Encyclopedia of Chemical Technology 2007; Wiley-VCH, Weinheim. It forms green crystals. The compound is produced on a large scale as a component of fertilizers and food additives.
Structure, stoichiometry, reactivity Like many metal monoxides, MnO adopts the rock salt structure, where cations and anions are both octahedrally coordinated. Also like many metal oxides, manganese(II) oxide is often nonstoichiometric: its composition can vary from MnO to MnO1.045.
Manganese(II) oxide undergoes the chemical reactions typical of an ionic oxide. Upon treatment with acids, it converts to the corresponding manganese(II) salt. Oxidation of manganese(II) oxide gives manganese(III) oxide.
Preparation and occurrence MnO occurs in nature as the rare mineral manganosite. It is prepared commercially by reduction of MnO2 with hydrogen, carbon monoxide, or methane, e.g.: MnO2 + H2 → MnO + H2O MnO2 + CO → MnO + CO2 Upon heating to 450°C, manganese(II) nitrate gives a mixture of oxides, denoted MnO2−x, which can be reduced to the monoxide with hydrogen at ≥750°C. MnO is particularly stable and resists further reduction. MnO can also be prepared by heating the carbonate:W.H. McCarroll (1994) Oxides- Solid State Chemistry, Encyclopedia of Inorganic Chemistry Ed. R. Bruce King, John Wiley & Sons MnCO3 → MnO + CO2 This calcining process is conducted anaerobically, lest Mn2O3 form.
An alternative route, most interest for demonstration purposes, is the "oxalate method". Also applicable to the synthesis of ferrous oxide and stannous oxide, it entails heating in an oxygen-free atmosphere (often CO2), hydrated manganese(II) oxalate:Arthur Sutcliffe (1930) Practical Chemistry for Advanced Students (1949 Ed.), John Murray - London. MnC2O4·2H2O → MnO + CO2 + CO + 2 H2O
Applications Together with manganese sulfate, MnO is a component of fertilizers and food additives. Many thousands of tons are consumed annually for this purpose. Other uses include: a catalyst in the manufacture of allyl alcohol, pigmenting ceramics and paints, coloring glass, bleaching tallow, and textile printing.
Magnetism Below 118 K, MnO is antiferromagnetic. MnO has the distinction of being one of the first compoundsJ.E Greedon, (1994), Magnetic oxides in Encyclopedia of Inorganic chemistry Ed. R. Bruce King, John Wiley & Sons to have its magnetic structure determined by neutron diffraction, the report appearing in 1951. This study showed that the Mn2+ ions form a face centered cubic magnetic sub-lattice where there are ferromagnetically coupled sheets that are anti-parallel with adjacent sheets.
Electronic structure Similar to NiO, MnO is classed as a strongly correlated material because of the localised 3d states associated with Mn atoms, and is an electrical insulator. Conventional approximations to the exchange-correlation functional in density functional theory (DFT) such as the local spin-density approximation (LSDA) severely underestimate the band gap of the material, and can even predict it to be metallic, depending on the choice of magnetic configuration. However, improved descriptions of the material's electronic structure, such as hybrid exchange-correlation functionals, DFT+U, the GW approximation, self-interaction corrected DFT, or coupled cluster theory, all recover the band gap with significantly improved accuracy. It has also been shown that such improved methods predict a band gap regardless of the choice of magnetic state.
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