Manganese(II) hydroxide

Manganese(II) hydroxide
Names
	Other names Manganese dihydroxide, manganese hydroxide, Manganous hydroxide, Pyrochroite
Identifiers
CAS Number	18933-05-6; 1310-97-0;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:143901;
ChemSpider	66594;
ECHA InfoCard	100.126.826
EC Number	606-171-3;
PubChem CID	73965;
CompTox Dashboard (EPA)	DTXSID10940448 DTXSID6061656, DTXSID10940448 ;
	InChI InChI=1S/Mn.2H2O/h;2*1H2/q+2;;/p-2 Key: IPJKJLXEVHOKSE-UHFFFAOYSA-L;
	SMILES [OH-].[OH-].[Mn+2];
Properties
Chemical formula	H2MnO2
Molar mass	88.952 g·mol−1
Appearance	white to pink solid
Density	3.258 g/cm3
Melting point	140 °C (284 °F; 413 K) decomposes
Solubility in water	0.00034 g/100 mL at 18 °C.
Solubility	soluble in acid
Refractive index (nD)	1.68
Structure
Crystal structure	hexagonal
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Manganese(II) hydroxide is the inorganic compound with the formula Mn (OH)₂. It is a white solid although samples darken quickly upon exposure to air owing to oxidation. It is poorly soluble in water.

Structure, preparation, and reactions

Mn(OH)₂ adopts the brucite structure, i.e. the arrangement of the atoms in the crystal are the same as the arrangement of the atoms in Mg(OH)₂. The Mn(II) centers are bonded to six hydroxide ligands. Each hydroxide ligand bridges to three Mn(II) sites. The O-H bonds are perpendicular to the planes defined by the oxygen atoms, projecting above and below these layers.^[2]

Manganese(II) hydroxide precipitates as a solid when an alkali metal hydroxide is added to an aqueous solution of Mn²⁺ salt:^[3]

Mn²⁺ + 2 NaOH → Mn(OH)₂ + 2 Na⁺

Manganese(II) hydroxide oxidises readily in air, as indicated by darkening of samples.

The compound adopts the brucite structure, as do several other metal dihydroxides.

References

^ Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0487-3.
^ Lutz, H.D.; Möller, H.; Schmidt, M. (1994). "Lattice vibration spectra. Part LXXXII. Brucite-type hydroxides M(OH)2 (M = Ca, Mn, Co, Fe, Cd) — IR and Raman spectra, neutron diffraction of Fe(OH)2". Journal of Molecular Structure. 328: 121–132. doi:10.1016/0022-2860(94)08355-x.
^ H. Lux "Manganese(IV) Hydroxide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1456.

[1] Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0487-3.

[2] Lutz, H.D.; Möller, H.; Schmidt, M. (1994). "Lattice vibration spectra. Part LXXXII. Brucite-type hydroxides M(OH)2 (M = Ca, Mn, Co, Fe, Cd) — IR and Raman spectra, neutron diffraction of Fe(OH)2". Journal of Molecular Structure. 328: 121–132. doi:10.1016/0022-2860(94)08355-x.

[brauer-3] H. Lux "Manganese(IV) Hydroxide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1456.

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