Manganese(II) hydroxide explained

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.^[1]

Manganese(II) hydroxide precipitates as a solid when an alkali metal hydroxide is added to an aqueous solution of Mn²⁺ salt:^[2]

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.

Notes and References

1. 10.1016/0022-2860(94)08355-x . 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 . 1994 . Lutz . H.D. . Möller . H. . Schmidt . M. . Journal of Molecular Structure . 328 . 121–132 .
2. 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.