Manganese(II) hydroxide

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.

Manganese(II) hydroxide precipitates as a solid when an alkali metal hydroxide is added to an aqueous solution of Mn2+ salt:
 * 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.