MnO42

MnO4^2−, the manganate(VI) ion, is an oxide of manganese in the +6 oxidation state. In aqueous solution it adopts a tetrahedral geometry around the central manganese atom and carries a −2 charge. The ion is most commonly encountered as manganate salts such as potassium manganate (K2MnO4) and sodium manganate (Na2MnO4), which are typically green in color.

Stability and behavior in solution: Manganate is relatively stable only under strongly basic conditions (high pH). In neutral or acidic solutions it tends to disproportionate, yielding permanganate (MnO4^−, manganese in the +7 state) and manganese dioxide (MnO2, manganese in the +4 state). The exact stoichiometry of the disproportionation depends on the environment (pH, concentrations, and presence of other species).

Redox properties: MnO4^2− acts as a moderate oxidizing agent, operating under basic conditions. It is less oxidizing than permanganate and is typically used in redox chemistry where basic media are involved. In most aqueous settings, manganate is not long-lived without ongoing basic stabilization, because of its tendency to disproportionate in the presence of acids or carbon dioxide.

Preparation and occurrence: Potassium manganate and related manganate salts are prepared by oxidation of MnO2 in strongly basic solution, often using a mild oxidant. MnO4^2− is not commonly found free in nature and is mainly encountered in laboratory redox chemistry and in certain industrial processes conducted under alkaline conditions.

See also: Permanganate, Manganese dioxide, Potassium manganate.