Does anyone know the reaction when the Mn(H2O)4(OH)2 ppt is left on standing, i.e. oxidised?
ON exposure to air the hydrxide is oxidised and darkens to the Mn(IV) oxide via the formation of Mn(III) sesquioxide Mn2O3 which is also black Mn(OH)2 --> Mn2O3 --> MnO2