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H2MnO4, a weak inorganic acid corresponding to hexavalent manganese. It has not been produced in free form and exists only in aqueous solutions. The anion MnO2 has a green tint. Manganic acid decomposes upon heating to form permanganic acid, HMnO4, and manganese dioxide, MnO2. Manganic acid salts are known as manganates, the most valuable of which is K2MnO4, which is used in the preparation of potassium permanganate, KMnO4 (according to the reaction 2K2MnO4 + C12 = 2KMnO4 + 2KC1).