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Cobalt(III) hydroxide or cobaltic hydroxide is a chemical compound with formula Co(OH) 3 or H 3CoO 3. It is an ionic compound, with trivalent cobalt cations Co3+ and hydroxyl anions OH− . The compound is known in two structurally different forms, "brownish-black" and "green". The brownish-black form is a stable solid and can be prepared by reaction of water solutions of cobalt(II) chloride and sodium hydroxide, followed by oxidation with ozone.[1] The green form, formerly thought to be cobalt(II) peroxide, apparently requires carbon dioxide as a catalyst. It can be prepared by adding hydrogen peroxide to a solution of cobalt(II) chloride in 96% ethanol at –30 to –35°С, then adding a 15% solution of sodium carbonate in water with intense stirring. The resulting dark green powder is fairly stable at liquid nitrogen temperature, but at room temperature it turns dark brown within a few days.[2]