Sesquioxide

A sesquioxide is an oxide containing three atoms of oxygen with two atoms (or radicals) of another element. For example, aluminium oxide (Al₂O₃) is a sesquioxide. Many sesquioxides contain the metal in the +3 oxidation state and the oxide ion, e.g., Al₂O₃, La₂O₃. The alkali metal sesquioxides are exceptions and contain both peroxide, (O2−
2) and superoxide, (O−
2) ions, e.g., Rb₂O₃ is formulated [(Rb+)
4(O2−
2)(O−
2)
2]. Sesquioxides of iron and aluminium are found in soil.