Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Cobalt (II,III) oxide is chemical compound with the formula Co3O4. It is a black solid, and a mixed valence compound, containing both Co(II) and Co(III) oxidation states. It can be formulated as CoIICoIII2O4 or CoO.Co2O3. Co3O4 adopts the normal spinel structure, with Co2+ ions in tetrahedral interstices and Co3+ ions in the octahedral interstices of the cubic close-packed lattice of oxide anions.