Another route to the synthesis of cobalt oxide nanoparticles is the thermal decomposition of organometallic compounds.  For example, heating the metal salen complex bis(salicylaldehyde)ethylenediiminecobalt(II) ("Co-salen") in air to 500 °C.  The precursor Co-salen can be obtained by reacting cobalt(II) acetate tetrahydrate in propanol at 50 °C under nitrogen atmosphere with the salen ligand (bis(salicylaldehyde)ethylenediimine).