Photolysis or thermolysis of mononuclear carbonyls generates di- and polymetallic carbonyls such as diiron nonacarbonyl (Fe(CO)). On further heating, the products decompose eventually into the metal and carbon monoxide.
:2 Fe(CO) → Fe(CO) + CO
The thermal decomposition of triosmium dodecacarbonyl (Os(CO)) provides higher-nuclear osmium carbonyl clusters such as Os(CO), Os(CO) up to Os(CO).
Mixed ligand carbonyls of ruthenium, osmium, rhodium, and iridium are often generated by abstraction of CO from solvents such as dimethylformamide (DMF) and 2-methoxyethanol. Typical is the synthesis of IrCl(CO)(PPh) from the reaction of iridium(III) chloride and triphenylphosphine in boiling DMF solution.