Carbonyl iron is a highly pure (97.5% for grade S, 99.5+% for grade R) iron, prepared by chemical decomposition of purified iron pentacarbonyl.

Nickel carbonyl (IUPAC name: tetracarbonylnickel) is a colorless organometallic complex that is a versatile reagent, first described in 1890 by Ludwig Mond. It was the first metal simple carbonyl complex to be reported.

Protein carbonyls are formed by a variety of oxidative mechanisms and can be used as an index of oxidative injury.