COcontaining

CO-containing refers to chemical species that include carbon monoxide (CO) as a ligand or structural unit. In organometallic and inorganic chemistry, CO can coordinate to a metal center to form metal carbonyl complexes, which constitute a major class of CO-containing compounds. The term can also be used more broadly for molecules that contain carbonyl groups (C=O); however, this article focuses on CO as a ligand in transition-metal chemistry.

Carbon monoxide binds to metals primarily through the carbon atom, creating a strong, linear M–CO bond. CO acts as a π-acceptor (backbonding from the metal to CO’s π* orbitals), which influences the electronic and geometric properties of the complex. Many carbonyl complexes follow the 18-electron rule, and common geometries include octahedral, square planar, and various cluster structures. The ligating strength and lability of CO depend on the metal, oxidation state, and ancillary ligands, allowing CO to be displaced or inserted in catalytic cycles.

Representative CO-containing compounds include iron pentacarbonyl Fe(CO)5, chromium hexacarbonyl Cr(CO)6, nickel tetracarbonyl Ni(CO)4, and cobalt carbonyl clusters such as Co2(CO)9. Manganese decacarbonyl Mn2(CO)10 and related clusters are also common. These species serve as precursors to other organometallic reagents, materials, and catalysts, and they are frequently employed to study carbonylation, hydroformylation, and related transformations.

Safety and handling are important, as CO is a toxic, colorless gas. Reactions and storage are conducted under strict ventilation and inert atmospheres to minimize exposure and hazardous release.