CObinding

CO-binding refers to the interaction in which carbon monoxide binds to another molecule, most commonly acting as a ligand to a metal center in inorganic or organometallic chemistry, or binding to heme and other metal sites in biology. CO is a small diatomic molecule with a lone pair on carbon and a vacant anti-bonding orbital, enabling sigma donation to a metal and pi back-donation from the metal to CO’s antibonding orbitals. This combination stabilizes a metal–CO bond and influences the electronic properties of the bound center.

In inorganic chemistry, carbon monoxide forms a class of compounds known as metal carbonyls. Classic examples include iron pentacarbonyl, Fe(CO)5, and nickel tetracarbonyl, Ni(CO)4. CO binding can be linear or bent depending on the metal and ligands, and the strength of binding rises with accessible back-donation from the metal. Spectroscopic and crystallographic methods are used to study bond lengths, angles, and CO stretching frequencies, which typically appear in the infrared region and shift with coordination environment.

In biology, CO binds tightly to ferrous heme iron in proteins such as hemoglobin and myoglobin, producing carboxyhemoglobin or carboxymyoglobin and reducing oxygen transport. CO can also inhibit enzymes like cytochrome c oxidase, affecting cellular respiration. The high affinity of CO for iron-containing centers has important physiological and toxicological implications.

Detection and application: CO-binding is leveraged in catalysis, including carbonylation reactions and hydroformylation, and is monitored in research and safety contexts using infrared spectroscopy, UV–visible spectroscopy, and sensor technologies. CObinding remains a central concept across chemistry and biochemistry for understanding ligand interactions and their consequences.