COsidoksille

COsidoksille is a term that appears in some Finnish-language chemistry writings to refer to carbon monoxide–related bonding interactions, especially the binding of CO ligands to transition metals in coordination and organometallic chemistry. The name combines CO, the chemical formula for carbon monoxide, with sidokset, meaning bonds or linkages, to emphasize the bonding motif between metal centers and CO ligands. In usage, COsidoksille is not a formal IUPAC designation but a descriptive label used in discussions of metal carbonyl chemistry.

In chemical terms, COsidoksille describes the interaction where carbon monoxide binds to a metal center through its carbon atom, forming terminal or bridged metal–CO bonds. CO is a strong σ-donor and a π-acceptor, engaging in back-donation from metal d orbitals into the CO π* antibonding orbitals. This synergic bonding weakens the C–O bond in the CO ligand and strengthens the metal–CO interaction. Infrared spectroscopy often reflects this bonding, with C–O stretching frequencies in the roughly 1800–2100 cm⁻¹ range, shifting according to the extent of backbonding and ligand environment.

Common examples of systems discussed under the COsidoksille concept include classic metal carbonyls such as Fe(CO)5, Ni(CO)4, and Co2(CO)8, as well as more complex polynuclear carbonyl clusters. These interactions underlie many catalytic processes, including hydroformylation and carbonylation, as well as fundamental studies of ligand field effects and backbonding.

See also: carbonyl ligand, metal carbonyls, π-backbonding, infrared spectroscopy of coordination compounds.