Organometallic chalcogen complexes. Part 18.—A diluted single crystal e.s.r. study of the electronic structure of tricobalt enneacarbonyl sulphide : antiaromaticity in a transition metal carbonyl cluster system

Abstract

An e.s.r. study of Co₃(CO)₉S (S=½) in solution and doped in single crystals of the diamagnetic host FeCo₂(CO)₉S has shown from a detailed analysis of the hyperfine interaction that the unpaired electron is in a non-degenerate molecular orbital of a₂ symmetry comprised primarily of an anti-bonding combination of d orbitals essentially localized in the plane of the cobalt atoms. These definitive results firmly substantiate the previous conclusions based on X-ray measurements of Co₃(CO)₉S and FeCo₂(CO)₉S that the unpaired electron in Co₃(CO)₉S has an appreciable conjugative destabilization effect (or antiaromatic character) in drastically altering the tricobalt geometry of Co₃(CO)₉S. The bonding in Co₃(CO)₉S and in the closely related Ni₃(C₅H₅)₃(CO)₂ complex is discussed in light of these observations.