Bonding properties of trinuclear metal carbonyls

Abstract

Extended Hückel molecular-orbital calculations have been performed on some trinuclear metal carbonyl species of Fe, Co, and Ni to identify their bonding properties. In addition, formal syntheses of these moieties by the addition of carbonyl ligands to a bare metal triangle and by aggregation of mononuclear carbonyl fragments have been illustrated. Differences between the structural forms and rigidity of complexes containing Ni₃(CO)₆^2– or M₃(CO)₉(M = Fe or Co) are rationalised on the basis of the frontier-orbital properties. The nickel compound offers only one cluster fragment orbital of a₂″ symmetry and this contributes to the apparently weak bonding to other groups along the principal axis.