NATURE OF METAL METAL INTERACTIONS IN SYSTEMS WITH BRIDGING LIGANDS .1. ELECTRONIC-STRUCTURE AND BONDING IN OCTACARBONYLDICOBALT

Self-consistent field calculations on Co2(CO)8 were used to examine its electronic structure through an analysis of the electron density. In the standard deformation density map, an accumulation zone extends from the cobalt nucleus toward the region of the Co-Co bent bond. This accumulation in the Co-Co bent-bond region is rather weak and could be due to coincidental accumulations in the vacant coordination site of each cobalt. However, through the use of various promolecules to produce different fragment deformation density maps, it can be concluded that the accumulation of density in the bent-bond region must be due at least in part to constructive interference between the two cobalt atoms. An analysis of the topology of the charge density of Co2(CO)8 shows interaction lines between the Co atoms and the C atoms with (3,-1) critical points, which are indicative of a bond. There is no interaction line connecting the Co atoms. Instead, there is a (3,+1) ring critical point close to the Co-Co midpoint. Therefore, although some constructive interference occurs between the two cobalt atoms, it is not sufficient to produce a Co-Co bond in the topology of the charge density.