Metal–metal bonding in bridged ligand systems: experimental and theoretical charge densities in Co3(μ3-CX)(CO)9 (X = H, Cl)

Experimental charge density studies on Co 3 (μ 3 -CX)(CO) 9 ( 1a X = H, 1b X = Cl) have been undertaken at 100 and 115 K respectively, using Mo Kα X-radiation. The nature of the metal–metal and metal–ligand interactions have been studied by means of deformation densities and by topological analysis of the density using the atoms in molecules (AIM) approach. DFT (B3LYP/6-311G**) calculations on 1a and 1b are in excellent agreement on a qualitative and quantitative level with the experimental conclusions. Within the conceptual framework of the AIM methodology, there is no direct bonding between the Co atoms, since no (3, –1) bond critical point in the density ρ is observed and hence no bond path exists between the metal atoms. The delocalisation indices δ (Co, Co) obtained from the DFT wave-functions indicate however that there are significant indirect Co...Co interactions mediated through the bridging alkylidyne ligand. The charge concentrations on the alkylidyne C atoms in 1a and 1b are significantly different, and indicate that the bonding of this atom to the Co 3 triangle is more localised in the case of 1b . .