THEORETICAL-STUDY OF THE BONDING IN MOLECULAR TRANSITION-METAL CATIONS

We review the bonding for both first-and second-row transition-metal positive ions with a variety of ligands. For singly charged ions we consider a range of interaction strengths from the weakly interacting noble gases to the covalently bonded dimethyls. We also consider several dications, since many of these systems are amenable to experimental study. The bonding, particularly for covalent systems, is found to arise generally from a mixture of the lowest atomic states. Polarization, sd and sp hybridization, and s-to-d and d-to-s promotion are various means of reducing the repulsion and enhancing the bonding. The relative importance of these effects depends on the separations between the lowest states of the metal ion. The loss of atomic d-d exchange energy in the molecule is also an important factor in determining the binding energies. The diversity of transition-metal bonding arises because the relative importance of these effects depends on the separation of the atomic states with different d occupancies. The calculations are able to explain the relative magnitudes of the first-and second-ligand binding energies for transition-metal ions bound to noble-gas, water, CO and CH3 ligands. © 1990 Taylor and Francis Group, LLC.