Ab initio studies of transition-metal compounds: The nature of the chemical bond to a transition metal

Modern quantum-theoretical calculations give not only accurate geometries, bond energies and other molecular properties of transition-metal compounds; the analysis of the complex numerical form of the electronic structure leads also to chemical models which are useful for an understanding of the chemical and physical properties of the molecules. Classification of the bonds into donative and covalent types is helpful for an understanding of the results of the calculations. Charge decomposition analysis (CDA) makes it possible to distinguish between the two types, and to quantify the Dewar-Chatt-Duncanson model of donor-acceptor interactions. The cover picture shows a schematic representation of the Dewar-Chatt-Duncanson description of the metal-ligand bonding and the mathematical formulae of the CDA for the ligand--->metal donation, the metal-->ligand back donation and the metal<->ligand repulsive polarisation.