Structure and bonding of the transition-metal carbonyl complexes M(CO)₅L (M = Cr, Mo, W) and M(CO)₃L (M = Ni, Pd, Pt; L = CO, SiO, CS, N₂, NO⁺, CN^- , NC^-, HCCH, CCH₂, CH₂, CF₂, H₂)

Quantum mechanical ab initio calculations at the MP2 and CCSD(T) level of theory using effective core potentials (ECP) for the metals with a valence basis set of DZP quality and a 6-31GKd) all-electron basis set for the other elements are reported for the complexes M(CO)₅L (M = Cr, Mo, W) and M(CO)₃L (M = Ni, Pd, Pt) with ligands L = CO, SiO, CS, N₂, NO⁺, CN^-, NC^-, HCCH, CCH₂, CH₂, CF₂, and H₂. The optimized geometries at MP2/II are in very good agreement with experiment. The theoretically predicted (CO)_nM-L bond dissociation energies at CCSD(T)/II using MP2/II optimized geometries also agree quite well with experimental data. The (CO)_nM-L bond is investigated using the charge decomposition analysis (CDA), which gives an interpretation of the donor-acceptor complexes in terms of charge donation, back-donation and repulsive polarization. The CDA results, which may be considered as a quantitative expression of the Dewar-Chatt-Duncanson model, are in agreement with the standard classification of the ligands.