title: Natural orbitals for chemical valence as descriptors of chemical bonding in transition metal complexes.
abstract: Natural orbitals for chemical valence (NOCV) are defined as the eigenvectors of the chemical valence operator defined by Nalewajski et al.; they decompose the deformation density (differential density, Deltarho) into diagonal contributions. NOCV were used in a description of the chemical bond between the organometallic fragment and the ligand in example transition-metal complexes: heme-CO ([FeN(5)C(20)H(15)]-CO), [Ni-diimine hydride]-ethylene ([N;N-Ni-H]-C(2)H(4), N;N = -NH-CH-CH-NH-), and [Ni(NH(3))(3)]-CO. DFT calculations were performed using gradient-corrected density functional theory (DFT) in the fragments resolution, using the fragment/ligand Kohn-Sham orbitals as a basis set in calculations for the whole fragment-ligand complex. It has been found that NOCV lead to a very compact description of the fragment-ligand bond, with only a few orbitals exhibiting non-zero eigenvalues. Results of NOCV analysis, compared with Mulliken populations analysis and Zigler-Rauk interaction-energy decomposition, demonstrate that the use of the natural valence orbitals allows for a separation of the sigma-donation and pi-back-donation contributions to the ligand-fragment bond. They can be also useful in comparison of these contributions in different complexes.
authors.affiliation: Department of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian University, R. Ingardena 3, 30-060, Cracow, Poland.
authors.forename: Mariusz
authors.initials: M
authors.lastname: Mitoraj
authors.forename: Artur
authors.initials: A
authors.lastname: Michalak
mesh_terms: D008670:Metals / Q000737:chemistry*; D008958:Models, Molecular; D028561:Transition Elements / Q000737:chemistry*
chemical_list: D008670:Metals; D028561:Transition Elements