title: Theoretical study of mononuclear nickel(I), nickel(0), copper(i), and cobalt(I) dioxygen complexes: new insight into differences and similarities in geometry and bonding nature.
abstract: Geometries, bonding nature, and electronic structures of (N^N)Ni(O2) (N^N = β-diketiminate), its cobalt(I) and copper(I) analogues, and (Ph3P)2Ni(O2) were investigated by density functional theory (DFT) and multistate restricted active space multiconfigurational second-order perturbation (MS-RASPT2) methods. Only (N^N)Ni(O2) takes a C(S) symmetry structure, because of the pseudo-Jahn-Teller effect, while all other complexes take a C(2V) structure. The symmetry lowering in (N^N)Ni(O2) is induced by the presence of the singly occupied δ(d(xy)-π(x)*) orbital. In all of these complexes, significant superoxo (O2-) character is found from the occupation numbers of natural orbitals and the O-O π* bond order, which is independent of the number of d electrons and the oxidation state of metal center. However, this is not a typical superoxo species, because the spin density is not found on the O2 moiety, even in open-shell complexes, (N^N)Ni(O2) and (N^N)Co(O2). The M-O and O-O distances are considerably different from each other, despite the similar superoxo character. The M-O distance and the interaction energy between the metal and O2 moieties are determined by the d(yz) orbital energy of the metal moiety taking the valence state. The binding energy of the O2 moiety is understood in terms of the d(yz) orbital energy in the valence state and the promotion energy of the metal moiety from the ground state to the valence state. Because of the participations of various charge transfer (CT) interactions between the metal and O2 moieties, neither the d(yz) orbital energy nor the electron population of the O2 moiety are clearly related to the O-O bond length. Here, the π bond order of the O2 moiety is proposed as a good measure for discussing the O-O bond length. Because the d electron configuration is different among these complexes, the CT interactions are different, leading to the differences in the π bond order and, hence, the O-O distance among these complexes. The reactivity of dioxygen complex is discussed with the d(yz) orbital energy.
authors.affiliation: Fukui Institute for Fundamental Chemistry, Kyoto University , Takano-Nishihiraki-cho 34-4, Sakyo-ku, Kyoto 606-8103, Japan.
authors.forename: Yue
authors.initials: Y
authors.lastname: Chen
authors.forename: Shigeyoshi
authors.initials: S
authors.lastname: Sakaki
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009532:Nickel / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D056831:Coordination Complexes; D003035:Cobalt; D003300:Copper; D009532:Nickel; D010100:Oxygen