title: The monoanionic pi-radical redox state of alpha-iminoketones in bis(ligand)metal complexes of nickel and cobalt.
abstract: The electronic structures of nickel and cobalt centers coordinated by two alpha-iminoketone ligands have been elucidated using density functional theory calculations and a host of physical methods such as X-ray crystallography, cyclic voltammetry, UV-vis spectroscopy, electron paramagnetic resonance spectroscopy, and magnetic susceptibility measurements. In principle, alpha-iminoketone ligands can exist in three oxidation levels: the closed-shell neutral form (L)0, the closed-shell dianion (L(red))(2-), and the open-shell monoanion (L*)(-). Herein, the monoanionic pi-radical form (L*)(-) of alpha-iminoketones is characterized in the compounds [(L*)2Ni] (1) and [(L*)2Co] (3), where (L*)(-) is the one-electron-reduced form of the neutral ligand (t-Bu)N=CH-C(Ph)=O. The metal centers in 1 and 3 are divalent, high-spin, and coupled antiferromagnetically to two ligand pi radicals. These bis(ligand)metal complexes can be chemically oxidized by two electrons to give the dications [trans-(L)2Ni(CH3CN)2](PF6)2 (2) and [trans-(L)2Co(CH3CN)2](PF6)2 (4), wherein the ligands are in the neutral form.
authors: Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany.
authors: Connie C
authors: CC
authors: Lu
authors: Eckhard
authors: E
authors: Bill
authors: Thomas
authors: T
authors: Weyhermüller
authors: Eberhard
authors: E
authors: Bothe
authors: Karl
authors: K
authors: Wieghardt
mesh_terms: D000838:Anions / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005609:Free Radicals / Q000737:chemistry; D007097:Imines / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D008024:Ligands; D008956:Models, Chemical; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D015032:Zinc / Q000737:chemistry
chemical_list: D000838:Anions; D005609:Free Radicals; D007097:Imines; D007659:Ketones; D008024:Ligands; D009942:Organometallic Compounds; D003035:Cobalt; D009532:Nickel; D015032:Zinc