title: Valence tautomerism in octahedral and square-planar phenoxyl-nickel(II) complexes: are imino nitrogen atoms good friends?
abstract: The two tetradentate ligands H(2)L and H(2)L(Me) afford the slightly distorted square-planar low-spin Ni(II) complexes 1 and 2, which comprise two coordinated phenolate groups. Complex 1 has been electrochemically oxidized into 1(+), which contains a coordinated phenoxyl radical, with a contribution from the nickel orbital. In the presence of pyridine, 1(+) is converted into 1(Py) (+), an octahedral phenolate nickel(III) complex with two pyridines axially coordinated: An intramolecular electron transfer (valence tautomerism) is promoted by the geometrical changes, from square planar to octahedral, around the metal center. The tetradentate ligand H(2)L(Me), in the presence of pyridine, and the hexadentate ligand H(2)L(Py) in CH(2)Cl(2) afford, respectively, the octahedral high-spin Ni(II) complexes 2(Py) and 3, which involve two equatorial phenolates and two axially coordinated pyridines. At 100 K, the one-electron-oxidized product 2(Py) (+) comprises a phenoxyl radical ferromagnetically coupled to the high-spin Ni(II) ion, with large zero-field splitting parameters, while 3(+) involves a phenoxyl radical antiferromagnetically coupled to the high-spin Ni(II) ion.
authors.affiliation: Laboratoire de Chimie Biomimétique, LEDSS, UMR CNRS 5616, Université J. Fourier, BP 53, 38041 Grenoble cedex 9, France.
authors.forename: Olaf
authors.initials: O
authors.lastname: Rotthaus
authors.forename: Fabrice
authors.initials: F
authors.lastname: Thomas
authors.forename: Olivier
authors.initials: O
authors.lastname: Jarjayes
authors.forename: Christian
authors.initials: C
authors.lastname: Philouze
authors.forename: Eric
authors.initials: E
authors.lastname: Saint-Aman
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Pierre
mesh_terms: D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D005029:Ethylenediamines / Q000737:chemistry; D007097:Imines / Q000737:chemistry*; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry*
chemical_list: D005029:Ethylenediamines; D007097:Imines; D009942:Organometallic Compounds; D010636:Phenols; C042329:phenoxy radical; D009532:Nickel; C011452:disalicylaldehyde ethylenediamine; D009584:Nitrogen