title: Five coordinate M(II)-diphenolate [M = Zn(II), Ni(II), and Cu(II)] Schiff base complexes exhibiting metal- and ligand-based redox chemistry.
abstract: Five-coordinate Zn(II), Ni(II), and Cu(II) complexes containing pentadentate N(3)O(2) Schiff base ligands [1A](2-) and [1B](2-) have been synthesized and characterized. X-ray crystallographic studies reveal five coordinate structures in which each metal ion is bound by two imine N-donors, two phenolate O-donors, and a single amine N-donor. Electron paramagnetic resonance (EPR) spectroscopic studies suggest that the N(3)O(2) coordination spheres of [Cu(1A)] and [Cu(1B)] are retained in CH(2)Cl(2) solution and solid-state superconducting quantum interference device (SQUID) magnetometric studies confirm that [Ni(1A)] and [Ni(1B)] adopt high spin (S = 1) configurations. Each complex exhibits two reversible oxidation processes between +0.05 and +0.64 V vs [Fc](+)/[Fc]. The products of one- and two-electron oxidations have been studied by UV/vis spectroelectrochemistry and by EPR spectroscopy which confirm that each oxidation process for the Zn(II) and Cu(II) complexes is ligand-based with sequential formation of mono- and bis-phenoxyl radical species. In contrast, the one-electron oxidation of the Ni(II) complexes generates Ni(III) products. This assignment is supported by spectroelectrochemical and EPR spectroscopic studies, density functional theory (DFT) calculations, and the single crystal X-ray structure of [Ni(1A)][BF(4)] which contains Ni in a five-coordinate distorted trigonal bipyramidal geometry.
authors.affiliation: School of Chemistry, University of Nottingham, Nottingham NG7 2RD, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Franks
authors.forename: Anastasia
authors.initials: A
authors.lastname: Gadzhieva
authors.forename: Laura
authors.initials: L
authors.lastname: Ghandhi
authors.forename: David
authors.initials: D
authors.lastname: Murrell
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Blake
authors.forename: E Stephen
authors.initials: ES
authors.lastname: Davies
authors.forename: William
authors.initials: W
authors.lastname: Lewis
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Moro
authors.forename: Jonathan
authors.initials: J
authors.lastname: McMaster
authors.forename: Martin
authors.initials: M
authors.lastname: Schröder
mesh_terms: D020134:Catalytic Domain; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008024:Ligands; D008958:Models, Molecular; D009532:Nickel / Q000737:chemistry*; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry*; D011789:Quantum Theory; D012545:Schiff Bases / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D008024:Ligands; D010636:Phenols; D012545:Schiff Bases; D003300:Copper; D009532:Nickel; D015032:Zinc