Five Coordinate M(II)-Diphenolate [M = Zn(II), Ni(II), and Cu(II)] Schiff Base Complexes Exhibiting Metal- and Ligand-Based Redox Chemistry

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• 作者：Mark Franks ; Anastasia Gadzhieva ; Laura Ghandhi ; David Murrell ; Alexander J. Blake ; E. Stephen Davies ; William Lewis ; Fabrizio Moro ; Jonathan McMaster ; Martin Schr枚der
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：January 18, 2013
• 年：2013
• 卷：52
• 期：2
• 页码：660-670
• 全文大小：560K
• 年卷期：v.52,no.2(January 18, 2013)
• ISSN：1520-510X

文摘

Five-coordinate Zn^II, Ni^II, and Cu^II complexes containing pentadentate N₃O₂ Schiff base ligands [1A]^{2鈥?/sup> and [1B]2鈥?/sup> 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 N₃O₂ coordination spheres of [Cu(1A)] and [Cu(1B)] are retained in CH₂Cl₂ 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 ZnII and CuII complexes is ligand-based with sequential formation of mono- and bis-phenoxyl radical species. In contrast, the one-electron oxidation of the NiII complexes generates NiIII 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)][BF₄] which contains Ni in a five-coordinate distorted trigonal bipyramidal geometry.}