Syntheses, electronic structures, and EPR/UV-Vis-NIR spectroelectrochemistry of nickel(II), copper(II), and zinc(II) complexes with a tetradentate ligand based on S-methylisothiosemicarbazide

摘要

Template condensation of 3, 5-di-tert-butyl-2-hydroxybenzaldehyde S-methylisothiosemicarbazone with pentane-2, 4-dione and triethyl orthoformate at elevated temperatures resulted in metal complexes of the type M~(II)L, where M = Ni and Cu and H_2L = a novel tetradentate ligand. These complexes are relevant to the active site of the copper enzymes galactose oxidase and glyoxal oxidase. Demetalation of Ni~(II)L with gaseous hydrogen chloride in chloroform afforded the metal-free ligand H2L. Then by the reaction of H2L with Zn(CH_3COO) _2?~2H_2O in a 1:1 molar ratio in 1:2 chloroform/methanol, the complex Zn~(II)L(CH_3OH) was prepared. The three metal complexes and the prepared ligand were characterized by spectroscopic methods (IR, UV-vis, and NMR spectroscopy), X-ray crystallography, and DFT calculations. Electrochemically generated one-electron oxidized metal complexes [NiL]+, [CuL]+, and [ZnL(CH _3OH)]~+ and the metal-free ligand cation radical [H _2L]~(+?) were studied by EPR/UV-vis-NIR and DFT calculations. These studies demonstrated the interaction between the metal ion and the phenoxyl radical.