Properties of the Nickel(III) Complex with 1,4,8,11-Tetraazacyclotetradecane-1,4,8,11-tetraacetate in Aqueous Solution

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• 作者：Mahammad Ali ; Israel Zilbermann ; Haim Cohen ; Alexander I. Shames ; and Dan Meyerstein
• 刊名：Inorganic Chemistry
• 出版年：1996
• 出版时间：August 28, 1996
• 年：1996
• 卷：35
• 期：18
• 页码：5127 - 5131
• 全文大小：334K
• 年卷期：v.35,no.18(August 28, 1996)
• ISSN：1520-510X

文摘

Oxidation oftrans-I-Ni^IIL, orNi^IIL_out, by ^{images/entities/bull.gif">}OH radicalswas carried out by irradiating N₂O saturatedsolutionscontaining the complex, prepared by mixing equimolar concentrations ofthe metal ion and the ligand at pH 3.50.The intermediate thus formed has a strong absorption band at 310nm and is stable for hours. That this unstablecomplex is a nickel(III) species was verified by EPR spectroscopyand its chemical reduction with ascorbic acid,which was found to be instantaneous. The most striking feature ofthe oxidation by ^{images/entities/bull.gif">}OH radicals, whicharepowerful single electron oxidizing agents, is that it produces anickel(III) species which is different from theelectrochemically produced one as manifested by their absorptionspectra and EPR signals. The radiolyticallyproduced nickel(III) species undergoes decarboxylation leading tothe production of CO₂, CH₂O, Ni^IIL'and Ni^IIL(L' = the new ligand produced after oxidative degradation of one ofthe N-acetate groups of the ligand). Theelectrochemical oxidation oftrans-I-Ni^IIL, orNi^II_outL, proceeds via the degradation of twoof the acetate armson average. The yield of CH₂O is ~2.0 mol per moleof the nickel(II) complex in electrochemicaloxidations.These observations point out that the two techniques producedifferent nickel(III) complexes which do notinterconvert. The mechanisms leading to the production ofNi^IIL' (oxidation by ^{images/entities/bull.gif">}OH radicals,radiolytically) andNi^IIL'' (electrochemically) differ from that proposed inthe literature.