Studies on the Reaction of Iron(II) with NO in a Noncoordinating Ionic Liquid

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• 作者：Svetlana Begel ; Ralph Puchta ; J枚rg Sutter ; Frank W. Heinemann ; Lutz Dahlenburg ; Rudi van Eldik
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：July 20, 2015
• 年：2015
• 卷：54
• 期：14
• 页码：6763-6775
• 全文大小：615K
• ISSN：1520-510X

文摘

In an earlier study we investigated the reaction of iron(II) chloride with NO in a strongly coordinating ionic liquid 1-ethyl-3-methylimidazolium dicyanamide [emim][dca] and showed that the actual reactive species in solution was [Fe^II(dca)₅Cl]^{4鈥?/sup>. For the present report we investigated in detail how this reaction could proceed in a noncoordinating ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate [emim][OTf]. The donor ability of OTf鈥?/sup> is much lower than that of dca鈥?/sup>, such that the solubility of FeCl₂ in [emim][OTf] strongly depended on other donors like water or chloride ions present or added to the ionic liquid. On increasing the chloride concentration in [emim][OTf], the tetrachloridoferrate complex [emim]₂[FeCl₄] was formed, as verified by X-ray crystallography. This complex undergoes reversible binding of NO, for which the UV鈥搗is spectral characteristics of the green鈥揵rown nitrosyl product resembled that found for the corresponding nitrosyl complexes formed in water and [emim][dca] as solvents. A detailed analysis of the spectra revealed that the {Fe鈥揘O}7 species has FeII鈥揘O鈥?/sup> character in contrast to FeIII鈥揘O鈥?/sup> as found for the other solvents. The formation constant, however, is much higher than in [emim][dca], lying closer to the value found for water as solvent. Surprisingly, the M枚ssbauer spectrum found in [emim][OTf] is very unusual and unsimilar to that found in water and [emim][dca] as solvents, pointing at a different electron density distribution between Fe and NO in {Fe鈥揘O}.7 First, the high isomer shift points to the presence of iron(II) species in solution, thus indicating that upon NO binding no oxidation to iron(III) occurs. Second, the negligible quadrupole splitting suggests a high local symmetry around the iron center. The nitrosyl product is suggested to be [FeIICl₃NO]鈭?/sup>, which is supported by electron paramagnetic resonance (EPR) and IR measurements. The nature of the Fe(II) complexes formed in [emim][OTf] depends on the additives required to dissolve FeCl₂ in this ionic liquid.}