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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >EPR Studies Associated with the Electrochemical Reduction of C_(60) and Supramolecular Complexes of C_(60) in Toluene-Acetonitrile Solvent Mixtures
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EPR Studies Associated with the Electrochemical Reduction of C_(60) and Supramolecular Complexes of C_(60) in Toluene-Acetonitrile Solvent Mixtures

机译：EPR研究与C_（60）和C_（60）的超分子配合物在甲苯-乙腈溶剂混合物中的电化学还原

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摘要

Electron paramagnetic resonance (EPR) studies at 295 K of the radical anion of buckminsterfullerene (C_(60)~(·-)) generated electrochemically by bulk-controlled potential electrolysis of neutral C_(60) in mixed toluene-acetonitrile solvents (5-20% v/v acetonitrile with 0.1-0.2 M n-Hex_4NPF_6 or n-Bu_4NPF_6 as the supporting electrolyte) have shown that at least three different forms of C_(60)~(·-) exist in solution. The radical anions have different g values and can thus be detected by EPR spectroscopy in the form of single line signals with different line widths. The familiar species with the broad line width signal (ΔH~(pp) = 6 mT) was present in a high percentage (ca. >95%) along with two species with narrow line width (ΔH~(pp) = 0.16 and 0.07 mT) signals that were present between 1 and 5% of the total concentration of C_(60)~(·-). The concentration of the species with narrow line width EPR signals increased with increasing time so that over a 20-h period their EPR signal intensity approximately doubled. The purity of the toluene was found to be very important in determining the number of species detected with sharp EPR signals. Although two species were always detected with sharp EPR signals, when lower purity toluene (<99%) was used, the number of species with narrow line width signals increased to >2. The increase in the sharp EPR signals with increasing time is not inconsistent with a slow reaction between C_(60)~(·-) and low levels of impurities in the solvent to form lower symmetry paramagnetic species, the narrow line width signals being very similar to those reported for substituted fullerene radicals. EPR and cyclic voltammetry experiments were conducted on C_(60) in the presence of several complexing agents, cyclotriveratrylene (CTV), the symmetrical tris-allyl substituted analogue of CTV [CTV(ALLYL)_3], and p-benzylcalix[5]arene. The intensity of the narrow and broad line width EPR signals decreased when C_(60)~(·-) was electrochemically generated in the presence of the complexing agents, indicating that the host-guest π-π interactions were sufficiently strong to alter the EPR signals of C_(60)~(·-). Cyclic voltammetry experiments performed on C_(60) in the presence of the complexing agents showed that the first four reduction processes of C_(60) split into two new processes upon complexation, with the time allowed for the host-guest reaction being critical in determining the voltammetric behavior.
机译：在混合甲苯-乙腈溶剂中中性C_（60）的本体控制电位电解以电化学方式产生的buckminsterfullerene（C_（60）〜（·-））自由基阴离子在295 K时的电子顺磁共振（EPR）研究以0.1-0.2 M n-Hex_4NPF_6或n-Bu_4NPF_6作为支持电解质的20％v / v乙腈表明，溶液中至少存在三种不同形式的C_（60）〜（·-）。自由基阴离子具有不同的g值，因此可以通过EPR光谱法以具有不同线宽的单线信号形式进行检测。常见的具有宽线宽信号（ΔH〜（pp）= 6 mT）的物种与两种具有窄线宽（ΔH〜（pp）= 0.16和0.07）的物种以高百分比（大约> 95％）的形式存在mT）信号出现在C_（60）〜（·-）总浓度的1-5％之间。具有窄线宽EPR信号的物质的浓度随时间的增加而增加，因此在20小时内，它们的EPR信号强度大约增加了一倍。发现甲苯的纯度对于确定使用清晰的EPR信号检测到的物种数量非常重要。尽管总是用清晰的EPR信号检测到两个物种，但是当使用较低纯度的甲苯（<99％）时，具有窄线宽信号的物种数量增加到> 2。 EPR信号的尖锐信号随时间的增加而增加，这与C_（60）〜（·-）与溶剂中杂质含量低，形成较低对称顺磁物质的反应缓慢不一致，窄线宽信号非常相似那些报道了取代的富勒烯自由基的化合物。 EPR和循环伏安法实验是在几种络合剂，环三偏二甲苯（CTV），CTV的对称三烯丙基取代的类似物[CTV（ALLYL）_3]和对苄基杯[5]芳烃的存在下对C_（60）进行的。当在络合剂存在下电化学生成C_（60）〜（·-）时，窄线和宽线宽EPR信号的强度降低，表明主体-客体的π-π相互作用足够强以改变EPR C_（60）〜（·-）的信号。在存在络合剂的情况下对C_（60）进行的循环伏安实验表明，络合后C_（60）的前四个还原过程分为两个新过程，主客体反应所需的时间对于确定伏安行为。

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