Artifacts in the electron paramagnetic resonance spectra of C60 fullerene ions:: Inevitable C120O impurity
Artifacts in the electron paramagnetic resonance spectra of C60 fullerene ions:: Inevitable C120O impurity
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DOI：
10.1021/ja011832f
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发表时间：
2002-04-24
影响因子：
15
通讯作者：
Reed, CA
中科院分区：
文献类型：
--
作者：
Paul, P;Kim, KC;Reed, CA
重新解释了C-60(N)富勒化物离子(n=2，3)的电子顺磁共振(EPR)谱和在固体C-60中观察到的EPR信号，还原程度不足和未被识别的C120O的存在，C120O是暴露在空气中的一种普遍存在的不可避免的杂质，已经损害了以前报道的大多数富勒化物的光谱。中央窄线宽信号(尖峰)归因于C120On-(n=奇数)。C-60(2-)光谱中轴向三重态(g类似于2.0015，D=26-29G)产生的信号归属于C120On-(n=2或4)。C120O的D值比C-60的D值更接近实际。来自“粉末”三联体(D类似于11G)的较不明显的信号被归因于C120On-(n=奇数)的聚集，该聚集体是由冻结的非玻璃化溶剂产生的。在高度提纯的C-60样品中，我们没有发现一个广泛的类似于30G信号的证据，该信号以前被认为是热可及的C-60三联体(2-)。C-60(2-)离子是EPR无声的。以前归因于C-60(3-)离子的四重态的信号被归因于C120O4-。当在严格的厌氧条件下从新提纯的C-60制备完全还原的样品时，C-60(-)和C-60(3-)的简单、真实的光谱变得可用。固体现成的C-60具有EPR信号(g类似于2.0025，增量H(Pp)类似于1.5G)，通常归因于自由基阳离子C-60(.+)。这种信号可以通过将高纯度的EPR沉默的C60暴露在黑暗中的氧气中来再现，在C-60中掺杂正宗的C-60(.+)盐可以提供具有更大线宽(DeltaH(Pp)=6-8G)的信号。结果表明，暴露于空气中的C-60样品的EPR信号来源于过氧化氢桥联的双基--C-60-O-O-C-60(.)或其分解产物，而不是来自C-60(.+)。固态C-60对氧气比以前所认为的更敏感，因此几乎不可能避免受到C120O的污染。
Aspects of the electron paramagnetic resonance (EPR) spectra Of C-60(n) fulleride ions (n = 2, 3) and the EPR signal observed in solid C-60 are reinterpreted, Insufficient levels of reduction and the unrecognized presence Of C120O, a ubiquitous and unavoidable impurity in air-exposed C-60, have compromised most previously reported spectra of fullerides. Central narrow line width signals ("spikes") are ascribed to C120On- (n = odd). Signals arising from axial triplets (g similar to 2.0015, D = 26-29 G) in the spectrum of C-60(2-) are ascribed to C120On- (n = 2 or 4). Their D values are more realistic for C120O than C-60. Less distinct signals from "powder" triplets (D similar to 11 G) are ascribed to aggregates of C120On- (n = odd) arising from freezing nonglassing solvents. In highly purified samples of C-60, we find no evidence for a broad similar to30 G signal previously assigned to a thermally accessible triplet of C-60(2-). The C-60(2-) ion is EPR-silent. Signals previously ascribed to a quartet state of the C-60(3-) ion are ascribed to C120O4-. Uncomplicated, authentic spectra of C-60(-) and C-60(3-) become available when fully reduced samples are prepared under strictly anaerobic conditions from freshly HPLC-purified C-60. Solid off-the-shelf C-60 has an EPR signal (g similar to 2.0025, DeltaH(pp) similar to 1.5 G) that is commonly ascribed to the radical cation C-60(.+). This signal can be reproduced by exposing highly purified, EPR-silent C60 to oxygen in the dark, Doping C-60 with an authentic C-60(.+) salt gives a signal with much greater line width (DeltaH(pp) = 6-8 G). It is suggested that the EPR signal in air-exposed samples of C-60 arises from a peroxide-bridged diradical, .C-60-O-O-C-60(.) or its decomposition products rather than from C-60(.+). Solid-state C-60 is more sensitive to oxygen than previously appreciated such that contamination with C120O is almost impossible to avoid.