Paul Parimal, Kim Kee-Chan, Sun Dayong, Boyd Peter D W, Reed Christopher A
Department of Chemistry, University of California, Riverside, California 92521-0403, USA.
J Am Chem Soc. 2002 Apr 24;124(16):4394-401. doi: 10.1021/ja011832f.
Aspects of the electron paramagnetic resonance (EPR) spectra of C60n- fulleride ions (n = 2, 3) and the EPR signal observed in solid C60 are reinterpreted. Insufficient levels of reduction and the unrecognized presence of C120O, a ubiquitous and unavoidable impurity in air-exposed C60, 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 approximately 2.0015, D = 26-29 G) in the spectrum of C602- are ascribed to C120On- (n = 2 or 4). Their D values are more realistic for C120O than C60. Less distinct signals from "powder" triplets (D approximately 11 G) are ascribed to aggregates of C120On- (n = odd) arising from freezing nonglassing solvents. In highly purified samples of C60, we find no evidence for a broad approximately 30 G signal previously assigned to a thermally accessible triplet of C60(2-). The C60(2-) ion is EPR-silent. Signals previously ascribed to a quartet state of the C60(3-) ion are ascribed to C120O4-. Uncomplicated, authentic spectra of C60- and C60(3-) become available when fully reduced samples are prepared under strictly anaerobic conditions from freshly HPLC-purified C60. Solid off-the-shelf C60 has an EPR signal (g approximately 2.0025, DeltaH(pp) approximately 1.5 G) that is commonly ascribed to the radical cation C60*+. This signal can be reproduced by exposing highly purified, EPR-silent C60 to oxygen in the dark. Doping C60 with an authentic C60*+ 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 C60 arises from a peroxide-bridged diradical, C60-O-O-C60 or its decomposition products rather than from C60*+. Solid-state C60 is more sensitive to oxygen than previously appreciated such that contamination with C120O is almost impossible to avoid.
对C60n-富勒化物离子（n = 2, 3）的电子顺磁共振（EPR）谱的各个方面以及在固态C60中观察到的EPR信号进行了重新解释。还原程度不足以及在暴露于空气中的C60中普遍存在且不可避免的杂质C120O的存在未被认识到，这损害了大多数先前报道的富勒化物光谱。中心窄线宽信号（“尖峰”）归因于C120On-（n =奇数）。C602-谱中轴向三重态产生的信号（g约为2.0015，D = 26 - 29 G）归因于C120On-（n = 2或4）。它们的D值对于C120O比C60更符合实际情况。来自“粉末”三重态（D约为11 G）的不太明显的信号归因于由冷冻非玻璃化溶剂产生的C120On-（n =奇数）聚集体。在高度纯化的C60样品中，我们没有发现先前归因于C60(2-)的热可及三重态的约30 G宽信号的证据。C60(2-)离子是EPR沉默的。先前归因于C60(3-)离子四重态的信号归因于C120O4-。当在严格厌氧条件下由新鲜HPLC纯化的C60制备完全还原的样品时，可获得简单、真实的C60-和C60(3-)光谱。市售的固态C60具有一个EPR信号（g约为2.0025，ΔH(pp)约为1.5 G），通常归因于自由基阳离子C60*+。通过在黑暗中将高度纯化的、EPR沉默的C60暴露于氧气可以重现该信号。用真实的C60*+盐掺杂C60会产生线宽更大得多的信号（ΔH(pp) = 6 - 8 G）。有人认为，暴露于空气中的C60样品中的EPR信号来自过氧化物桥连的双自由基C60 - O - O - C60或其分解产物，而不是来自C60*+。固态C60对氧气比先前认为的更敏感，以至于几乎不可能避免被C120O污染。
