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由于C_(60)具有奇特的球形笼状结构以及不寻常的物理、化学性质,所以C_(60)及其衍生物成了当前物理、化学及材料科学等各个学科研究的前沿课题,特别是集中于A_xC_(60)这类化合物的研究,因为在K_3C_(60),Rb_3C_(60)及Rb_2CsC_(60)等化合物里测到了使人感兴趣的超导电性.但是在对A_xC_(60)等C_(60)负离子盐的核磁共振(NMR)研究中,有一个反常的现象始终困扰着研究者.纯C_(60)无论是晶形粉末还是在苯、甲苯中的溶液,用NMR测得的化学位移δ均为143(相对于TMS),而碱金属掺杂的K_3C_(60)的~(13)C谱线中心位移δ186,溶液中抗磁性C_(60)~(-n)(n可能为6)的化学位移为157.显然,这种实验现象与对传统的化学位移的认识产生了矛盾.化学位移理论认为,核周围空间电子云的分布使外磁场中的原子核受到电子云屏蔽,对抗磁性的核来说,化学位移应向高场移动,而C_(60)~(n-)的化学位移(相对于中性的C_(60))却向低场移动.
Due to its peculiar spherical cage structure and its unusual physical and chemical properties, C 60 and its derivatives have become the frontier topics in various disciplines such as physics, chemistry and materials science. In particular, In the study of A_xC_ (60), we found superconductivity in compounds such as K_3C_ (60), Rb_3C_ (60) and Rb_2CsC_ (60) (60) There is an anomaly in the nuclear magnetic resonance (NMR) study of anion salts that has plagued researchers. Pure C 60 (60) Whether it is a crystalline powder or a solution in benzene or toluene, the chemical shift measured by NMR δ is 143 (relative to TMS), while the center of ~ (13) C of alkali metal doped K_3C_ (60) is δ186, and the diamagnetic C_ (60) ~ (-n) ) Of the chemical shift of 157. Obviously, this experimental phenomenon and the traditional knowledge of chemical shift contradictions.Calibration theory that the distribution of nuclear space around the nuclear electron cloud in the external magnetic field by the electron cloud shield against magnetic Of the nuclei, the chemical shifts should move toward higher fields, whereas the chemical shifts of C 60 (n -) (relative to neutral C 60 )) But moved to the low field.