【作者】 车宇樑；

【导师】 刘子阳；

【作者基本信息】 浙江大学 ， 无机化学， 2009， 博士

【摘要】 本文对一些大碳笼的富勒烯和内嵌含Ca大笼金属富勒烯的合成、提取、分离及结构表征进行了系统探索,得到了一系列的高纯度样品,进行了光谱学表征和Ca@C94单晶结构分析,结合密度泛函理论计算,揭示了大碳笼空心富勒烯C96和金属富勒烯Ca@C94的结构与性质的规律。在实验中我们对常规的富勒烯合成法-电弧放电方法进行了优化,利用高温煅烧,原位活化,反相放电等手段改进了电弧放电合成,提高了富勒烯和金属富勒烯产率。对放电得到的富勒烯烟炱利用二氯苯进行了多次重复提取,有效的富集了大笼富勒烯和大笼金属富勒烯。在高效液相色谱分离方面,我们改进了分离路线,首次用氯苯作为流动相,在第一轮分离时在Buckyprep M柱上快速的除去C60、C70和C84等小笼富勒烯,大大提高了用常规甲苯流动相分离的效率,同时还有效的富集了大碳笼产物。用二甲苯、甲苯、苯等流动相和三种柱子的交叉配合对目标产物做多步HPLC分离,得到了一系列大笼含Ca金属富勒烯Ca@C82、Ca@C84、Ca@C88、Ca@C90(Ⅰ,Ⅱ)、Ca@C92、Ca@C94(Ⅰ,Ⅱ)和Ca@C96。其中Ca@C92、Ca@C94(Ⅰ,Ⅱ)和Ca@C96是首次分离得到,也是目前分离到的最大碳笼的Ca金属富勒烯。Ca@C92和Ca@C94(Ⅰ)分别与已经分离到的Yb@C92和Yb@C94有较为相似的紫外可见近红外光谱,这意味着它们可能有相似的碳笼结构,而这些结构与+3价如Er和Dy等金属富勒烯表现出明显不同的吸收峰谱图。由于Ca为典型的+2离子,上述相似性表明Yb@C92和Yb@C94中,Yb的价态也很可能是+2价。因此Ca可以做为一种其它稀土富勒烯内包元素的价态指示剂,通过相同大小碳笼的紫外可见近红外光谱的比较,有助于判断其相应La系或其它族系内包金属的价态,这无疑是非常有意义的。液相色谱多步分离的同时还得到一系列如C86、C88、C90(Ⅰ,Ⅱ)、C92、C94(Ⅰ,Ⅱ)、C96(Ⅰ,Ⅱ,Ⅲ,Ⅳ)、C100和C102大碳笼空心富勒烯及异构体。其中C96的三个异构体C96(Ⅰ,Ⅱ,Ⅲ)、C100和C102是首次分离得到,也是目前得到的最大的空心富勒烯。C96的4个异构体中,C96(Ⅰ)在Buckyprep M柱上表现出来的保留时间特别短,极有可能具有相对很小的极性,而C96(Ⅳ)和C96(Ⅲ)表现出更好的结构稳定性和较高的产率。4个C96异构体还表现出不同的颜色和不同的紫外可见近红外光谱吸收行为。合成得到的绝大部分含Ca大笼金属富勒烯和空心大笼富勒烯都属于small bandgap系列。在C96实验分离的基础上,我们同时展开了理论计算。我们对C96IPR碳笼先进行了AM1和PM3的半经验计算,初步挑选了20个能量较为稳定的异构体,并在此基础上进行了高精度的密度泛函理论研究。在B3LYP/6-31G*水平上,计算了这些碳笼的总能量和能级差(最高空轨道与最低占据轨道之间),得到了一些动力学和热力学都稳定的碳笼。利用这些计算结果及其色谱行为性质,我们对4个从实验上分离得到的C96异构体的可能碳笼结构进行了推断和归属。其中181：C2是计算得到的最稳定的笼很有可能对应于C96(Ⅳ)这个实验分离得到产率丰度最高的异构体。C96(Ⅰ)明显短时的色谱保留行为很可能对应于偶极矩为零且形状较圆的183：D2,初步推测C96(Ⅱ)和C96(Ⅲ)可能分别对应146：Cs和182：C2这两个碳笼。另外,我们成功地得到了Ca@C94(I)与八乙基卟啉镍在甲苯溶液中共结晶的单晶体,目前最大碳笼的单晶体Ca@C3v-C94Ni(OEP)2(CH3C6H5),并对其进行了X射线晶体衍射测试和结构解析。结果表明,碳笼具有134：C3ν,构型。笼的位置虽然有无序,但比其它一些富勒烯晶体结构的有序程度高很多。Ca离子位于靠近三重轴接近富勒烯球面交叉处末端连接六边形的C-C键的下方,最短的Ca-C键距离为2.358 A。这个特别短的Ca-C距离表明Ca与碳笼有很强的共价作用。经过密度泛函理论计算进一步证明了这个碳笼与Ca形成的金属富勒烯稳定性是所有C94IPR碳笼Ca包合物中最高的。更多还原

【Abstract】 Synthesis, extraction, isolation and structure resolution of large empty fullerenes and Ca-containing large endohedral fullerenes are explored systematically. A series of above mentioned samples isomer free with high purity are obtained. Optical absorption and mass spectrum characterizations, single crystal X-ray diffraction measurement together with density functional theory calculation were performed to enlighten possible structure properties of these large cage empty fullerenes and the endohedral ones.General synthetic method for fullerene - direct current arc (DC) discharge method was tried optimization experimentally. High temperature precalcination and opposite direction discharge were adopted, which increased the yields effectively. Raw soot are extracted in o-dichlorobenzene solvent repeatedly, and it is found to have special effect for the enrichment of large fullerene and endohedral cages with this treatment. During multi-step high-performance liquid chromatography (HPLC) isolation, different separation methods were tried. Chlorobenzene was used as mobile phase at the first stage on the Buckyprep M column to remove C60, C70, C84 and other small cage fullerenes for the first time reported, which greatly increases the isolation and enrichment efficiency of large cage comparing with conventional isolation method with toluene flow. Several kinds of columns cooperating with various kinds of mobile solvents xylene, toluene, benzene as HPLC conditions, large cage Ca-containing endohedral fullerenes such as Ca@C82, Ca@C84, Ca@C88, Ca@C90(Ⅰ,Ⅱ), Ca@C92, Ca@C94(Ⅰ,Ⅱ) and Ca@C96 are completely isolated isomer free. Among those, Ca@C92, Ca@C94(I, II) and Ca@C96 are the largest Ca-containing endohedral fullerene till now, which were isolated for the first time without ever reporting. Ca@C92 and Ca@C94(I) gave similar ultraviolet-visible-near infrared (UV-Vis-NIR) absorption spectra with those of Yb@C92 and Yb@C94, respectively, indicating that they might possess very similar cage structures. However, Ca-containing endohedral fullerenes have distinctly different absorption spectra with those of+3 oxidation state endohedral fullerenes such as Er and Dy. As Ca possesses constant+2 oxidation state in Ca-metallofullerenes, the above similar property suggests that Yb probably possess +2 oxidation state too. So Ca could be an indicator of charge state for other rare earth endohedral fullerene encapsulated, and it is very meaningful for us to estimate the oxidation state of other metals incased in their endohedral fullerene cages by comparing their UV-Vis-NIR absorption spectra with those of the corresponding Ca-containing endohedral fullerenes.We also obtained a series of large empty fullerene and their isomers such as C86, C88, C90(Ⅰ，Ⅱ), C92, C94(Ⅰ，Ⅱ), C96(Ⅰ，Ⅱ，Ⅲ，Ⅳ), C100 and C102. It is for the first time the C96(Ⅰ，Ⅱ，Ⅲ), C100 and C102, which are the largest cage, were isolated up to now. Among the four isomers of C96, C96(Ⅰ) shows especially short retention time on Buckyprep M column, while C96(Ⅲ) and C96(Ⅳ) show higher stability and abundance. These four C96 isomers show different colors as well as spectroscopic characteristics. Most Ca-containing large endohedral fullerenes and large empty fullerenes synthesized in our experiment belong to small band gap series according to their optical absorption onset values.Theoretical calculations were carried out simultaneously for the four C96 isomers. We firstly performed semi-empirical calculations (AM1 and PM3) on C96 IPR cages, selecting 20 low-lying energy isomer cages, and then further calculations using density function theory (DFT) with high precision level on those low-lying energy cages were thoroughly done. At B3LYP/6-31G* level, we calculated the total energy and the band gap values of HOMO-LUMO for each of the above 20 cages. As a result, both thermodynamically and kinetically stable cages are found. Possible structures of the four C96i somers obtained experimentally were tried assigning by the calculation results jointing with their HPLC behavior characteristics.181:C2, the most stable cages by calculation results, was tentatively assigned to C96(Ⅳ), which showed much higher abundance experimentally. C96(Ⅰ) showed much shorter chromatographically retention time, so it seems reasonable to be associated with 183:D2 cage, possessing relative zero dipole value and being round shape. The possible structures for C96(Ⅱ) and C96(Ⅲ) are likely to corresponding to 146:Cs and 182:C2cage symmetries in our primary conjecture, respectively. On the other hand, Ca@C94(I) successfully co-crystallized with NiⅡ(octa-ethylporphyrin) in toluene solvent. Single crystal of the largest cage metallofullerene at present Ca@C3v-C94Ni(OEP)2(CH3C6H5) was obtained and structure determined by single crystal X-ray diffraction measurement, followed by structure resolution. Crystal structure indicated that, the cage possessed of 134:C3v cage symmetry. Although there was somewhat disorder of the cage position, but it has relatively higher order level than most other crystal structures of endohedral fullerene presented. The Ca ion located below one of the 6:6 ring junctions that radiated from the C3 axis close to fullerene cage surface. The closest Ca-C distance is 2.358 A. This particular short Ca-C distance suggests that there was strong covalent function between Ca ion and the carbon cage. DFT calculations further revealed that Ca@C94-134:C3v was the most stable one among all those IPR C94 cage Ca endohedral fullerenes.更多还原