超大碳笼金属富勒烯的合成、分离与结构性质表征

Fullerenes are the only soluble form of elemental carbon with distinct molecular structures. As a result, the research on fullerenes, especially the structural determination of giant fullerenes with cage sizes larger than C90, which are viewed as finite-length end-capped carbon nanotubes, is expected to present valuable information about the formation mechanism of carbon nanotubes. However, current investigations on fullerenes mainly focus on such species of cage sizes ranging from C50 to C90, whereas results of large fullerenes are really rare because of their low yield and low stability. In this proposal, inspired by recent achievements in the successful isolation of some large endohedral metallofullerenes like Sm2@C104, La2@C100 and La2C2@C100, we intend to synthesize such giant fullerenes with the arc discharge method by putting some metallic clusters inside the cages to stabilize them, finally obtaining such hybrid molecules as M2C2@C100-120 or M3N@C100-120 which should be readily soluble in trichlorobenzene and thus are isolable with HPLC. Consequently, we are planning to isolate ca.10 novel large fullerenes and determine their molecular structures using different methods, especially the single crystal X-ray crystallographic method which can provide unambiguous structural information. Selective synthesis of certain large species and the stabilization effect of the metallic cluster on the cages are our main concerns, trying to get some general rules about the formation mechanism of the large fullerenes encapsulating metallic clusters, providing valuable clue for the formation of carbon nanotubes.

富勒烯是具有确定结构且可溶的碳分子，超大碳笼富勒烯可以看作是两端封口的短碳纳米管，对其进行结构精确测定将有助于揭开碳纳米管形成之谜。然而，目前对富勒烯的研究大多集中在碳笼大小C60到C90之间的物种，而对超大碳笼富勒烯（>C90）的报道非常少，主要是由于大碳笼内部较大空腔导致其稳定性和溶解性降低。本项目拟通过内部金属掺杂来稳定超大碳笼，采用电弧法，原位生成内包金属团簇富勒烯，如含有M2C2或M3N团簇的超大碳笼富勒烯C90-C120等。使用具有高溶解能力的三氯苯或采用“衍生化提取法”，得到10种以上新型大碳笼金属富勒烯异构体，采用多种表征手段，尤其是X-射线单晶衍射法确定其分子结构并适当考察其物理化学性质，期望得到关于超大碳笼金属富勒烯结构稳定性及其形成机理的初步规律，加深对碳纳米管生成过程的理解。

超大碳笼富勒烯可以看作是两端封口的短碳纳米管，对其进行精确的结构测定将有助于揭开碳纳米管形成之谜。本项目提出“内支撑”策略，即通过内部金属团簇掺杂来稳定超大碳笼，有效解决了大碳笼富勒烯内部空腔较大导致其稳定性和溶解性降低的难题。发展了“磁场辅助催化合成”电弧法，获得一系列内包多种金属团簇的超大碳笼富勒烯，如包含Y2C2团簇的C92-C130等；发展了“路易斯酸沉淀法”代替常用的溶剂提取法，结合高效液相色谱分离技术，获得了数十种大碳笼金属富勒烯异构体，并采用多种实验手段对其分子结构和物理化学性质进行了系统表征，发现了一系列新规律。代表性成果如下：（1） 获得一系列内嵌双金属大碳笼富勒烯M2@C2n（M = Y, Er, Lu；2n = 82-86），发现碳笼的限域效应导致内部原本相互排斥的金属离子间成键的反常现象，成果被英国皇家学会Chemistry World突出报道：“中国科学家首次实现了这种难形成的键合...”；（2）采用X-射线单晶衍射手段精确表征了一系列内嵌碳化物团簇大碳笼富勒烯M2C2@C2n（M = Y, La, Er, Lu；2n = 80-98）的结构，发现内部金属团簇构型与碳笼尺寸间选择性匹配的新规律，为设计合成相应的分子器件提供了有益的参考；（3）获得一系列氮化物团簇大碳笼富勒烯M3N@C2n（M = Y, Er, Lu；2n = 80-88），发现内部平面型团簇对碳笼形状的决定性影响；（4）通过优化合成条件，获得了全新的单金属富勒烯物种Eu@C74-88，揭示出内部金属“包入能”对杂化分子结构的影响规律及一系列已知金属富勒烯碳笼间的相互转换规律，对深入理解富勒烯及纳米管的形成机理提供了借鉴；（5） 获得了迄今最大的金属富勒烯碳笼Y2C2@C1(1660)-C108，对其分子结构、稳定性及电化学性质等进行了深入研究；（6）打破了金属团簇富勒烯必包含稀土金属的铁律，成功获得了多例不含稀土元素的金属团簇富勒烯Ti3C3@C80和Ti2C2@C78,82等，发现了全新的C3-环丙烷配位模式，为配位化学提供了新的素材。本项目已发表研究论文17篇，其中在IF>9的期刊发表论文9篇；申请专利2项，培养研究生5名。