内嵌金属富勒烯结构和化学反应性的理论研究

Exploring the nature of interactions between metal and carbon atoms or one metal atom and another one is a very important subject in the science of endohedral metallofullerenes because it is helpful to understand the stabilization of metal atoms (or metallic cluster) to a carbon cage. Herein, by means of a combined quantum chemistry and statistical mechanics, we firstly plan to study the stability differences of various endohedral metallofullerene isomers. In this way, the geometric configuration of those endohedral metallofullerene discovered in experiments can be determined unambiguously. Then, based on the nature bonding orbital (NBO) and Atoms in Molecules (AIM) theory, a systemic investigation will be performed to probe interactions between metal atoms or metal and nonmetal atoms. In terms of those results, we can assess the component of ionic and covalent interactions in those metal-carbon and encapsulated metal-metal bonds, and the ionic model of endohedral metallofullerene can be amended. It can be expected that an intact description of electronic structures and bonding nature of endohedral metallofullerene will be presented after we finish this section. To further understand the chemical reactivity of endohedral metallofullerenes, we will use density functional theory to investigate a series of chemical reactions, including D-A reaction, [2+2] cycloaddition, 1,3-dipole cycloaddition, and Bingel-Hirsch reaction, occurring at different sites of a carbon cage. By comparing the difference of reaction activities, the influence of encapsulated metal atoms or cluster on the chemical reactivity of a C-C bond or a carbon atom will be probed. Finally, some derivatives of divergent endohedral metallofullerenes will be designed according to those basic reactions. We hope that applications of them to photoelectric materials or fullerene polymerization can be achieved.

研究内嵌金属富勒烯的内嵌金属原子与碳原子、金属与金属之间的相互作用有助于深刻理解内嵌金属原子（团簇）对碳笼的稳定化作用。本项目拟首先使用量子化学与统计热力学结合的方法研究内嵌金属富勒烯的稳定性，以确定它们的几何结构。然后，使用NBO理论和AIM方法揭示金属-金属、金属-非金属原子之间的相互作用类型，并在此基础上表征键合作用中离子组分和共价组分的大小，修正现有离子模型，比较完整和准确地揭示内嵌金属富勒烯的电子结构和金属-金属、金属非金属原子之间的成键特征。最后使用DFT方法比较一系列内嵌金属富勒烯上不同类型碳原子或碳-碳键上各种化学反应（D-A反应、[2+2]苯炔加成、1,3-偶极环加成、Bingel-Hirsch加成等）的活性差异，揭示内嵌金属（团簇）对碳笼化学反应性的影响。在此基础上，我们将利用相关反应设计一些内嵌金属富勒烯衍生物，并期望它们能实现高效光电转换或内嵌金属富勒烯的主链聚合。

本项目通过从头算密度泛函理论对新型内嵌金属富勒烯的热力学稳定性、几何结构、理化性质、主客相互作用机制进行了详尽的研究。本项目在研期间的主要工作包括：（1）通过密度泛函理论结合统计热力学分析探究了新颖金属富勒烯（Sc2O@C78、La2C96、Th@C76、Sc2C70、VxSc3-xN@C80、Ti2C2@C82、Sc3X@C80 (X = C, N, and O)、Sc2UN@C80 and Sc2UC@C80、U@C80、U@C2n(70≤2n≤74)）的热力学稳定性；（2）使用自然价键轨道分析和分子中原子的理论对以上提到的金属富勒烯中金属与主族碳之间的相互作用进行研究，揭示了其离子键和共价键的本质，这将对金属富勒烯的离子模型做进一步修正；（3）基于反应动力学以及热力学分析，揭示了金属富勒烯表面上的化学反应机理，主要包括Diels-Alder反应、[2+2]苯炔加成、1，3-偶极反应、Bingel-Hirsch反应等，并提出了影响反应位点选择的决定性因素，揭示了#1911C64的氯化和脱氯分别受动力学和热力学两方面的控制；（4）通过密度泛函理论设计新颖的、高效的主体分子O6-corona[6]arene纳米环，它可以通过非共价相互作用（π-π作用）对富勒烯C60和C70进行有效识别。