Density Functional Study On Endohedral Metallofullerenes

Modern scientific computations, especially those based on the density functional theory (DFT), offer us a powerful tool to explore various aspects of chemistry, materials sciences and condensed matter physics, thanks to the rapid developments of related theories, algorithms as well as computer hardware. In this dissertation, by means of DFT computations, we studied a series of endohedral complexes based on representive fullerene cages, namely C68, C72, C78, C80 and C82 as well as recently proposed boron fullerene B80. The trapped metal species include La, La2, Sc3N and Sc3NC clusters. The geometrical structures, electronic properties, metal motion as well as spectrum features of the corresponding endohedral metallofullerenes have been investigated.The dissertation is structured as follows.In Chapter 1, we review the exciting discovery of fullerenes as well as endohedral metallofullerenes (EMFs). Their current research status and future prospects are also introduced.In Chapter 2, we introduce the DFT method as well as the software packages involved in this dissertation.In Chapter 3, the motion of a single lanthanum atom inside a C82(C2v) fullerene cage has been investigated by means of the hybrid density functional method (B3LYP). The obtained potential energy surface (PES) suggests that the encapsulated La atom can oscillate only around the minimum energy potential well, which is apparently different from the scenario of a giant bowl-shaped movement at room temperature described by Nishibori et al. Interestingly, our calculations show that the La atom may probably undergo a boat-shaped movement when the temperature is high enough. In addition, the computed 13C NMR spectrum of the C2v [La@C82]-is in an excellent agreement with the experimental nuclear magnetic resonance (NMR) spectrum, which confirms that the isomer of La@C82 with the C2v symmetry is the most stable.In Chapter 4, by means of relativistic density functional theory method (DFT) based on the zeroth-order regular approximation (ZORA), we compare the two isomers, i.e.#10611 and #10958 of La2@C72 in the view of both kinetic and thermodynamic stability. The calculated 139La chemical shift for isomer #10611 is in excellent agreement with the experimental observation, suggesting that isomer #10611 is the main configuration of this metallofullerene molecule. To further confirm this conclusion, the electronic absorption spectra of these two isomers are simulated using relativistic time-dependent density functional theory (TDDFT) method, again isomer #10611 agrees reasonably well with the experimental results.In Chapter 5, the geometries, electronic and spectroscopic properties of two representative endohedral derivatives of Bgo fullerene, namely La2@B80 and Sc3N@B80, and the possibility for their production were investigated by means of density functional computations. The very favorable binding energies suggest a considerable possibility to experimentally realize these novel endohedral metalloborofullerenes. Infrared absorption spectra and 11B NMR spectra were also computed to assist future experimental characterization.In Chapter 6, inspired by the recent experimental observation, we explored the possibility for encapsulating an unusual Sc3NC unit in three representative fullerene cages, namely, C68, C78 and C80, by means of density functional computations. The geometries, electronic and electrochemical redox properties of the corresponding EMFs, Sc3NC@C2n (2n = 68,78 and 80), were investigated. These novel EMFs all have very favorable binding energies, implying a considerable possibility for experimental realization.The recently observed m/z= 1121 peak in the mass spectroscopy was characterized as Sc3NC@Cgo. Notably the lowest-energy isomer of Sc3NC@C78 has a non-IPR C78 outer cage, the possibility to accommodate five atoms inside a fullerene as small as C68 is also intriguing. Moreover, the intracluster and metal-cage covalent interactions were revealed by quantum theory of atoms in molecules study. Infrared absorption spectra and 13C NMR spectra were also computed to assist future experimental characterization.