Acta Physico-Chimica Sinica

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Stability and Formation Mechanism of Endohedral Metal Carbonitride Clusterfullerenes

Junjie Shi1, Ziqi Hu2, Yihao Yang2, Yuxiang Bu1, Zujin Shi2   

  1. 1 School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, P. R. China;
    2 National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China
  • Received:2019-07-25 Revised:2019-08-09 Accepted:2019-08-09 Published:2019-08-14
  • Contact: Yuxiang Bu, Zujin Shi E-mail:byx@sdu.edu.cn;zjshi@pku.edu.cn
  • Supported by:
    This project was supported by the National Natural Science Foundation of China (21875002, 21873056) and National Basic Research Program of China (2017YFA024901).

Abstract: Fullerene molecules have nano-scale cavities in which various metal or metal clusters of different sizes can be embedded to form metallofullerenes with unique core-shell structures. The physical and chemical properties of metallofullerenes can be modified through the interaction between the encapsulated metals and the fullerene cages. As such, the investigation of metallofullerenes with novel structures has been a principal research focus in the field of fullerenes. In this study, we investigated the size matching effect between encapsulated clusters and fullerene cages for the endohedral metal carbonitride clusterfullerenes in order to discover new metallofullerenes. The stability and electronic structure of the metallofullerenes formed by encapsulating M3NC clusters (M=Y, La, Gd) into D2(186)-C96 and D2(35)-C88 fullerenes were studied using quantum chemical calculations. It was found that the fullerene cages formed stable structures by accepting six electrons transferred from the encapsulated clusters. The change in configuration of the encapsulated clusters was clarified by a comparison with the corresponding M3N@C2n metal nitride clusterfullerenes; the size matching effect between M3NC cluster and fullerene cage was elucidated on the basis of the calculated results and previous studies on Sc3NC@Ih(7)-C80. For the D2(186)-C96 fullerene, the Gd3NC cluster was found to have smaller changes in the configuration as compared with the La3NC cluster, proving that Gd3NC is more suitable than La3NC for encapsulation in the D2(186)-C96 fullerene cage. In addition, it was determined that the La3NC cluster requires a large structural change to maintain its planar configuration. For the D2(35)-C88 fullerene cage, the Y3NC cluster is more suitable than Gd3NC for encapsulation owing to the smaller size of the Y3NC cluster. The spatial distribution of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of Gd3NC@D2(186)-C96 were found to be similar to those of Gd3N@D2(186)-C96. However, a unique endohedral cluster-based occupied molecular orbital was found for Gd3NC@D2(186)-C96. This orbital is derived from the interaction between the NC unit and the Gd atoms. The spatial distribution of the HOMO of Y3NC@D2(35)-C88 is similar to that of Y3N@D2(35)-C88, while the LUMO of Y3NC@D2(35)-C88 has a much larger contribution from the endohedral cluster as compared to Y3N@D2(35)-C88. Thus, the addition of a carbon atom in the cluster has a remarkable impact on the electronic structure of the metallofullerenes. With respect to structural characteristics, we found that the three fullerene cages, D2(186)-C96, D2(35)-C88, and Ih(7)-C80, have a uniform distribution of five-membered carbon atom rings; these fullerenes can be greatly stabilized in the form of C2n6- anions. However, the formation mechanism of fullerenes and metallofullerenes, at present, is poorly understood. Based on the structural analysis, we propose a direct mechanism for the formation of fullerenes without the Stone-Wales isomerization, i.e., the rearrangement of five-membered rings through the addition of carbon atoms and the transformation into larger carbon cages while maintaining stable structural units.

Key words: Fullerene, Metallofullerene, Density functional theory, Electronic structure, Rare-earth element

MSC2000: 

  • O641