(Invited) Molecular Structures of La2C2@C90-C104: The Effect of Inserting a C2-Unit

Giant fullerenes (e.g. C>90) show clear connections with short carbon nanotubes. Herein we report the X-ray structures of eight EMFs containing a La2C2 cluster, namely, La2C2@C2(41)-C90, La2C2@D3(85)-C92, La2C2@C1(132)-C94, La2C2@C2(157)-C96, La2C2@C1(175)-C98, La2C2@D5(450)-C100, La2C2@Cs(574)-C102, and La2C2@C2(816)-C104. It is evident that the cage length increases roughly along with increasing of the carbon atom number, resulting in an increase of the La-La distance. This is a clear indication that giant fullerenes tend to grow along the long axis to achieve a tubular appearance. Encapsulation of a large La2C2 cluster inside D5(450)-C100 induces a 5% axial compression of the cage, as compared with the structure of La2@D5(450)-C100.[1] Moreover, it is demonstrated that the defective cage of C2(816)-C104 is a starting point to form the other tubular cages known so far, i.e., D5(450)-C100, Cs(574)-C102, and D3d(822)-C104, presenting evidence for the top-down formation mechanism of fullerenes.[2] Overall, our experimental results have unambiguously confirmed that insertion of a C2-unit exerts a synergistic effect in stabilizing these giant cages. [3] References ： Cai, W.; Bao, L.; Zhao, S.; Xie, Y-P.; Akasaka, T.; Lu J. Am. Chem. Soc. 2015, 137, 10292-10296. Cai, W.; Li, F-F.; Bao, L.; Xie, Y-P.; Lu J. Am. Chem. Soc. 2016, 138, 6670-6675. Zhao, S.; Zhao, P. Cai, W.; Bao, L.; Chen, M.; Xie, Y-P.; Zhao, X.; Lu J. Am. Chem. Soc. 2017, 139, 4724–4728.