(Invited) Stabilization of Giant Fullerenes C2(41)-C90 , D3(85)-C9 2 , C1(132)-C94 , C2(157)-C96 , C1(175)-C98 , D5(450)-C100 , Cs(574)-C102 and C2(816)-C104 by Encapsulation of a Large La2C2 Cluster

Endohedral metallofullerenes (EMFs) with a composition of M2C2n may exist as di-EMFs, M2@C2n, or as carbide cluster metallofullerenes (CCMFs), M2C2@C2n-2. Thus care needs to be taken to distinguish between these two possibilities. However, there are rare examples for M2C2@C90-104 and the configuration of the carbide cluster is not clear in these cages. Herein we report the isolation and single-crystal X-ray crystallographic characterization of eight unprecedented EMFs containing a La2C2 cluster, namely, La2C2@C2(41)-C9 0, La2C2@D3(85)-C92, La2C2@C1(132)-C9 4, 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 and the Ni···cage distance as well. 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. Moreover, it is demonstrated that the defective cage of C2(816)-C104 is a starting point to form the other three 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. Overall, our experimental results have unambiguously confirmed that La2C92-10 6 tend to form CCMFs La2C2@C90- 104 instead of di-EMFs La2@C92-10 6 . R eferences： [1] Lu, X.*; Akasaka, T.*; Nagase, S. Acc. Chem. Res. 2013, 46, 1627-1635. [2] Cai, W.; Bao, L.; Zhao, S.; Xie, Y-P.; Akasaka, T.; Lu X. J. Am. Chem. Soc. 2015, 137, 10292-10296. [3] Cai, W.; Li, F-F.; Bao, L.; Xie, Y-P.; Lu X*. J. Am. Chem. Soc. 2016, 138, 6670-6675.