Herein we report the isolation and single-crystal X-ray crystallographic characterization of eight unprecedented 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 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 La2C92-106 tend to form CCMFs La2C2@C90-104 instead of di-EMFs La2@C92-106.
 Lu, X.*; Akasaka, T.*; Nagase, S. Acc. Chem. Res. 2013, 46, 1627-1635.