Isolation and Crystallographic Characterization of Lu3N@C2n (2n=80–88): Cage Selection by Cluster Size

The small Sc3N cluster has only been found in such small cages as C2n (2n=68, 78, 80, 82), whereas the large M3N (M=Y, Gd, Tb, Tm) clusters choose those larger cages C2n (2n=82–88). Herein, concrete experimental evidence is presented to establish the size effect of the internal metallic cluster on selecting the outer cage of endohedral metallofullerenes (EMFs) by using a medium‐sized metal, lutetium, which possesses an ionic radius between Sc and Gd. A series of lutetium‐containing EMFs have been obtained and their structures are unambiguously determined as Lu3N@Ih(7)‐C80, Lu3N@D5h(6)‐C80, Lu3N@C2v(9)‐C82, Lu3N@Cs(51365)‐C84, Lu3N@D3(17)‐C86, and Lu3N@D2(35)‐C88 by single‐crystal X‐ray diffraction crystallography. It was confirmed that the encaged Lu3N cluster always adopts a planar geometry in Lu3N@C80‐88 isomers to ensure substantial metal‐cage/metal‐nitrogen interactions. As a result, the Lu3N cluster selects the C2v(9)‐C82 cage, which also encapsulates Sc3N, instead of the Cs(39663)‐C82 cage which is more suitable for M3N (M=Y, Gd, Tb, Tm). However, different from Sc3N, Lu3N can also template the C84–88 cages which are absent for Sc3N‐containing EMFs, confirming clearly the size effect of the internal cluster on selecting the outer cage. Size effect of the internal metallic cluster on the outer cage is deduced from the unambiguous crystallographic results for a series of lutetium‐containing trimetallic nitride endohedral metallofullerenes, namely Lu3N@Ih(7)‐C80, Lu3N@D5h(6)‐C80, Lu3N@C2v(9)‐C82, Lu3N@Cs(51365)‐C84, Lu3N@D3(17)‐C86 and Lu3N@D2(35)‐C88, thus presenting a practical strategy for the controlled synthesis of metallofullerenes with desired cage structures by choosing a suitable metal.