Trapping a C2 radical in endohedral metallofullerenes: Synthesis and structures of (Y2C2)@C82 (isomers I, II, and III)

Three isomers of yttrium carbide (Y 2 C 2 ) endohedral metallofullerenes, i.e., (Y 2 C 2 )@C 8 2 (I, II, III), have been synthesized and chromatographically isolated for the first time. The structures of (Y 2 C 2 )@C 8 2 (I, II, III) metallofullerenes have been characterized by 1 3 C NMR measurements, whose molecular symmetries have been determined to be C s , C 2 v , and C 3 v , respectively. In addition, a pure diyttrium metallofullerene, Y 2 @C 8 2 (III), has also been synthesized and structurally characterized. The 1 3 C NMR structural analyses indicate that (Y 2 C 2 )@C 8 2 (III) has exactly the same fullerene cage as that of Y 2 @C 8 2 (III). On the basis of the results, we propose a C 2 -trapping and loss of growth mechanism of dimetallofullerenes of (M 2 C 2 )@C 8 2 and M 2 @C 8 2 from M 2 @C 8 4 , respectively.