Crystallographic Characterization of Er2C2@C80-88: Cluster Stretching with Cage Elongation

Six dierbium carbide endohedral metallofullerenes have been synthesized and chromatographically isolated. Single-crystal X-ray diffractometry unambiguously ascertains their structures as Er2C2@C-2v(5)-c(80), Er2C2@C-5(6)-c(82), Er(2)c(2) @(15)-C-84, Er2C2@C-2v (9)-C-86, Er2C2@C-5(15)-C-86, and Er2C2@C-5(32)-C-88, respectively. The Er center dot center dot center dot Er distances of the major erbium sites inside the C-5(6)-C-82, C-2v(5)-C-80, C-5(15)-C-84, C-5(15)-C-86, C-2v(9)-C-86, and C-5(32)-C-88 cages are 3.801, 3.860, 4.062, 4.066, 4.307, and 4.372 angstrom, respectively, which show a linear tendency with an increase in the major axis of the fullerene cages (8.064, 8.238, 8.508, 8.582, 8.815, and 8.953 angstrom, respectively). Furthermore, the electrochemical and molecular orbital analyses reveal that the redox chemistry of the Er2C2@C(80-88 )isomers is associated with the carbon cage, which is different from the situations found for typical dimetallofullerenes, such as Y-2@C-82, Er-2@C82-84, and Lu-2@C-82,(86) isomers, which show metal-dependent oxidation processes, indicating the importance of C-2 insertion in carbide cluster metallofullerenes.