Making connections between metallofullerenes and fullerenes: electrochemical investigations

The square-wave voltammetry for a series of related fullerenes and metallofullerenes measured in pyridine solutions containing 0.10 M tetra-n-butylammonium perchlorate is reported. Several dimetallic metallofullerenes, M-2@C-x (where M=Sc or Er, and x=82 or 84), are found to have similar voltammetric responses regardless of metal identity or carbon number. Assignment of formal charges to the fullerene cage suggests that these metallofullerenes are isoelectronic and have related molecular orbital structures. The voltammetry of the empty C-82 and D-2d-C-84 cages are also alike, but are different from the square-wave voltammetry of the C-60, C-70, and D-2-C-84. The similarity of the voltammetry for C-82 and D-2d-C-84, and for the C-82 and C-84 metallofullerenes is consistent with a related electronic structure for these species. There, however, is no clear correspondence between the voltammetry of the metallofullerenes and their corresponding empty cage fullerene. (C) 2000 Elsevier Science Ltd. All rights reserved.