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  • A missing link in the transformation from asymmetric to symmetric metallofullerene cages implies a top-down fullerene formation mechanism.

A missing link in the transformation from asymmetric to symmetric metallofullerene cages implies a top-down fullerene formation mechanism.

Nature chemistry (2013-09-24)
Jianyuan Zhang, Faye L Bowles, Daniel W Bearden, W Keith Ray, Tim Fuhrer, Youqing Ye, Caitlyn Dixon, Kim Harich, Richard F Helm, Marilyn M Olmstead, Alan L Balch, Harry C Dorn
ABSTRACT

Although fullerenes were discovered nearly three decades ago, the mechanism of their formation remains a mystery. Many versions of the classic 'bottom-up' formation mechanism have been advanced, starting with C2 units that build up to form chains and rings of carbon atoms and ultimately form those well-known isolated fullerenes (for example, I(h)-C60). In recent years, evidence from laboratory and interstellar observations has emerged to suggest a 'top-down' mechanism, whereby small isolated fullerenes are formed via shrinkage of giant fullerenes generated from graphene sheets. Here, we present molecular structural evidence for this top-down mechanism based on metal carbide metallofullerenes M2C2@C1(51383)-C84 (M = Y, Gd). We propose that the unique asymmetric C1(51383)-C84 cage with destabilizing fused pentagons is a preserved 'missing link' in the top-down mechanism, and in well-established rearrangement steps can form many well-known, high-symmetry fullerene structures that account for the majority of solvent-extractable metallofullerenes.

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