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

• Published in: Nature chemistry Vol. 5; no. 10; pp. 880 - 885
• Main Authors: Zhang, Jianyuan, Bowles, Faye L., Bearden, Daniel W., Ray, W. Keith, Fuhrer, Tim, Ye, Youqing, Dixon, Caitlyn, Harich, Kim, Helm, Richard F., Olmstead, Marilyn M., Balch, Alan L., Dorn, Harry C.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.10.2013; Nature Publishing Group
• Subjects: 639/638/440; 639/925/357/73; Analytical Chemistry; Biochemistry; Carbon; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Crystallography, X-Ray; Fullerenes; Fullerenes - chemistry; Gadolinium - chemistry; Graphene; Inorganic Chemistry; Magnetic Resonance Spectroscopy; Molecular Structure; Organic Chemistry; Physical Chemistry; Solvents; Solvents - chemistry; Symmetry; Yttrium - chemistry; United States > US; Virginia
• ISSN: 1755-4330; 1755-4349
• DOI: 10.1038/nchem.1748

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 C 2 units that build up to form chains and rings of carbon atoms and ultimately form those well-known isolated fullerenes (for example, I h -C 60 ). 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 M 2 C 2 @ C 1 (51383)-C 84 (M = Y, Gd). We propose that the unique asymmetric C 1 (51383)-C 84 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. An asymmetric pentalene-containing C 1 (51383)-C 84 fullerene cage is found in two different metal carbide metallofullerenes. This particular cage can, in simple steps, rearrange into many well-known fullerene cages that are more stable and more symmetric, suggesting it is likely that metallofullerenes are generated by a ‘top-down’ formation mechanism.