Isomeric Sc₂O@C₇₈ Related by a Single-Step Stone–Wales Transformation: Key Links in an Unprecedented Fullerene Formation Pathway

Abstract

High Resolution Image Download MS PowerPoint Slide It has been proposed that the fullerene formation mechanism involves either a top-down or bottom-up pathway. Despite different starting points, both mechanisms approve that particular fullerenes or metallofullerenes are formed through a consecutive stepwise process involving Stone–Wales transformations (SWTs) and C 2 losses or additions. However, the formation pathway has seldomly been defined at the atomic level due to the missing-link fullerenes. Herein, we present the isolation and crystallographic characterization of two isomeric clusterfullerenes Sc 2 O@ C 2 v (3) -C 78 and Sc 2 O@ D 3 h (5) -C 78, which are closely related via a single-step Stone–Wales (SW) transformation. More importantly, these novel Sc 2 O@C 78 isomers represent the key links in a well-defined formation pathway for the majority of solvent-extractable clusterfullerenes Sc 2 O@C 2 n ( n = 38–41), providing molecular structural evidence for the less confirmed fullerene formation mechanism. Furthermore, DFT calculations reveal a SWT with a notably low activation barrier for these Sc 2 O@C 78 isomers, which may rationalize the established fullerene formation pathway. Additional characterizations demonstrate that these Sc 2 O@C 78 isomers feature different energy bandgaps and electrochemical behaviors, indicating the impact of SW defects on the energetic and electrochemical characteristics of metallofullerenes.