Regulating the electronic and spin structure of endohedral metallofullerenes: a case investigation of Sc₃N@C₈₀ and Sc₃C₂@C₈₀

The electrochemical and paramagnetic properties of endohedral metallofullerenes (EMFs) have drawn extensive attention due to their huge potential in the fields of molecular devices, biomedicines, quantum information processing, etc. Exohedral modification of the fullerene carbon cage, such as in the classical Prato reaction, is an effective and facile approach to regulate the electronic structure and molecular dynamics of EMFs. In this work, novel pyrrolidine products of Sc3N@C80 and Sc3C2@C80 were successfully synthesized via Prato reactions using L-cysteine and paraformaldehyde. Structure characterizations demonstrated that two regioisomers with a [5,6] and a [6,6] cycloaddition on the Ih-C80 cage were obtained both for Sc3N@C80 and Sc3C2@C80. Besides, the [6,6]-monoadduct of Sc3N@C80 was thermally stable while the [5,6]-monoadduct exhibited a retro-cycloaddition ability to recover the pristine Sc3N@C80. Electrochemical measurements revealed that the redox potential of Sc3N@C80 could be tuned via such exohedral modifications. Furthermore, the paramagnetic property and internal dynamics of the encapsulated Sc3C2 cluster of Sc3C2@C80 can be well-regulated by controlling the spin density of the molecule. The present work could provide a new approach to regulate the electronic and/or spin structure of EMFs.