A molecular brake hoop for the motion of metal atoms inside fullerene cage

Molecular machines have attracted extensive attention due to their fancy concept and their potential to influence the science and technology. The dynamic motion of encapsulated metallic clusters is a distinctive character for endohedral metallofullerenes. For the development of molecular rotors based on metallofullerenes, the most challenging issue is how to control the motion of untouchable metallic cluster inside fullerene cage. In this work, we report a molecular brake hoop for the motion of metal atoms inside fullerene cage. A cycloparaphenylene of [12]CPP was employed to hoop the metallofullerene and produce two supramolecular complexes of Sc₃N@C₈₀⊂[12]CPP and Sc₂C₂@C₈₂⊂[12]CPP. Moreover, the temperature-dependent ⁴⁵Sc nuclear magnetic resonance spectroscopy (NMR) was employed to detect the motion of internal Sc₃N and Sc₂C₂ clusters. ⁴⁵Sc NMR results reveal that the [12]CPP can slow down the rotation of internal metallic cluster through host-guest interaction, and thus the [12]CPP can be considered as a molecular brake hoop for the internal metal motion of metallofullerenes. Furthermore, by means of this molecular brake hoop, the motion of metal atoms inside fullerene cage have expanded range of velocity. In addition, theoretical calculations on Sc₃N@C₈₀⊂[12]CPP were executed to illustrate the molecular orientation as well as internal Sc₃N rotation. This study would promote the research of endohedral metallofullerene as a molecular rotor.[Figure not available: see fulltext.]