The hidden features of fullerene rotation in the crystal lattice

Abstract

Rotational dynamics in the crystal lattice is a characteristic attribute of fullerenes caused by their spherical shape. It lies in the background of various multifaceted phenomena, ranging from severe disorder, often hampering diffraction studies of fullerenes, to rotational order–disorder transitions or controlled switching of molecular orientations in nanoscale devices. Understanding these dynamics and their real-space presentation still remains a complex problem, especially for endohedral metallofullerenes, as their encapsulated species may show additional rotational degrees of freedom. In this work, we used variable-temperature single-crystal X-ray diffraction (VT SC-XRD) to elaborate on the phase transition in Sc₃N@C₇₀ crystals caused by the rotation of fullerene molecules. Snapshots of the molecular rotation taken with 10 K steps in a broad temperature range provided in-depth description of the process and revealed details usually overlooked by SC-XRD studies of metallofullerenes. In particular, analysis of thermal ellipsoids at various temperatures allowed to distinguish hidden static disorder from apparent dynamic disorder caused by thermal motion. The results mark a leap to the fundamental understanding of the unique metallofullerene structural characters, paving the way to control fullerene movement state in single molecule devices built from fullerenes.