Dy@D2(21)-C84: isolation and crystallographic characterization of a rare trivalent C84-based monometallofullerene

Abstract

Monometallofullerenes (mono-EMFs), which only contain one metal atom inside the fullerene cage, are the most basic yet crucial prototypes to understand the structures and characteristics of EMFs. However, although trivalent mono-EMFs are relatively abundant, M@C₈₂ dominates the category so that larger fullerene cages (>C₈₂) have seldom been isolated and structurally elucidated possibly because of their low production yield and poor kinetic stability. Herein, for the first time, a dysprosium-containing mono-EMF with a C₈₄ cage, namely, Dy@D₂(21)-C₈₄, has been successfully synthesized and obtained by using a facile method involving Lewis-acid treatment and HPLC separations. Unambiguous X-ray results demonstrate that the C₈₄ cage possesses the rare D₂(21) symmetry, and all disordered Dy sites distribute along a band of ten contiguous hexagons, demonstrating the unique interaction between the trivalent Dy ion and C₈₄ cage. Notably, this is the first instance of a trivalent M³⁺ (M = rare earth metals) and a D₂(21)-C₈₄ cage-based mono-EMF isomer that has been documented. Further theoretical calculations confirm its prevailing at high temperatures for EMF formation, and also reveal that the encapsulation of a trivalent Dy ion in this carbon cage is energetically more favorable than those of other C₈₄-based mono-EMFs. This work not only adds a precious member with large cages (>C₈₂) to the renowned trivalent mono-EMF family but also provides new insights into the intriguing metal–cage interactions of such novel EMFs for deeply understanding their unique structures and stabilities.