Pyramidal Nd2ScN inside an icosahedral C80 cage

Abstract

Engineering the structure of the M₃N cluster within a fullerene cage by the combination of versatile metal ions is one of the most powerful strategies to build metallofullerenes with fine-tuned structures and properties. However, alongside their compositional versatility, mixed-metal clusters pose a challenge for structural elucidation because of the overlapping positions of different metal atoms. Here, we expand the size of metal ions in M₂ScN@C₈₀ to M = Nd³⁺ (R³⁺ = 0.983 Å), whose large ionic radius results in the pyramidalization of encapsulated Nd₂ScN, which is the first example of a pyramidal M₂ScN cluster inside C₈₀. The combination of the pyramidalization, strong alteration of Nd–N and Sc–N bond lengths, and an overlap of two cluster orientations results in four nitrogen sites, which were unambiguously located by single crystal X-ray diffraction (SC-XRD). We demonstrate that judicious modelling of non-metal and overlapping metal positions is paramount for precise SC-XRD determination of structural parameters in metallofullerenes, which will otherwise suffer from erroneous structural interpretations. These results deepen our understanding of the fascinating M₃N@C₈₀ and pave the way for better control over the fine-tuning of their structures and properties.