Small-bandgap endohedral metallofullerenes in high yield and purity

Abstract

The idea¹ that fullerenes might be able to encapsulate atoms and molecules has been verified by the successful synthesis of a range of endohedral fullerenes, in which metallic or non-metallic species are trapped inside the carbon cage^{2,3,4,5,6,7,8,9,10,11,12,13}. Metal-containing endohedral fullerenes have attracted particular interest as they might exhibit unusual material properties associated with charge transfer from the metal to the carbon shell. However, current synthesis methods have typical yields of less than 0.5%, and produce multiple endohedral fullerene isomers, which makes it difficult to perform detailed studies of their properties. Here we show that the introduction of small amounts of nitrogen into an electric-arc reactor allows for the efficient production of a new family of stable endohedral fullerenes encapsulating trimetallic nitride clusters, Er_xSc_3-xN@C₈₀ (x = 0–3). This ‘trimetallic nitride template’ process generates milligram quantities of product containing 3–5% Sc₃N@C₈₀, which allows us to isolate the material and determine its crystal structure, and its optical and electronic properties. We find that the Sc₃N moiety is encapsulated in a highly symmetric, icosahedral C₈₀ cage, which is stabilized as a result of charge transfer between the nitride cluster and the fullerene cage. We expect that our method will provide access to a range of small-bandgap fullerene materials, whose electronic properties can be tuned by encapsulating nitride clusters containing different metals and metal mixtures.