Small-bandgap endohedral metallofullerenes in high yield and purity

The idea(1) that fullerenes might be able to encapsulate atoms and molecule s has been verified by the successful synthesis of a range of endohedral fu llerenes, in which metallic or nan-metallic species are trapped inside the carbon cage(2-13). Metal-containing endohedral fullerenes have attracted pa rticular interest as they might exhibit unusual material properties associa ted with charge transfer from the metal to the carbon shell. However, curre nt synthesis methods have typical yields of less than 0.5%, and produce mul tiple endohedral fullerene isomers, which makes it difficult to perform det ailed studies of their properties. Here we show that the introduction of sm all amounts of nitrogen into an electric-are reactor allows for the efficie nt production of a new family of stable endohedral fullerenes encapsulating trimetallic nitride clusters, ErxSc3-xN@C-80 (x = 0-3). This 'trimetallic nitride template' process generates milligram quantities of product contain ing 3-5% Sc3N@C-80, which allows us to isolate the material and determine i ts crystal structure, and its optical and electronic properties. We find th at the Sc3N moiety is encapsulated in a highly symmetric, icosahedral C-80 cage, which is stabilized as a result of charge transfer between the nitrid e cluster and the fullerene cage. We expect that our method will provide ac cess to a range of small-bandgap fullerene materials, whose electronic prop erties can be tuned by encapsulating nitride clusters containing different metals and metal mixtures.