Nitride clusters in fullerene cages

focus of fundamental and applied materials research since the first preparation of macroscopic C60 quantities by Krätschmer et al. in 1990 [1]. The ability to encage atoms and small molecules opened the door to new structures which are highly reactive under standard conditions. Up to now low production yields and a time consuming multi stage separation hampered the search for applications of endohedral fullerenes. Fullerenes with a triscandium nitride cluster inside as for instance Sc3N@C80 (Fig. 1) have been discovered in 1999, when molecular nitrogen was entering a fullerene reactor accidentally [2]. In our present work the influence of the reactor atmosphere on the fullerene formation and distribution has been studied systematically. Various nitrogen sources in combination with different group 3 and rare earth metals have been investigated. A significant enhancement of the Sc3N@C80 yield in the fullerene extract was first obtained replacing N2 by calcium carbamide. Even a selective Sc3N@C80 formation with relative yields up to 90 % was achieved by the use of ammonia gas. Our „reactive atmosphere fullerene burning method“ has been successfully applied to produce other trimetal nitride fullerenes, e.g. Ho3N@C80, Er3N@C80 or Er2Sc@C80 as the main fullerene structure in the soot extract [3]. This is illustrated by the high-performance liquid chromatogram in Fig. 2, which is strongly dominated by the Ho3N@C80 peak. By a single extraction step to remove hydrocarbon byproducts these endohedrals are available in reasonable purities. To provide analytical grade fullerenes only one chromatographic separation step is required, compared to the multistage standard technique for the isolation of endohedral fullerenes. Our approach represents an important progress towards a low cost synthesis of these fascinating structures.