Metallofullerenes DOI: 10.1002/ange.200802777 Trimetallic Nitride Endohedral Fullerenes: Experimental and Theoretical Evidence for the M 3 N 6+ @C 2n 6 model** Manuel N. Chaur, Ramón Valencia, Antonio Rodríguez-Fortea, Josep M. Poblet,* and Luis Echegoyen* The discovery of Sc 3 N@C 80 by Dorn and co-workers in 1999 represented the beginning of a new field in the chemistry of endohedral fullerenes. [1] In less than a decade, the family of the metallic nitride endohedral fullerenes (MNEFs) was considerably expanded with the encapsulation of a new Group III metal (Y), [2] lanthanides (Er, Ho, Lu, Tm, Gd, Dy, Tb, Nd, Pr, and Ce) [2–10] and mixed-metal clusters. [11] Upon increasing the size of the encapsulated metal (from Sc to Gd), the yield of production of MNEFs usually decreases and a distribution of metallofullerenes is obtained, with cages ranging from C 68 to C 88 . [9] The C 80 cage, however, remains the most abundant product. Recently, Echegoyen and co- workers reported the preparation of clusterfullerenes, such as Nd 3 N@C 2n (40  n  49), and observed the predominant formation of the larger cage C 88 . [9] It has been assumed that there is a formal transfer of six electrons from the encapulated guest to the fullerene cage. Poblet and co-workers associated the exceptional stability of C 80 (I h ) to the large HOMO–LUMO gap of the MNEF after encapsulation of the metallic nitride (MN) cluster by the carbon cage. [12] Based on the electron-transfer model, they not only rationalized the occurrence of the most abundant species that have been experimentally characterized, they were also able to predict the cage isomer for systems that have yet to be prepared. [13, 14] Popov and Dunsch performed a systematic and detailed study for the most stable isomers of M 3 N@C 2n (M = Sc, Y; 34  n  49). In most of the cases, the cage structures predicted by both groups coincide. [15] Herein we report the synthesis, electrochemistry, and theoretical characterization of the large MNEFs M 3 N@C 2n family (M = La, Ce, and Pr; n = 46 and 48). The combined electrochemical and computational analyses of the series from M 3 N@C 80 to M 3 N@C 96 verify the ionic model M 3 N 6+ @ C 2n 6 for MNEFs. M 3 N@C 2n (M = La, Ce, and Pr) metallofullerenes were synthesized in a conventional Krätschmer–Huffman arc reactor using a reactive gas atmosphere. [2] Graphite rods were packed with the corresponding metal oxide and graphite powder and then burned in a helium/ammonia atmosphere. The larger MNEFs were purified, isolated, and identified using HPLC, mass spectrometry, and energy dispersive spectroscopy (EDS) (see Supporting Information). Electro- chemical studies were conducted in a 0.05 m solution of NBu 4 PF 6 in o-dichlorobenzene (o-DCB). A 2 mm diameter glassy carbon disk was used as the working electrode. Ferrocene was added at the end of the experiments for internal reference of the potentials. Figure 1 shows the cyclic voltammograms (CVs) and the Osteryoung square-wave voltametry (OSWV, anodic part) of M 3 N@C 92 (M = La, Ce, and Pr) metallofullerenes. These compounds exhibit two irreversible reduction steps and a Figure 1. Cyclic voltammograms and Osteryoung square-wave voltam- metry (OSWV) of La 3 N@C 92 , Ce 3 N@C 92 , and Pr 3 N@C 92 in 0.05 m NBu 4 PF 6 /o-DCB with ferrocene as internal standard and a scan rate of 0.1 Vs 1 . [*] R. Valencia, Dr. A. Rodríguez-Fortea, Prof. Dr. J. M. Poblet Departament de Química Física i Inorgànica Universitat Rovira i Virgili c/Marcel·lí Domingo s/n, 43007 Tarragona (Spain) Fax: (+ 34) 977-559-563 E-mail: josepmaria.poblet@urv.cat M. N. Chaur, Prof. Dr. L. Echegoyen Department of Chemistry, Clemson University 219 Hunter Laboratories, Clemson, SC 29631-0973 (USA) Fax: (+ 1) 864-656-6613 [**] We acknowledge support from the MEC of Spain (projects CTQ2005-06909-C02-01/BQU and the Ramón y Cajal Program (A.R.F.)) and from the DGR of the Autonomous Government of Catalonia (2005SGR-00104 and a doctoral fellowship (R.V.)). Financial support from the National Science Foundation (Grant number CHE-0509989) is also greatly appreciated (M.N.C. and L.E.). The material presented herein is based on work supported by the National Science Foundation while L.E. was working there. All opinions, findings, conclusions, or recommendations expressed herein are those of the authors and do not necessarily reflect the views of the National Science Foundation. (M = La, Ce, and Pr; n = 46 and 48) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.200802777. Angewandte Chemie 1453 Angew. Chem. 2009, 121, 1453 –1456  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim