Synthesis and Isolation of the Titanium-Scandium Endohedral Fullerenes-Sc2TiC@Ih-C80, Sc2TiC@D5h-C80 and Sc2TiC2@Ih-C80: Metal Size Tuning of the TiIV/TiIII Redox Potentials

Author(s): Junghans, K; Ghiassi, KB; Samoylova, NA; Deng, Q; Rosenkranz, M; Olmstead, MM; Balch, AL; Popov, AA | Abstract: © 2016 The Authors. Published by Wiley-VCH Verlag GmbH a Co. KGaA. The formation of endohedral metallofullerenes (EMFs) in an electric arc is reported for the mixed-metal Sc–Ti system utilizing methane as a reactive gas. Comparison of these results with those from the Sc/CH4and Ti/CH4systems as well as syntheses without methane revealed a strong mutual influence of all key components on the product distribution. Whereas a methane atmosphere alone suppresses the formation of empty cage fullerenes, the Ti/CH4system forms mainly empty cage fullerenes. In contrast, the main fullerene products in the Sc/CH4system are Sc4C2@C80(the most abundant EMF from this synthesis), Sc3C2@C80, isomers of Sc2C2@C82, and the family Sc2C2 n(2 n=74, 76, 82, 86, 90, etc.), as well as Sc3CH@C80. The Sc–Ti/CH4system produces the mixed-metal Sc2TiC@C2 n(2 n=68, 78, 80) and Sc2TiC2@C2 n(2 n=80) clusterfullerene families. The molecular structures of the new, transition-metal-containing endohedral fullerenes, Sc2TiC@Ih-C80, Sc2TiC@D5h-C80, and Sc2TiC2@Ih-C80, were characterized by NMR spectroscopy. The structure of Sc2TiC@Ih-C80was also determined by single-crystal X-ray diffraction, which demonstrated the presence of a short Ti=C double bond. Both Sc2TiC- and Sc2TiC2-containing clusterfullerenes have Ti-localized LUMOs. Encapsulation of the redox-active Ti ion inside the fullerene cage enables analysis of the cluster–cage strain in the endohedral fullerenes through electrochemical measurements.