Synthesis and Isolation of the Titanium–Scandium Endohedral Fullerenes—Sc(2)TiC@I(h)‐C(80), Sc(2)TiC@D (5h)‐C(80) and Sc(2)TiC(2)@I(h)‐C(80): Metal Size Tuning of the Ti(IV)/Ti(III) Redox Potentials

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/CH(4) and Ti/CH(4) systems 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/CH(4) system forms mainly empty cage fullerenes. In contrast, the main fullerene products in the Sc/CH(4) system are Sc(4)C(2)@C(80) (the most abundant EMF from this synthesis), Sc(3)C(2)@C(80), isomers of Sc(2)C(2)@C(82), and the family Sc(2)C(2 n) (2 n=74, 76, 82, 86, 90, etc.), as well as Sc(3)CH@C(80). The Sc–Ti/CH(4) system produces the mixed‐metal Sc(2)TiC@C(2 n) (2 n=68, 78, 80) and Sc(2)TiC(2)@C(2 n) (2 n=80) clusterfullerene families. The molecular structures of the new, transition‐metal‐containing endohedral fullerenes, Sc(2)TiC@I(h)‐C(80), Sc(2)TiC@D (5h)‐C(80), and Sc(2)TiC(2)@I(h)‐C(80), were characterized by NMR spectroscopy. The structure of Sc(2)TiC@I(h)‐C(80) was also determined by single‐crystal X‐ray diffraction, which demonstrated the presence of a short Ti=C double bond. Both Sc(2)TiC‐ and Sc(2)TiC(2)‐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.