Synthesis and Characterization of Two Isomers of Th@C: Th@(9)-C and Th@(5)-C.

Actinide endohedral fullerenes have demonstrated remarkably different physicochemical properties compared to their lanthanide analogues. In this work, two novel isomers of Th@C were successfully synthesized, isolated, and fully characterized by mass spectrometry, X-ray single crystallography, UV-vis-NIR spectroscopy, Raman spectroscopy, and cyclic voltammetry. The molecular structures of the two isomers were determined unambiguously as Th@(9)-C and Th@(5)-C by single-crystal X-ray diffraction analysis. Raman and UV-vis-NIR spectroscopies further confirm the assignment of the cage isomers. Electrochemical gaps suggest that both Th@(9)-C and Th@(5)-C possess a stable closed-shell electronic structure. The computational results further confirm that Th@(9)-C and Th@(5)-C exhibit a unique four-electron charge transfer from the metal to the carbon cage and are among the most abundant isomers of Th@C.