Th@ C 2 (14)-C 86 and Th@ C 3 (18)-C 86 : two missing C 86 isomers stabilized by the encapsulation of thorium

Two missing cage isomers of C 86 have been successfully stabilized by the encapsulation of the actinide ion Th. The two novel isomers of Th@C 86 were synthesized using the arc-discharge method and characterized using mass spectrometry, single-crystal X-ray crystallography, UV-vis-NIR spectroscopy and DFT calculations. The molecular structures of the two isomers were unambiguously assigned to Th@ C 2 (14)-C 86 and Th@ C 3 (18)-C 86 by crystallographic analysis. Both of these cage isomers of C 86 have been predicted by computational studies but have never been experimentally confirmed until now. DFT computation reveals that both Th@ C 2 (14)-C 86 and Th@ C 3 (18)-C 86 present closed-shell electronic configurations with formally Th( iv ), consistent with other previously reported Th based mono-metallofullerenes. Th@ C 2 (14)-C 86 has emerged as the third lowest-energy isomer with significant predicted abundance at temperatures of fullerene formation. Th@ C 3 (18)-C 86 , on the other hand, represents an unexpected isomer with low thermodynamic stability, but significant abundance. Its formation was further rationalized as a kinetically trapped intermediate obtained from the lowest-energy and abundant Th@ C 2 (8)-C 84 , by a C 2 insertion and a single Stone–Wales transformation. This study highlights the unique impact of actinides on the stabilization of fullerene cage isomers and also provides a more in-depth understanding into the stabilization mechanism of fullerene cage isomers.