isomers using systematic sampling of the thorium positions inside the carbon cage. We show that the experimentally observed isomers are indeed the lowest-energy structures when the conformational space is properly explored. The earlier misassignment is traced to convergence into higher-energy local minima caused by strong, directional Th-cage covalent interactions. Bonding analysis confirms the formal Th(IV) oxidation state, and the revised UV-vis-NIR spectra are consistent with the experimental results. Our results emphasize the importance of extensive conformational sampling for the reliable theoretical characterization of actinide endohedral fullerenes.
Kaminský et al. (2026) studied this question.