Strong covalent Th-Th bond inside C80

An unprecedented thorium-thorium bond has been characterized inside the icosahedral I_h(7)-C₈₀ carbon cage. The single-crystal X-ray diffraction of Th₂@I_h(7)-C₈₀ unambiguously determined that the two encapsulated Th atoms are separated by 3.816 Å, accurately reproduced by DFT calculations at SR-PBE0/TZP level. The overall agreement between the crystallographic, XAS, and quantum-computational results conclusively shows that the two encapsulated Th ions have formal charges of +3 and confirm the existence of a strong covalent Th-Th bond, which has been estimated to have an effective bond order (EBO) of 0.99 and a bond energy higher than 40 kcal/mol. The computational studies reveal that the overlap between 7s/6d hybrid thorium orbitals is so large that the bond still prevails at Th-Th separations larger than 6 Å, suggesting that this Th-Th bond is, up to now, the strongest one among the known actinide-actinide or lanthanide-lanthanide interactions.

J. Zhuang, R. Morales-Martínez, J. Zhang, Y. Wang, Y.-R. Yao, C.Pei, A.Rodríguez-Fortea, S. Wang, L. Echegoyen, C. de Graaf, J. M. Poblet & N. Chen, Characterization of a strong covalent Th3+–Th3+ bond inside an Ih(7)-C80 fullerene cage, Nature Comm. 12, 2372 (2021)