Actinide-Actinide Bonding: Electron Delocalisation and & sigma;-Aromaticity in the Tri-Thorium Cluster [{Th(& eta;(8)-C8H8)(& mu;-Cl)(2)}(3)K-2]

The tri-thorium cluster [{Th(& eta;(8)-C8H8)(& mu;(3)-Cl)(2)}(3){K(THF)(2)}(2)](& INFIN;) (Nature 2021, 598, 72-75) was reported to feature intriguing & sigma;-aromatic bonding between the thorium atoms, a mode of metal-metal bonding unique in the actinide series. However, the presence of this bonding motif has since been challenged by others. Here, we computationally explore electron delocalisation in a molecular cluster fragment of [{Th(& eta;(8)-C8H8)(& mu;(3)-Cl)(2)}(3){K(THF)(2)}(2)](& INFIN;) and examine its responses to an applied magnetic field using a variety of methods. We also discuss the importance of the choice of basis set for the Th atoms and issues regarding locating QTAIM bond critical points. When taken together, the computed data consistently suggest the presence of delocalised Th-Th bonding and Th-3 & sigma;-aromaticity.