(Invited) Synthesis and Structural Characterization of Actinide Cluster Fullerenes

Abstract

The hollow internal cavity of fullerene buckyballs has been known to be able to encapsulate novel metallic units, especially those otherwise very reactive or virtually impossible to prepare clusters. In this talk, we will present our recent studies of novel cluster endohedral fullerenes, focusing on their unique encapsulated clusters and bonding motifs. The synthesis and characterization of U2C@C80 gives an unprecedented look into a long sought after but heretofore unknown U=C bond which lacks heteroatom support, allowing for detailed structural and electronic insights.Novel actinide cluster fullerenes, U2C2@Ih (7)-C80 and U2C2@D 3h (5)-C78, were synthesized and fully characterized by mass spectrometry, single crystal X-ray crystallography, UV-vis-NIR , Raman spectroscopy, IR spectroscopy, as well as density functional and multireference wavefunction calculations. The encapsulated U2C2 is the first example of a uranium carbide cluster featuring two U centers bridged by a C≡C unit. The U-C bond distances in these U2C2 clusters are in the range between 2.130-2.421 Å. While the U2C2 cluster in U2C2@C80 adopts a butterfly-shaped geometry with a U-C2-U dihedral angle of 112.7°and a U-U distance of 3.855 Å, the U-U distance in U2C2@C78 is 4.164 Å and the resulting U-C2-U dihedral angle is increased to 149.1°. The combined experimental and quantum-chemical results suggest that the formal U oxidation state is +IV in the U2C2 cluster.