Interconversions between Uranium Mono-metallo­fullerenes: Mechanistic Implications and Role of Asymmetric Cages

The
isolation and structural characterization of three new monometallic
uranium metallo­fullerenes, U@D2(21)-C84, U@Cs(15)-C86, and U@C1(11)-C86, allowed us to complete an interconversion map for all the characterized
uranium mono-metallo­fullerenes. The topological analysis reveals
that asymmetric fullerene cages, which may be formed by roll and wrap
processes directly from graphene, are the starting points for a series
of highly symmetric fullerene structures via top-down and bottom-up
growth mechanisms. Moreover, some asymmetric intermediates, such as C1(28324)-C80, can serve as precursors
to form either larger cages in consecutive growing processes or smaller
cages during cascade shrinking processes. This work provides evidence
for both top-down and bottom-up processes happening simultaneously
during the arcing processes. This study also sheds light on the prediction
of possible cage structures for minor products produced in low yields
in the soot.