Recently, a new member of the lanthanum-containing metallofullerene family has been isolated and its structure determined from X-ray crystallographic analysis, namely LaTd@Cs(Td, 17490), even with two pairs of connected pentagons, hence violating the isolated-pentagon rule (IPR). In order to explain the interesting observation, a computational treatment is suggested for evaluations of the relative populations of nonisomeric metallofullerenes. As a comparative reference structure, the most stable La@cCs isomer is selected — the IPR-C 2(76)-cage based endohedral La@cCs(76). In the relevant temperature region, the La 76@cTd(76, 17490) species should be considerably more populated compared to La@cTd(2). The new computational stability treatment is applicable to a wider spectrum of nonisomeric metallofullerenes.
Fullerenes, Nanotubes and Carbon Nanostructures 22(1-3), pp.299-306