Towards Relative Populations of Non-Isomeric Metallofullerenes: La@C76( ) vs. La2@C76( ,17490)

Recently, a new member of the lanthanum-containing metallofullerene family has been isolated and its structure determined from X-ray crystallographic analysis, namely La @C ( ,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@C isomer is selected — the IPR-C ( )-cage based endohedral La@C ( ). In the relevant temperature region, the La @C ( ,17490) species should be considerably more populated compared to La@C ( ). The new computational stability treatment is applicable to a wider spectrum of nonisomeric metallofullerenes.