Covalent interactions depend on the distances between metals and fullerenes for thermodynamically stable M@C78 (M = La, Ce, and Sm)

Thermodynamic selectivity occurs between fullerenes and metals in M@C₇₈ (M = La, Ce, Sm), including non-IPR C₁(22 595)-C₇₈; the different number of electrons transferred from metals to C₇₈ leads to the first EMF with diradical features.