Exohedral Complexes of Lanthanide Atoms with the C ₆₀ Fullerene Cage: Hexagonal versus Pentagonal Ring Coordination

The formation, properties, and applications of lanthanide (Ln) endohedral fullerenes remain the most extensively studied aspect of the interactions between the metal species and carbon nanoclusters. In comparison, the related information on the exohedral Ln–fullerene systems is limited. We analyzed theoretically the geometries, bonding, and selected electronic properties for the entire lanthanide series, for both η 5 and η 6 patterns of their exohedral coordination to C 60 . We found that the bonding strength, the geometries, and the positive charge acquired by Ln atoms follow similar qualitative and semi-quantitative trends in the exohedral η 5 and η 6 coordinations. The spin behavior of the complexes constitutes a particularly interesting aspect, with both ferromagnetic and antiferromagnetic coupling observed. The η 5 coordination exhibits a stronger trend to increase the molecular spin. Thus, further studies are needed for spintronic applications and in superconductive lanthanide–fullerene complexes, in which the Ln coordination to pentagonal rings of C 60 plays an important role.