Interaction of Lanthanide Atoms with the External Surface of C80 Fullerene Cage: η5 vs. η6 Coordination

We performed a theoretical analysis (the PBE-D2/DNP level of the density functional theory with the use of the DSPP pseudopotentials) of the geometries, bonding and frontier orbital energies, spin and charge distribution for the entire series (from La to Lu) of lanthanide atoms interacting with Ih−C80 cage, for both η5 and η6 exohedral coordination patterns. In certain regards, the exohedral η5 and η6 coordination of Ln atoms to the C80 fullerene cage exhibits similar qualitative and semi-quantitative trends (the bonding strength, shortest Ln…C distances, charge and spin of lanthanide atoms). The most interesting aspect is the molecular spin of the complexes, where we observed different patterns of ferromagnetic and antiferromagnetic coupling. Three complexes represent an extreme, when the antiferromagnetic coupling results in zero or close-to-zero molecular spin. In some cases, the molecular spin is a simple sum of 2 e of the isolated C80 cage and the spin of an isolated Ln atom. However, the most common situation is when another 2 e spin adds: it is best illustrated with Eu (spin of 7 e for the atomic ground state), where the molecular spin of its η5 and η6 complexes is not about 9 e but reaches almost 11 e.