The role of the encapsulated atom in the vibrational spectrа of La@C60–Lu@C60 lanthanide endofullerenes

Instead of the four experimentally derived infrared (IR) lines observed for C60 fullerene, the IR spectrum of Ln@C60 endofullerenes contains a variety of lines in the 20–1500 cm−1 range that correspond to the metal–cage and cage vibrational modes. Here, we present the frequencies and intensities of these lines for lanthanide endofullerenes calculated using the quantum-chemistry PRIRODA software package. Additionally, their structures, symmetries, spins and dipole moments are investigated. The lines found in the near IR (20–160 cm−1) range correspond to the translational motion of encapsulated lanthanide atoms (metal–cage vibrational modes). The far-IR range corresponds to the experimentally observed absorption region in the IR spectrum of endofullerenes with higher symmetry. This correspondence indicates that the frequencies are determined by the structure and symmetry of the carbon-cage fragment adjacent to the metal atom, as only the nearest atoms of the carbon cage are involved in these vibrations. It is shown that the magnitude of the splitting of the vibrational frequencies of the encapsulated metal atom is determined by the symmetry of its position in the fullerene. For isomers of the same symmetry, the metal-atom vibrational frequencies depend on the valence of the lanthanide metal.