M@C50 as Higher Intermediates towards Large Endohedral Metallofullerenes: Theoretical Characterization, Aromatic and Bonding Properties from Relativistic DFT Calculations

In recent years, endohedral metallofullerenes involving the C50 cages have been observed experimentally to encapsulate several metal atoms. This is the last step in a bottom-up growing mechanism to produce the most commonly observed large metallofullerenes. Nonetheless, currently, there is a lack of theoretical rationalization of such compounds. We now report, for the first time, a comprehensive theoretical study extending the experimentally known M@C50 species to endohedral group 3 and 4 elements using dispersion-corrected density functional theory. For C50 fullerene, isomers Cs (266) and D5h (271) are the most energetically favorable cages to host these metals, despite being far from the ground state of neutral C50 fullerene. Interestingly, properties of these endohedral compounds are highly comparable to those of the tri- and tetra-anions of the correspondent hollow fullerene cages. It is found that metal–cage binding energies larger than −5 eV are directly related to relative abundances experimentally...