Feature of the endohedral metallofullerene Y@C82 and Gd@C82 polymerization under high pressure

The paper was published in J. Phys. Chem. C (2022).

Fullerenes have attracted the attention of researchers since their discovery and further development of large-scale production. The unique symmetric structure, attractive physical and chemical properties make fullerenes promising for many fields of science and technology. An attractive feature of fullerenes is the possibility of tuning and modifying their structure in various ways. The accessibility of the outer surface allows functionalization, while the vast cavity inside the molecule can be used for introducing various guest atoms that can significantly change the physicochemical properties of the fullerene without essential structural distortion. For example, the endohedral metal atoms may lead to the appearance of magnetic moments in fullerenes and further apply them in quantum electronics and medicine. It is extremely interesting to study the physicochemical properties of endohedral metallofullerene (EMF), including their behavior under pressure. However, so far the lack of methods for their large-scale synthesis has not allowed such experimental studies.

The situation has changed since we developed a method for the synthesis of fullerene endohedral complexes in macroscopic quantities. In our recent work, we showed that introduction of Sc2C2 cluster inside a fullerene cavity significantly changes its behavior under pressure. To clarify the influence of metal ions on the polymerization behavior of fullerenes, it is important to investigate the behavior of EMF with only single guest metal ion inside, which would allow to exclude the anisotropic effects associated with the low symmetry of the Sc2C2 complex.

Here we present the first study of the properties under high pressures of the gadolinium and yttrium endohedral metallofullerenes as bulk material. The polymerization processes of both complexes were studied theoretically and experimentally. It was shown that the presence of the metal ions significantly affects the polymerization of endohedral complexes which are studied at high pressures up to 40 GPa. It was found that the process of polymerization of both classes of endohedral complexes is similar to each other but differs from the pure fullerene polymerization. DFT simulation results demonstrated that both metal ions dramatically change the fullerene bonding process by the polarization of the carbon bonds which leads to their increased chemical activity. The values of the bulk modulus were calculated for the resulting polymerized materials using the Raman measurements at a pressure range of 3-27 GPa. The moduli were equal to ~340 GPa for gadolinium and yttrium endohedral complexes which is lower than the B value of diamond (443 GPa) but comparable with Sc2C2@C82 (330 GPa).