Understanding electronic structures, chemical bonding, and fluxional behavior of Lu2@C2n (2n=76-88) by a theoretical study

Endohedral metal-metal-bonding fullerenes, in which encapsulated metals form covalent metal-metal bonds inside, are an emerging class of endohedral metallofullerenes. Herein, we reported quantum-chemical studies on the electronic structures, chemical bonding, and dynamic fluxionality behavior of endohedral metal-metal-bonding fullerenes Lu-2@C-2n (2n = 76-88). Multiple bonding analysis approaches, including molecular orbital analysis, the natural bond orbital analysis, electron localization function, adaptive natural density partitioning analysis, and quantum theory of atoms in molecules, have unambiguously revealed one two-center two-electron sigma covalent bond between two Lu ions in fullerenes. Energy decomposition analysis with the natural orbitals for chemical valence method on the bonding nature between the encapsulated metal dimer and the fullerene cage suggested the existence of two covalent bonds between the metal dimer and fullerenes, giving rise to a covalent bonding nature between the metal dimer and fullerene cage and a formal charge model of [Lu-2](2+)@[C-2n](2-). For Lu-2@C-76, the dynamic fluxionality behavior of the metal dimer Lu-2 inside fullerene C-76 has been revealed via locating the transition state with an energy barrier of 5 kcal/mol. Further energy decomposition analysis calculations indicate that the energy barrier is controlled by a series of terms, including the geometric deformation energy, electrostatic interaction, and orbital interactions. Published under an exclusive license by AIP Publishing.

Automated summary

This study investigates the electronic structures, chemical bonding, and dynamic fluxionality behavior of endohedral metal-metal-bonding fullerenes through various bonding analysis methods. The results reveal the existence of a two-center two-electron sigma covalent bond between encapsulated metals inside fullerenes. Additionally, two covalent bonds are found between the metal dimer and fullerenes, leading to a covalent bonding nature between the metal dimer and fullerene cage. Furthermore, the dynamic fluxionality behavior of the metal dimer inside the fullerene is revealed, and the energy barrier for this behavior is analyzed.