Small Molecules in C60 and C70: Which Complexes Could Be Stabilized?

Area of Science:

• Computational Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Endohedral fullerene complexes are synthesized with small molecules, but their stability requires further investigation.
• Numerous computational studies exist, yet accurately describing host-guest interactions, particularly dispersion forces, remains a challenge.

Purpose of the Study:

• To estimate the stabilization energies of endohedral complexes formed by C60 and C70 fullerenes with various small molecules.
• To identify the key physical factors governing the stability of these complexes.
• To assess the suitability of C60 and C70 cages for hosting different guest molecules.

Main Methods:

• Symmetry-Adapted Perturbation Theory (SAPT) was employed to calculate stabilization energies.
• SAPT was chosen for its accurate description of dispersion contributions in host-guest interactions, surpassing standard DFT methods.

Main Results:

• Endohedral complexes of C60 and C70 with H2, N2, CO, HCN, H2O, H2S, NH3, CH4, CO2, C2H2, H2CO, and CH3OH were evaluated.
• All tested guests were found to be stable within the larger C70 fullerene cage.
• The smaller C60 cage was too small to host H2CO and CH3OH, and potentially other larger molecules.
• Except for H2 and H2CO, stabilization in C60 was approximately 30 kJ/mol.
• For H2 and H2O, stabilization was comparable or greater in C60 than in C70, demonstrating a supramolecular effect.
• Dispersion interactions were the dominant stabilization force in most complexes, with induction playing a role for H2O.

Conclusions:

• Endohedral fullerene complexes with a range of small molecules can be stable, with C70 being a more versatile host than C60 for larger guests.
• Dispersion forces are the primary drivers of stabilization, with induction being significant in specific cases like water.
• Understanding these stability factors is vital for the rational design of future experiments and applications of endohedral fullerenes.