Anion-encapsulating fullerenes behave as large anions: a DFT study

Area of Science:

• Computational Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Fullerenes, particularly C60, are carbon allotropes with unique electronic properties.
• Endohedral fullerenes, where atoms or molecules are encapsulated within the fullerene cage, are of interest for their modified characteristics.
• Understanding the electronic interactions between encapsulated species and the fullerene cage is crucial for designing new materials.

Purpose of the Study:

• To investigate the electronic structure and bonding in endohedral fullerene complexes (X-@C60).
• To quantify the exothermic nature of anion encapsulation within C60.
• To elucidate the charge distribution and bonding mechanisms between the encapsulated anion and the fullerene cage.

Main Methods:

• Density Functional Theory (DFT) calculations using the M06L functional with specific basis sets (6-311++G(d,p)//6-31G(d,p)).
• Analysis of molecular electrostatic potential (MESP) to understand charge distribution.
• Quantum Theory of Atoms in Molecules (QTAIM) analysis to study charge, electron delocalization, and bond properties.

Main Results:

• The endohedral reaction of C60 with various anions (X-) is highly exothermic (37.8–65.2 kcal mol-1).
• Encapsulated anions transfer significant electron density to the C60 cage, making it behave as a large, closed-shell anion.
• MESP and QTAIM analyses confirm substantial electron sharing and multicenter charge-shift bonding between the anion and the fullerene cage.

Conclusions:

• The C60 fullerene cage effectively acts as a closed-shell anion when encapsulating various anions.
• Solvent effects significantly reduce the exothermicity of the encapsulation reaction.
• The observed behavior is consistent across different fullerene sizes (C60, C70, C84, C90) and encapsulated anions.