Are U-U Bonds Inside Fullerenes Really Unwilling Bonds?

Area of Science:

• Inorganic Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Previous studies on diuranium endohedral metallofullerenes (EMFs) like U2@C80 indicated weaker U-U interactions compared to Th2@C80.
• Classical actinide chemistry often neglects the possibility of covalent U-U bonds.

Purpose of the Study:

• To investigate the feasibility of forming covalent U-U bonds in smaller diuranium EMFs.
• To understand the nature and strength of U-U bonding within various fullerene cages.

Main Methods:

• Laser ablation synthesis of dimetallic U2@C2n species (2n ≥ 50).
• Mass spectrometric detection.
• Density Functional Theory (DFT), CASPT2 calculations, and Molecular Dynamics (MD) simulations.

Main Results:

• Successful formation of diuranium EMFs with strong U(5f3)-U(5f3) triple bonds, exhibiting an effective bond order greater than 2 in smaller cages like C60.
• U-U bond formation competes with U-cage interactions, influencing U-U distances in crystalline structures.
• Significant 5f-5f orbital interactions contribute to covalent bonding around 2.5 Å, with additional 7s6d orbital overlap detected above 4 Å.

Conclusions:

• Covalent U-U triple bonds can be formed within smaller fullerene cages, challenging traditional actinide chemistry.
• Metal ions in EMFs act as templates for cage formation rather than mere confined entities.
• The study provides crucial insights into the bonding characteristics of uranium within nanoscale carbon structures.