Diuranium(IV) Carbide Cluster U₂C₂ Stabilized Inside Fullerene Cages

Area of Science:

• Inorganic Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Actinide chemistry offers unique electronic properties due to variable oxidation states.
• Fullerene cages provide a confined environment for stabilizing unusual molecular structures.
• Previous studies on actinide clusters in fullerenes have shown strong covalent bonding.

Purpose of the Study:

• To synthesize and characterize novel actinide cluster fullerenes containing uranium carbide.
• To investigate the bonding, structure, and electronic properties of encapsulated U2C2 clusters.
• To explore the role of fullerene cages in stabilizing unique actinide cluster geometries.

Main Methods:

• Synthesis of U2C2@C80 and U2C2@C78 fullerene compounds.
• Characterization using mass spectrometry, X-ray crystallography, NMR, XAS, Raman, and IR spectroscopy.
• Computational analysis using density functional theory and multireference wave function calculations.

Main Results:

• Successful synthesis and characterization of U2C2@C80 and U2C2@C78, featuring the first uranium carbide cluster with two U centers bridged by C≡C.
• U-C bond distances range from 2.130 to 2.421 Å, with U-U distances of 3.855 Å (in C80) and 4.164 Å (in C78).
• The U2C2 clusters exhibit predominantly ionic U-C bonding, unlike previously reported covalent U═C bonds, with U oxidation state of +4.

Conclusions:

• The encapsulation within fullerene cages stabilizes novel actinide clusters.
• The U2C2 clusters demonstrate predominantly ionic bonding, differing from strong covalent U═C bonds.
• This approach enables the stabilization of actinide clusters not accessible via conventional synthetic routes.