Fullerenium salts: a new class of C60-based compounds

Area of Science:

• Solid-state chemistry
• Materials science
• Supramolecular chemistry

Background:

• Fullerenes are allotropes of carbon with unique electronic properties.
• Stabilizing highly oxidized fullerene species in the solid state has been a significant challenge.
• Hole-doped C60 compounds are theoretically predicted to exhibit high-temperature superconductivity and magnetism.

Purpose of the Study:

• To prepare and characterize a solid-state fullerene salt with a 2+ oxidized fullerene.
• To investigate the structural and electronic properties of this novel compound.
• To explore the potential for superconductivity and magnetism in this system.

Main Methods:

• Utilizing the strong Lewis acid arsenic pentafluoride (AsF5) as an oxidizing agent.
• Employing high-resolution structural analysis to determine the crystal lattice arrangement.
• Characterizing the electronic properties, including energy gap and conductivity.

Main Results:

• Successful synthesis and characterization of the fullerene salt C60(AsF6)2.
• Discovery of a novel 1D "zigzag" polymer structure formed by C60(2+) units linked by [2+2] cycloaddition and single bonds.
• Observation of semiconducting behavior with an energy gap of approximately 70 meV, instead of expected superconductivity or magnetism.

Conclusions:

• The synthesized fullerene dication salt adopts a unique polymerized structure.
• The polymerization and reduced symmetry lead to semiconducting properties, deviating from predictions for hole-doped C60.
• The small energy gap suggests potential proximity to a metallic phase, warranting further investigation.