Fullerenes with metal atoms bonded directly to the outside of the fullerene cage, or exohedral metallofullerenes, could have applications in advanced materials. The steric and electronic properties of C₆₀ are well-suited to preparing exohedral metallofullerenes with transition metals in low oxidation states. C₆₀ has multiple possible binding sites on its surface, so multinuclear exohedral metallofullerenes can be synthesized and connected using organic linkers to form coordination polymers.

Shun-Ze Zhan, Shantou University, China, and Jinan University, Guangzhou, China, Dan Li, Jinan University, and colleagues have synthesized the one-dimensional mixed-valence cuprofullerene pyrazolate polymer {Cu₆[(μ₃-η²:η²:η²)₂-C₆₀](FPz)₆Cl·3C₆H₅Cl]_∞ (partial structure pictured, FPz = 4-(trifluoromethyl)pyrazolate). The team prepared the polymer under solvothermal conditions at 180 °C, using Cu₂O, C₆₀, and HFPz as reactants in the presence of pyridine with chlorobenzene as the solvent.

The desired product was obtained in the form of black crystals. According to the researchers, the compound is the first example of a polymer based on a bis-adduct hexanuclear exohedral metallofullerene. The structure features three copper atoms bound to either side of one C₆₀ cage. These units are then bridged by six FPz units and one Cl center to form a linear coordination polymer. The compound shows delocalized mixed valency with copper in Cu^I and Cu^II states and has semiconductor properties.

• A 1D Mixed-Valence Cuprofullerene Pyrazolate Polymer as a Semiconductor Material,
  Jia-Jing Zhong, Shun-Ze Zhan, Yanzhou Li, You-Shi Guo, Seik Weng Ng, Yi-Fei Deng, Dan Li,
  Inorg. Chem. 2022.
  https://doi.org/10.1021/acs.inorgchem.2c01478