UCN@Cs(6)-C82: An Encapsulated Triangular UCN Cluster with Ambiguous U Oxidation State [U(III) versus U(I)]

Understanding the chemical behavior of actinide elements is essential for the effective management and use of actinide materials. In this study, we report an unprecedented eta(2) (side-on) coordination of U by a cyanide in a UCN cluster, which was stabilized inside a C-82 fullerene cage. UCN@C-s(6)-C-82 was successfully synthesized and fully characterized by mass spectrometry, single crystal X-ray crystallography, cyclic voltammetry, spectroscopy, and theoretical calculations. The bonding analysis demonstrates significant donation bonding between CN- and uranium, and covalent interactions between uranium and the carbon cage. These effects correlate with an observed elongated cyanide C-N bond, resulting in a rare case where the oxidation state of uranium shows ambiguity between U(III) and U(I). The discovery of this unprecedented triangular configuration of the uranium cyanide cluster provides a new insight in coordination chemistry and highlights the large variety of bonding situations that uranium can have.

Automated summary

This study reveals an unprecedented eta(2) coordination of uranium by cyanide in a UCN cluster stabilized inside a C-82 fullerene cage. The unique bonding interactions between CN- and uranium, as well as uranium and the carbon cage, result in a rare case where the oxidation state of uranium shows ambiguity between U(III) and U(I). This discovery provides new insights in coordination chemistry and highlights the diverse bonding situations that uranium can exhibit.