High Coordination Numbers of Actinides (An) in AnC₁₃⁺ Rings (An = Th and U)

An intriguingly high abundance of both ThC₁₃⁺ and UC₁₃⁺ cluster cations was observed in a previous mass spectrometry experiment; however, the structural identification of these cations has not yet been completed. In this study, we determined the lowest lying structures of ThC₁₃⁺ and UC₁₃⁺ clusters using an unbiased structural search method. The 13-coordinate planar ring configuration was the most stable for both ThC₁₃⁺ and UC₁₃⁺ cluster cations. The C-An bonds in ThC₁₃⁺ and UC₁₃⁺ show a small degree of covalency, originating from the overlap of the s, d, and f orbitals of the An atoms with C 2p orbitals of both π and σ characteristics. The infrared and electronic absorption spectra of the most favorable planar ring configurations were theoretically simulated to facilitate the identification of the molecular structures in future experiments. This study provides an in-depth understanding of the experimental mass spectra.