Computational Investigation of the Bonding in [(η⁵–Cp′)₃(η¹–Cp′)M]^1– (M = Pu, U, Ce)

Despite the similar ionic radii for Ce³⁺, U³⁺, and Pu³⁺, [(η⁵–Cp′)₃(η¹–Cp′)­Ce]^1– (Cp′ = C₅H₄SiMe₃, 1-Ce) displays a significantly longer η¹–Cp′ distance in the solid state compared to the U³⁺ and Pu³⁺ analogues. To better understand this observation, a theoretical investigation was undertaken to examine the differences in bonding between the actinides 1-Pu and 1-U and how they compare with 1-Ce. The results show that although the bonding is largely ionic and dominated by ligand (2p)–metal (6d/5d) interactions, the polarization of 5f orbitals plays a significant role for 1-Pu and 1-U compared to the 4f-orbitals of 1-Ce. The lack of Ce­(4f) interactions is compensated for by increased participation of the Ce­(5d) orbitals relative to the actinide 6d orbitals, particularly for the σ-bound η¹–Cp′ ligand. The use of multiple theoretical approaches including topological, localization, and energy decomposition approaches shows that 1-Pu and 1-U are very similar in covalent character compared to 1-Ce, though the composition and energy of the different interactions suggest that 1-U presents the strongest overall interactions.