Density Functional Theory Analysis of the Importance of Coordination Geometry for 5f36d1 versus 5f4 Electron Configurations in U(II) Complexes.

Density functional theory (DFT) calculations on four known and seven hypothetical U(II) complexes indicate the importance of coordination geometry in favoring 5f36d1 versus 5f4 electronic ground states. The known [Cp″3U]-, [Cptet3U]-, and [U(NR2)3]- [Cp″ = C5H3(SiMe3)2, Cptet = C5Me4H, and R = SiMe3] anions were found to have 5f36d1 ground states, while a 5f4 ground state was found for the known compound (NHAriPr6)2U. The UV-visible spectra of the known 5f36d1 compounds were simulated via time-dependent DFT and are in qualitative agreement with the experimental spectra. For the hypothetical U(II) compounds, the 5f36d1 configuration is predicted for [U(CHR2)3]-, [U(H3BH)3]-, [U(OAr')4]2-, and [(C8H8)U]2- (OAr' = O-C6H2tBu2-2,6-Me-4). In the case of [U(bnz')4]2- (bnz' = CH2-C6H4tBu-4), a 5f3 configuration with a ligand-based radical was found as the ground state.