Theoretical Design of cis‐Bis(imido)uranium Iodides – Electronic Structures and Spectroscopic Properties

Abstract

AbstractTo understand the structural and electronic properties of uranium complexes, the cis‐bis(imido)uranium iodides cis‐[U(NPh)2(THF)3I2] (3Ph) and cis‐[U(NPh)2(THF)2I2] (2Ph) have been designed, and their structures and properties have been calculated by density functional theory (DFT) and time‐dependent DFT. Four isomers (3Ph1, 3Ph2, 2Ph1, 2Ph2) were addressed in the study; these isomers have the structural feature that one iodide atom is trans to one imido group in the axial direction, and the other iodine atom is cis to the other imido group in the equatorial plane. The total system energies, geometry parameters, and vibrational spectra were similar among the respective isomers. Analyses of the electronic structures in tetrahydrofuran solution revealed that these isomeric complexes show mixed π(U=N) and π(Ph) character for the highest occupied molecular orbital (HOMO) and HOMO–1; the lone pairs of electrons of the iodine atom are dominant in the energetically lower occupied orbitals. U(f)‐type orbitals contribute to the low‐lying unoccupied orbitals, as has been generally accepted for analogous hexavalent trans‐dioxouranium complexes. Three main absorption peaks were observed for 3Ph1/3Ph2 and 2Ph1/2Ph2 from time‐dependent long‐range‐corrected functional calculations. The first one originates from the π(U=N) bonds and the phenyl groups, and the third is related to character of the iodine atoms [σ(U–I) and π(I)]; combined π(I) and π(U=N) character is attributed to the middle peak. We also calculated the experimentally known trans‐U(NPh)2(THF)3I2 (trans‐3Ph). The comparison of trans‐3Ph, 3Ph1, and 3Ph2 indicates that the cis/trans isomerism has a relatively large effect on their structural and electronic properties.