How the Ancillary Ligand X Drives the Redox Properties of Biscyclopentadienyl Pentavalent Uranium Cp(2)U(═N-Ar)X Complexes
Résumé
Relativistic zero order regular approximation (ZORA) density functional theory computations, coupled with the conductor-like screening model for solvation effects, are used to investigate the redox properties of a series of biscyclopentadienyl pentavalent uranium(V) complexes Cp(2)U(═N-Ar)X (Ar = 2,6-Me(2)-C(6)H(3); X = OTf, C(6)F(5), SPh, C═CPh, NPh(2), Ph, Me, OPh, N(TMS)(2), N═CPh(2)). Regarding the U(V)/U(IV) and U(VI)/U(V) couple systems, a linear correlation (R(2) ∼ 0.99) is obtained at the ZORA/BP86/TZP level, between the calculated ionization energies and the measured experimental E(1/2) half-wave oxidation potentials (U(VI)/U(V)) and between the electron affinities and the reduction potentials E(1/2) (U(V)/U(IV)). The study brings to light the importance of solvation effects that are needed in order to achieve a good agreement between the theory and experiment. Introducing spin-orbit coupling corrections slightly improves this agreement. Both the singly occupied molecular orbital and the lowest unoccupied molecular orbital of the neutral U(V) complexes exhibit a majority 5f orbital character. The frontier molecular orbitals show a substantial ancillary ligand X σ and/or π character that drives the redox properties. Moreover, our investigations allow estimating the redox potentials of the X = Ph, X = C(6)F(5), and N(TMS)(2) U(V) complexes for which no experimental electrochemical data exist.
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