A DFT and experimental investigation of the electron affinity of the triscyclopentadienyl uranium complexes Cp3UX

Relativistic Density Functional Theory (DFT) based methods coupled with the Conductor-like Screening Model (COSMO) for a realistic solvation approach are used to investigate the electron affinity ( EA) of a series of triscyclopentadienyl uranium complexes Cp3UX (X=Cl, BH4, SPh, (SPr)-Pr-i and (OPr)-Pr-i) related to the U(IV)/U(III) redox system. E-1/2 half-wave potentials have been measured in solution (THF) under the same rigorous conditions for all the species under consideration. A good correlation (r(2) = 0.99) is found between the computed EA values, either in the gas phase or in solution, and the experimental half-wave potentials; the study brings to light the importance of spin-orbit coupling effects which must be taken into account in order to achieve the observed agreement between theory and experiment. The influence of the electron donating character of the X ligand on the orbital involved in the reduction process, namely the lowest unoccupied molecular orbital (LUMO) of the neutral U(IV) complexes, and on the EAs is discussed.