Density functional theory (DFT) calculations of VI/V reduction potentials of uranyl coordination complexes in non-aqueous solutions

Abstract

Of particular interest within the +6 uranium complexes is the linear uranyl(vi) cation and it forms numerous coordination complexes in solution and exhibits incongruent redox behavior depending on coordinating ligands. This DFT study predicts VI/V reduction potentials of a range of uranyl(vi) complexes in non-aqueous solutions within ∼0.10−0.20 eV of experiment.

Uranyl‐Bound Tetra‐Dentate Non‐Innocent Ligands: Prediction of Structure and Redox Behaviour Using Density Functional Theory

“…In contrast, disruptions of the conjugation through the introduction of an aliphatic chain linker between the alternative double bonds, for example ‘bi‐pyen’ and ‘bi‐pytmd’ ligands, resulted in the ligands becoming redox‐inactive (innocent) during the reduction . We have also drawn similar conclusions for these systems in a recent reduction potential prediction study using DFT methods . However, for the alaskaphyrin complexes of higher actinyls such as [NpO 2 ] 2+ and [PuO 2 ] 2+ , one‐electron reduction was confirmed (from the calculated Mulliken unpaired electron spin densities) to lead to metal‐based reduction .…”

“…This UAKS cavity combined with the CPCM solvation approach has been applied to solutes for the accurate prediction of solvation free energies . Furthermore, the suitability of this approach for the prediction of actinyl reduction potentials in solution, and ligand exchange reactions in aqueous solution, have been demonstrated previously . Furthermore, the M06 functional has been used for single point energy calculations at the B3LYP/B1 geometries with the CPCM‐UAKS solvation model employing the B2 basis; this level of theory is referred to as the M06/B2/(CPCM)//B3LYP/B1 level.…”

“…In the alternative isodesmic approach, rather than utilizing the reference electrode couple (Fc/Fc + ), the reduction free energy of an experimentally known similar uranyl complex is employed. [23,33,42] Scheme 1. Thermodynamic cycle used for RFE prediction.…”

“…These two functionals have already been examined for actinide computational chemistry and the results indicate that they are useful and applicable for the current research. Approximation of the core orbitals of U with a small‐core effective‐core potential (SC‐ECP) has been reported to reproduce accurate redox potentials and thermodynamics properties . Thus in this study U has been similarly described with a pseudo potential approach in which the 60 core electrons are treated using the Stuttgart‐Dresden‐Dolg (SDD) potential and the 32 valence electrons are treated explicitly.…”

“…[9] We have also drawn similar conclusions for these systems in a recent reduction potential prediction study using DFT methods. [23] However, for the alaskaphyrin complexes of higher actinyls such as [NpO 2 ] 2 + and [PuO 2 ] 2 + , one-electron reduction was confirmed (from the calculated Mulliken unpaired electron spin densities) to lead to metal-based reduction. [9] Thus when the alaskaphyrin ligand is coordinated with a [UO 2 ] 2 + cation, it exhibits redox-active (non-innocent) behaviour, and in contrast, if it is coordinated with either a [NpO 2 ] 2 + or [PuO 2 ] 2 + , it exhibits redox-inactive (innocent) behaviour.…”