Systematic DFT study of gas phase and solvated uranyl and neptunyl complexes [AnO₂X₄]ⁿ (An = U, Np; X = F, Cl, OH, n = -2; X = H₂O, n = +2)

The six-valent uranyl and neptunyl complexes [An^VIO ₂X₄]ⁿ (An = U, Np; X = F, Cl, OH, n = -2; X = H₂O, n = +2) have been studied within the framework of density functional theory. The relative stabilities of the cis and trans isomers, structural properties, charge distribution, and ligand binding energies have been determined using the modified Perdew-Burke-Ernzerhof functional at the all-electron scalar relativistic level. Uranyl and neptunyl complexes with different ligands have been compared in a systematic fashion, demonstrating close similarity of these actinides in oxidation state VI. In addition, the effect of an aqueous solution has been taken into account with the polarizable continuum model COSMO. Computed averaged ligand binding energies permit one to rationalize the observed different stabilities of the title species in aqueous media.