Density Functional Theory Studies of UO₂²⁺ and NpO₂⁺ Complexes with Carbamoylmethylphosphine Oxide Ligands

Abstract

The UO₂²⁺ and NpO₂⁺ extraction complexes with <i>n</i>-octyl­(phenyl)-<i>N</i>,<i>N</i>-diisobutylmethylcarbamoyl phosphine oxide (CMPO) and diphenyl-<i>N</i>,<i>N</i>-diisobutylcarbamoyl phosphine oxide (Ph₂CMPO) have been investigated by density functional theory (DFT) in conjunction with relativistic small-core pseudopotentials. For these extraction complexes, especially the complexes of 2:1 (ligand/metal) stoichiometry, UO₂²⁺ and NpO₂⁺ predominantly coordinate with the phosphoric oxygen atoms. The CMPO and Ph₂CMPO ligands have higher selectivity for UO₂²⁺ over NpO₂⁺, and for all of the extraction complexes, the metal–ligand interactions are mainly ionic. In most cases, the complexes with CMPO and Ph₂CMPO ligands have comparable metal–ligand binding energies, that is, the substitution of a phenyl ring for the <i>n</i>-octyl group at the phosphoryl group of CMPO has no obvious influence on the extraction of UO₂²⁺ and NpO₂⁺. Moreover, hydration energies might play an important role in the extractability of CMPO and Ph₂CMPO for these actinyl ions