Theoretical study on the extraction behaviors of MoO22+ with organophosphorous extractants

Abstract

99Mo is the parent isotope of 99mTc, which is commonly used in nuclear medicine, so the studies on the extraction of 99Mo have been attracted extensive attention. There are some experimental investigations about the extraction of Mo(VI) using the organophosphorous extractants including O-donor Cyanex 272 (HLa) and S-donor Cyanex 301 (HLb). We explored the coordination and complexing nature of Mo(VI) with HLa and HLb using scalar relativistic density functional theory. The electrostatic potentials and frontier molecular orbitals of HLa and HLb show that the former has stronger nucleophilic ability compared to the latter. All the MoO22+ complexes with HLa and HLb are tetra-coordinated structures. The values of Wiberg bond indices (WBIs) indicate that the Mo-S bonds have more covalency than Mo-O bonds. The energy decomposition analysis reveals that the interaction between MoO22+ ion with HLa is stronger than that with HLb, which is also supported by the thermodynamic energy. The thermodynamic energy indicates that [MoO2(H2O)2(NO3)]+ is the dominant initial species and reaction [MoO2(H2O)2(NO3)]++HL → [MoO2L(NO3)] + H++2H2O is the most preferred in the extraction process. This work elucidates the electronic structures and complexing nature of MoO22+ with Cyanex 272 and Cyanex 301 ligands and provides the useful theoretical information on designing acidic phosphorous extractants of MoO22+.