Theoretical Exploration of Transplutonium Element Separation by Phosphine Oxide-Functionalized Ligands with Different Backbones

At present, transplutonium materials have applications in industry and basic and applied research. In order to obtain the corresponding heavy actinides, separation between these heavy actinides is essential. Currently, the development of efficient separation extractants is urgent and requires an in-depth investigation of the structures and properties of ligands and transplutonium complexes. In this work, we investigated the extraction and separation capacity of three phosphine oxide ligands (Ph₂PyPO, Ph₂BipyPO, Ph₂BPPhen) toward transplutonium cations of Am³⁺-Cf³⁺ by means of quasi-relativistic density functional theory. The Ph₂BPPhen ligand has better affinity for transplutonium elements by the electronic property analysis of ligands. The Mayer bonding order and quantum theory of atoms in molecules reveal that the strength of the An-O bonds progressively increases between Am and Cf. Energy decomposition analysis suggests that the covalent interaction between An(III) and the ligand in An<b>L</b>(NO₃)₃ is enhanced between Am and Cf. In terms of the extraction reactions of An<b>L</b>(NO₃)₃, the separation effect of the ligand is superior to that of [An<b>L</b>₂(NO₃)]²⁺. This work demonstrates how ligand backbone modifications influence bonding and extraction, providing insights for designing transplutonium extractants.