Designing ligands for radiological safety: Oxasapphyrins in actinide sequestration

Abstract The search for suitable macrocyclic ligands for efficient sequestering of the radioactive actinide ions has been a fundamental topic of research. This search for chelating agents is prevalent in the field of radiation protection as well, since both the processes of decontamination and decorporation require efficient sequestration of the radioactive ions. The efficiency of sequestration is a function of the thermodynamics, thereby the bonding characteristics of the complexes. In this study, the bonding properties of actinyl ions, namely uranyl, neptunyl, and plutonyl in a mixed (N, O) donor ligand, named oxasapphyrin, environment, were analyzed in details using a quasi-relativistic density functional theory-based approach. The ligand was observed to sequester the uranyl ion more efficiently than the other two ions. Moreover, predominance of the charge transfer from ligand “p” orbitals to metal “d” orbitals was observed. Interestingly, the participation of the “f” orbitals of these 5f elements was noted to be significantly less. The detailed findings about the bonding features of the actinyl-oxasapphyrin complexes are anticipated to provide insights toward designing improved ligands for the sequestration of the actinyl ions.