Theoretical Insights Into Modification Of Nitrogen Donor Ligands To Improve Performance On Am(?)/Eu(?) Separation

Separation of actinides?An????from lanthanides?Ln????is one of the important steps of spent fuel reprocessing,which has great significance for the sustainable development of nuclear energy.Nitrogen donor ligands have been considered to be promising agents for separating trivalent actinides?An?III??from lanthanides?Ln?III??.Thereinto,how to decorate these ligands for better extraction performance is urgent to design“perfect”separating extractants.In this work,we systematically explored a series of heterocyclic N-donor ligands?L¹=dipyridazino[4,3-c:3?,4?-h]acridine,L²=dipyridazino[3,4-a:4?,3?-j]phenazine,L³=2,6-di?ci-nnolin-3-yl?pyridine?)as well as their substituted derivatives,and compared their extraction and complexation ability toward An?III?and Ln?III?ions by using quasi-relativistic density functional theory?DFT?.The main conclusions are summarized as follows:?1?The calculated ESP values indicate that the three nitrogen atoms are the preferred binding sites for metal ions,and alkyl substituents enhance the metal ion affinity of the ligands.The E_Protrot values reveal that the alkyl and MeO substituted ligands tend to be slightly easier to protonate.We found that the pyridazine N-atoms probably play a notable role in electron donation to metal cations by molecular orbital?MO?and bond order analyses.Besides,the rigid ligands?L¹ and L²?exhibit higher selective abilities for the Am?III?/Eu?III?separation compared with the flexible ligand?L³?.?2?Thermodynamics results suggest that these N-donor ligands possess higher coordination affinity toward Am?III?over Eu?III?.For each ligand,the 1:2?metal:ligand?extraction reaction is predicted to be most probable in the separation process.Introduction of an alkyl group on the lateral chain or an electron-donating group on the main chain gives rise to better extraction performance of the ligands,and the CyMe4 or MeO substitued ligands show higher extraction and separation ability.Simultaneous introduction of CyMe4 and MeO groups can enhance the extraction ability of the ligand to metal ions,but separating ability depends on the differences of the extraction capacity of An?III?and Ln?III?.This work can help to gain more in-depth understanding the selectivity differences of similar N-donor ligands and provide more theoretical insights into design of novel extractants for An?III?/Ln?III?separation.