Effects of Electron‐Withdrawing and ‐Donating Substituents in N‐Donor Scorpionate Ligands and the Metal 5 f/4 f Orbitals on Am(III)/Eu(III) Complexation and Separation

Abstract The separation of trivalent lanthanides and actinides remains a challenge in the processing of nuclear waste because of their chemical similarities. Revealing the bonding nature of the lanthanide/ actinide ions with ligands in the complexes is essential for designing robust ligands for lanthanides/ actinides separation. In this work, the bonding and separation properties of the scorpion‐type ligands (tri(1H‐pyrazol‐3‐yl)methane) with Am(III)/Eu(III) were studied using a relativistic density functional method. To study the substituent effect the electron‐withdrawing (−Br and −CF 3 ) and electron‐donating (−CH 3 and −OCH 3 ) substituents are introduced into the pyrazole ring to regulate the electron density of the coordinating N atom. The NBO, AIM and thermodynamic analyses show that Am(III) formed stronger bonds with the ligands than Eu(III), and the difference between Am(III) and Eu(III) was mainly due to the stronger bonding ability of Am 5 f orbitals than Eu 4 f orbitals. Analysis of the properties of the ligand and the metal‐N bond in the complex shows that the electron‐donating substituents increase the electron density on the donor N atom and thus make the formed metal‐N bond shorter and stronger, while the electron‐withdrawing substituents have the opposite effect. Thermodynamic analysis showed that these ligands had good separation effect for Am and Eu.