Theoretical Probing of Size-Selective Crown Ether Macrocycle Ligands for Transplutonium Element Separation

Area of Science:

• Nuclear Chemistry
• Theoretical Chemistry
• Materials Science

Background:

• Separating chemically similar transplutonium elements from actinides in spent nuclear fuel is a significant challenge.
• Understanding complexation behavior is crucial for designing effective separation ligands.
• Experimental studies on transplutonium elements are difficult, making theoretical calculations valuable.

Purpose of the Study:

• To investigate the coordination mechanism between transplutonium elements (americium, curium, berkelium, californium) and two specific crown ether macrocyclic ligands.
• To evaluate the suitability of these ligands for in-group separation of transplutonium elements.
• To provide theoretical insights for developing advanced ligands for nuclear fuel reprocessing.

Main Methods:

• Quasi-relativistic density functional theory (DFT) calculations were employed.
• Systematic investigation of coordination mechanisms between actinides and ligands.
• Analysis of geometrical structures, bonding nature, and thermodynamic properties.

Main Results:

• Complexes of [Anbp18c6]+ and [Anbpp18c6]+ showed similar structures with actinides in the ligand cavities.
• Coordination ability of pendent arm atoms was stronger than the macrocycle itself.
• H2bp18c6 exhibited stronger metal ion coordination than H2bpp18c6.
• Bonding strength decreased from americium to californium, indicating size selectivity.
• H2bp18c6 demonstrated higher extraction capacity, while H2bpp18c6 showed better in-group separation.

Conclusions:

• Both ligands exhibit size selectivity for actinide cations due to steric constraints.
• H2bp18c6 is more effective for overall extraction capacity.
• H2bpp18c6 is superior for the in-group separation of transplutonium elements.
• These findings offer theoretical guidance for designing macrocyclic ligands for transplutonium element separation in nuclear fuel reprocessing.