Characterization of Lanthanide Complexes with Bis-1,2,3-triazole-bipyridine Ligands Involved in Actinide/Lanthanide Separation

The
complexation of selected trivalent lanthanide ions with derivatives
of the tetranitrogen donor ligands 6,6′-bis-1R,1H-1,2,3-triazol-4-yl-2,2′-bipyridines (BTzBPs, R = alkyl or
aryl) was investigated in solid state and in solution. An anhydrous
solid [Ce­(Bn-BTzBP)­(NO3)3] (Bn = benzene) complex
was synthesized and characterized by single-crystal X-ray diffraction.
Eu­(III) complexes with the 2-ethyl­(hexyl) derivative EH-BTzBP in methanol
were studied by time-resolved fluorescence spectroscopy. Earlier studies
have identified the EH-BTzBP as a potentially useful solvent extraction
reagent for the separation of americium from lanthanide metal ions,
a challenging component of advanced nuclear fuel cycles for actinide
transmutation. To help identify species formed in the extraction process,
the influence of 2-bromohexanoic acid (identified as an essential
component of the separation system) on Eu­(III) complexes was investigated.
Comparison with an organic phase after extraction of Eu­(III) by EH-BTzBP
and 2-bromohexanoic acid showed that both 1:1 and 1:2 (Eu/EH-BTzBP)
complexes are involved in the extraction. UV–visible spectrophotometry
was used to compare Eu­(III) stability constants with those of other
Ln­(III) complexes.

本研究针对选定的三价镧系离子（trivalent lanthanide ions）与四氮供体配体（tetranitrogen donor ligands）6,6′-双(1R-1H-1,2,3-三唑-4-基)-2,2′-联吡啶（BTzBPs，R为烷基或芳基）衍生物之间的配位作用，分别在固态与溶液体系中开展了系统探究。我们合成了无水固态配合物[Ce(Bn-BTzBP)(NO3)3]（Bn为苯），并通过单晶X射线衍射（single-crystal X-ray diffraction）对其结构进行了完整表征。针对甲醇体系中结合2-乙基己基衍生物EH-BTzBP的铕(III)配合物，本研究采用时间分辨荧光光谱法（time-resolved fluorescence spectroscopy）展开了分析。前期研究已表明，EH-BTzBP可作为潜在的高效溶剂萃取试剂（solvent extraction reagent），用于从镧系金属离子中分离镅（americium）——而这正是锕系元素嬗变（actinide transmutation）先进核燃料循环（advanced nuclear fuel cycles）中极具挑战性的核心环节。为明确萃取过程中生成的配位物种，本研究探究了2-溴己酸（2-bromohexanoic acid，该分离体系的必需组分）对铕(III)配合物的影响。对比经EH-BTzBP与2-溴己酸萃取铕(III)后的有机相可知，1:1型与1:2型（Eu/EH-BTzBP）配合物均参与了本次萃取过程。本研究采用紫外-可见分光光度法（UV–visible spectrophotometry），对比了铕(III)配合物与其他三价镧系配合物的稳定常数（stability constants）。