Bessen Nathan P, Popov Ivan A, Heathman Colt R, Grimes Travis S, Zalupski Peter R, Moreau Liane M, Smith Kurt F, Booth Corwin H, Abergel Rebecca J, Batista Enrique R, Yang Ping, Shafer Jenifer C
Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401, United States.
Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
Inorg Chem. 2021 May 3;60(9):6125-6134. doi: 10.1021/acs.inorgchem.1c00257. Epub 2021 Apr 18.
The separation of trivalent lanthanides and actinides is challenging because of their similar sizes and charge densities. S-donating extractants have shown significant selectivity for trivalent actinides over lanthanides, with single-stage americium/lanthanide separation efficiencies for some thiol-based extractants reported at >99.999%. While such separations could transform the nuclear waste management landscape, these systems are often limited by the hydrolytic and radiolytic stability of the extractant. Progress away from thiol-based systems is limited by the poorly understood and complex interactions of these extractants in organic phases, where molecular aggregation and micelle formation obfuscates assessment of the metal-extractant coordination environment. Because S-donating thioethers are generally more resistant to hydrolysis and oxidation and the aqueous phase coordination chemistry is anticipated to lack complications brought on by micelle formation, we have considered three thioethers, 2,2'-thiodiacetic acid (TDA), (2,5)-tetrahydrothiophene-2,5-dicarboxylic acid, and 2,5-thiophenedicarboxylic acid (TPA), as possible trivalent actinide selective reagents. Formation constants, extended X-ray absorption fine structure spectroscopy, and computational studies were completed for thioether complexes with a variety of trivalent lanthanides and actinides including Nd, Eu, Tb, Am, Cm, Bk, and Cf. TPA was found to have moderately higher selectivity for the actinides because of its ability to bind actinides in a different manner than lanthanides, but the utility of TPA is limited by poor water solubility and high rigidity. While significant competition with water for the metal center limits the efficacy of aqueous-based thioethers for separations, the characterization of these solution-phase, S-containing lanthanide and actinide complexes is the most comprehensively available in the literature to date. This is due to the breadth of lanthanides and actinides considered as well as the techniques deployed and serves as a platform for the further development of S-containing reagents for actinide separations. Additionally, this paper reports on the first bond lengths for Cf and Bk with a neutral S donor.
三价镧系元素和锕系元素的分离具有挑战性，因为它们的尺寸和电荷密度相似。含硫供体萃取剂对三价锕系元素显示出比对镧系元素更高的选择性，据报道，一些基于硫醇的萃取剂的单级镅/镧系元素分离效率超过99.999%。虽然这种分离可以改变核废料管理的局面，但这些体系往往受到萃取剂水解稳定性和辐射稳定性的限制。由于基于硫醇的体系在有机相中存在复杂且尚未完全理解的相互作用，限制了其发展，其中分子聚集和胶束形成会混淆对金属-萃取剂配位环境的评估。由于含硫硫醚通常更耐水解和氧化，且预计水相配位化学不会因胶束形成而产生复杂情况，我们考虑了三种硫醚，即2,2'-硫代二乙酸（TDA）、(2,5)-四氢噻吩-2,5-二羧酸和2,5-噻吩二羧酸（TPA），作为可能的三价锕系元素选择性试剂。完成了硫醚与多种三价镧系元素和锕系元素（包括钕、铕、铽、镅、锔、锫和锎）配合物的生成常数、扩展X射线吸收精细结构光谱和计算研究。发现TPA对锕系元素具有适度更高的选择性，因为它与镧系元素结合的方式不同，但TPA的实用性受到水溶性差和刚性高的限制。虽然水相硫醚与水对金属中心的显著竞争限制了其分离效果，但这些含硫的镧系元素和锕系元素溶液相配合物的表征是迄今为止文献中最全面的。这是由于所考虑的镧系元素和锕系元素的范围以及所采用的技术，并且为进一步开发用于锕系元素分离的含硫试剂提供了一个平台。此外，本文报道了锎和锫与中性硫供体形成的配合物的首个键长。
