Aqueous Complexes for Efficient Size-based Separation of Americium from Curium

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• 作者：Mark P. Jensen ; Renato Chiarizia ; Ilya A. Shkrob ; Joseph S. Ulicki ; Brian D. Spindler ; Daniel J. Murphy ; Mahmun Hossain ; Adri谩n Roca-Sabio ; Carlos Platas-Iglesias ; Andr茅s de Blas ; Teresa Rodr铆guez-Blas
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：June 16, 2014
• 年：2014
• 卷：53
• 期：12
• 页码：6003-6012
• 全文大小：409K
• 年卷期：v.53,no.12(June 16, 2014)
• ISSN：1520-510X

文摘

Complexation of the adjacent actinide ions americium(III) and curium(III) by the ligand N,N鈥?bis[(6-carboxy-2-pyridyl)methyl]-1,10-diaza-18-crown-6 (H<sub>2sub>bp18c6) in aqueous solution was studied to quantify and characterize its americium/curium selectivity. Liquid鈥搇iquid extraction and spectrophotometric titration indicated the presence of both fully deprotonated and monoprotonated complexes, An(bp18c6)<sup>+sup> and An(Hbp18c6)<sup>2+sup> (An = Am or Cm), at the acidities that would be encountered when treating nuclear wastes. The stability constants of the complexes in 1 M NaNO<sub>3sub> determined using competitive complexation were log 尾<sub>101sub> = 15.49 卤 0.06 for Am and 14.88 卤 0.03 for Cm, indicating a reversal of the usual order of complex stability, where ligands bind the smaller Cm<sup>IIIsup> ion more tightly than Am<sup>IIIsup>. The Am/Cm selectivity of bp18c6<sup>2鈥?/sup> that is defined by the ratio of the Am and Cm stability constants (尾<sub>101sub> Am/尾<sub>101sub> Cm = 4.1) is the largest reported so far for binary An<sup>IIIsup>鈥搇igand complexes. Theoretical density functional theory calculations using the B3LYP functional suggest that the ligand鈥檚 size-selectivity for larger 4f- and 5f-element cations arises from steric constraints in the crown ether ring. Enhanced 5f character in molecular orbitals involving actinide鈥搉itrogen interactions is predicted to favor actinide(III) complexation by bp18c6<sup>2鈥?/sup> over the complexation of similarly sized lanthanide(III) cations.