Kou Fei, Yang Suliang, Qian Hongjuan, Zhang Lihua, Beavers Christine M, Teat Simon J, Tian Guoxin
Radiochemistry Department, China Institute of Atomic Chemistry, PO Box 275-126, Beijing 102413, China.
Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, CA 94720, USA.
Dalton Trans. 2016 Nov 22;45(46):18484-18493. doi: 10.1039/c6dt02930b.
Tetraalkyldiglycolamide (TRDGA) ligands have potential utilization for the separation of actinide and lanthanide ions in the nuclear industry as chelates in aqueous solution if water-soluble or as extractants in organic solvents if water-insoluble. Here, a spectral titration method is extensively applied to investigating the complexation of fluorescent Sm(iii), Eu(iii), and Tb(iii) with TRDGA ligands in aqueous solutions and a solvent extraction system. In aqueous solutions using N,N,N',N'-tetramethyldiglycolamide (TMDGA, L) as chelate, three successive complex species of Ln(iii), including [LnL], [LnL], and [LnL], are identified for each Ln(iii) (Ln = Sm, Eu, and Tb), and their stability constants are determined with fluorescence spectral titration method at 25 °C in 1 M NaNO. The coordination mode in [LnL] is illustrated by single-crystal structures of the solid compounds LnL(ClO) (Ln = Sm, Eu, Tb, and L = TMDGA) grown from aqueous solutions by slow evaporation. The crystal structures show that in the complexes Ln(iii) ions are coordinated by nine oxygen atoms from three tridentate L ligands in a distorted tricapped trigonal prism geometry. To provide parallels to solvent extraction chemistry, the extracted Ln(iii) complexes with N,N'-dimethyl-N,N'-dioctyldiglycolamide (DMDODGA, L, a lipophilic analogue of TMDGA) are prepared, and the fluorescence spectra are collected as well for comparison. The fluorescence spectra of the extracted Ln(iii) complexes with L in an organic phase of 40-60% (v/v) n-octanol-kerosene are nearly identical to the corresponding deconvoluted spectra of [LnL] in aqueous solution. The similarity in fluorescence spectra suggests that Ln(iii) ion in the extracted complexes is also coordinated by three tridentate L ligands and that the nitrate anions acting just as counterions do not directly bond to Ln(iii) in the organic phase of solvent extraction.
四烷基二甘醇酰胺（TRDGA）配体在核工业中具有潜在应用，若其为水溶性，则可作为螯合剂用于水溶液中锕系和镧系离子的分离；若为水不溶性，则可作为萃取剂用于有机溶剂中。在此，光谱滴定法被广泛应用于研究荧光性Sm(iii)、Eu(iii)和Tb(iii)与TRDGA配体在水溶液和溶剂萃取体系中的络合作用。在以N,N,N',N'-四甲基二甘醇酰胺（TMDGA，L）作为螯合剂的水溶液中，对于每种Ln(iii)（Ln = Sm、Eu和Tb），鉴定出三种连续的Ln(iii)络合物物种，包括[LnL]、[LnL]和[LnL]，并在25℃、1M NaNO条件下用荧光光谱滴定法测定了它们的稳定常数。通过从水溶液中缓慢蒸发生长出的固体化合物LnL(ClO)（Ln = Sm、Eu、Tb，L = TMDGA）的单晶结构说明了[LnL]中的配位模式。晶体结构表明，在络合物中，Ln(iii)离子由来自三个三齿L配体的九个氧原子以扭曲的三棱柱几何构型配位。为了与溶剂萃取化学进行对比，制备了与N,N'-二甲基-N,N'-二辛基二甘醇酰胺（DMDODGA，L，TMDGA的亲脂性类似物）形成的萃取Ln(iii)络合物，并收集了荧光光谱用于比较。在40 - 60%（v/v）正辛醇 - 煤油有机相中，与L形成的萃取Ln(iii)络合物的荧光光谱与水溶液中[LnL]相应的去卷积光谱几乎相同。荧光光谱的相似性表明，萃取络合物中的Ln(iii)离子也由三个三齿L配体配位，并且在溶剂萃取的有机相中，仅作为抗衡离子的硝酸根阴离子不直接与Ln(iii)键合。
