Complexation of trivalent actinide and lanthanide ions by glycolic acid: a TRLFS study
Complexation of trivalent actinide and lanthanide ions by glycolic acid: a TRLFS study
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乙醇酸络合三价锕系元素和镧系元素离子：一项 TRLFS 研究
DOI：
10.1039/b204679b
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
I. Grenthe
中科院分区：
文献类型：
--
作者：
T. Stumpf;T. Fanghänel;I. Grenthe
用时间分辨激光荧光光谱法研究了Cm（III）和Eu（III）乙醇酸盐体系的络合作用。在痕量Cm（III）和Eu（III）浓度（分别约为10−7和10−6 mol L−1）、不同乙醇酸浓度和不同pH值下，使用NaClO 4作为背景电解质进行了测量。为了研究金属离子浓度对络合反应的影响，还进行了更高Eu（III）浓度（10 - 3 mol L-1）下的测量。通过在低pH（[H+]）下将乙醇酸浓度从0.1改变到0.5 mol L-1，
= 10−3 mol L−1）逐步形成乙醇酸络合物[Cm（HOCH 2CO 2 −）n（H2O）9 − 2n]3 −
n与n
= 1-4的化合物。通过在1 M乙醇酸盐中在4.5和12.0之间改变pH，从发光发射光谱中鉴定出三种Cm（III）物质：（i）水合四乙醇酸盐络合物[Cm（HOCH 2CO 2-）4（H2O）]-
(Cm/复合物1），其最大峰位于602.3 nm，发光寿命为206 ± 3 µs，（ii）混合氢氧化物-乙醇酸盐复合物[Cm（HOCH 2CO 2-）4（OH）]2-
(Cm/络合物2），其峰最大值在605.6 nm，并且寿命与Cm/络合物1相同，以及（iii）螯合络合物[Cm（HOCH 2CO 2-）3（-OCH 2CO 2-）（OH）]3-或[Cm（HOCH 2CO 2-）2（-OCH 2CO 2-）2（H2O）]3-
(Cm/复合物3）
(peak最大611.3 nm），其在乙醇酸盐的一个或两个配位α-OH基团去质子化后产生，发光发射寿命为295 ± 15 µs。在铕体系中，只有相应的Eu/络合物1和3的证据。相应的铕混合氢氧化物-乙醇酸盐复合物在光谱上不可检测。的发光衰减是不同的，在CM和Eu系统中的pH范围从7.8至10.5，一个双指数衰减行为观察到的CM系统，而Eu系统显示单指数衰减。这表明螯合过程的动力学对于Cm（III）比对于Eu（III）慢得多。在Eu/络合物3中配位的α-O−基团的质子化速率比在Cm/络合物3的情况下快得多。在铕浓度为3 × 10−6和1 × 10−3 mol L−1时，观察到Eu（III）/乙醇酸盐络合物的不同光谱，表明在高金属离子浓度下形成多核Eu（III）/乙醇酸盐络合物。
Complexation in the Cm(III) and Eu(III) glycolate systems has been studied by time-resolved laser fluorescence spectroscopy (TRLFS). Measurements have been performed at trace Cm(III) and Eu(III) concentrations (about 10−7 and 10−6 mol L−1, respectively), at different concentrations of glycolic acid and at different pH using NaClO4 as background electrolyte. Measurements at higher Eu(III) concentrations (10−3 mol L−1) have also been performed in order to study the influence of metal ion concentration on the complexation reaction. By varying the glycolic acid concentration from 0.1 to 0.5 mol L−1 at low pH ([H+]
= 10−3 mol L−1) the stepwise formation of glycolate complexes [Cm(HOCH2CO2−)n(H2O)9 − 2n]3 −
n with n
= 1–4 were confirmed spectroscopically. By varying the pH between 4.5 and 12.0 in 1 M glycolate three Cm(III) species were identified from the luminescence emission spectra (i) a hydrated tetraglycolate complex [Cm(HOCH2CO2−)4(H2O)]−
(Cm/complex 1) with a peak maximum at 602.3 nm and a luminescence emission lifetime of 206 ± 3 µs, (ii) a mixed hydroxide–glycolate complex [Cm(HOCH2CO2−)4(OH)]2−
(Cm/complex 2) with a peak maximum at 605.6 nm and the same lifetime as Cm/complex 1 and (iii) a chelate complex [Cm(HOCH2CO2−)3(−OCH2CO2−)(OH)]3− or [Cm(HOCH2CO2−)2(−OCH2CO2−)2(H2O)]3−
(Cm/complex 3)
(peak maximum 611.3 nm) which is generated after deprotonation of one or two of the coordinated α-OH groups of the glycolate with a luminescence emission lifetime of 295 ± 15 µs. In the europium system there is evidence only for the corresponding Eu/complex 1 and 3. The corresponding europium mixed hydroxide–glycolate complex is not detectable spectroscopically. The luminescence decay is different in the Cm and Eu systems in the pH range from 7.8 up to 10.5; a bi-exponential decay behaviour was observed for the Cm system, while the Eu system shows mono-exponential decay. This indicates that the kinetics of the chelating process is much slower for Cm(III) than for Eu(III). The rate of protonation of the coordinated α-O− group in the Eu/complex 3 is much faster than in the case of Cm/complex 3. Different spectra were observed for Eu(III)/glycolate complexes at europium concentrations of 3 × 10−6 and 1 × 10−3 mol L−1 indicating the formation of poly-nuclear Eu(III)/glycolate complexes at high metal ion concentration.