Entropy-controlled solvolytic dissociation kinetics of lanthanide(III) complexes with polyaminocarboxylates in aqueous solutions.
Entropy-controlled solvolytic dissociation kinetics of lanthanide(III) complexes with polyaminocarboxylates in aqueous solutions.
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水溶液中镧系元素 (III) 与聚氨基羧酸盐配合物的熵控制溶剂解离动力学。
DOI：
10.1021/ic001053k
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发表时间：
2001
影响因子：
4.6
通讯作者：
T. Yotsuyanagi
中科院分区：
文献类型：
--
作者：
S. Saito;H. Hoshino;T. Yotsuyanagi
本文研究了稀土(III)-无环多氨基羧酸盐络合物在溶剂分解反应中形成惰性络合物的因素，为高效液相色谱和高效毛细管电泳法等分析方法中动力学控制的选择性奠定了基础。通过金属和配体交换反应，在间歇体系中测定了稀土络合物的溶剂分解和酸辅助解离过程的速率常数。所用试剂为8-amino-2-[(2-amino-5-methylphenoxy)methyl]-6-methoxyquinoline-N，N，N‘，N’-四乙酸(Quin2)和O，O‘-双(2-氨基苯基)乙二醇-N，N，N’，N‘-四乙酸(BAPTA)作为八齿配体，反式-1，2-二氨基环己烷-N，N，N’，N‘-四乙酸(CyDTA)作为六齿配体。结果表明，随Ln(III)离子半径的不同，Quin_2络合物的溶解速率常数在5.7×10~(-3)x S(~(-1))(La~(3+))~1.7×10~(-6)x S(~(-1))(Ru~(3+))之间变化，而BAPTA络合物则不存在这种单调关系。在活化参数中，值得注意的是有一个相当大的负活化熵，最高可达-250J×mol(-1)×K(-1)，这是导致Ln-多氨基羧酸盐络合物惰性的原因。我们的数据表明，除了配体的碱性对Ln(III)络合物的缓慢解离动力学起着重要作用外，有利于Ln(III)离子配位数较大的配体的多重配位是形成活化负熵的关键。
The factors involved in the formation of an inert complex in terms of solvolysis reaction have been studied for lanthanide(III)-acyclic polyaminocarboxylate complexes, as the basis for kinetically controlled selectivity used in analytical methodologies such as HPLC and HPCE. The rate constants for solvolysis and acid-assisted dissociation processes of the lanthanide complexes were determined in a batch system through metal- and ligand-exchange reactions. The reagents used were 8-amino-2-[(2-amino-5-methylphenoxy)methyl]-6-methoxyquinoline-N,N,N',N'-tetraacetic acid (Quin2) and O,O'-bis(2-aminophenyl)ethylene glycol-N,N,N',N'-tetraacetic acid (BAPTA) as octadentate ligands and trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CyDTA) as a hexadentate ligand. It has been found that the rate constants for solvolysis vary from 5.7 x 10(-3) x s(-1) (La3+) to 1.7 x 10(-6) x s(-1) (Lu3+) depending on the ionic radii of Ln(III) ions for the Quin2 complexes, while no such monotonic dependence was observed for the BAPTA complexes. Among the parameters of activation, it is worth noting that there is a considerably large negative entropy of activation, of up to -250 J x mol(-1) x K(-1), and it is this which is responsible for the inertness of the Ln-polyaminocarboxylate complexes. Our data suggest that multiple ligation of the ligand in favor of the large coordination number of Ln(III) ions is of key importance for formation of the negative entropy of activation, in addition to the basicity of the ligand which also plays a significant role in the slow dissociation kinetics of the Ln(III) complexes.