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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Impact of ligand protonation on higher-order metal complexation kinetics in aqueous systems
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Impact of ligand protonation on higher-order metal complexation kinetics in aqueous systems

机译：配体质子化对水性体系高阶金属络合动力学的影响

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The impact of ligand protonation on the complexation kinetics of higher-order complexes is quantitatively described. The theory is formulated on the basis of the usual situation for metal complex formation in aqueous systems in which the exchange of water for the ligand in the inner coordination sphere is rate-determining (Eigen mechanism). We derive expressions for the general case of lability of MLn species that account for the contributions from all outer-sphere complexes to the rate of complex formation. For dynamic complexes, dissociation of ML is usually the rate-determining step in the overall process MLn -> M. Under such conditions, it is the role of ligand protonation in the step ML -> M that is relevant for the kinetic flux. 1:2 complexes of Cd(II) with pyridine-2,6-dicarboxylic acid fall into this category, and their lability at a microelectrode is reasonably well predicted by the differentiated approach. For non-dynamic systems, the kinetic flux arising from dissociation of higher-order complexes contributes to the rate-determining step. In this case, the weighted contribution of protonated and unprotonated outer-sphere complexes in all contributing dissociation reactions must be taken into account. The kinetic flux arising from the dissociation of 1:2 complexes of Ni(II) with bicine at a conventional electrode was quite well described by this combined approach. The results establish the generic role of ligand protonation within the overall framework of metal complexation kinetics in which complexes may be dynamic to an extent that depends on the operational time scale of the measurement technique.
机译：定量描述了配体质子化对高阶络合物的络合动力学的影响。该理论是根据水性体系中金属络合物形成的一般情况制定的，在水性体系中水在内部配位球体内交换配体是决定速率的（本征机理）。我们推导了MLn物种不稳定性的一般情况下的表达式，这些表达式解释了所有外圈复合物对复合物形成速率的贡献。对于动态络合物，ML的解离通常是整个过程MLn-> M的决定速率的步骤。在这种情况下，步骤ML-> M的配体质子化作用与动力学通量有关。 Cd（II）与2,6-吡啶-2-甲酸吡啶的1：2配合物属于这一类，并且通过微分方法可以很好地预测它们在微电极上的不稳定性。对于非动力学系统，由高阶络合物解离产生的动量有助于确定速率。在这种情况下，必须考虑质子化和非质子化的外层球体在所有离解反应中的加权贡献。通过这种组合方法可以很好地描述在常规电极上Ni（II）与Bicine的1：2配合物解离所产生的动力学通量。结果在金属络合动力学的整个框架内确立了配体质子化的一般作用，其中络合物在一定程度上可能是动态的，这取决于测量技术的操作时间尺度。

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