Kinetic studies of ligand substitution rates for the Ru(NH3)5(H2O)2+ ion in Nafion films
Kinetic studies of ligand substitution rates for the Ru(NH3)5(H2O)2+ ion in Nafion films
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Nafion 薄膜中 Ru(NH3)5(H2O)2 离子的配体取代率的动力学研究
DOI：
10.1021/ja00280a001
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发表时间：
1986
期刊：
影响因子：
--
通讯作者：
N. Lewis
中科院分区：
文献类型：
--
作者：
Charles M. Lieber;Michael H. Schmidt;N. Lewis
测量了许多吡啶与 Nafion 结合的 Ru(NH/sub 3/)/sub 5/(H/sub 2/O)/sup 2 +/ 复合物反应的取代率。反应活性已通过电化学技术确定，该技术还可以确定反应过程中的位点热力学和异质性。通过聚合物膜厚度的变化研究扩散系数效应，并通过光学吸收技术在平衡条件下确定分配系数。发现分配系数校正速率定律在 Nafion 结合 (Ru/sup II/) 中是一阶的，在聚合物相中的配体浓度中是一阶的。发现各种吡啶配体的分配系数校正的双分子速率常数变化了 5 倍，这与在水溶液中观察到的相对恒定的取代速率形成对比。此外，空间位阻配体（例如 2-丙基吡啶）在 Nafion 结合的 Ru/sup II/ 离子上表现出令人惊讶的高取代率常数。这些速率数据表明，在电极修饰时可能会发生显着的分子反应性变化，并且对于用于电催化的化学修饰电极的设计具有影响。
Substitution rates have been measured for reaction of a number of pyridines with the Nafion-bound Ru(NH/sub 3/)/sub 5/(H/sub 2/O)/sup 2 +/ complex. Reaction activities have been determined by electrochemical techniques, which also allow for determination of site thermodynamics and heterogeneity during the course of the reaction. Diffusion-coefficient effects are investigated by variation in polymer film thickness, and partition coefficients have been determined under equilibrium conditions by optical absorbance techniques. The partition-coefficient corrected rate law is found to be first order in Nafion-bound (Ru/sup II/) and first order in ligand concentration in the polymer phase. The partition-coefficient corrected bimolecular rate constants for a variety of pyridine ligands are found to vary by a factor of 5, which contrasts with the relatively constant substitution rates observed in aqueous solution. Also, sterically hindered ligands, such as 2-propylpyridine, exhibit surprisingly high substitution rate constants on the Nafion-bound Ru/sup II/ ion. These rate data indicate that pronounced molecular reactivity changes can occur upon electrode modification and have implications with respect to the design of chemically modified electrodes for use in electrocatalysis.