A survey of ligand effects upon the reaction entropies of some transition metal redox couples
A survey of ligand effects upon the reaction entropies of some transition metal redox couples
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DOI：
10.1002/chin.197922065
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发表时间：
1979-02
期刊：
影响因子：
--
通讯作者：
E. Yee;R. J. Cave;K. L. Guyer;P. Tyma;M. J. Weaver
中科院分区：
文献类型：
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作者：
E. Yee;R. J. Cave;K. L. Guyer;P. Tyma;M. J. Weaver
用非等温电化学电池测定了水溶液中M（III）/（11）型过渡金属氧化还原电对的反应熵lS 0，以探讨配体结构对离子-溶剂相互作用性质的影响。用不同的金属M检验了六种M（OHZ）~+，~ + ' ~ +形式的水电对，得到阿索~+值在36-49 eu范围内。为了研究用氨和简单阴离子配体取代水溶液的效果，使用Ru（II I）/（II I）对，因为两种氧化态的相对取代惰性允许使用循环伏安法测定AS '。氨胺配体逐步取代水溶液导致阿索的大量减少，这归因于氨胺与水溶液配体相比，配体-溶剂氢键的程度较小。用阴离子配体取代水和氨也导致阿索，的显著降低。还检查了许多含有螯合配体的M（III）/（II）对。发现Co（111）/（111）对与相应的Ru（111）/（111）和Fe（111）/（111）对之间的阿索_（10）有很大的差别。建议的解释是配体构象和电子离域效应的差异。注意到外层溶剂结构效应对水络合物的电子交换所观察到的大重组能的可能贡献。估计的阿索，从非等温电池测量所需的假设的有效性进行了讨论。
The reaction entropies lSo,, of a number of transition metal redox couples of the form M ( I I I ) / ( 11) in aqueous solution have bcen determined using nonisothermal electrochemical cells in order to explore the effect of varying the ligand structure upon the nature of the ion-solvent interactions. Examination of six aquo couples of the form M ( O H Z ) , , ~ + ' ~ + with varying metal M yielded ASo,, values in the range 36-49 eu. In order to scrutinize the effect of replacing aquo with ammine and simple anionic ligands, R u ( l I I ) / ( I I ) couples were employed since the relativc substitution inertness of both oxidation states allowed AS',, to be determined using cyclic voltammetry. The stepwise replacement of aquo by ammine ligands results in substantial reductions in ASo,, which are attributed to the smaller extent of ligand-solvent hydrogen bonding for ammine compared with aquo ligands. Substitution of both aquo and ammine by anionic ligands also resulis in substantial reductions in ASo,,. A number of M ( I I I ) / ( I I ) couples containing chelating ligands were also examined. Sizable differcnces in ASo,, were found between Co(lll)/(ll) couples and the corresponding R u ( l l l ) / ( l l ) and Fe(lll)/(ll) couples. Suggested explanations are differences in ligand conformation and electron delocalization effects. The possible contribution of outer-sphere solvent structuring effects to the large reorganization energies observed for electron exchange of aquo complexes is noted. The validity of the assumptions required for the estimation of ASo,, from nonisothermal cell measurements is discussed.