Electrochemical investigation of Mn4O4-cubane water-oxidizing clusters
Electrochemical investigation of Mn4O4-cubane water-oxidizing clusters
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DOI：
10.1039/b901419e
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发表时间：
2009-01-01
影响因子：
3.3
通讯作者：
Spiccia, Leone
中科院分区：
文献类型：
--
作者：
Brimblecombe, Robin;Bond, Alan M.;Spiccia, Leone
锰团簇中的高价态是自然界中发现的最重要的催化剂之一，光系统II的水氧化复合物的功能的关键特征。我们描述了一个详细的电化学研究的两个生物启发锰氧配合物，[Mn 4 O 4L 6]（L =二苯基次膦酸盐（1）和双（对甲氧基苯基）次膦酸盐（2）），在溶液中，连接到电极表面和悬浮在Nafion膜。这些配合物含有由次膦酸盐配体稳定的立方[Mn 4 O 4]（6+）核。它们以前已被证明是活性和持久的光催化剂，用于将水氧化为分子氧。通过两种方法的电极固定化沉积的膜所产生的催化光电流的比较表明，掺杂的催化剂在Nafion的结果在较高的光电流比观察到的固体层的立方烷在电极表面上。在二氯甲烷溶液中，在循环伏安法条件下，单电子氧化过程1/1（+）和2/2（+）分别是可逆和准可逆的。在本体电解的较长时间尺度上检测到1（+）和2（+）的一些分解。这两种化合物也经历了一个双电子，在二氯甲烷中的化学不可逆的还原，与一个机制，这是依赖于扫描速率和质子供体的存在下的影响。当浸入电解质水溶液中时，还原过程表现出有限的化学可逆性。这些数据提供了深入了解这些分子在光辅助电解水的催化操作，并强调了强电子捐赠配体环境的锰离子的立方烷的能力，光催化水氧化在低过电位的重要性。
High valence states in manganese clusters are a key feature of the function of one of the most important catalysts found in nature, the water-oxidizing complex of photosystem II. We describe a detailed electrochemical investigation of two bio-inspired manganese-oxo complexes, [Mn4O4L6] (L = diphenylphosphinate (1) and bis(p-methoxyphenyl)phosphinate (2)), in solution, attached to an electrode surface and suspended within a Nafion film. These complexes contain a cubic [Mn4O4](6+) core stabilized by phosphinate ligands. They have previously been shown to be active and durable photocatalysts for the oxidation of water to dioxygen. A comparison of catalytic photocurrent generated by films deposited by two methods of electrode immobilization reveals that doping of the catalyst in Nafion results in higher photocurrent than was observed for a solid layer of cubane on an electrode surface. In dichloromethane solution, and under conditions of cyclic voltammetry, the one-electron oxidation processes 1/1(+) and 2/2(+) were found to be reversible and quasi-reversible, respectively. Some decomposition of 1(+) and 2(+) was detected on the longer timescale of bulk electrolysis. Both compounds also undergo a two-electron, chemically irreversible reduction in dichloromethane, with a mechanism that is dependent on scan rate and influenced by the presence of a proton donor. When immersed in aqueous electrolyte, the reduction process exhibits a limited level of chemical reversibility. These data provide insights into the catalytic operation of these molecules during photo-assisted electrolysis of water and highlight the importance of the strongly electron-donating ligand environment about the manganese ions in the ability of the cubanes to photocatalyze water oxidation at low overpotentials.