Oxidation states and CO ligand exchange kinetics in a self-assembled monolayer of a triruthenium cluster studied by in situ infrared spectroscopy.
Oxidation states and CO ligand exchange kinetics in a self-assembled monolayer of a triruthenium cluster studied by in situ infrared spectroscopy.
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DOI：
10.1002/chem.200401340
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发表时间：
2005-08
期刊：
影响因子：
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通讯作者：
Wei Zhou;S. Ye;M. Abe;T. Nishida;K. Uosaki;M. Osawa;Y. Sasaki
中科院分区：
文献类型：
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作者：
Wei Zhou;S. Ye;M. Abe;T. Nishida;K. Uosaki;M. Osawa;Y. Sasaki
研究了以氧为中心的三钌簇合物[Ru（3）（mu 3-O）（mu-CH 3COO）6（CO）（L1）（L2）]（L1 = [（NC 5 H4）CH 2NHC（O）（CH 2）10 S-]2，L2 = 4-甲基吡啶）在金电极表面的自组装单分子膜（SAM）在水溶液和非水溶液中的氧化态和CO配体交换动力学. SAM表现出三个连续的单电子转移和四个氧化态，其特征在于电化学，原位红外光谱，并在原位和频产生（SFG）振动光谱测量。Ru团簇中心的电子局域态通过中心Ru离子的氧化或还原而转变为电子离域态。这些变化是由SAM中三钌簇合物的CO配体和桥连乙酸根配体的红外光谱所揭示的。这两种配体的红外吸收都强烈地依赖于Ru簇合物中心的氧化态。SAM中中心Ru离子的单电子氧化引发CO配体释放过程。然后溶剂分子可以占据CO位点以产生不含CO的SAM。这种无CO SAM在CO饱和溶液中的单电子还原导致CO配体重新配位到SAM中。这两个过程都可以通过调节电极电位来精确控制。首次用原位红外光谱和SFG测量研究了SAM中CO交换循环的动力学，包括释放和配位。CO交换循环显著依赖于温度。反应速率随溶液温度的降低而大大降低，这是CO配体交换过程中的一个重要因素。CO的释放和协调的活化能已被评估从在不同温度下获得的反应速率常数。
Oxidation states and CO ligand exchange kinetics in a self-assembled monolayer (SAM) of an oxo-centered triruthenium cluster [Ru(3)(mu3-O)(mu-CH3COO)6(CO)(L1)(L2)] (L1 = [(NC5H4)CH2NHC(O)(CH2)10S-]2, L2 = 4-methylpyridine) have been extensively investigated on the surface of a gold electrode in aqueous and nonaqueous solutions. The SAM exhibits three consecutive one-electron transfers and four oxidation states, which have been characterized by electrochemistry, in situ infrared spectroscopy, and in situ sum frequency generation (SFG) vibrational spectroscopy measurements. The original electron-localized state of the Ru cluster center was changed to electron delocalization states by oxidation or reduction of the central Ru ions. These changes are revealed by the IR absorptions of the CO ligand and the bridging acetate ligands of the triruthenium cluster in the SAM. The IR absorptions of the two kinds of ligands are strongly dependent on the oxidation state of the Ru cluster center. One-electron oxidation of the central Ru ion in the SAM triggers a CO ligand liberation process. Solvent molecules may then occupy the CO site to result in a CO-free SAM. One-electron reduction of this CO-free SAM in a CO-saturated solution leads to re-coordination of the CO ligand into the SAM. Both processes can be precisely controlled by tuning the electrode potential. The kinetics of the CO exchange cycle in the SAM, including liberation and coordination, has been investigated by in situ IR and SFG measurements for the first time. The CO exchange cycle is significantly dependent on the temperature. The reaction rate greatly decreases with decreasing solution temperature, which is an important factor in the CO ligand exchange process. The activation energies of both CO liberation and coordination have been evaluated from the reaction rate constants obtained at various temperatures.