Bimolecular electron and energy transfer reactivity of exchange-coupled dinuclear iron(III) complexes.
Bimolecular electron and energy transfer reactivity of exchange-coupled dinuclear iron(III) complexes.
复制标题
交换耦合双核铁(III)络合物的双分子电子和能量转移反应性。
DOI：
10.1021/ic010659l
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发表时间：
2001
影响因子：
4.6
通讯作者：
McCusker,JK
中科院分区：
文献类型：
--
作者：
Weldon,BT;Wheeler,DE;Kirby,JP;McCusker,JK
人们研究了光敏剂和交换耦合过渡金属配合物之间的双分子猝灭，试图通过实验建立海森堡自旋交换和化学反应性之间的联系。受体是双核 FeIII 化合物的氧代/羟基双羧基类的成员，其中氧桥的质子化提供了调节簇内自旋交换幅度的方法。含有RuII聚吡啶基敏化剂和FeIII络合物的溶液的光激发导致RuII发色团的3MLCT激发态的发射猝灭；纳秒时间分辨吸收测量表明，猝灭部分是通过电子转移发生的。通过改变桥接羧酸盐以提供一系列[Fe2O(H)(O2CR)2(Tp)2]n+(n= 0, 1, 2)形式的复合物，实现了电子转移驱动力(ΔG0ET)与自旋交换幅度变化的解耦。电化学测量揭示了整个系列中团簇还原电位的大于 500 mV 的变化（即，R = CH3to CF3），而变温磁化率测量表明金属中心之间的自旋交换具有相应的不变性（Joxo= -119 ± 4 cm-1 和 JHydroxo= -18 ± 2 cm-1for H= −2JS1·S2)。结构分析表明，对于给定系列（即氧桥或羟基桥接）内的所有分子，与电子转移相关的重组能（λ）应该是相同的；同样，系列之间的 Δλ 预计也会很小。两个扩展系列的猝灭速率的比较明确表明，重组能和电子转移驱动力考虑因素都不能解释氧桥（大自旋交换）和羟基桥（小自旋交换）猝灭剂之间反应性的差异。考虑到能量转移的贡献，可以确定氧桥和羟基桥猝灭剂之间的反应性差异必须在于 Dexter 能量转移和/或电子转移的相对速率，后者的起源与 ΔG0ET 或 λ 以外的其他因素相关。最后，讨论了双核 FeIII 猝灭剂内的自旋交换在多大程度上可以被确定为影响这些反应模式的关键变量。
Bimolecular quenching between photosensitizers and exchange-coupled transition metal complexes has been studied in an effort to experimentally establish a link between Heisenberg spin exchange and chemical reactivity. The acceptors are members of the oxo/hydroxo-biscarboxylato class of dinuclear FeIIIcompounds, where protonation of the oxo bridge provides a means for modulating the magnitude of spin exchange within the cluster. Photoexcitation of solutions containing RuIIpolypyridyl sensitizers and the FeIIIcomplexes results in quenching of emission from the3MLCT excited state of the RuIIchromophores; nanosecond time-resolved absorption measurements demonstrate that quenching occurs, in part, by electron transfer. Decoupling electron transfer driving force (ΔG0ET) from changes in the magnitude of spin exchange was achieved by varying the bridging carboxylate to afford a series of complexes of the form [Fe2O(H)(O2CR)2(Tp)2]n+(n= 0, 1, 2). Electrochemical measurements reveal a greater than 500 mV shift in cluster reduction potential across the series (i.e., R = CH3to CF3), whereas variable-temperature magnetic susceptibility measurements demonstrate a corresponding invariance in spin exchange between the metal centers (Joxo= −119 ± 4 cm-1andJhydroxo= −18 ± 2 cm-1forH= −2JS1·S2). Structural analyses suggest that reorganization energies (λ) associated with electron transfer should be identical for all molecules within a given series (i.e., oxo or hydroxo bridged); likewise Δλ between the series is expected to be small. A comparison of quenching rates for the two extended series firmly establishes that neither reorganization energy nor electron transfer driving force considerations can account for differences in reactivity between oxo-bridged (large spin exchange) and hydroxo-bridged (small spin exchange) quenchers. Upon consideration of energy transfer contributions, it is determined that reactivity differences between the oxo- and hydroxo-bridged quenchers must lie in the relative rates of Dexter energy transfer and/or electron transfer, with the origin of the latter linked to something other than ΔG0ETor λ. Finally, the extent to which spin exchange within the dinuclear FeIIIquenchers can be identified as the key variable influencing these reactivity patterns is discussed.