Electron transfer in mixed-valence biferrocenium salts : effect of zero-point energy difference and pronounced anion dependence
Electron transfer in mixed-valence biferrocenium salts : effect of zero-point energy difference and pronounced anion dependence
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混合价二茂铁盐中的电子转移：零点能量差的影响和明显的阴离子依赖性
DOI：
10.1021/ic00011a002
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发表时间：
1991
影响因子：
4.6
通讯作者：
Shiang Li
中科院分区：
文献类型：
--
作者：
T. Dong;Chi;T. Hsu;Shyi;Shiang Li
光反应在络合物中被强烈抑制，而基态的非辐射衰变是一个更有效的竞争者。这种速率抑制的部分原因可能是在反向系统间交叉之前出现的，因为激活途径的更大的能量势垒允许更多的竞争性双重态非辐射衰变。然而，这种衰减可以被容纳的程度受到观察到的阿累尼乌斯图线性的限制。在过渡状态级别，其他可能的原因很容易想象。如果过渡态为七坐标，则配合物可能比二胺具有更高的空间拥挤和应变能。另一种可能是，整个配体所需的迁移是一个困难而缓慢的过程，因此失活和/或重新协调有更大的竞争机会。最后，二胺配合物通过七坐标物种的微秒寿命进行反应。如果配合物的行为类似，那么它的中间体可能更有可能恢复到起始物质，因为离开配体的双齿性质。结束语。我们已经提出的证据表明，光化学Cr-N键断裂发生后，在边缘位移反应中，双齿配体有可能从一个配位位点迁移到另一个配位位点。由于我们的证明依赖于立体化学变化的假设，未来将寻求更多的证据。用适当的立体化学指示牌设计实验来证明群体迁移是相当直接的。不幸的是，很难找到一个体系，在这个体系中，起始化合物可以被制备和明确地表征，并通过包括立体化学在内的产物鉴定来探索其光化学。然而，这项工作表明，复杂的配体运动是可能的，对这种现象的进一步研究是容易处理的，值得追求。
that the photoreaction is strongly inhibited in the en complex and that nonradiative decay to the ground state is a more effective competitor. Part of this rate inhibition in the en complex could arise prior to reverse intersystem crossing because the larger energy barrier for the activated route allows more competitive doublet nonradiative decay. However, the extent to which such decay can be accommodated is restricted by the observed linearity of the Arrhenius plot. At the transition-state level, other possible reasons are easy to imagine. If the transition state is seven-coordinate, then it may be more sterically crowded and have higher strain energy for the en complex than for the diammine. Alternatively, it may be that the required migration of the whole en ligand is a difficult and slow process so that deactivation and/or recoordination have a greater opportunity to compete. Finally, the diammine complex reactsz7 via a seven-coordinate species of microsecond lifetime. If the en complex behaves similarly, then its intermediate might be more likely to revert to starting material because of the bidentate nature of the leaving ligand. Concluding Remarks. We have presented evidence that after photochemical Cr-N bond breaking has occurred, it is possible for the reacting bidentate ligand to migrate from one coordination site to another in an edge displacement reaction. Since our proof relies on the assumption of stereochemical change, in the future additional evidence will be sought. It is fairly straightforward to design experiments with appropriate stereochemical sign-posting to prove group migration incontrovertably. Unfortunately, it is difficult to identify systems in which the starting compound can be prepared and unambiguously characterized and its photochemistry explored with product identification including stereochemistry. The work has shown, however, that complex ligand motions are likely and that further study of such phenomena is tractable and worth pursuing.