Conformation-Determined Through-Bond versus Through-Space Electronic Communication in Mixed-Valence Systems with a Cross-Conjugated Urea Bridge
Conformation-Determined Through-Bond versus Through-Space Electronic Communication in Mixed-Valence Systems with a Cross-Conjugated Urea Bridge
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DOI：
10.1002/chem.201405332
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发表时间：
2015-01-19
影响因子：
4.3
通讯作者：
Yao, Jiannian
中科院分区：
文献类型：
--
作者：
Gong, Zhong-Liang;Zhong, Yu-Wu;Yao, Jiannian
合成了双三芳胺2和具有直链反，反脲桥的环化二钌6（PF 6）（2），以及双三芳胺3和具有折叠式顺，顺-N，N-二甲基脲桥的环化二钌8（PF 6）（2）。这些分子的线性或折叠构象由2、3和其他相关化合物的单晶X射线结构支持。这些化合物显示出两个连续的阳极氧化还原波（N中心点+/0或Ru-III/II过程），电位间隔为110-170 mV。这表明通过交叉共轭脲桥在两个氧化还原末端之间存在有效的电子耦合。通过光谱电化学测量研究了电子耦合程度。具有线性构象的混合价（MV）化合物观察到了明显的价间电荷转移（IVCT）跃迁。IVCT转变也可以被识别为折叠的MV化合物，尽管具有弱得多的强度。DFT结果支持线性和折叠化合物分别通过键和空间途径进行电子通信。通过TDDFT计算再现了MV化合物的IVCT跃迁。为了进行比较，合成并研究了具有咪唑烷-2-酮桥的双三芳胺和双钌配合物以及含脲的单三芳胺和单钌配合物。
Bis-triarylamine 2 and cyclometalated diruthenium 6(PF6)(2) with a linear trans, trans-urea bridge have been prepared, together with the bis-triarylamine 3 and cyclometalated diruthenium 8(PF6)(2) with a folded cis, cis-N, N-dimethylurea bridge. The linear or folded conformations of these molecules are supported by single-crystal X-ray structures of 2, 3, and other related compounds. These compounds display two consecutive anodic redox waves (N center dot+/0 or Ru-III/II processes) with a potential separation of 110-170 mV. This suggests that an efficient electronic coupling is present between two redox termini through the cross-conjugated urea bridge. The degree of electronic coupling has been investigated by using spectroelectrochemical measurements. Distinct intervalence charge-transfer (IVCT) transitions have been observed for mixed-valent (MV) compounds with a linear conformation. The IVCT transitions can also be identified for the folded MV compounds, albeit with a much weaker intensity. DFT results support that the electronic communication occurs by a through-bond and through-space pathway for the linear and folded compounds, respectively. The IVCT transitions of the MV compounds have been reproduced by TDDFT calculations. For the purpose of comparison, a bistriarylamine and a diruthenium complex with an imidazolidin-2-one bridge and a urea-containing mono-triarylamine and monoruthenium complex have been synthesized and studied.