Kang Mei Ting, Meng Miao, Tan Ying Ning, Cheng Tao, Liu Chun Y
Department of Chemistry, Jinan University, 601 Huang-Pu Avenue West, Guangzhou, P.R. China.
Chemistry. 2016 Feb 24;22(9):3115-26. doi: 10.1002/chem.201504033. Epub 2016 Jan 25.
Assembling two quadruply bonded dimolybdenum units Mo2 (DAniF)3 (DAniF=N,N'-di(p-anisyl)formamidinate) with 1,4-naphthalenedicarboxylate and its thiolated derivatives produced three complexes [{Mo2 (DAniF)3 }2 (μ-1,4-O2 CC10 H6 CO2 )], [{Mo2 (DAniF)3 }2 (μ-1,4-OSCC10 H6 COS)], and [{Mo2 (DAniF)3 }2 (μ-1,4-S2 CC10 H6 CS2 )]. In the X-ray structures, the naphthalene bridge deviates from the plane defined by the two Mo-Mo bond vectors with the torsion angle increasing as the chelating atoms of the bridging ligand vary from O to S. The mixed-valent species exhibit intervalence transition absorption bands with high energy and very low intensity. In comparison with the data for the phenylene analogues, the optically determined electronic coupling matrix elements (Hab =258-345 cm(-1) ) are lowered by a factor of two or more, and the electron-transfer rate constants (ket ≈10(11) s(-1) ) are reduced by about one order of magnitude. These results show that, when the electron-transporting ability of the bridge and electron-donating (electron-accepting) ability of the donor (acceptor) are both variable, the former plays a dominant role in controlling the intramolecular electron transfer. DFT calculations revealed that increasing the torsion angle enlarges the HOMO-LUMO energy gap by elevating the (bridging) ligand-based LUMO energy. Therefore, our experimental results and theoretical analyses verify the superexchange mechanism for electronic coupling and electron transfer.
将两个四重键合的二钼单元Mo₂(DAniF)₃（DAniF = N,N'-二（对茴香基）甲脒）与1,4-萘二甲酸及其硫醇化衍生物组装，得到了三种配合物[{Mo₂(DAniF)₃}₂(μ-1,4-O₂CC₁₀H₆CO₂)]、[{Mo₂(DAniF)₃}₂(μ-1,4-OSCC₁₀H₆COS)]和[{Mo₂(DAniF)₃}₂(μ-1,4-S₂CC₁₀H₆CS₂)]。在X射线结构中，萘桥偏离由两个Mo-Mo键向量所定义的平面，随着桥连配体的螯合原子从O变为S，扭转角增大。混合价态物种表现出具有高能量和非常低强度的价间跃迁吸收带。与亚苯基类似物的数据相比，光学测定的电子耦合矩阵元素（Hab = 258 - 345 cm⁻¹）降低了两倍或更多，电子转移速率常数（ket ≈ 10¹¹ s⁻¹）降低了约一个数量级。这些结果表明，当桥的电子传输能力以及供体（受体）的给电子（吸电子）能力都可变时，前者在控制分子内电子转移中起主导作用。密度泛函理论计算表明，增大扭转角会通过提高基于（桥连）配体的LUMO能量来扩大HOMO-LUMO能隙。因此，我们的实验结果和理论分析验证了电子耦合和电子转移的超交换机制。
