Takeyama Tomoyuki, Tsushima Satoru, Takao Koichiro
Laboratory for Zero-Carbon Energy, Institute of Innovative Research, Tokyo Institute of Technology, 2-12-1 N1-32, O-okayama, Meguro-ku, Tokyo 152-8550, Japan.
Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Bautzner Landstraße 400, 01328 Dresden, Germany.
Inorg Chem. 2021 Aug 2;60(15):11435-11449. doi: 10.1021/acs.inorgchem.1c01449. Epub 2021 Jul 18.
Uranyl(VI) complexes with pentadentate NO-donating Schiff base ligands having various substituents at the (R) and/or (R) positions on phenolate moieties, R,R-saldien, were synthesized and thoroughly characterized by H nuclear magnetic resonance, infrared, elemental analysis, and single-crystal X-ray diffraction. Molecular structures of UO(R,R-saldien) are more or less affected by the electron-donating or -withdrawing nature of the substituents. The redox behavior of all UO(R,R-saldien) complexes was investigated to understand how substituents introduced onto the ligand affect the redox behavior of these uranyl(VI) complexes. As a result, the redox potentials of UO(R,R-saldien) in dimethyl sulfoxide increased from -1.590 to -1.213 V with an increase in the electron-withdrawing nature of the substituents at the R and R positions. The spectroelectrochemical measurements and theoretical calculation [density functional theory (DFT) and time-dependent DFT calculations] revealed that the center U of each UO(R,R-saldien) complex undergoes one-electron reduction to afford the corresponding uranyl(V) complex, [UO(R,R-saldien)], regardless of the difference in the substituents. Consequently, the redox active center of uranyl(VI) complexes seems not to be governed by the redox potentials but to be determined by whether the LUMO is centered on a U 5f orbital or on one π* orbital of a surrounding ligand.
合成了铀酰（VI）与在酚盐部分的（R）和/或（R）位置具有各种取代基的五齿供氮席夫碱配体R，R - saldien形成的配合物，并通过氢核磁共振、红外光谱、元素分析和单晶X射线衍射对其进行了全面表征。UO（R，R - saldien）的分子结构或多或少受到取代基给电子或吸电子性质的影响。研究了所有UO（R，R - saldien）配合物的氧化还原行为，以了解引入配体上的取代基如何影响这些铀酰（VI）配合物的氧化还原行为。结果，在二甲基亚砜中，UO（R，R - saldien）的氧化还原电位随着R和R位置上取代基吸电子性质的增加而从 - 1.590 V升高到 - 1.213 V。光谱电化学测量和理论计算[密度泛函理论（DFT）和含时DFT计算]表明，每个UO（R，R - saldien）配合物的中心U经历单电子还原，得到相应的铀酰（V）配合物[UO（R，R - saldien）]，而与取代基的差异无关。因此，铀酰（VI）配合物的氧化还原活性中心似乎不由氧化还原电位决定，而是由最低未占分子轨道（LUMO）是集中在U 5f轨道上还是集中在周围配体的一个π*轨道上决定。
