Schönfeld Sophie, Dankhoff Katja, Baabe Dirk, Zaretzke Marc-Kevin, Bröring Martin, Schötz Konstantin, Köhler Anna, Hörner Gerald, Weber Birgit
Inorganic Chemistry IV, University of Bayreuth, Universitätsstraße 30, 95448 Bayreuth, Germany.
Institute of Inorganic and Analytical Chemistry, Technical University of Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.
Inorg Chem. 2020 Jun 15;59(12):8320-8333. doi: 10.1021/acs.inorgchem.0c00725. Epub 2020 Jun 4.
In this work, two iron(II) coordination compounds with a NO coordinating Schiff base-like ligand bearing a redox active tetrathiafulvalene (TTF) unit and pyridine or -1,2-bis(4-pyridylethylene) as an axial ligand are synthesized. Crystals suitable for single X-ray structure analysis were obtained for the new ligand. The complexes were characterized by magnetic susceptibility measurements, -dependent UV-vis spectroscopy, and cyclic voltammetry. Both complexes display spin transition behavior below room temperature with values of 146 and 156 K. The mononuclear iron(II) complex [FeL(py)] is relatively stable up to 400 K compared to similar complexes, showing no loss of axial ligands upon heating. Temperature dependent Mössbauer spectroscopy was conducted for the coordination polymer {[FeL(bpee)]} to get more information regarding the origin of the stepwise spin crossover (SCO) behavior observed in the magnetic measurements. The change of the spin state is accompanied by a change of the optical properties, which can be monitored by VT-UV-vis spectroscopy for the mononuclear complex and has been analyzed in theoretical studies. The redox behavior of the iron(II) complexes reveals three reversible redox steps which are located at the iron center and at the TTF unit of the ligand. Oxidation of the TTF unit induces characteristic changes in the UV-vis spectrum that can be followed by spectroelectrochemical UV-vis spectroscopy. Addressing the potential of the iron-centered redox process results in similar changes in the UV-vis spectrum, which indicates an electronic coupling of the redox active unit with the metal center under certain circumstances.
在本工作中，合成了两种铁（II）配位化合物，其具有带有氧化还原活性四硫富瓦烯（TTF）单元的类NO配位席夫碱配体，并以吡啶或-1,2-双（4-吡啶基乙烯）作为轴向配体。获得了适用于单晶X射线结构分析的新配体晶体。通过磁化率测量、变温紫外-可见光谱和循环伏安法对配合物进行了表征。两种配合物在室温以下均表现出自旋转变行为，转变温度分别为146 K和156 K。与类似配合物相比，单核铁（II）配合物[FeL(py)]在高达400 K时相对稳定，加热时轴向配体无损失。对配位聚合物{[FeL(bpee)]}进行了变温穆斯堡尔光谱研究，以获取更多关于磁性测量中观察到的逐步自旋交叉（SCO）行为起源的信息。自旋态的变化伴随着光学性质的变化，对于单核配合物可通过变温紫外-可见光谱监测，并且已在理论研究中进行了分析。铁（II）配合物的氧化还原行为揭示了位于铁中心和配体的TTF单元上的三个可逆氧化还原步骤。TTF单元的氧化会引起紫外-可见光谱中的特征变化，可通过光谱电化学紫外-可见光谱跟踪。研究以铁为中心的氧化还原过程的电位会导致紫外-可见光谱发生类似变化，这表明在某些情况下氧化还原活性单元与金属中心存在电子耦合。
