Spin state variability in Fe2+ complexes of substituted (2-(pyridin-2-yl)-1,10-phenanthroline) ligands as versatile terpyridine analogues.
Spin state variability in Fe2+ complexes of substituted (2-(pyridin-2-yl)-1,10-phenanthroline) ligands as versatile terpyridine analogues.
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DOI：
10.1039/c7dt00422b
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发表时间：
2017-05
影响因子：
4
通讯作者：
H. Petzold;P. Djomgoue;G. Hörner;Silvio Heider;C. Lochenie;Birgit Weber;T. Rüffer;Dieter Schaarschmidt
中科院分区：
文献类型：
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作者：
H. Petzold;P. Djomgoue;G. Hörner;Silvio Heider;C. Lochenie;Birgit Weber;T. Rüffer;Dieter Schaarschmidt
合成了[Fe(L)2]2+(L=2-(6-R1-吡啶-2-基)-1，10-邻菲咯啉，R1=H，甲氧基，溴，-(1H-吡唑-1-基)或L=2-(3-methoxy-pyridin-2-yl)-1，10-phenanthroline))自旋交叉配合物。这些空气稳定且耐用的络合物表现出SCO行为，其转变温度t1/2非常不同，从130K到600K不等，具体取决于取代模式。详细描述了用~1H核磁共振波谱研究SCO在这一系列溶液中的热力学和动力学。通过在吡啶的邻位引入一个额外的吡唑供体(R1)，N6八面体配位球扩展到具有三角十二面体结构的N8配位。这导致了高自旋态的强烈稳定和质子自旋的纵向弛豫增加。较大的R1值归因于不同的电子结构，具有非轨道简并的五重基态和较大的与第一激发态的能量分离。这些结果也得到了穆斯堡尔谱学的支持。N8配位球在高自旋态下稳定了络合物，没有发现SCO的迹象。密度泛函理论计算证实了实验得到的t1/2的级数，并允许在实验上不可及的自旋态下计算复杂结构。这一系列的络合物可以以化学可逆的方式氧化成Fe3+络合物。有趣的是，观察到N8配位络合物的氧化电位最低。
Fe2+ spin crossover complexes [Fe(L)2]2+ (L = 2-(6-R1-pyridin-2-yl)-1,10-phenanthroline with R1 = H, methoxy, bromo, -(1H-pyrazol-1-yl) or L = 2-(3-methoxy-pyridin-2-yl)-1,10-phenanthroline) were prepared. These air stable and durable complexes show SCO behaviour with very different transition temperatures T1/2 ranging from 130 K to 600 K depending on the substitution pattern. The use of 1H NMR spectroscopy to elucidate the thermodynamics and kinetics of SCO in a solution of this series is described in detail. By introduction of an additional pyrazole donor (R1) in the ortho-position to the pyridine, the N6 octahedral coordination sphere is expanded to N8 coordination with a trigonal dodecahedral structure. This leads to a strong stabilization of the high spin state and an increased longitudinal relaxation R1 of the proton spins. The larger R1 values were ascribed to different electronic structures with non-orbital degenerate quintet ground states and a larger energetic separation from the first excited state. These results are also supported by Mössbauer spectroscopy. The N8 coordination sphere stabilizes the complex in the high spin state and no indication for SCO was found. DFT calculations confirmed the experimentally obtained order of T1/2 and allowed the calculation of the complex structure in experimentally non-accessible spin states. Complexes of this series can be oxidized to the Fe3+ complexes in a chemically reversible fashion. Interestingly, the lowest oxidation potential was observed for the N8 coordinated complex.