A solvent- and temperature-dependent intramolecular equilibrium of diamagnetic and paramagnetic states in Co complexes bearing triaryl amines.
A solvent- and temperature-dependent intramolecular equilibrium of diamagnetic and paramagnetic states in Co complexes bearing triaryl amines.
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DOI：
10.1039/c8dt02538j
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发表时间：
2018-09
影响因子：
4
通讯作者：
Linda Schnaubelt;H. Petzold;E. Dmitrieva;M. Rosenkranz;H. Lang
中科院分区：
文献类型：
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作者：
Linda Schnaubelt;H. Petzold;E. Dmitrieva;M. Rosenkranz;H. Lang
合成了含有三个氧化还原活性中心（一个Co2+离子和两个三芳胺（塔拉）单元）的配合物[Co(L)2](ClO4)2 （L = o-取代2-（吡啶-2-基）-1,10-菲罗啉1a-c）。采用循环伏安法和EPR/ uv -可见-近红外光谱电化学方法测定了[Co(L)2](ClO4)2 （L = 1a-c）的氧化步骤顺序。在乙腈溶液中，在室温下，第一次氧化是共心氧化，其次是在更高的阳极电位下的塔拉氧化。在极性较弱的溶剂二氯甲烷溶液中，氧化顺序颠倒。以Co3+/2+为中心的氧化还原事件导致了顺磁性高自旋（HS） Co2+和抗磁性低自旋（LS） Co3+状态之间的自旋转变，并通过1H NMR和EPR谱证实了这一点。[Co(L)2](ClO4)2经单电子氧化后，在[Co(L)2]3+ (L = 1a-c)中发现了反磁性[Co3+(L)]3+与顺磁性[Co2+(L)(L+)]3+态之间的平衡。循环伏安法表明，[Co2+(L)(L+)]3+介导的[Co2+(L)2]2+和[Co3+(L)2]3+氧化还原态之间的分子间电子转移增强。原位生成的[Co(L)2]3+的变温可见-近红外光谱显示了[Co3+(L)2]3+和[Co2+(L+)(L)]3+状态之间的温度依赖的氧化还原平衡（L = 1a-c）。从相应的EPR光谱中观察到的宽谱线和不可探测谱线推断出[HS-Co2+(L+)(L)]3+ (L = 1a,c)中HS-Co2+离子与Tara+自由基之间的磁耦合。完全氧化为[LS-Co3+(L+)2]5+ (L = 1a,c)导致具有非相互作用自旋的Tara双自由基的特征EPR谱。
Complexes [Co(L)2](ClO4)2 (L = o-substituted 2-(pyridine-2-yl)-1,10-phenanthrolines 1a-c) containing three redox active centres (a Co2+ ion and two triaryl amine (Tara) units) have been synthesised. The order of oxidation steps in [Co(L)2](ClO4)2 (L = 1a-c) was determined using cyclic voltammetry and EPR/UV-vis-NIR spectroelectrochemistry. In acetonitrile solutions, at room temperature, the first oxidation is Co-centred followed by the Tara oxidation at more anodic potentials. The order of oxidation is inverted in solutions of the less polar solvent dichloromethane. The Co3+/2+-centred redox event leads to a spin transition between the paramagnetic high-spin (HS) Co2+ and the diamagnetic low-spin (LS) Co3+ state, which was proven using 1H NMR and EPR spectroscopy. After one-electron oxidation of [Co(L)2](ClO4)2, an equilibrium between the diamagnetic [Co3+(L)]3+ and paramagnetic [Co2+(L)(L+)]3+ state in [Co(L)2]3+ (L = 1a-c) was found. Cyclic voltammetry showed enhanced intermolecular electron transfer between the [Co2+(L)2]2+ and [Co3+(L)2]3+ redox states mediated by [Co2+(L)(L+)]3+. Variable temperature vis-NIR spectroscopy of in situ generated [Co(L)2]3+ revealed a temperature-dependent redox equilibrium between the [Co3+(L)2]3+ and the [Co2+(L+)(L)]3+ states (L = 1a-c). Magnetic coupling between the HS-Co2+ ion and the Tara+ radical in [HS-Co2+(L+)(L)]3+ (L = 1a,c) was deduced from broad and undetectable lines observed in the corresponding EPR spectra. Complete oxidation to [LS-Co3+(L+)2]5+ (L = 1a,c) leads to characteristic EPR spectra of Tara biradicals with non-interacting spins.