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首页> 外文期刊>Chemistry: A European journal >Class III delocalization and exciton coupling in a bimetallic bis-ligand radical complex
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Class III delocalization and exciton coupling in a bimetallic bis-ligand radical complex

机译：双金属双配体自由基络合物中的III类离域和激子耦合

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The geometric and electronic structure of an oxidized bimetallic Ni complex incorporating two redox-active Schiff-base ligands connected via a 1,2-phenylene linker has been investigated and compared to a monomeric analogue. Information from UV/Vis/NIR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, electrochemistry, and density functional theory (DFT) calculations provides important information on the locus of oxidation for the bimetallic complex. The neutral bimetallic complex is conformationally dynamic at room temperature, which complicates characterization of the oxidized forms. Comparison to an oxidized monomer analogue 1 provides critical insight into the electronic structure of the oxidized bimetallic complex 2. Oxidation of 1 provides [1.]~+, which is characterized as a fully delocalized ligand radical complex; the spectroscopic signature of this derivative includes an intense NIR band at 4500 cm-1. Oxidation of 2 to the bis-oxidized form affords a bis-ligand radical species [2.]~(2+). Variable temperature EPR spectroscopy of [2.]~(2+) shows no evidence of coupling, and the triplet and broken symmetry solutions afforded by theoretical calculations are essentially isoenergetic. [2.]~(2+) is thus best described as incorporating two non-interacting ligand radicals. Interestingly, the intense NIR intervalence charge transfer band observed for the delocalized ligand-radical [1.]~+ exhibits exciton splitting in [2.]~(2+), due to coupling of the monomer transition dipoles in the enforced oblique dimer geometry. Evaluating the splitting of the intense intervalence charge transfer band can thus provide significant geometric and electronic information in less rigid bis-ligand radical systems. Addition of excess pyridine to [2.]~(2+) results in a shift in the oxidation locus from a bis-ligand radical species to the Ni~(III)/ Ni~(III) derivative [2(py)_4]~(2+), demonstrating that the ligand system can incorporate significant bulk in the axial positions. Split personality: A bis-ligand radical complex with minimal coupling between delocalized monomeric units exhibits exciton splitting of the intense intervalence charge-transfer band due to coupling of the monomer transition dipoles in the enforced oblique dimer geometry (see illustration).
机译：已研究了氧化的双金属Ni配合物的几何和电子结构，该配合物包含通过1，2-亚苯基连接体连接的两个氧化还原活性席夫碱配体，并将其与单体类似物进行了比较。来自UV / Vis / NIR光谱，电子顺磁共振（EPR）光谱，电化学和密度泛函理论（DFT）计算的信息为双金属配合物的氧化轨迹提供了重要信息。中性双金属配合物在室温下呈构象动力学，这使氧化形式的表征复杂化。与氧化的单体类似物1的比较提供了对氧化的双金属配合物2的电子结构的关键见解。1的氧化提供了[1.]〜+，其特征是完全离域的配体自由基配合物;该衍生物的光谱特征包括在4500 cm-1处的强烈NIR谱带。将2氧化为双氧化形式可得到双配体自由基物质[2.]〜（2+）。 [2.]〜（2+）的可变温度EPR光谱未显示耦合迹象，理论计算提供的三重态和对称破损溶液基本上是等能量的。因此，最好将[2.]〜（2+）描述为结合了两个非相互作用的配体基团。有趣的是，由于单体过渡偶极子在强制倾斜的二聚体几何结构中的耦合，在离域的配体-自由基[1.]〜+上观察到的强烈的NIR间隔电荷转移带在[2.]〜（2+）中表现出激子分裂。 。因此，评估强间隔电荷转移带的分裂可以在刚性较低的双配体自由基体系中提供重要的几何和电子信息。在[2.]〜（2+）中添加过量吡啶会导致氧化位点从双配体自由基转移到Ni〜（III）/ Ni〜（III）衍生物[2（py）_4] 〜（2+），表明配体系统可以在轴向位置上结合大量的本体。分裂个性：由于配体偶极偶极子在强制倾斜的二聚体几何结构中耦合，双分子配体自由基复合物在离域单体单元之间具有最小耦合，表现出强间隔电荷转移带的激子分裂。

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