Redox-induced spin-state switching and mixed valency in quinonoid-bridged dicobalt complexes.
Redox-induced spin-state switching and mixed valency in quinonoid-bridged dicobalt complexes.
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DOI：
10.1002/chem.201302858
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发表时间：
2014-03
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通讯作者：
David Schweinfurth;Yvonne Rechkemmer;S. Hohloch;Naina Deibel;Irina Peremykin;J. Fiedler;Raphael Marx;P. Neugebauer;J. van Slageren;B. Sarkar
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作者：
David Schweinfurth;Yvonne Rechkemmer;S. Hohloch;Naina Deibel;Irina Peremykin;J. Fiedler;Raphael Marx;P. Neugebauer;J. van Slageren;B. Sarkar
配合物 [{(tmpa)Co(II) }2 (μ-L(1) )(2-) ](2+) (1(2+) ) 和 [{(tmpa)Co(II) }2 (μ-L(2) )(2-) ](2+) (2(2+) )，其中 tmpa=三(2-吡啶甲基)胺，H2 L(1) 合成并表征了=2,5-二-[2-(甲氧基)-苯胺基]-1,4-苯醌和H2 L(2)=2,5-二-[2-(三氟甲基)-苯胺基]-1,4-苯醌。 2(2+) 的结构分析揭示了钴中心周围的扭曲八面体配位，以及与高自旋 Co(II) 中心匹配的钴配体键长。对 1(2+) 和 2(2+) 的超导量子干涉装置 (SQUID) 磁力研究与存在两个弱交换耦合的高自旋钴 (II) 离子一致，其耦合性质似乎取决于桥接配体上的取代基，1(2+) 为反铁磁性，2(2+) 为铁磁性。两种配合物均表现出多个单电子氧化还原步骤，并通过循环伏安法和紫外/可见/近红外光谱电化学对这些步骤进行了研究。对于 1(2+) ，可以化学分离单电子氧化混合价 1(3+) 和双电子氧化等价 1(4+) 形式的纯形式，并在结构和磁性上表征它们。因此，该系列提供了研究可逆电子转移对分子总自旋态影响的机会。与 2(2+) 相比，对于 1(4+) ，金属-配体距离和醌配体内的距离表明存在两个低自旋 Co(III) 中心，从而表明典型的非无辜配体 L 的无辜性。磁性数据通过显示用一氧化分子时磁矩减少大约一半（忽略自旋交换效应）来证实这些观察结果。 电子，以及双电子氧化时顺磁响应的消失，这证实了与电子转移步骤相关的自旋态的变化。
The complexes [{(tmpa)Co(II) }2 (μ-L(1) )(2-) ](2+) (1(2+) ) and [{(tmpa)Co(II) }2 (μ-L(2) )(2-) ](2+) (2(2+) ), with tmpa=tris(2-pyridylmethyl)amine, H2 L(1) =2,5-di-[2-(methoxy)-anilino]-1,4-benzoquinone, and H2 L(2) =2,5-di-[2-(trifluoromethyl)-anilino]-1,4-benzoquinone, were synthesized and characterized. Structural analysis of 2(2+) revealed a distorted octahedral coordination around the cobalt centers, and cobalt-ligand bond lengths that match with high-spin Co(II) centers. Superconducting quantum interference device (SQUID) magnetometric studies on 1(2+) and 2(2+) are consistent with the presence of two weakly exchange-coupled high-spin cobalt(II) ions, for which the nature of the coupling appears to depend on the substituents on the bridging ligand, being antiferromagnetic for 1(2+) and ferromagnetic for 2(2+) . Both complexes exhibit several one-electron redox steps, and these were investigated with cyclic voltammetry and UV/Vis/near-IR spectroelectrochemistry. For 1(2+) , it was possible to chemically isolate the pure forms of both the one-electron oxidized mixed-valent 1(3+) and the two-electron oxidized isovalent 1(4+) forms, and characterize them structurally as well as magnetically. This series thus provided an opportunity to investigate the effect of reversible electron transfers on the total spin-state of the molecule. In contrast to 2(2+) , for 1(4+) the metal-ligand distances and the distances within the quinonoid ligand point to the existence of two low-spin Co(III) centers, thus showing the innocence of the quintessential non-innocent ligands L. Magnetic data corroborate these observations by showing the decrease of the magnetic moment by roughly half (neglecting spin exchange effects) on oxidizing the molecules with one electron, and the disappearance of a paramagnetic response upon two-electron oxidation, which confirms the change in spin state associated with the electron-transfer steps.