Mandal Abhishek, Grupp Anita, Schwederski Brigitte, Kaim Wolfgang, Lahiri Goutam Kumar
†Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
‡Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany.
Inorg Chem. 2015 Aug 17;54(16):7936-44. doi: 10.1021/acs.inorgchem.5b01017. Epub 2015 Jul 31.
The new compounds (bpy)2Os(II)(μ-L1(2-))Os(II)(bpy)22 (12) and (pap)2Os(II)(μ-L1(2-))Os(II)(pap)22 (22) (H2L1 = 1,4-dihydroxy-9,10-anthraquinone, bpy = 2,2(/)-bipyridine, and pap = 2-phenylazopyridine) and (bpy)2Os(II)(μ-L2(•-))Os(II)(bpy)23 (33) and (pap)2Os(II)(μ-L2(2-))Os(II)(pap)22 (42) (H2L2 = 1,4-diamino-9,10-anthraquinone) have been analytically identified as the meso and rac diastereoisomers, respectively. The paramagnetic 33 was also characterized by crystal structure determination. In CD3CN solution, 33 displays rather narrow but widely split (13 > δ > -8 ppm) resonances in the (1)H NMR spectrum, yet no EPR signal was observed down to 120 K. Cyclic voltammetry and differential pulse voltammetry reveal several accessible redox states on oxidation and reduction, showing that the replacement of 1,4-oxido by imido donors causes cathodic shifts and that the substitution of bpy by the stronger π-accepting pap ligands leads to a strong increase of redox potentials. Accordingly, system 3(n) with the lowest (2+/3+) potential was synthetically obtained in the mono-oxidized (3+) form. The (3+) intermediates display small comproportionation constants Kc of about 10(3) and long-wavelength near-infrared absorptions; an EPR signal with appreciable g splitting (1.84, 1.96, and 2.03) was only observed for 4(3+), which exhibits the smallest spin density on the osmium centers. An oxidation state formulation Os(III)(μ-L(•3-))Os(III) with some Os(II)(μ-L(2-))Os(III) contribution was found to best describe the electronic structures. UV-vis-NIR absorption spectra were recorded for all accessible states by OTTLE spectroelectrochemistry and assigned on the basis of TD-DFT calculations. These results and additional EPR measurements suggest rather variegated oxidation state situations, e.g., the pap ligands competing with the bridge L for electrons, while the oxidation produces mixed spin systems with variable metal/ligand contributions.
新化合物(bpy)₂Os(II)(μ - L₁²⁻)Os(II)(bpy)₂₂(1₂)和(pap)₂Os(II)(μ - L₁²⁻)Os(II)(pap)₂₂(2₂)(H₂L₁ = 1,4 - 二羟基 - 9,10 - 蒽醌，bpy = 2,2′ - 联吡啶，pap = 2 - 苯基偶氮吡啶)以及(bpy)₂Os(II)(μ - L₂•⁻)Os(II)(bpy)₂₃(3₃)和(pap)₂Os(II)(μ - L₂²⁻)Os(II)(pap)₂₂(4₂)(H₂L₂ = 1,4 - 二氨基 - 9,10 - 蒽醌)已分别被分析鉴定为内消旋和外消旋非对映异构体。顺磁性的3₃也通过晶体结构测定进行了表征。在CD₃CN溶液中，3₃在¹H NMR谱中显示出相当窄但分裂广泛(13 > δ > - 8 ppm)的共振峰，然而在低至120 K时未观察到EPR信号。循环伏安法和差分脉冲伏安法揭示了氧化和还原过程中有几个可及的氧化还原态，表明用亚氨基供体取代1,4 - 氧化基团会导致阴极位移，并且用更强的π - 接受性pap配体取代bpy会导致氧化还原电位大幅增加。因此，以单氧化(3⁺)形式合成得到了具有最低(2⁺/3⁺)电位的体系3(n)。(3⁺)中间体显示出约为10³的小归中常数Kc和长波长近红外吸收；仅在4(3⁺)中观察到具有明显g分裂(1.84、1.96和2.03)的EPR信号，其在锇中心上的自旋密度最小。发现氧化态公式[Os(III)(μ - L•³⁻)Os(III)]³⁺并带有一些[Os(II)(μ - L²⁻)Os(III)]³⁺的贡献最能描述电子结构。通过OTTLE光谱电化学记录了所有可及态的紫外 - 可见 - 近红外吸收光谱，并基于TD - DFT计算进行了归属。这些结果和额外的EPR测量表明存在相当多样化的氧化态情况，例如，pap配体与桥连配体L竞争电子，而氧化产生具有可变金属/配体贡献的混合自旋体系。
