Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208 016, India.
Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741 246, India.
Dalton Trans. 2019 Feb 7;48(5):1795-1813. doi: 10.1039/c8dt03778g. Epub 2019 Jan 15.
Using a potentially tridentate o-aminophenol-based redox-active ligand HL (2-[2-(benzylthio)phenylamino]-4,6-di-tert-butylphenol) in its deprotonated form, [Cu(L)] has been synthesized and crystallized as [Cu(L)]·CHCl (1·CHCl). A cyclic voltammetry experiment (in CHCl; V vs. SCE (saturated calomel electrode)) on 1·CHCl exhibits two oxidative (E = 0.20 V (peak-to-peak separation, ΔE = 100 mV) and E = 0.90 V (ΔE = 140 mV)) and two reductive (E = -0.52 V (ΔE = 110 mV) and E = -0.92 V (ΔE = 120 mV)) responses. Upon oxidation using a stoichiometric amount of Fe(η-CH), 1·CHCl yielded Cu(L) (2). Structural analysis (100 K) reveals that 1·CHCl is a four-coordinate bis(iminosemiquinonato)copper(ii) complex (CuNO coordination), and that the thioethers remain uncoordinated. The twisted geometry of 1 (distorted tetrahedral) results in considerable changes in the electronic structure, compared to well-known square-planar analogues. Crystallographic analysis of 2 both at 100 K and at 293 K reveals that it is effectively a four-coordinate complex with a CuNOS coordination; however, a substantial interaction with the other phenolate O is observed. The metal-ligand bond distances and metric parameters associated with the o-aminophenolate rings indicate a valence-tautomeric (VT) equilibrium involving monocationic (iminosemiquinonato)(iminoquinone)copper(ii) and bis(iminoquinone)copper(i). Complex 1·CHCl is a three-spin system and a magnetic study (4-300 K) established that it has a S = 1/2 ground-state, owing to the strong antiferromagnetic coupling between the unpaired spin of the copper(ii) and the iminosemiquinonate(1-) π-radical anion. Electron paramagnetic resonance (EPR) spectral studies corroborate this result. Complex 2 is diamagnetic and the existence of VT in 2 was probed using variable-temperature (248-328 K) H NMR and EPR (100-298 K) spectral measurements and X-ray photoelectron spectroscopic studies at 298 K. Remarkably, modification of the well-studied 2-anilino-4,6-di-tert-butylphenol by incorporation of a benzylthioether arm leads to the occurrence of VT in 2. The electronic structure of 1·CHCl and 2 has been assigned using density functional theory (DFT) calculations at the B3LYP-D3 level of theory. Time-dependent (TD)-DFT calculations have been performed to elucidate the origin of the observed UV-VIS-NIR absorptions.
使用潜在的三齿邻氨基酚基氧化还原活性配体 HL（2-[2-（苄硫基）苯氨基]-4,6-二叔丁基苯酚）的去质子形式，合成了[Cu（L）]，并结晶为[Cu（L）]·CHCl（1·CHCl）。1·CHCl 在 CHCl 中的循环伏安实验（V 与 SCE（饱和甘汞电极）相比）表现出两个氧化（E = 0.20 V（峰到峰分离，ΔE = 100 mV）和 E = 0.90 V（ΔE = 140 mV））和两个还原（E = -0.52 V（ΔE = 110 mV）和 E = -0.92 V（ΔE = 120 mV））响应。使用化学计量的[Fe（η-CH）]（PF）氧化 1·CHCl，得到[Cu（L）]（PF）（2）。结构分析（100 K）表明 1·CHCl 是一个四配位双（亚氨基半醌）铜（ii）配合物（CuNO 配位），硫醚保持未配位。与众所周知的平面正方形类似物相比，1 的扭曲几何形状（扭曲四面体）导致电子结构发生了相当大的变化。2 的晶体学分析在 100 K 和 293 K 时都表明它实际上是一个四配位配合物，具有 CuNOS 配位；然而，观察到与其他酚盐 O 的大量相互作用。邻氨基酚环相关的金属-配体键距离和度量参数表明涉及单阳离子（亚氨基半醌）（亚氨基醌）铜（ii）和双（亚氨基醌）铜（i）的价态互变异构（VT）平衡。复合物 1·CHCl 是一个三自旋系统，磁研究（4-300 K）确定它具有 S = 1/2 的基态，这是由于铜（ii）的未配对自旋与亚氨基半醌（1-）π-自由基阴离子之间的强反铁磁耦合所致。电子顺磁共振（EPR）光谱研究证实了这一结果。2 是抗磁性的，使用变温（248-328 K）H NMR 和 EPR（100-298 K）光谱测量以及 298 K 时的 X 射线光电子能谱研究探测了 2 中 VT 的存在。值得注意的是，通过在 2-苯胺基-4,6-二叔丁基苯酚中加入苄硫醚臂对其进行修饰，导致 2 中发生 VT。1·CHCl 和 2 的电子结构使用 B3LYP-D3 理论水平的密度泛函理论（DFT）计算进行了分配。进行了时间相关（TD）-DFT 计算，以阐明观察到的紫外-可见-近红外吸收的起源。
