Department of Chemistry , Indian Institute of Technology Guwahati , Guwahati 781039 , Assam , India.
Department of Chemistry , R. K. Mission Residential College , Narendrapur, Kolkata 700103 , India.
Inorg Chem. 2019 Feb 4;58(3):1782-1793. doi: 10.1021/acs.inorgchem.8b01931. Epub 2018 Aug 28.
The noninnocent ligand HL contained a bulky phenyl substituent at the ortho position to the aniline moiety. The ligand reacted with 0.5 equiv of CuCl·2HO in the presence of EtN under air and provided the corresponding Cu(II)-bis(imonosemiquinone) complex (1). The complex upon oxidation by a stoichiometric amount of ferrocenium hexafluorophosphate (FcPF) yielded the four-coordinate [Cu(II)-(imonosemiquinone)(iminoquinone)]PF complex (3), while the oxidation by an equivalent amount of CuCl·2HO produced the five-coordinate Cu(I)-bis(iminoquinone)Cl complex (2). Thus, a ligand-based oxidation followed by ligand-to-metal electron-transfer was realized for the latter oxidation process. Removal of the Cl ion from complex 2 rendered the four-coordinate complex 4. The oxidation state of both Cu(I) and iminoquinone moieties remained unaltered upon the change in the coordination number. All the complexes were characterized by X-ray crystallography. Complexes 2, 3, and 4 were diamagnetic with an S = 0 ground state as evident by electron paramagnetic resonance (EPR) and H NMR measurements. The UV-vis-NIR spectra of all the complexes were dominated by charge-transfer transitions. Two oxidations and two reductions waves were noticed in the cyclic voltammogram (CV) of complex 1. Complex 2 and complex 3 underwent one oxidation and three reductions. Unlike complex 3, which experienced ligand-based oxidation, in complex 2 the oxidation was metal-centered [oxidation of Cu(I)-to-Cu(II)]. UV-vis-NIR spectral changes during the fixed-potential coulometric one-electron oxidation and thereafter EPR analysis consolidated the metal-based oxidation in complex 2. Complex 2 was air stable; however, it oxidized KO to oxygen molecule, and complex 1 was formed in due course as evident by UV-vis-NIR spectral changes and EPR measurements. Time dependent density functional theory calculations have been incorporated to assign the transitions that appeared in the UV-vis-NIR spectra of the complexes.
HL 配体的苯胺部分邻位带有一个大体积的苯基取代基。该配体在空气存在下与 0.5 当量的 CuCl·2HO 和 EtN 反应，提供相应的 Cu(II)-双(亚单氧醌)配合物 (1)。该配合物通过化学计量量的 ferrocenium hexafluorophosphate (FcPF) 氧化生成四配位的 [Cu(II)-(亚单氧醌)(亚醌)]PF 配合物 (3)，而当量的 CuCl·2HO 氧化生成五配位的 Cu(I)-双(亚醌)Cl 配合物 (2)。因此，对于后一种氧化过程，实现了基于配体的氧化，然后是配体到金属的电子转移。从配合物 2 中去除 Cl 离子得到四配位配合物 4。配位数变化时，Cu(I)和亚醌部分的氧化态保持不变。所有配合物均通过 X 射线晶体学进行了表征。配合物 2、3 和 4 均为顺磁性，电子顺磁共振 (EPR) 和 1H NMR 测量表明其基态为 S = 0。所有配合物的紫外-可见-近红外光谱均由电荷转移跃迁主导。在配合物 1 的循环伏安图 (CV) 中观察到两个氧化和两个还原波。与经历基于配体的氧化的配合物 3 不同，在配合物 2 中，氧化是金属中心的 [Cu(I)到 Cu(II)的氧化]。配合物 2 和 3 经历了一次氧化和三次还原。与配合物 3 不同，在配合物 2 中，氧化是金属中心的氧化。配合物 2 空气稳定；然而，它将 KO 氧化为氧分子，并且随着 UV-vis-NIR 光谱变化和 EPR 测量，复合物 1 随之形成。时变密度泛函理论计算已被纳入，以分配出现在配合物紫外-可见-近红外光谱中的跃迁。
