The Effects of Coordinated Molecules of Two Gly-Schiff Base Copper Complexes on Their Oxygen Reduction Reaction Performance

In this study, two simple Schiff base copper complexes [Cu(H2O)2(HL)]·2H2O (Complex 1) (H3L = 2-OH-4-(OH)-C6H2CH=NCH2CO2H) and [Cu(py)2(HL)] (Complex 2) (Py = pyridine) were initially achieved and authenticated by single-crystal X-ray structure analyses (SXRD), powder X-ray diffraction analyses (PXRD), FT-IR spectroscopy, and elemental analyses. The SXRD reveals that the Cu2+ center in Complex 1 exhibited a distorted square pyramidal geometry, which is constructed based on phenolate oxygen, water molecules, carboxylate oxygen, and imine nitrogen from a deprotonated H3L ligand in an NO4 fashion. The Cu2+ atom in Complex 2 had distorted square pyramidal geometry, and was coordinated with two pyridine molecules and one Gly-Schiff base ligand, exhibiting an N3O2 binding set. Additionally, the free water molecules in Complex 1 linked independent copper complexes by intermolecular hydrogen bond to form a 2D framework. However, the one-dimensional chain supramolecular structure of Complex 2 was formed by the intermolecular O–H…O hydrogen bonds. The oxygen reduction performance of the two complexes was analyzed by cyclic voltammetry (CV) and the rotating disk electrode (RDE) method. Both complexes could catalyze the conversion of oxygen to water through a predominant four-electron pathway, and the Cu–NxOy moieties might be the functional moieties for the catalytic activity. The catalytic pathways and underlying mechanisms are also discussed in detail, from which the structure–activity relationship of the complexes was obtained.

在这项研究中，最初合成了两种简单的席夫碱铜配合物[Cu(H₂O)₂(HL)]·2H₂O（配合物1）（H₃L = 2 - 羟基 - 4 -（羟基）- C₆H₂CH = NCH₂CO₂H）和[Cu(py)₂(HL)]（配合物2）（Py = 吡啶），并通过单晶X射线结构分析（SXRD）、粉末X射线衍射分析（PXRD）、傅里叶变换红外光谱（FT - IR）和元素分析进行了验证。SXRD表明，配合物1中的Cu²⁺中心呈现出扭曲的四方锥几何构型，它是由来自去质子化的H₃L配体的酚氧、水分子、羧基氧和亚胺氮以NO₄形式构建而成。配合物2中的Cu²⁺原子具有扭曲的四方锥几何构型，并与两个吡啶分子和一个甘氨酸 - 席夫碱配体配位，呈现出N₃O₂配位形式。此外，配合物1中的游离水分子通过分子间氢键将独立的铜配合物连接起来，形成一个二维框架。然而，配合物2的一维链状超分子结构是由分子间O - H…O氢键形成的。通过循环伏安法（CV）和旋转圆盘电极（RDE）方法分析了这两种配合物的氧还原性能。两种配合物都能通过主要的四电子途径催化氧气转化为水，并且Cu - NₓOᵧ部分可能是催化活性的功能部分。还详细讨论了催化途径和潜在机制，由此得出了配合物的构效关系。