In biological systems, nitrite reductase enzymes (NIRs) are responsible for reduction of nitrite (NO₂⁻) to nitric oxide (NO). These NIRs have mostly Cu- or Fe-containing active sites, surrounded by amine-containing ligands. Therefore, mononuclear Cu complexes with N-donor ligands are highly relevant in the development of NIR model systems and in the mechanistic investigation of the nitrite reduction reaction. Herein, we report on a terpyridine-based Cu^II complex with square planar geometry for H⁺-assisted electrochemical reduction of NO₂⁻. Through electrochemical measurements, spectroscopic characterization and isotope-labelling experiments we propose a mechanistic reaction pathway involving an unstable HNO₂ state. The Cu^I intermediate, formed electrochemically, was isolated and its molecular structure was deduced, showing linkage isomerism of the nitrite ligand. Moreover, qualitative and quantitative product analysis by GC-MS shows N₂O formed as a side product along with the main product NO. Furthermore, by obtaining single crystals and conducting structural analysis we were able to determine the structural arrangement and redox state of the complex after electrochemical treatment.

中文翻译：

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一种基于三吡啶的铜络合物，用于将亚硝酸盐电化学还原为一氧化氮


在生物系统中，亚硝酸盐还原酶 （NIR） 负责将亚硝酸盐 （NO₂⁻） 还原为一氧化氮 （NO）。这些 NIR 主要具有含 Cu 或 Fe 的活性位点，周围环绕着含胺的配体。因此，具有 N 供体配体的单核 Cu 配合物与 NIR 模型系统的开发和亚硝酸盐还原反应的机理研究高度相关。在此，我们报道了一种基于三吡啶的 Cu^II 配合物，具有方形平面几何形状，用于 H⁺ 辅助电化学还原 NO₂⁻。通过电化学测量、光谱表征和同位素标记实验，我们提出了一种涉及不稳定 HNO₂ 状态的机理反应途径。分离电化学形成的 Cu 中间体并推导出其分子结构，显示亚硝酸盐配体的键合异构性。此外，通过 GC-MS 进行的定性和定量产物分析显示，N₂O 与主要产物 NO 一起形成为副产物。此外，通过获得单晶并进行结构分析，我们能够确定电化学处理后复合物的结构排列和氧化还原状态。