Chen Jing-Huo, Wei Donghui, Yang Guang, Ma Jian-Gong, Cheng Peng
Green Catalysis Center, and College of Chemistry, Zhengzhou University, Zhengzhou, Henan 450001, P. R. China.
Dalton Trans. 2020 Jan 28;49(4):1116-1123. doi: 10.1039/c9dt04263f.
Dissolution-recrystallization structural transformation (DRST) is a powerful tool to unravel unequivocally the mechanism of dynamic conversion processes, based on the structures of the initial reactants, final products and sometimes intermediates isolated from the reaction mixture. Herein, we illustrate the details of the conversion processes of (CuIpz)3 into [CuII(OH)pz]6 (pzH = 4-chloro-3,5-diphenylpyrazole) through DRSTs. Based on crystal structure determination and spectroscopic methods, the most encountered species, (CuIpz)3, is in equilibrium with (CuIpz)4 in solution with the tetramer becoming dominant at low temperature, indicating an entropy-controlled conversion between these two structural isomers. The CuI trimer/tetramer in solution further experiences an oxidation if exposed to the open air, resulting in the formation of a pentanuclear mixed-valence intermediate CuI3CuII2(OMe)2pz5 which can be isolated as single crystals at -20 °C and has been structurally characterized for the first time. The final product isolated from the solution is the fully oxidized hexanuclear [CuII(OMe)pz]6, which is easily transformed into [CuII(OH)pz]6 in the presence of humidity.
溶解-重结晶结构转变（DRST）是一种强大的工具，可基于从反应混合物中分离出的初始反应物、最终产物以及有时的中间体的结构，明确地揭示动态转化过程的机制。在此，我们通过DRST阐述了（CuIpz）3转化为[CuII(OH)pz]6（pzH = 4-氯-3,5-二苯基吡唑）的转化过程细节。基于晶体结构测定和光谱方法，最常见的物种（CuIpz）3在溶液中与（CuIpz）4处于平衡状态，四聚体在低温下占主导，这表明这两种结构异构体之间存在熵控制的转化。溶液中的CuI三聚体/四聚体如果暴露在空气中会进一步发生氧化，生成五核混合价中间体CuI3CuII2(OMe)2pz5，该中间体可在-20°C下分离为单晶，并且首次对其进行了结构表征。从溶液中分离出的最终产物是完全氧化的六核[CuII(OMe)pz]6，在有湿度的情况下它很容易转化为[CuII(OH)pz]6。
