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.

中文翻译：

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吡唑铜系统中结构转变的系统研究：一个案例研究。

溶解-重结晶结构转化（DRST）是一种强大的工具，可以根据初始反应物，最终产物以及有时从反应混合物中分离出的中间体的结构，明确揭示动态转化过程的机理。在这里，我们说明了通过DRST将（CuIpz）3转换为[CuII（OH）pz] 6（pzH = 4-氯-3,5-二苯基吡唑）的过程的细节。根据晶体结构确定和光谱方法，最常遇到的物质（CuIpz）3与溶液中的（CuIpz）4处于平衡状态，四聚体在低温下占优势，表明这两种结构异构体之间存在熵控制的转化。如果暴露在室外，溶液中的CuI三聚体/四聚体还会进一步氧化，导致形成五核混合价中间体CuI3CuII2（OMe）2pz5，可以在-20°C下将其分离为单晶，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，在有湿气的情况下很容易转化为[CuII（OH）pz] 6。