Comparative Study of Experiments and Calculations on the Polymorphisms of 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) Precipitated by Solvent/Antisolvent Method,The Journal of Physical Chemistry C

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Comparative Study of Experiments and Calculations on the Polymorphisms of 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) Precipitated by Solvent/Antisolvent Method
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2016-02-24 00:00:00 , DOI: 10.1021/acs.jpcc.6b00304
Xianfeng Wei ₁ , Jinjiang Xu ₁ , Hongzhen Li ₁ , Xinping Long ₁ , Chaoyang Zhang ₁

Affiliation

2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is the most powerful explosive. However, the application of this compound is limited by its high sensitivity and serious polymorphic transformations. Thus, elucidating the mechanism of crystallization and polymorphic transformation of CL-20 is crucial. This work presents a comparative study of experiments and calculations to clarify the mechanism of CL-20 precipitation using an solvent/antisolvent method. Calculations show that the β-formed CL-20 conformations are always the most energetically favored. These conformations have generally the highest content in solutions, and the intermolecular conformational transformations in solutions have low energy barriers. In addition, it is predicted that the β-CL-20 crystal possesses the lowest lattice energy among all polymorphs. The calculated results are successfully applied to explain the experimental observations, as β-CL-20 crystal is initially precipitated from most of the highly supersaturated solutions and then converted into ε-CL-20 crystal. This precipitation is kinetically controlled by the dominance of β-CL-20 molecules in a metastable phase and rapid crystallization. The final conversion into ε-CL-20 crystal is attributed to its low energy barrier for polymorphic transformation and stability, that is, the conversion is dynamically dominated. Furthermore, calculated coherent energy densities (CEDs) of various CL-20 polymorphs, including hydrates with different hydration degrees, agree well with the thermal stabilities, as the higher CED corresponds to the higher thermal stability. Therefore, the complex crystallization of CL-20 is elucidated by combining experimental observations with theoretical calculations and simulations.

中文翻译：

溶剂/反溶剂法沉淀的2,4,6,8,10,12-六硝基-2,4,6,8,10,12-六氮杂异纤锌矿型结构烷烃（CL-20）多态性的实验和计算的比较研究

2,4,6,8,10,12-六硝基-2,4,6,8,10,12-六氮杂异纤锌矿型结构烷烃（CL-20）是最强大的爆炸物。但是，该化合物的应用受到其高灵敏度和严重的多态性转化的限制。因此，阐明CL-20的结晶和多晶型转变的机制至关重要。这项工作提供了实验和计算的比较研究，以阐明使用溶剂/反溶剂方法的CL-20沉淀的机理。计算表明，β型的CL-20构象始终是最受能量青睐的。这些构象通常在溶液中含量最高，并且溶液中的分子间构象转化具有低能垒。另外，据预测，在所有多晶型物中，β-CL-20晶体具有最低的晶格能量。由于β-CL-20晶体首先从大多数高度过饱和的溶液中沉淀出来，然后转化为ε-CL-20晶体，因此计算结果成功地用于解释实验观察。该沉淀受β-CL-20分子在亚稳相和快速结晶过程中的动力学控制。最终转化为ε-CL-20晶体归因于其低能垒，可实现多态转化和稳定性，也就是说，该转化是动态主导的。此外，包括较高水合度的水合物在内的各种CL-20多晶型物的计算相干能密度（CED）与热稳定性非常吻合，因为CED越高，热稳定性就越高。所以，

更新日期：2016-02-24

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