Two new polymorphs of piroxicam (Forms VI and VII) were discovered by melt crystallization and crystal structure prediction (CSP). High-quality single crystals were grown from melt microdroplets for structural solution by X-ray diffraction. Relative to the previously known polymorphs obtained mainly by solution crystallization, the new polymorphs are thermodynamically less stable, confirming melt crystallization as an important complement to solution crystallization in polymorph discovery. Although early workers reported that piroxicam is thermally unstable and unsuitable for melt crystallization, our use of melt microdroplets circumvented this problem because of the short exposure to a high temperature. Our CSP identified all known polymorphs of piroxicam including the two new forms with an energy ranking in reasonable agreement with the observed order, as well as low-energy structures not observed by experiment.

中文翻译：

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吡罗昔康的多晶型：熔融结晶和晶体结构预测的新多晶型物

通过熔融结晶和晶体结构预测（CSP）发现了吡罗昔康的两个新的多晶型物（形式VI和VII）。通过X射线衍射从熔融微滴中生长出高质量的单晶，以用于结构溶液。相对于以前已知的主要通过溶液结晶获得的多晶型物，新的多晶型物在热力学上不稳定，从而证实了熔融结晶是多晶型物发现中溶液结晶的重要补充。尽管早期的工作人员报告说吡罗昔康是热不稳定的，不适合熔融结晶，但由于短暂暴露于高温下，我们使用熔融微滴可避免该问题。