Evaluation of the Appropriate Use of Characterization Methods for Differentiation between Cocrystals and Physical Mixtures in the Context of Energetic Materials

Abstract

Cocrystallization is an attractive method by which to tune the physical properties of energetic materials. However, in the absence of single-crystal X-ray diffraction (SC-XRD), rigorously characterizing the results of cocrystallization attempts can be difficult. Specifically, differentiating between physical mixtures and true cocrystalline materials is challenging due to the propensity for energetic molecules to form solvates and/or polymorphs. The suitability and limitations of morphological analysis, vibrational (infrared and Raman) spectroscopy, and powder XRD are discussed within the context of six previously published materials claimed to be cocrystals but lacking SC-XRD structures. It was found that in all six cases the data originally published are consistent with crystallization of physical mixtures of the two starting components; in three of these cases the crystallization procedures were reproduced and the characterization data support the presence of physical mixtures. Data interpretation is co...