Understanding the Relationship between Molecular Assembly and Polymorph Selection of 4,4′,5,5′-Tetranitro-1H,1′H-[2,2′-biimidazole]-1,1′-diamine in Solution

The unpredictable occurrence and variation of polymorphs in solutions have sparked interest in the study of the molecular mechanisms of polymorphism with advancements in experimental and computational technologies. However, the understanding of the mechanisms behind solution polymorphism remains incomplete. This research represents the first exploration of the relationship between molecular aggregation patterns in solutions and polymorphs for low-sensitivity and highly energetic materials. A set of order parameters for 4,4 ',5,5 '-tetranitro-1H,1 ' H-[2,2 '-biimidazole]-1,1 '-diamine (DATNBI) was successfully established and was used to predict polymorph tendencies in various systems, verifying that the greater solute-solvent interactions are more favorable for the formation of form alpha. Additionally, we analyze the stability and transformation relationships of forms alpha and beta of different monomers and dimers in the gas phase and solvents using density function theory. The experimental results were largely consistent with the predictions, except in the case of antisolvent crystallization in the acetonitrile, which might be manipulated by crystallization rate and lower energy barrier of form transformation. This study suggests that the polymorphism of DATNBI is likely determined by the dimer states in the solution, meaningful to controlling polymorphism in explosive crystallization.