Intermolecular Interaction Hierarchy in Unsolvated, Solvate, and Cocrystal Forms of 6-Chloro-3-(trifluoromethyl)[1,2,4]triazolo[4,3- b ]pyridazine under High Pressure

The 6-chloro-3-trifluoromethyl[1,2,4]triazolo[4,3- b ]pyridazine, C 6 H 2 N 4 F 3 Cl, and its cocrystal with 6-chloro-3(2H)-pyridazinone, stable at ambient conditions, have been studied at varied thermodynamic conditions. High-pressure and low-temperature X-ray studies revealed that both compounds retain their ambient-conditions crystal structures up to 0.70 and 3.16 GPa for C 6 H 2 N 4 F 3 Cl and C 6 H 2 N 4 F 3 Cl·C 4 H 3 N 2 OCl, respectively. However, at high pressure, a C 6 H 2 N 4 F 3 Cl·CH 3 OH solvate could also be obtained. Its formation leads to the replacement of the dominant CH···N hydrogen bonds present in the unsolvated form by OH···N and CH···O interactions involving both C 6 H 2 N 4 F 3 Cl and CH 3 OH molecules. Apart from that, the hierarchy of other short contacts of the same type, present in both forms, is changed on solvate formation. On the other hand, the C 6 H 2 N 4 F 3 Cl·C 4 H 3 N 2 OCl cocrystal is characterized by multiple types of intermolecular contacts, as there are numerous atoms able to form various intermolecular interactions. Thus, the unsolvated, solvate, and cocrystal forms are characterized by distinct interaction hierarchies, dominated by CH···N, OH···N/CH···O, and NH···O interactions, respectively. Overall, these results demonstrate how pressure and solvation can selectively modify intermolecular interaction hierarchies in multicomponent crystal systems.