Co-Crystallization of NTO with Planar Heteroaromatic Compounds: Effects of Hydrogen Bonding

The co-crystallization behavior of the energetic compound 3-nitro-1,2,4-triazol-5-one (NTO) with planar heteroaromatic coformers is examined to assess its impact on molecular interactions and thermal stability. NTO is co-crystallized with 3-aminopyrazole (APRZ), 1,2,4-triazole (TRZ), 4-amino-1,2,4-triazole (ATRZ), and imidazole (IMD) at specific molar ratios in polar protic solvents. The crystalline structures obtained are analyzed through single-crystal X-ray diffraction, nuclear magnetic resonance (NMR) spectroscopy, and infrared (IR) spectroscopy techniques. Thermogravimetric analysis (TG) is used to evaluate the effect on explosive characteristics. Single crystal X-ray diffraction (SCXRD) data demonstrate that the co-crystals displayed unique lattice structures in contrast to the pure components, suggesting notable intermolecular interactions between NTO and the coformers. Structural analysis reveals that planar NTO molecules are organized into layers parallel to the planar configurations of APRZ, TRZ, ATRZ, and IMD. Instead of π–π interactions, it is observed that strong hydrogen bonds between the molecular rings serve as the primary driving force for co-crystal formation. The thermogravimetric analysis reveals that the co-crystals underwent disintegration close to the melting point of NTO, subsequently decomposing and exhibiting thermal behavior characteristic of two distinct substances.