Energetic coordination compounds: self-assembled from the nitrogen-rich energetic C-C bonded pyrazoles and triazoles

In energetic materials research, energetic coordination compounds (ECCs) have received much attention due to their high thermal stability and insensitivity to mechanical stimuli. The energetic characteristics of ECCs can be modified by combining various metal cations, potent anions, and ligands. In this study, we have synthesized two energetic ligands, 5-(4-nitro-1H-pyrazol-3-yl)-1H-1,2,4-triazol-3-amine (NPTA) and (Z)-N-(5-(4-nitro-1H-pyrazol-3-yl)-2,4-dihydro-3H-1,2,4-triazol-3-ylidene)nitramide (NPTN), from a commercially viable starting material and reacted them with nitrate salts of various 3d metals (e.g., Ni, Co, Zn) to obtain six new ECCs, [Ni(NPTA)(H₂O)₃]₂·2NO₃ (1), [Co(NPTA)(H₂O)₃]₂·2NO₃ (2), [Zn(NPTA)(H₂O)₃]₂·2NO₃ (3), [Ni(NPTN)(H₂O)₃]₂ (4), [Co(NPTN)(H₂O)₃]₂ (5), and [Zn(NPTN)(H₂O)₃]₂ (6) under ambient conditions. All the newly prepared ECCs were characterised through PXRD, IR, SEM, and TGA-DSC analysis. Furthermore, single crystal analysis proved that 1-6 are dimeric complexes. Moreover, 1-6 show excellent density ranges from 1.94 to 2.06 g cm^-3 and remarkable thermal stability (216-352 °C), and are highly insensitive towards impact (>40 J) and friction (>360 N), describing their potential as high performing energetic materials. All the ECCs revealed good enthalpy of combustion (-6.3 to -9.94 kJ g^-1). Additionally, the Hirshfeld surface and 2D fingerprint analysis were used to understand the close contact of atoms within the molecules. High crystal densities, thermal stabilities and low sensitivities make the synthesized ECCs interesting for further studies and potential applications as safe high-energy dense materials.