Eco-friendly Trifoliate Stable Energetic Zinc Nitrate Coordination Compounds: Synthesis, Structures, Thermal and Explosive Properties

Three trifoliate environmental friendly coordination compounds, [Zn(SCZ)(3)](NO3)(2) (1) (SCZ = semicarbazide), [Zn(CHZ)(3)](NO3)(2) (2) (CHZ = carbohydrazide), and [Zn(MCZ)(3)](NO3)(2)H2O (3) (MCZ = methyl carbazate), were synthesized by the reaction of zinc nitrate with its corresponding ligands. The products were characterized by elemental analysis and FT-IR spectroscopy. Furthermore, compound 1 and 2 were characterized by X-ray single crystal diffraction. The crystal structures of both 1 and 2 belong to the monoclinic P2(1)/c space group. Remarkably, in all the three compounds, the central zinc cations are six-coordinated with three oxygen atoms of carbonyl groups and three terminal nitrogen atoms of the hydrazine groups from three SCZ / CHZ / MCZ molecules, which can form three five-member (Zn-O-C-N-N) rings and exhibit a distorted octahedron. Thermal stabilities of 1 to 3 were studied by differential scanning calorimetry (DSC) and showed that they are all thermostable. The non-isothermal kinetics parameters were calculated by the Kissinger's method and Ozawa's method, respectively. The energies of combustion, enthalpies of formation, critical temperature of thermal explosion, entropies of activation (S), enthalpies of activation (H), and free energies of activation (G) were measured and calculated. Sensitivity tests revealed that 1-3 are insensitive to mechanical stimuli. The studies of all these three zinc compounds showed that they have potential applications as heat-stable insensitive energetic materials, especially the semicarbazide coordination compound 1, which has higher crystal density.