Alkaline earth metal salts of 3,6-bis-nitroguanyl-1,2,4,5-tetrazine: Promising perchlorate-free environmentally friendly pyrotechnic components

Alkaline earth metal salts (magnesium, 2; calcium, 3; strontium, 4; barium, 5) with nitrogen-rich 3,6-bis-nitroguanyl-1,2,4,5-tetrazine anion (DNGTz(2-)) were prepared and characterized by elemental analysis, infrared, and multinuclear NMR spectroscopy. All new compounds were further characterized by single-crystal X-ray diffraction measurements. Full analysis of the crystal structures and graph sets of hydrogen bonds were conducted out. The results revealed a large-scale conjugation effect of DNGTz anion in all four salts and a middle to high densities ranging from 1.751 (2) to 2.296 (5) g center dot cm(-3). Both 3 and 4 were one-dimensional coordination polymers and show zig-zag chain, whereas 5 crystalized in a two-dimensional sql topological network. Differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis revealed the good thermal stability of all the new salts. Meanwhile, their specific heat capacities are in inverse proportion to atomic number of the metal cations. The constant-volume combustion energy of 2-5 was determined experimentally, and the standard molar enthalpy of formation was backcalculated to evaluate their energetic performance. Impact sensitivity test disclosed that all the four metal salts were insensitive towards impact with a value higher than 40 J. Flame burning test supports their potential application as the environmentally friendly perchlorate-free pyrotechnic components.