A series of nitrogen-rich "green" Energetic Materials (EMs), some with improved sensitivity, thermostability, and very low toxicity, were synthesized on the basis of 3,5-diamino-1,2,4-triazole (DAT) and 1,2,4,5-tetrazine building blocks. Since DAT contains several nucleophilic reactive sites, obtaining selective reactivity and specific isomeric products with 1,2,4,5-tetrazine precursors is a challenging task. We developed reaction conditions under which specific isomers could be prepared. On evaluating these compounds for their energetic properties, we found that N5,N5'-(1,2,4,5-tetrazine-3,6-diyl)-bis(1H-1,2,4-triazole-3,5-diamine) 1 has very high thermostability (onset of decomposition temperature at 357 °C) and it is insensitive to impact (Im > 98 J), friction (>360 N) and electrostatic discharge (2512 mJ). A detonation velocity (Vod) of 8180 m s-1 was calculated for compound 1 and it was found to have extremely low toxicity in human cells (normal dermal fibroblasts) and in environmental bacteria (Vibrio fischeri). In combination with oxidants, compound 1 can generate 1225 L of gases (per kg of energetic mixture of an oxidant and compound 1), which makes this material a prospective component in solid propellants and a very good candidate for the development of solid state gas generators for clean fire-extinguishing systems and for a broad range of other civil and defense applications that require the use of "green" and insensitive EMs.