The reaction of [N₂H₅]⁺₂[SO₄]²^- with barium 5,5‘-azotetrazolate gave new high-energy-density materials (HEDM) based on the 5,5‘-azotetrazolate dianion. The dihydrazinium salt of [N₄C−NN−CN₄]²^-1, its dihydrate 2, and its dihydrazinate 3 were prepared in high yield. Synthesis in water afforded yellow needles of [N₂H₅]₂⁺[N₄C−NN−CN₄]²^-·2H₂O (2): monoclinic, P2/c, a = 8.958(2) Å, b = 3.6596(7) Å, c = 16.200(3) Å, β = 96.834(3)°, V = 527.3(2) Å³, Z = 2; synthesis in anhydrous hydrazine gave yellow [N₂H₅]₂⁺[N₄C−NN−CN₄]²^-·2N₂H₄ (3): triclinic, P1̄, a = 4.6208(6) Å, b = 8.585(1) Å, c = 9.271(1) Å, α = 108.486(2)°, β = 95.290(2)°, γ = 102.991(2)°, V = 334.51(8) Å³, Z = 1. The compounds were characterized by elemental analysis and vibrational (IR, Raman) and multinuclear NMR spectroscopy (¹H, ¹³C, ¹⁴N, ¹⁵N). The new compounds represent new high-nitrogen HEDMs with one of the highest nitrogen contents reported to date ([N₂H₅]⁺₂[N₄C−NN−CN₄]²^- 85.2%; [N₂H₅]⁺₂[N₄C−NN−CN₄]²^-·2H₂O 73.3%; [N₂H₅]⁺₂[N₄C−NN−CN₄]²^-·2N₂H₄ 85.7%). The standard heat of formation of the solvate-free compound 1 was computed at the MP2(FULL)/6-311+G(d,p) level of theory to be ΔH°_f = 264 kcal mol^-¹, which translates to 1147 kcal kg^-¹ and is one of the highest ever reported. The compounds are stable at room temperature, almost insensitive to friction and impact, but detonate violently when the explosion is initiated, e.g., by rapid heating over the decomposition temperature or by using an initiator.

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