An increasing attention
has been witnessed to the field of crystal
engineering of energetic materials very recently. This study revealed
the synthesis, structure, and energetic properties of 4,6-dinitro-1-(4-amino-1,2,4-
triazole-2-yl)-1H-indazole (3) with
two polymorphic forms, α-3 and β-3. The 4,6-dinitro-indazole derivative α-3 with
a wave-like stacking structure was synthesized by one-step reaction
at room temperature. Interestingly, the β-3 could
be formed at 78 °C. It is noteworthy that plate-shaped α-3 crystals could transform to β-3 with
needle-shaped crystals. The single-crystal diffraction data revealed
that β-3 is nearly coplanar and features closer
layer-by-layer package structure, thereby exhibiting increases of
0.08 g cm–3 (4.7%), 36.6 kJ mol–1 (6.1%), 667 m s–1 (9%), 3.4 GPa (15.5%), 88 °C
(49%), 6 J (23%), and 97 N (43%) in density, heat of formation (ΔH), detonation velocity (D) and pressure
(P), decomposition temperature (T
dec), impact sensitivity (IS), and friction sensitivity
(FS) compared to α-3, respectively. Compared to
TNT, the β-3 (D = 8061 m s–1, P = 25.4 GPa, IS = 32 J, FS = 320
N) possesses better detonation properties and sensitivities. Based
on experimental results and theoretical analysis, this study provides
an effective strategy for improving the performance of energetic materials
in molecular design and crystal configuration.