Energetic multifunctionalized nitro/nitramino isomeric pyrazole–tetrazole hybrids: enhancing density and detonation properties through hydrogen bonding and π–π interactions

Abstract

This study focuses on synthesizing high-density isomeric pyrazole–tetrazoles and their energetic salts, with a particular emphasis on improving detonation performance. First synthesized was 5-(3,4-dinitro-1H-pyrazol-5-yl)-1H-tetrazole (H₂DNP-5T, 3), an isomer of 5-(3,4-dinitro-1H-pyrazol-4-yl)-1H-tetrazole (H₂DNP-4T) followed by synthesis of the nitramine derivative N-(4-nitro-5-(1H-tetrazol-5-yl)-1H-pyrazol-3-yl)nitramide (H₃NANP-5T, 11) to further enhance detonation properties. Crystal packing and NCI analysis were used to gain insight into the impact of significant interactions such as hydrogen bonding and π–π interactions on density enhancement. Isomeric pyrazole–tetrazole (H₂DNP-5T) demonstrated high density and superior detonation properties compared to its 4-substituted derivative, H₂DNP-4T, attributed to increased inter-hydrogen bonding interactions, a high packing coefficient (73.1%), and π–π interactions. All substances were characterized spectroscopically using NMR, IR, and elemental analyses. The structures of compounds H₂DNP-5T, H₃NANP-5T, and 4 were further confirmed by single-crystal X-ray diffraction. Using EXPLO5 software, the detonation parameters of energetic materials based on experimental density and computed heat of formation were determined. Furthermore, the nitramine derivative H₃NANP-5T (D_v: 8846 m s⁻¹; P: 33.2 GPa) and its energetic salts 13 (D_v: 9414 m s⁻¹; P: 34.5 GPa) and 14 (D_v: 9088 m s⁻¹; P: 33.9 GPa) exhibit outstanding detonation properties comparable to RDX. Comprehensive molecular and crystal-level insights into the impact of positional isomerism which hold significance for the design and development of new energetic materials.