Constructing energetic coordination polymers through mixed-ligand strategy: way to achieve reduced sensitivity with significant energetic performance

Abstract

This paper investigates the synthesis, crystal structure, thermal properties, and energetic performance of two 1D coordination polymers (CPs). The CPs, namely, [Zn(atrz)(DNBA)₂(H₂O)₂]_n (1) and [Cd(atrz)(DNBA)₂(H₂O)₂]_n (2), were designed and synthesized based on the nitrogen-rich ligand 4,4′-azobis-1,2,4-triazole (atrz) and 3,5-dinitrobenzoic acid (HDNBA) via a mixed ligand strategy using a simple and environment-friendly method. The CPs were characterized by various spectroscopic and analytical techniques along with single-crystal X-ray diffraction (SCXRD). SCXRD analysis reveals a distorted octahedral geometry around the metal ions (Zn/Cd), leading to the formation of a 1D coordination polymer while constructing a 2D structural framework through intermolecular hydrogen bonding. Both the CPs exhibit similar thermal stability but considerably differ in their heat of formation values (1 = −894.43, 2 = 1635.93 kJ mol⁻¹). CP 2 has higher detonation velocity (7.24 km s⁻¹) and pressure (23.67 GPa) compared to 1 (detonation velocity: 6.28 km s⁻¹, detonation pressure: 17.57 GPa) owing to its higher heat of formation and density. Both the CPs exhibit ideal insensitivity to friction and impact stimuli, ensuring their safety during transportation and processing. The value of average activation energy obtained from isoconversion ASTM E698 for 1 and 2 was reported to be 143.8 and 168.0 kJ mol⁻¹, respectively. This study explores the development of energetic CPs through the mixed ligand strategy based on the atrz ligand and incorporating HDNBA as the co-ligand to reduce the sensitivity while maintaining the comparable energetic performance of previously reported atrz-based complexes. This paper also highlights the potential use of CPs as explosives by demonstrating higher energetic performance.