Adjusting the Coordination Configuration by Changing Electrostatic Potential: Introducing N/O/S Heteroatoms Based on the Electronic Effect

Abstract

Energetic coordination compounds (ECCs) have demonstrated unique advantages in regulating the physicochemical properties of energetic materials through the design of organic ligands. The fundamental approach involves altering the electron cloud density distribution of organic ligands to modify the characteristics of coordination sites and, thus, achieve new coordination configurations. In this study, Mulliken charge distribution and surface electrostatic potential analysis were used to elucidate the effects of pyridinic N, pyrrolic N, oxazolic O, and thiazolic S on the electron cloud density of carbohydrazide groups through the induction effect and conjugate effect. Furthermore, three AgClO₄-based ECCs were synthesized based on 1H-imidazole-4-carbohydrazide, oxazole-4-carbohydrazide, and thiazole-4-carbohydrazide. Single-crystal X-ray diffraction analysis revealed that [Ag(IZ-4-CA)ClO₄]_n has a one-dimensional (1D) chain structure, while Ag₂(OZCA)₂(ClO₄)₂ and Ag₂(SZCA)₂(ClO₄)₂ exhibit zero-dimensional structures. The 1D structure, with good planarity, results in [Ag(IZ-4-CA)ClO₄]_n having lower mechanical sensitivity (IS = 21 J, FS = 80 N). The introduction of oxazolic O enhances oxygen balance (OB), leading to a higher predicted detonation velocity and pressure for Ag₂(OZCA)₂(ClO₄)₂ (D = 6.4 km s^–1, P = 23.6 GPa). Although the introduction of thiazolic S is unfavorable for improving oxygen balance, Ag₂(SZCA)₂(ClO₄)₂ exhibits the highest initial decomposition temperature among the three, at 232 °C. Additionally, initiation tests demonstrated that three ECCs can successfully detonate cyclotrimethylenetrinitramine (RDX), indicating good initiation capabilities.