Modulating the 4-R-1,5-diaminotetrazole pentazolate salts properties by substituent effects

Abstract

Substituent effects play a pivotal role in modulating the properties of organic ionic compounds through the synergistic electronic and steric effects. It is one of the core theoretical foundations for studying structure-property relationships in materials science and organic chemistry. However, in-depth examination of the substituent effects on significant cyclo-pentazolate anion (cyclo-N5−) salts has not been studied. Herein, to explore how different substituents (R) in 4-R-1,5-diaminotetrazolium cations affect the properties of their cyclo-N5− salts, four types of cyclo-N5− salts bearing distinct substituents (−CH3, −CH2COCH3, −CH2CONH2, and −CH2COOCH3) were designed and synthesized. Analysis of using X-ray single-crystal diffraction indicates that the crystal structures of these salts vary significantly based on the substituents. Among them, the cyclo-N5− salt with the −CH3 substituent exhibits optimal crystal density and stability. The −CH2CONH2 group improves crystal stability via increased hydrogen-bonding capacity. In contrast, −CH2COCH3 and −CH2COOCH3 lead to reduced stability and crystal density due to larger steric bulk and lack of hydrogen-bonding interactions. Additionally, Hirshfeld surface analysis and fingerprint plots were employed to investigate interionic interaction regions, revealing extensive van der Waals interactions and the formation of N–H···N hydrogen bonds. The cyclo-N5− salt with the −CH3 substituent displays the highest detonation performance (D: 8811.47 m·s−1; P: 26.94 GPa), which benefits from a higher enthalpy of formation.