Coordination polymerization of nitrogen-rich linkers and dicyanamide anions toward energetic coordination polymers with low sensitivities

Abstract

The design and synthesis of energetic materials (EMs) with high energy and reliable stabilities has attracted much attention in the field of EMs. In this work, we employed a strategy of the coordination polymerization of mild dicyanamide ions (DCA⁻), two isomeric ligands 1-methyl-5-aminotetrazole (1-MAT) and 2-methyl-5-aminotetrazole (2-MAT) to construct energetic coordination polymers (ECPs). Four new ECPs {[Co(DCA)₂(1-MAT)₂]·H₂O}_n1, [Cu(DCA)₂(1-MAT)]_n2, [Cd(DCA)₂(1-MAT)₂]_n3 and [Cd(DCA)₂(2-MAT)₂]_n4 were successfully synthesized through solvent evaporation routes. Compounds 1 and 4 display 1D chains, while 2 and 3 exhibit 2D-layered structures. Compounds 1–3 with the 1-MAT ligand all exhibit reliable thermal stabilities (> 200 °C). The calculated heats of detonation (ΔH_det) of 1–3 are all higher than 1.4 kJ g⁻¹, which are higher than traditional explosive TNT (1.22 kJ g⁻¹) and the reported ECP AgMtta (HMtta = 5-methyl-1H-tetrazole, ΔH_det = 1.32 kJ g⁻¹). Furthermore, sensitivity testing demonstrates that 1–4 features low mechanical sensitivity to external mechanical action in contrast with the extremely sensitive azide-based ECPs [Cu₃(2-MAT)₂(N₃)₆]_n. In addition, compound 2 shows hypergolic properties via an ‘oxidizer-fuel’ drop experiment, demonstrating its application prospects in the field of propellants. This work details an approach of synthesizing multipurpose ECPs with reliable stabilities by introducing mild dicyanamide anions into nitrogen-rich skeletons.