Energetic azide-based coordination polymers: Sensitivity tuning through diverse structural motifs

Abstract

Energetic coordination polymers (ECPs), as a new class of energetic materials (EMs), have attracted extensive attention in recent years. However, controllable modulation of mechanical sensitivities and the establishment of structure-function theoretical models of ECPs to meet different applications remain great challenges. Herein, we designed and synthesized four azide-based ECPs, [Cd2(N3)2(datz)2]n1 (Hdatz = 3,5-diamino-1,2,4-triazole), [Cd(N3)2(brt)2]n2 (brt = 4,4′-bi-1,2,4-triazole), [Cd(N3)2(btzp)]n3 (btzp = 1,3-di(tetrazol-1-yl)propane), and [Cd2(N3)4(btzb)]n4 (btzb = 1,4-bis(tetrazol-1-yl)butane). Because of the existence of consolidated network structures, high-energy linkers, and diverse structural motifs, compounds 1–4 exhibit reliable thermal stabilities, tunable mechanical sensitivities, and considerable heats of detonation (ΔHdet) with the ΔHdet values of 3.390, 3.412, 3.947 and 4.504 kJ·g−1, respectively, which are two times higher than those of commercial LA (lead azide) and the reported AgMtta (AgMtta = [Ag(Mtta)]n, HMtta = 5-methyl-1H-tetrazole). The sensitivity measurements demonstrate that the sensitivity toward impact of 1–4 displays in the following order: 1 (>40 J) ≪ 2 (8 J) < 3 (2.5 J) < 4 (2 J). In particular, compound 1 features scarce insensitivity compared with sensitive 2, 3, 4 and most of known azide-based EMs. Furthermore, theoretical calculations, structural analyses, and experimental results revealed that the different sensitivities of the four ECPs are mainly dependent on two different structure models for the first time. The insensitive 1 is “body frame structure” model, while the sensitive 2–4 belong to “non-body frame structure” model. Our study enlightens new insights into structures behind mechanical sensitivities for optimizing advanced EMs.