High-energy-density-materials (HEDM) with high performance have attracted worldwide research groups over the last decades.1,2 Nitrogen-rich heterocyclic complexes and salts are able to fulfill many requirements in the challenging field of energetic materials research, because they are generally highly endothermic with high densities and proper sensitivities. Klapötke, Shreeve and others research groups performed various studies on high-nitrogen modern energetic complexes and salts based on imidazole derivatives,3–5 triazole derivatives,6–8 and tetrazole derivatives.9–18
In recent years, a series of energetic coordination compounds were synthesized using transition metal ions such as MnII, FeII, CoII, NiII, CuII, ZnII, and CdII as central metal cations, and chloride,19 perchlorate,20 nitrate,20 picrate,21–23 and azido24–31 ions as anions. The perchlorate metal compounds had better sensitivity properties than chloride and nitrate compounds. The picrate and styphnate compounds are more flame sensitive. Especially azide compounds have been studied because of the versatile coordination modes of the azido anions (N3–). The azido ion can bind the metal atoms by μ-1 mode as a monodentate bridging ligand, μ-1,3 and μ-1,1 modes as a bidentate ligand, and μ-1,1,3 mode as tridentate ligand. In addition, the azide compounds can release a great amount of energy, which can be concluded from the average bond energies of N–N (160 kJ·mol–1), N=N (418 kJ·mol–1), and N≡N (954 kJ·mol–1). To demonstrate it by some examples, the azido groups of compounds [Mn3(N3)6(admtrz)4]n27 (admtrz = 4-amino-3,5-dimethyl-1,2,4-triazole) and [Cd3(N3)6(admtrz)4]n30 have three different coordination modes: μ-1, μ-1,3 and μ-1,1 modes. Zhu reported the nickel(II) hydrazine azide, which is a potential powerful primary explosive.32 Sheng also reported tetraamminediazido cobalt(III) perchlorate (DACP), which is very sensitive to laser excitation with 635 nm.33 We synthesized and investigated the crystal structures, the thermal decomposition mechanisms, and sensitivity properties of [Zn(HZ)2(N3)2]n (HZ = hydrazine),25 [Cd2(HZ)2(N3)4]n,29 Mn(CHZ)2(N3)2 (CHZ = carbohydrazide),34 [Cu(en)(N3)2]n (en = ethylenediamine),24 Co(en)2(N3)2(NO3),24 [Cd(en)(N3)2]n,28 Cu(IMI)4(N3)2 (IMI = imidazole),26 and Ni(IMI)4(N3)2,26 and found that the azido groups show different coordination modes. These compounds have potential application as energetic materials.
In order to deepen the studies on the metal azide compounds, a new multi-ligand coordination compound, [Cu(pn)(N3)2]n (1), was synthesized, and the crystal structure, the thermal decomposition mechanism, and sensitivity properties were studied in the presented work.