Cupric coordination compounds with multiple anions: a promising strategy for the regulation of energetic materials

To seek new high energetic materials, N-methylene-C-bridged nitrogen-rich heterocycle 1-((4,5-diamino-4H-1,2,4-triazol-3-yl)methyl)-1H-1,2,4-triazol-3,5-diamine (DATMTDA) (2) was first synthesized, and two copper coordination compounds ([Cu₁₂(OH)₄(ClO₄)₄(H₂O)₄(DATMTDA)₁₂](ClO₄)₁₆·12H₂O (3) and [Cu₃(OH)(ClO₄)(DATMTDA)₃](ClO₄)₃(NO₃) (4)) based on 2 were formed by introducing different anions. These compounds were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction analysis. The crystal structures of compounds 3 and 4 are similar and crystallize in monoclinic systems with the P2₁/c space group, while the central copper atoms show different coordination behaviors. However, the structure of compounds 3 and 4 is analogous to a three dimensional structure owing to the O atom of OH^-, forming coordinate bonds with three copper cations. The NBO charge of 2 was calculated using density functional theory to understand its coordination modes. The Hirshfeld surface calculation reveals that 3 and 4 have strong intermolecular interactions. The thermal decomposition processes, non-isothermal kinetics, and enthalpies of formation and sensitivities of these compounds were investigated. By introducing one NO₃^- of compound 4 to replace one ClO₄^- in compound 3, compound 4 shows lower density and lower decomposition peak temperature but lower sensitivity and a higher formation enthalpy than compound 3. The complex 4 possesses an outstanding catalytic effect for the decomposition of AP than that of complex 3. The results illustrate the possibility of introducing various anions into energetic coordination compounds for the regulation of energetic materials.