Auxiliary ligand-directed synthesis of 3D energetic coordination polymer from discrete complex: enhanced energy density, thermal stability and energy performance
Since nitrogen-rich coordination polymers were found to be potential energetic materials, numerous energetic coordination polymers (ECPs) have been reported. Among them, 3D ECPs exhibit a remarkable energy content, high thermal stability and insensitivity. Therefore, the design and synthesis of 3D ECPs is an efficient way to explore the potential use of novel ECPs. However, the reaction between energetic ligands and metal ions does not always result in 3D ECPs. Furthermore, to date, the strategy of modulating a non-3D complex into 3D complex has not been realized. 3,5-Dinitrosalicylic acid (H2DNS) is an organic energetic compound with multi-chelating points. The reaction between H2DNS and Cu(NO3)2·3H2O results in discrete coordination complexes, as reported previously. After attempting different experimental parameters we obtained a new discrete complex, Cu(DNS)2·2[(CH3)2NH2] (1), with a moderate energetic performance. To demonstrate the strategy to tune the energy properties of a complex, a 3D ECP, Cu2(DNS)(tetrazole)(H2O) (2), was synthesized through the incorporation of 1H-tetrazole into the coordination structure of H2DNS. The crystal structures, sensitivity, thermal stability, and detonation performances of these two complexes were well investigated. The mechanical sensitivity and thermal stability of Cu(DNS)–Cu(tetrazole)2 mixed salts were also investigated. The results show the overwhelming superiority of the 3D ECP over the discrete coordination complex in terms of density, sensitivity, thermal stability, and energy performance. The Cu(DNS)–Cu(tetrazole)2 mixed salts were found to be inferior in sensitivity and thermal stability to both complexes 1 and 2.