Multidimensional Energetic Coordination Polymers as Flame Colorants: Intriguing Architecture and Excellent Performance

A flexible and multifunctional 4-hydroxy-3,5-dinitropyrazole (DNPO) ligand was produced while seeking "green" energetic coordination polymers (ECPs). A series of alkali metal and alkaline earth metal ECPs of DNPO were successfully prepared and comprehensively characterized using elemental analysis, infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. All ECPs were characterized via single-crystal X-ray diffraction. They have high crystal densities ranging from 1.743 (ECP-6) to 3.399 g cm^-3(ECP-5). Furthermore, various shapes of zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) supramolecular structures were found for the preparation of ECP, and each metal was combined in a specific and characteristic manner. All the prepared ECPs show excellent thermal stability, and the decomposition temperatures are higher than 347.0 °C (ECP-9) and 418.0 °C (ECP-1), due to the numerous coordination bonds and the network structure of the complex. The sensitivities toward impact and friction were tested using standard methods, and most of ECPs (ECP-1, ECP-2, and ECP-6 to ECP-9) can be considered insensitive to impact and friction, with values higher than 40 J and 360 N, respectively. ECP-3, ECP-4, and ECP-5 are sensitive toward impact (30, 12, and 8 J, respectively), while they are insensitive toward friction (≥360 N). Upon their combustion, these ECPs exhibit a series of unique flame colors, making them promising flame colorants for various ecofriendly pyrotechnic formulations.