Since the black powder, the first known explosive, was discovered by ancient Chinese in the seventh century, people have been finding powerful, stable, reliable and low-cost energetic materials for military equipment and civil industry. To obtain a better explosive performance, an efficient strategy is to load unstable chemical bonds [1][2][3], as well as to combine fuel with oxidizer components in a proper ratio for achieving sufficient combustion and rapid detonation [4][5][6]. An effective way is to incorporate fuel and oxidizer properties into a single molecule [7], as demonstrated by a series of classical organic nitro group/nitrogen-rich molecules, such as trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), cyclotrimethylene trinitramine (RDX), cyclotetramethylene tetranitramine (HMX), hexanitrohexaazaisowurtzitane (CL-20) and octanitrocubane (ONC) (Fig. S1). Loading more nitro groups and higher structural tension into a single molecule does improve explosive performance, but usually leads to complicated and not cost-effective synthetic procedures. By a trade-off of detonation performance and cost, HMX is regarded as the best military high-energetic explosives nowadays [7], although it is neither the most powerful one nor the cheapest one.Parallel to the intensive studies on molecule engineering on the backbone of nitrogen-rich organic energetic molecules [8,9], the exploration of advanced energetic materials extends to the crystal engineering on their energetic co-crystals [10-13], energetic salts [14][15][16][17][18][19][20], as well as coordination polymers or metal-organic frameworks [21][22][23][24][25][26][27]. The essential strategy is to control the intermolecular packing/linkage of the energetic organic fuel and oxidizer components in crystals by non-covalent interactions to modify/enhance the explosive performance and/or to reduce the sensitivity to a practicable level. However, for a specific energetic molecular component, it is highly challenging to predict/engineer the crystal structure of its co-crystals, salts, or metal-organic frameworks [10], and the examples with good detonation performance, high stability and low cost are still scarce.Here we present a promising solution, i.e., assembly of both low-cost organic fuel and oxidizer components into a closely packed, high-symmetry ternary compounds (vide infra), to achieve advanced energetic materials with a nice combination of high explosive power, high stability, and low cost. The presented materials belong to the so-called molecular perovskites [28] with a general formula of ABX 3 , which topologically mimic the cubic structure of the very well-known inorganic perovskites, the simplest high-symmetry structure for ternary compounds, but have at least one organic molecular component (usually A component). Recently, molecular perovskites have attracted growing attention, as illustrated by the extensive studies on methyl-ammonium lead iodide for high performance solar cells [29][30][31][32], and the phase transitions together with the ...
Metal-free energetic materials generally have the advantages of high gas yield and metal-free residue after combustion or explosion, enabling them to be widely used as explosives and propellant components. As part of a series of our investigations on ABX 3 molecular perovskite high-energetic materials, here we report five new metal-free members, (H 2 A)[NH 4 (ClO 4 ) 3 ], by using different organic cations H 2 A 2+ , i.e., 1-hydroxy-1,4diazabicyclo[2.2.2]octane-1,4-diium for DAP-O4, piperazine-1,4-diium for PAP-4, 1methyl-piperazine-1,4-diium for PAP-M4, homopiperazine-1,4-diium for PAP-H4, and 1methyl-1,4-diazabicyclo-[2.2.2]octane-1,4-diium for DAP-M4, respectively. Together with the previously reported member, (H 2 dabco)[NH 4 (ClO 4 ) 3 ] (DAP-4, H 2 dabco 2+ = 1,4diazabicyclo[2.2.2]octane-1,4-diium), these six metal-free molecular perovskite high-energetic materials provide nice instances to fine-tune the oxygen balance, crystal density, thermal stability, and detonation performance, by changing the A-site organic cations solely. The density functional theory (DFT) calculations and the Kamlet−Jacob (K−J) equation suggested that improving the oxygen balance while keeping the spherical shape of the organic cations to match the anionic cage in these metal-free energetic materials facilitates obtaining a better detonation performance, providing an important clue for designing advanced practicable high-energetic materials. It is worth noting that three compounds (PAP-4, PAP-H4, and DAP-O4) are expected to exceed the performances of RDX as both explosive and propellant, in which DAP-O4 has the highest detonation heat (6.21 kJ mol −1 ), detonation velocity (8.900 km s −1 ), and detonation pressure (35.7 GPa), as well as a higher specific impulse value (262 s).
In recent years, molecular perovskite energetic materials have attracted more attention because of their simple synthesis processes, high thermal stabilities, excellent performances, and great significance as a design platform for energetic materials. To explore the possibility of the application of molecular perovskite energetic materials in heat-resistant explosives, four silver(I)-based molecular perovskite energetic compounds, (H2A)[Ag(ClO4)3], where H2A = piperazine-1,4-diium (H2pz2+) for PAP-5, 1-methyl-piperazine-1,4-diium (H2mpz2+) for PAP-M5, homopiperazine-1,4-diium (H2hpz2+) for PAP-H5, and 1,4-diazabicyclo[2.2.2]octane-1,4-diium (H2dabco2+) for DAP-5, were synthesized by a one-pot self-assembly strategy and structurally characterized. The single-crystal structures indicated that PAP-5, PAP-M5, and DAP-5 possess cubic perovskite structures while PAP-H5 possesses a hexagonal perovskite structure. Differential thermal analyses showed that their onset decomposition temperatures are >308.3 °C. For PAP-5 and DAP-5, they have not only exceptional calculated detonation parameters (D values of 8.961 and 8.534 km s–1 and P values of 42.4 and 37.9 GPa, respectively) but also the proper mechanical sensitivity (impact sensitivities of ≤10 J for PAP-5 and 3 J for DAP-5 and friction sensitivities of ≤5N for both PAP-5 and DAP-5) and thus are of interest as potential heat-resistant primary explosive components.
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