New Application of Hydroxyl Groups: Ligands for High Density Metal Organic Frameworks

Abstract

Energetic metal organic frameworks (MOFs) with energetic anions as ligands can be used as new-generation explosives. Many powerful anions have been introduced into energetic MOFs to improve the properties; however, the hydroxyl as a common group for energetic MOFs has rarely been studied. In this article, we present two examples of energetic MOFs ([Cu(atz)(NO 3 )(OH)] n ) and [Zn(ata)(OH)] (atz = 4-amino-1,2,4-triazole; ata = 5-amino-1H-tetrazole) with the hydroxyl group as the ligand. Crystal structure analyses reveal that the two compounds possess compact two-dimensional (2-D) structures with densities up to 2.41 g cm À3 and 2.54 g cm À3 , respectively. These two compounds have excellent physicochemical properties. The results demonstrate that a hydroxyl group as the ligands could commendably increase the densities of energetic MOFs, thereby enhancing the detonation performance. It is anticipated this work will open a new direction for the development of energetic MOFs.

Facile synthesis and superior properties of a nitrogen-rich energetic Zn-MOF with a 2D azide-bridged bilayer structure

“…Since the first EMOF synthesized by Hope-Weeks et al in 2012, 14 some 1D, 2D and 3D EMOFs with novel structures have been designed and prepared for the sake of increasing the nitrogen content or improving their thermostability and insensitivity, so as to realize their application in high-energy propellants with green and insensitive features. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] What needs to be explained here is that a high nitrogen content not only leads to high energetic performance but also means a large amount of nitrogen gas rather than residual carbon in the combustion products of EMOFs, which is consistent with the demand for green and sustainable chemistry. On the other hand, although Pb-containing compounds, including Pb-MOFs, are the most widely-used combustion promoters in propellants, [32][33][34][35][36] the toxic nature of Pb makes them very harmful to the environment.…”

“…14,20,28,48–50 The calculated parameters used in the detonation reaction are shown in Table S2 †. The heat of detonation of [Zn 2 (atz) 3 (N 3 )] n by DFT calculation is 3.431 kcal g −1 (14.36 kJ g −1 ), which is much higher than Δ H det of RDX (5.80 kJ g −1 ), 27 CL-20 (6.16 kJ g −1 ) 27 and most EMOFs, such as CHP (5.23 kJ g −1 ), 13 ZnHHP (2.93 kJ g −1 ), 20 [Ag(atrz) 1.5 (NO 3 )] n (4.85 kJ g −1 ) 21 and [Pb(HBTI)] n (4.85 kJ g −1 ). 26 Zn 2 C 3 H 6 N 18 → 2Zn + 3C + 2NH 3 + 8N 2 …”

“…The calculated detonation velocity and detonation pressure are respectively 8.034 km s −1 and 25.96 GPa, which are higher than those of TNT (7.178 km s −1 , 20.5 GPa) and two typical 2D EMOFs, i.e., CHHP (6.205 km s −1 , 17.96 GPa) and ZnHHP (7.016 km s −1 , 23.58 GPa). 20,27 From Kamlet-Jacob's equations, the relatively lower detonation velocity and detonation pressure of [Zn 2 (atz) 3 (N 3 )] n compared with certain nitrogen-rich EMOFs such as [Co(HTATT)] n and [Cu(atrz) 3 (NO 3 ) 2 ] n mainly derive from its low density (1.541 cm g −1 ), which is mainly caused by the loose pore structure. Nevertheless, this disadvantage can be very hopefully overcome by subsequent modifications for its abundant pores, such as introducing small energetic molecules or ions.…”

“…Although azides are sensitive, tetrazole-containing EMOFs are highly insensitive, which has been verified in some research studies. 27,29,35,51 On the other hand, the azide groups in [Zn 2 (atz) 3 (N 3 )] n are located in the interlayer of the bilayer structure, which could be protected by the less insensitive Zn-atz layers, thus lowering the sensitivity of the EMOF.…”

One‐Step Fabrication of High‐Performance Energetic Metal‐Organic Framework [Cu(atrz)3[NO3]2]n Films and its Tunable Crystal Structure

“…Thermites, a subset of metastable intermolecular composites (MIC) composed of Al and metal oxides (e. g., CuO [16], Fe 2 O 3 [17], and MoO 3 [18]), have been widely utilized in the fabrication of thermal NOC. Nevertheless, this has led to a gap in the development of gas explosion NOC, due to the lack of gas-producing elements (C, H, O, and N in particular) in the aluminum-based MIC components [19,20]. This potentially limits their diversity, since certain applications require a rapid, high pressure discharge as an energetic input to a process.…”