Modulating Energetic Characteristics of Multicomponent 1D Coordination Polymers: Interplay of Metal-Ligand Coordination Modes

Energetic coordination polymers (ECPs) based on tetrazole N-oxides: green nitrogen-rich energetic complexes of variable dimensions

In recent years, it has been demonstrated that the energetic properties of many tetrazole-containing compounds can be enhanced through the formation of the corresponding N-oxides. The introduction of N-O groups increases the oxygen balance of tetrazole compounds, while providing additional coordination sites and enriching the coordination modes between tetrazole compounds and metal ions. The introduction of O atoms alters the polarity of the substance from N to N-O, the packing and density increase and therefore the detonation velocity (VD) and pressure (P) also increase. Based on this, energetic coordination polymers (ECPs) with tetrazole N-oxides serving as ligands possess extremely high research value. In this paper, we aim to summarize the existing ECPs based on tetrazole N-oxides briefly and discuss their advantages, emphasizing their excellent stability and application prospects.

Highly Dense N-N-Bridged Dinitramino Bistriazole-Based 3D Metal-Organic Frameworks with Balanced Outstanding Energetic Performance

Due to the inherent conflict between energy and safety, the construction of energetic materials or energetic metal-organic frameworks (E-MOFs) with balanced thermal stability, sensitivity, and high detonation performance is challenging for chemists worldwide. In this regard, in recent times self-assembly of energetic ligands (high nitrogen- and oxygen-containing small molecules) with alkali metals were probed as a promising strategy to build high-energy materials with excellent density, insensitivity, stability, and detonation performance. Herein, based on the nitrogen-rich N,N'-([4,4'-bi(1,2,4-triazole)]-3,3'-dial)dinitramide (H2BDNBT) energetic ligand, two new environmentally benign E-MOFs including potassium [K2BDNBT]n (K-MOF) and sodium [Na2BDNBT]n (Na-MOF) have been introduced and characterized by NMR, IR, TGA-DSC, ICP-MS, PXRD, elemental analyses, and SCXRD. Interestingly, Na-MOF and K-MOF demonstrate solvent-free 3D dense frameworks having crystal densities of 2.16 and 2.14 g cm-3, respectively. Both the E-MOFs show high detonation velocity (VOD) of 8557-9724 m/s, detonation pressure (DP) of 30.41-36.97 GPa, positive heat of formation of 122.52-242.25 kJ mol-1, and insensitivity to mechanical stimuli such as impact and friction (IS = 30-40 J, FS > 360 N). Among them, Na-MOF has a detonation velocity (9724 m/s) superior to that of conventional explosives. Additionally, both the E-MOFs are highly heat-resistant, having higher decomposition (319 °C for K-MOF and 293 °C for Na-MOF) than the traditional explosives RDX (210 °C), HMX (279 °C), and CL-20 (221 °C). This stability is ascribed to the extensive structure and strong covalent interactions between BDNBT2- and K(I)/Na(I) ions. To the best of our knowledge, for the first time, we report dinitramino-based E-MOFs as highly stable secondary explosives, and Na-MOF may serve as a promising next-generation high-energy-density material for the replacement of presently used secondary thermally stable energetic materials such as RDX, HNS, HMX, and CL-20.

Assembly of 1D Helical Energetic Coordination Polymers Using a Flexible Bridged Furazan-triazole Cation

Two new energetic coordination compounds with 1D helical chain structures have been synthesized. First, the polyamine precursor 4,5-diamino-2-((4-amino-1,2,5-oxadiazole-3-yl)methyl)-2,4-dihydro-3H-1,2,4-triazole-3-imino chloride salt (TATAF-Cl) is obtained by incorporating 4-(chloromethyl)-1,2,5-oxadiazol-3-amine with 4H-1,2,4-triazole-3,4,5-triamine. Using a simple hydrothermal method, two energetic complexes, Ag(TATAF)(ClO4)2 (ECP-1) and Ag(TATAF)(NO3)2·H2O (ECP-2), with a helical 1D MOF structure of furazan and triazole were synthesized. Compounds ECP-1 and ECP-2 have relatively high nitrogen and oxygen content (N + O%: 52.04%, 61.04%), excellent crystal density (2.229 g cm-3, 2.116 g cm-3 at 298 K) and high heat of detonation (1.18 kcal g-1, 1.06 kcal g-1), good detonation performance (P: 35.34 GPa, 29.52 GPa; Dv: 8412 m s-1, 7794 m s-1), and moderate sensitivity (IS: 8 J, 13 J; FS: 72 N, 64 N). Structurally, the Ag+ of the two ECPs is coordinated with two energetic cations, two perchlorates, or one nitrate via tetragonal coordination to form a single helical structure that is interspersed up and down in two directions.

In situ growth of copper-based energetic complexes on GO and an MXene to synergistically promote the thermal decomposition of ammonium perchlorate

In this work, using tri(5-aminotetrazolium)triazine (H3TATT) as an energetic ligand, two new energetic complexes (ECs), Cu(HTATT)(H2O)2 (EC-Cu1) and [Cu3(TATT)2(H2O)2]n (EC-Cu2), have been synthesized under hydrothermal conditions. Their crystal structures, thermal decomposition behaviors and specific heat capacities were determined respectively. In addition, two ECs were combined with GO (graphene oxide) and an MXene (Ti3C2TX) respectively by an in situ growth strategy to obtain four carbon nanomaterials/EC composites, which were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The effects of two ECs and four composites on the thermal decomposition of AP were studied by differential scanning calorimetry (DSC). Among them, the sample containing 8 wt% composite (GO/EC-Cu2) has the best promoting effect on AP, causing the high temperature decomposition peak to overlap with the low temperature decomposition peak of AP, reducing the decomposition peak temperature of AP from 443.6 °C to 308.9 °C, and the heat release is up to 4875 J g-1. Compared with ECs acting solely on AP, composite materials have stronger synergistic and promoting effects. This study provides a new example of the synthesis of carbon nanomaterial/EC composites and the improvement of the performance of AP-based solid propellants.