“Green” Pyrotechnics: A Chemists' Challenge

Nitrogen-Rich Tetranuclear Metal Complex as a New Structural Motif for Energetic Materials

For designing energetic materials (EMs), the most challenging issue is to achieve a balance between energetic performance and reliable stability. In this work, we employed an efficient and convenient method to synthesize a new class of EMs: nitrogen-rich tetranuclear metal complexes [M(Hdtim)(H₂O)₂]₄ (M = Zn 1, Mn 2; H₃dtim = 1H-imidazol-4,5-tetrazole) with the N content of >46%. The structural analyses illustrate that isomorphous compounds 1 and 2 feature isolated hollow ellipsoid tetranuclear units, which are linked by both π-π interactions and hydrogen-bonding interactions to give a 3D supramolecular architecture. Compounds 1 and 2 exhibit prominent energetic characteristics: excellent detonation performances and reliable thermal, impact, and friction stabilities. Being nitrogen-rich tetrazolate compounds, the enthalpies of combustion of 1 (-11.570 kJ g^-1) and 2 (-12.186 kJ g^-1) are higher than those of classical EMs, RDX and HMX, and they possess high positive heats of formation. Sensitivity tests demonstrate that 1 and 2 are insensitive to external mechanical action. Excellent energetic performances and low sensitivities promote 1 and 2 to serve as a new class of promising EMs with a desirable level of safety.

Energetic isomers of 1,2,4,5-tetrazine-bis-1,2,4-triazoles with low toxicity

A series of nitrogen-rich “green” Energetic Materials (EMs), some with improved sensitivity, thermostability, and very low toxicity, were synthesized on the basis of 3,5-diamino-1,2,4-triazole (DAT) and 1,2,4,5-tetrazine building blocks.

Alkali and alkaline earth metal salts of tetrazolone: structurally interesting and excellently thermostable

Alkali and alkaline earth metal salts of tetrazolone were first reported and may be promising potential candidates of new green insensitive energetic materials.

Pursuing reliable thermal analysis techniques for energetic materials: decomposition kinetics and thermal stability of dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50)

Reliable kinetics of thermolysis for a novel explosive dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) was obtained using a variety of thermoanalytical and kinetic methods and verified by modeling of adiabatic self-heating.

Synthesis of six-coordinate mono-, bis-, and tris(tetrazolato) complexes via [3 + 2] cycloadditions of nitriles to silicon-bound azido ligands

A convenient synthetic route to poly(tetrazolato) silicon complexes is described based on the four reactive centres of the N-rich, highly endothermic tetraazides of the type Si(N₃)₄(L₂). Hypercoordinate azido(tetrazolato) silicon complexes Si(N₃)₂(N₄C-R)₂(L₂), R = CH₃, C₆H₅, 4-C₆H₄CH₃ (4a, 5, 6, 7) and Si(N₃)₂(N₄C-L)₂ (9, L = 2-C₅H₄N), L₂ = 2,2'-bipyridine, 1,10-phenanthroline, with SiN₆ skeletons were synthesised via multiple [3 + 2] dipolar cycloaddition reactions starting from Si(N₃)₄(L₂) and a nitrile. The isolated new complexes were characterised by standard analytical methods, single crystal X-ray diffraction and differential scanning calorimetry (4a,b). Tetrazolato ligand linkage isomerism was observed for complex 4a. The crystallographically characterised methyl tetrazolato complexes and plausible configurational and linkage isomers were evaluated by DFT calculations at the B3LYP/6-311G(d,p) level.

The first organocopper tetrazole derivative: synthesis and characterization

1-(5-Amino-3-azapentyl)tetrazole dihydrochloride (HL·2HCl) was prepared by heterocyclization of diethylenetriamine with triethyl orthoformate and sodium azide followed by treatment with potassium carbonate and hydrochloric acid. The reaction of CuCl2, HL·2HCl and triethylamine (NEt3) in a molar ratio of 1 : 1 : 3 in water was found to generate a novel organometallic tetrazole derivative Cu2L2Cl2. This compound is present as a binuclear centrosymmetric molecular complex, in which C-deprotonated tetrazole L acts as a chelating ligand via the two amino N and tetrazole ring C coordination sites and the two copper atoms are linked together through two tetrazole ring N(4)-C(5) bridges. This complex is the first organocopper tetrazole derivative. When the molar ratio of the reagents in the abovementioned reaction was changed to 1 : 2 : 2, the complex Cu(HL)2Cl2 was formed along with Cu2L2Cl2. Pure Cu(HL)2Cl2 was isolated after reaction of the reagents in a molar ratio of 1 : 3 : 6. The complex Cu(HL)2Cl2 is present as a mononuclear molecular complex, with a chelating coordination mode of HL via the two amino N atoms only. Both complexes as well as HL·2HCl were characterized by single-crystal X-ray analysis.

Trifluoromethanesulfonimide catalysed synthesis of 1-substituted-1H-1,2,3,4-tetrazoles using glycerol as green solvent at room temperature

A direct synthetic protocol is developed for the synthesis of 1-substituted-1 H-1,2,3,4-tetrazoles via a three-component condensation of primary amines, triethyl orthoformate and sodium azide in the presence of 5 mol% of trifluoromethanesulfonimide (HNTf2) in glycerol at room temperature with good to excellent yields.

An enhanced extended hook method to realize tetranuclear metal clusters embedded in energetic metal–organic framework channels

Rare tetranuclear Zn clusters were successfully embedded into energetic 3D metal–organic framework channels by an extended bifunctional tetrazolate–carboxylate hook ligand.

A biography of potassium complexes as versatile, green energetic materials

This review covers flourishing green potassium complexes that have been developed as energetic materials.

Rendering non-energetic microporous coordination polymers explosive

A stable microporous coordination polymer is transformed into a sensitive primary explosive by simple infiltration with an organic oxidizer.

The effect of detonation polycrystalline diamond modification on the thermal decomposition of RDX

A moderate amount of DPD modification as a catalyst accelerated the decomposition of RDX, while excess modification conversely obstructed the decomposition.

Metal-organic fireworks: MOFs as integrated structural scaffolds for pyrotechnic materials

A new approach to formulating pyrotechnic materials is presented whereby constituent ingredients are bound together in a solid-state lattice. This reduces the batch inconsistencies arising from the traditional approach of combining powders by ensuring the key ingredients are 'mixed' in appropriate quantities and are in intimate contact. Further benefits of these types of material are increased safety levels as well as simpler logistics, storage and manufacture. A systematic series of new frameworks comprising fuel and oxidiser agents (group 1 and 2 metal nodes & terephthalic acid derivatives as linkers) has been synthesised and structurally characterised. These new materials have been assessed for pyrotechnic effect by calorimetry and burn tests. Results indicate that these materials exhibit the desired pyrotechnic material properties and the effect can be correlated to the dimensionality of the structure. A new approach to formulating pyrotechnic materials is proposed whereby constituent ingredients are bound together in a solid-state lattice. A series of Metal-organic framework frameworks comprising fuel and oxidiser agents exhibits the desired properties of a pyrotechnic material and this effect is correlated to the dimensionality of the structure.

Efficient Synthesis of 5-Substituted 1H-Tetrazoles Catalysed by Silver(I) Bis(trifluoromethanesulfoyl)Nimide

An efficient method is developed for the synthesis of 5-substituted 1H-tetrazoles through the [3 + 2] cycloaddition reaction of nitriles with sodium azide using silver(I) bis(trifluoromethanesulfonyl)imide (AgNTf2) as a catalyst. This procedure provides mild reaction conditions, short reaction times and high yields.

Low-migratory ionic ferrocene-based burning rate catalysts with high combustion catalytic efficiency

1-(Ferrocenylmethyl)alkylimidazolium-based ionic compounds with low-migration, high thermal stability and catalytic activity in the thermal degradation of ammonium perchlorate were synthesized and characterized.

The nitration pattern of energetic 3,6-diamino-1,2,4,5-tetrazine derivatives containing azole functional groups

A study of nitration patterns was conducted on 3,6-diamino-1,2,4,5-tetrazines derivatives, revealing the specificity of their nitration, as well as the stability of the formed nitramines towards hydrolysis.

In situ synthesized 3D heterometallic metal–organic framework (MOF) as a high-energy-density material shows high heat of detonation, good thermostability and insensitivity

A 3D heterometallic metal–organic framework has been synthesized in situ using Mtta formed from acetonitrile and azide, and structurally characterized.

Two nitrogen-rich Ni(ii) coordination compounds based on 5,5′-azotetrazole: synthesis, characterization and effect on thermal decomposition for RDX, HMX and AP

Two novel efficient burning promoters of solid propellants based on Ni salt and azotetrazole have been successfully prepared and characterized.

Environmental impacts of perchlorate with special reference to fireworks--a review

Perchlorate is an inorganic anion that is used in solid rocket propellants, fireworks, munitions, signal flares, etc. The use of fireworks is identified as one of the main contributors in the increasing environmental perchlorate contamination. Although fireworks are displayed for entertainment, its environmental costs are dire. Perchlorates are also emerging as potent thyroid disruptors, and they have an impact on the ecology too. Many studies have shown that perchlorate contaminates the groundwater and the surface water, especially in the vicinity of fireworks manufacturing sites and fireworks display sites. The health and ecological impacts of perchlorate released in fireworks are yet to be fully assessed. This paper reviews fireworks as a source of perchlorate contamination and its expected adverse impacts.