Energetic Salts Based on Furazan‐Functionalized Tetrazoles: Routes to Boost Energy

Based on the backbone of the furazan‐tetrazole structure, routes were developed to improve the properties of energetic materials. Two types of high‐density energetic salts were designed, prepared, and fully characterized. Single‐crystal X‐ray analyses support the structural characteristics for two amino salts. A majority of the salts exhibited good detonation properties, high thermal stabilities, and relatively low impact and friction sensitivities. Hydroxylammonium and hydrazinium salts, 1 – 3 and 1 – 4 , which have relatively high densities (1.84 and 1.74 g cm^?3,, respectively), acceptable impact and friction sensitivities (14 J, 160 N and 28 J, 360 N), and good detonation pressures (38.3 and 32.2 GPa) and velocities (9323 and 9094 m s^?1), have performance properties superior to 1,3,5‐trinitro‐1,3,5‐triazinane (RDX) and triaminotrinitrobenzene (TATB).     

Synthesis,Characterization, and Energetic Properties of 6‐Amino‐tetrazolo[1,5‐b]‐1,2,4,5‐tetrazine‐7‐N‐oxide: A Nitrogen‐Rich Material with High Density

The synthesis and energetic properties of a novel N‐oxide high‐nitrogen compound, 6‐amino‐tetrazolo[1,5‐b]‐1,2,4,5‐tetrazine‐7‐N‐oxide, are described. Resulting from the N‐oxide and fused rings system, this molecule exhibits high density, excellent detonation properties, and acceptable impact and friction sensitivities, which suggests potential applications as an energetic material. Compared to known high‐nitrogen compounds, such as 3,6‐diazido‐1,2,4,5‐tetrazine (DiAT), 2,4,6‐tri(azido)‐1,3,5‐triazine (TAT), and 4,4′,6,6′‐tetra(azido)azo‐1,3,5‐triazine (TAAT), a marked performance and stability increase is seen. This supports the superior qualities of this new compound and the advantage of design strategy.     

3,4,5‐Trinitropyrazole‐Based Energetic Salts

High‐density energetic salts that are comprised of nitrogen‐rich cations and the 3,4,5‐trinitropyrazolate anion were synthesized in high yield by neutralization or metathesis reactions. The resulting salts were fully characterized by ¹H, ¹³C NMR, and IR spectroscopy; differential scanning calorimetry; and elemental analysis. Additionally, the structures of the 3,5‐diaminotriazolium and triaminoguanidinium 3,4,5‐trinitropyrazolates were confirmed by single‐crystal X‐ray diffraction. Based on the measured densities and calculated heats of formation, the detonation performances (pressure: 23.74–31.89 GPa; velocity: 7586–8543 ms^?1; Cheetah 5.0) of the 3,4,5‐trinitropyrazolate salts are comparable with 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB; 31.15 GPa and 8114 ms^?1). Impact sensitivities were determined to be no less than 35 J by hammer tests, which places these salts in the insensitive class.     

Energetic 4,4′‐Oxybis[3,3′‐(1‐hydroxytetrazolyl)]furazan and Its Salts

Energetic compounds that incorporate multiple nitrogen‐rich heterocycles are of great interest for high‐density energetic materials. A facile synthetic strategy to combine an oxy bridge and furazan groups, as well as tetrazole‐ols, into a molecule ( 5 ) was found. Some energetic salts based on 5 were prepared by neutralization. All of the compounds were fully characterized. Additionally, the structure of 7 has been elucidated by single‐crystal XRD analysis. Physicochemical and energetic properties were also studied; these show that these newly designed energetic salts exhibit good thermal stabilities. Hydroxylammonium salt ( 6 ) has a detonation performance and sensitivities comparable with those of 1,3,5‐trinitroperhydro‐1,3,5‐triazine (RDX).     

3,6,7‐Triamino‐[1,2,4]triazolo[4,3‐b][1,2,4]triazole: A Non‐toxic,High‐Performance Energetic Building Block with Excellent Stability

A novel strategy for the design of energetic materials that uses fused amino‐substituted triazoles as energetic building blocks is presented. The 3,6,7‐triamino‐7H‐[1,2,4]triazolo[4,3‐b][1,2,4]triazolium (TATOT) motif can be incorporated into many ionic, nitrogen‐rich materials to form salts with advantages such as remarkably high stability towards physical or mechanical stimuli, excellent calculated detonation velocity, and toxicity low enough to qualify them as “green explosives”. Neutral TATOT can be synthesized in a convenient and inexpensive two‐step protocol in high yield. To demonstrate the superior properties of TATOT, 13 ionic derivatives were synthesized and their chemical‐ and physicochemical properties (e.g., sensitivities towards impact, friction and electrostatic discharge) were investigated extensively. Low toxicity was demonstrated for neutral TATOT and its nitrate salt. Both are insensitive towards impact and friction and the nitrate salt combines outstanding thermal stability (decomposition temperature=280 °C) with promising calculated energetic values.     

Thermally Stable 3,6‐Dinitropyrazolo[4,3‐c]pyrazole‐based Energetic Materials

3,6‐Dinitropyrazolo[4,3‐c]pyrazole was prepared using an efficient modified process. With selected cations, ten nitrogen‐rich energetic salts and three metal salts were synthesized in high yield based on the 3,6‐dinitropyrazolo[4,3‐c]pyrazolate anion. These compounds were fully characterized by IR and multinuclear NMR spectroscopies, as well as elemental analyses. The structures of the neutral compounds 4 and its salt 16 were confirmed by single‐crystal X‐ray diffraction showing extensive hydrogen‐bonding interactions. The neutral pyrazole precursor and its salts are remarkably thermally stable. Based on the calculated heats of formation and measured densities, detonation pressures (22.5–35.4 GPa) and velocities (7948–9005 m s^?1) were determined, and they compare favorably with those of TNT and RDX. Their impact and friction sensitivities range from 12 to >40 J and 80 to 360 N, respectively. These properties make them competitive as insensitive and thermally stable high‐energy density materials.     

Synthesis and Characterization of 3,5‐Diamino‐1,2,4‐triazolium Dinitramide

3,5‐Diamino‐1,2,4‐triazole ( 1 , guanozol) was protonated with diluted hydrochloric acid, nitric acid, as well as perchloric acid forming 3,5‐diamino‐1,2,4‐triazolium chloride hemihydrate ( 2 ), 3,5‐diamino‐1,2,4‐triazolium nitrate ( 3 ) and 3,5‐diamino‐1,2,4‐triazolium perchlorate ( 4 ), respectively. In a second step 4 reacted with potassium dinitramide forming 3,5‐diamino‐1,2,4‐triazolium dinitramide ( 5 ) and low soluble potassium perchlorate. Compounds 2 – 5 were characterized by low temperature single X‐ray diffraction, IR and Raman as well as multinuclear NMR spectroscopy, mass spectrometry and differential scanning calorimetry. The heats of formation of 1 – 5 were calculated by the CBS‐4M method to be 81.1 ( 1 ), 124.7 ( 2 ), –76.1 ( 3 ), –25.2 ( 4 ) and 138.7 ( 5 ) kJ·mol^–1. With these values as well as the X‐ray densities several detonation parameters were calculated using both computer codes EXPLO5.03 and EXPLO5.04. In addition, the sensitivities of 1 – 5 were determined by the BAM drophammer and friction tester as well as a small scale electrical discharge device.     

Carbonyl and Oxalyl Bridged Bis(1,5‐Diaminotetrazole)‐Based Energetic Salts

High density energetic salts containing nitrogen rich cations and carbonyl‐ or oxalylbis(diamino‐tetrazole) anions, which were obtained from cyanogen azide and hydrazine, were readily synthesized. In every case, a new family of energetic salts 3 – 14 were characterized by vibrational spectroscopy, multinuclear (¹H, ¹³C, ¹⁵N) NMR, elemental analyses, density, differential scanning calorimetry and impact sensitivity. Compound 12 was structured by single crystal X‐ray diffraction. The densities of 3 ‐ 14 , determined by gas pycnometer, range between 1.500 and 1.676 g cm^?3. The heats of formation and detonation properties for these stable salts were calculated by using Gaussian 03 and Cheetah 5.0, respectively.     

Insensitive and Thermostable Energetic Materials Based on 3‐Ureido‐4‐tetrazole‐furazan: Synthesis,Characterization, and Properties

Energetic salts composed of ureido, furazan, and tetrazole were prepared by simple and efficient chemical routes to explore new insensitive and thermostable energetic materials. 3‐Ureido‐4‐tetrazole‐furazan ( 3 ) and its ammonium salt ( 5 ) and hydrazinium salt ( 6 ) were confirmed by single‐crystal X‐ray diffraction. The thermal stabilities of the synthesized salts were studied using differential scanning calorimetry, and the detonation performances of these salts were calculated using EXPLO 5 V6.01. All the salts exhibit good thermal stability (Td: 148–259 °C) and mechanical sensitivities (IS > 40 J, FS > 360 N), and their detonation velocities range from 7316 to 8655 m · s^–1. Compounds 6 and 10 are potential candidates as novel insensitive and heat‐resistant explosives because of their high detonation temperatures of 247 and 256 °C, good detonation velocities of 8432 and 8523 m · s^–1, and good detonation pressures of 25.6 and 26.8 GPa.     

High‐Oxygen‐Balance Furazan Anions: A Good Choice for High‐Performance Energetic Salts

3,4‐Diaminofurazan was conveniently converted into energetic salts of 3,4‐dinitraminofurazan that were paired with nitrogen‐rich cations in fewer than three steps. Seven energetic salts were prepared and fully characterized by multinuclear (¹H, ¹³C) NMR and IR spectroscopy, differential scanning calorimetry (DSC), and elemental analysis. In addition, the structures of the ammonium salt ( 2 ), hydrazinium salt ( 4 ), hydroxylammonium salt ( 5 ), aminoguanidinium salt ( 7 ), diaminoguanidinium salt ( 8 ) and triaminoguanidinium salt of 3,4‐dinitraminofurazan ( 9 ) were further confirmed by single‐crystal X‐ray diffraction. The densities of these salts were between 1.673 ( 8 ) and 1.791 g cm^?3 ( 5 ), whilst their oxygen balances were between ?48.20 % ( 9 ) and ?6.25 % ( 5 ). These salts showed high thermal stabilities, with decomposition temperatures between 179 ( 5 ) and 283 °C ( 6 ). Their sensitivities towards impact and friction were measured by BAM equipment to be between <1 J ( 9 ) and >40 J ( 6 – 8 ) and 64 N ( 9 ) and >360 N ( 6 ), respectively. The detonation performance of these compounds, which was calculated by using the EXPLO5 program, revealed detonation pressures of between 28.0 ( 6 ) and 40.5 GPa ( 5 ) and detonation velocities of between 8404 ( 6 ) and 9407 m s^?1 ( 5 ).     

4‐Nitro‐3‐(5‐tetrazole)furoxan and Its Salts: Synthesis,Characterization, and Energetic Properties

A series of new energetic salts based on 4‐nitro‐3‐(5‐tetrazole)furoxan (HTNF) has been synthesized. All of the salts have been fully characterized by nuclear magnetic resonance (¹H and ¹³C), infrared (IR) spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). The crystal structures of neutral HTNF ( 3 ) and its ammonium ( 4 ) and N‐carbamoylguanidinium salts ( 9 ) have been determined by single‐crystal X‐ray diffraction analysis. The densities of 3 and its nine salts were found to range from 1.63 to 1.84 g cm^?3. Impact sensitivities have been determined by hammer tests, and the results ranged from 2 J (very sensitive) to >40 J (insensitive). Theoretical performance calculations (Gaussian 03 and EXPLO 5.05) provided detonation pressures and velocities for the ionic compounds 4 – 12 in the ranges 25.5–36.2 GPa and 7934–8919 m s^?1, respectively, which make them competitive energetic materials.     

Nitrogen‐rich Salts based on 3‐Dinitromethyl‐[1,2,4]triazine: Synthesis,Characterization, and Performance

1,1‐Diamino‐2,2‐dinitroethylene (FOX‐7), one of the most well‐known energetic materials, has attracted broad attention around the world. To extend the chemistry of FOX‐7, we present here a series of energetic salts based on 3‐dinitromethyl‐[1,2,4]triazine, which is prepared from FOX‐7. All these salts were fully characterized using ¹H NMR, ¹³C NMR, IR, and elemental analysis. In addition, the potassium salt ( 2 ), ammonium salt ( 5 ), and guanidinium salt ( 7 ) were further confirmed by single‐crystal X‐ray diffraction. Extensive hydrogen bonds were observed in these salts. The salts exhibit moderate densities varying from 1.63 to 1.76 g · cm^–3. All the compounds possess good thermal stability with decomposition temperatures from 118 to 267 °C. The detonation performance for salts were calculated by using EXPLO 5, their detonation velocities are in the range from 6807 to 8614 m · s^–1 and detonation pressures fall between 18.8 to 31.6 GPa. All the salts exhibit very low mechanical sensitivity, which indicates their potential application as insensitive energetic materials.     

Cocrystals of 2,6‐dichloroaniline and 2,6‐dichlorophenol plus three new pseudopolymorphs of their coformers

The structures of cocrystals of 2,6‐dichlorophenol with 2,4‐diamino‐6‐methyl‐1,3,5‐triazine, C₆H₄Cl₂O·C₄H₇N₅, (III), and 2,6‐dichloroaniline with 2,6‐diaminopyrimidin‐4(3H)‐one and N,N‐dimethylacetamide, C₆H₅Cl₂N·C₄H₆N₄O·C₄H₉NO, (V), plus three new pseudopolymorphs of their coformers, namely 2,4‐diamino‐6‐methyl‐1,3,5‐triazine–N,N‐dimethylacetamide (1/1), C₄H₇N₅·C₄H₉NO, (I), 2,4‐diamino‐6‐methyl‐1,3,5‐triazine–N‐methylpyrrolidin‐2‐one (1/1), C₄H₇N₅·C₅H₉NO, (II), and 6‐aminoisocytosine–N‐methylpyrrolidin‐2‐one (1/1), C₄H₆N₄O·C₅H₉NO, (IV), are reported. Both 2,6‐dichlorophenol and 2,6‐dichloroaniline are capable of forming definite synthon motifs, which usually lead to either two‐ or three‐dimensional crystal‐packing arrangements. Thus, the two isomorphous pseudopolymorphs of 2,4‐diamino‐6‐methyl‐1,3,5‐triazine, i.e. (I) and (II), form a three‐dimensional network, while the N‐methylpyrrolidin‐2‐one solvate of 6‐aminoisocytosine, i.e. (IV), displays two‐dimensional layers. On the basis of these results, attempts to cocrystallize 2,6‐dichlorophenol with 2,4‐diamino‐6‐methyl‐1,3,5‐triazine, (III), and 2,6‐dichloroaniline with 6‐aminoisocytosine, (V), yielded two‐dimensional networks, whereby in cocrystal (III) the overall structure is a consequence of the interaction between the two compounds. By comparison, cocrystal–solvate (V) is mainly built by 6‐aminoisocytosine forming layers, with 2,6‐dichloroaniline and the solvent molecules arranged between the layers.     

Energetic N,N′‐Ethylene‐Bridged Bis(nitropyrazoles): Diversified Functionalities and Properties

A new class of N,N′‐ethylene‐bridged bis(nitropyrazoles) was synthesized and fully characterized. The highly efficient formation of the N,N′‐ethylene bridge was accomplished using dibromoethane and ammonium or potassium pyrazolate. Further functional‐group transformations of diaminobis(pyrazole) and dichlorobis(pyrazole) gave rise to diversified derivatives, including dinitramino‐, diazido‐ and hexanitrobis(pyrazole). Single‐crystal X‐ray diffractions were obtained for hexanitro and diazido derivatives to illustrate the structural characteristics. Heats of formation and detonation performance were calculated by using Gaussian 03 and EXPLO5 v6.01 programs, respectively. Because of the different functionalized groups, the impact and friction sensitivities of these new compounds range from insensitive to sensitive. Among them, the hexanitro derivative displays the most promising overall energetic properties (density (ρ)=1.84 g cm^?3; decomposition temperature (T_d)=250 °C; detonation pressure (P)=34.1 GPa; detonation velocity (v_D)=8759 m s^?1; impact sensitivity (IS)=25 J; friction sensitivity (FS)=160 N), which is competitive with those of 1,3,5‐trinitrotriazacyclohexane (ρ=1.80 g cm^?3; T_d=205 °C; P=35.0 GPa; v_D=8762 m s^?1; IS=7 J; FS=120 N).     

Synthesis,Crystal Structure,and Thermal Behavior of a Novel Insensitive Energetic Cocrystal Composed of 3,3′‐Bis(1,2,4‐oxadiazole)‐5,5′‐dione and 4‐Amino‐1,2,4‐triazole

A novel insensitive energetic cocrystal consisting of 3,3′‐bis(1,2,4‐oxadiazole)‐5,5′‐dione and 4‐amino‐1,2,4‐triazole in a 1:2 molar ratio was prepared and characterized. The structure of this cocrystal was characterized by single‐crystal X‐ray diffraction. The crystal structure of the cocrystal is a monoclinic system with P1 space group. Properties of the cocrystal studied included thermal decomposition and detonation performance. This cocrystal has a crystal density of 1.689 g · cm^–3 at 173 K and good detonation performance (D = 6940 m · s^–1, P = 20.9 GPa). Moreover, measured impact and friction sensitivities (IS > 40 J, FS > 360 N) show that it can be classified as an insensitive energetic material. Its thermodynamic properties indicate that it has moderate thermal stability with a sharp exothermic peak (244 °C, 5 K · min^–1) and a high critical temperature of thermal explosion (523 K). In view of the observations above, it may serve as a promising alternative to known explosives such as TNT.     

Synthesis and Characterization of 5‐(1,2,4‐Triazol‐3‐yl)tetrazoles with Various Energetic Functionalities

In this contribution the synthesis and full structural as well as spectroscopic characterization of three 5‐(1,2,4‐triazol‐3‐yl)tetrazoles along with selected energetic moieties like nitro, nitrimino, and azido groups are presented. The main goal is a comparative study on the influence of those variable energetic moieties on structural and energetic properties. A complete characterization including IR and Raman as well as multinuclear NMR spectroscopy of all compounds is presented. Additionally, X‐ray crystallographic measurements were performed and reveal insights into structural characteristics as well as inter‐ and intramolecular interactions. The standard enthalpies of formation were calculated for all compounds at the CBS‐4M level of theory and reveal high positive heats of formation for all compounds. The calculated detonation parameters (using the EXPLO5.05 program) are in the range of 8000 m s^?1 (8097 m s^?1 ( 5 ), 8020 m s^?1 ( 6 ), 7874 m s^?1 ( 7 )). As expected, the measured impact and friction sensitivities as well as decomposition temperatures strongly depend on the energetic moiety at the triazole ring. The C? C connection of a triazole ring with its opportunity to introduce a large variety of energetic moieties and a tetrazole ring, implying a large energy content, leads to the selective synthesis of primary and secondary explosives.     

Preparation,Crystal Structure,and Thermal Analysis of Two Energetic Salts Based on Nitro Phenolic Compounds with Diamino‐glyoxine

As a key research objective for environmentally friendly energetic materials, energetic salts without heavy metal have received wide attention. The energetic salts DAG · PA · H₂O ( 1 ) and DAG · TNR · H₂O ( 2 ) were synthesized by using diamino‐glyoxine (DAG) and picric acid (PA) or 2, 4,6‐trinitro‐resorcinol (TNR) as raw materials, and their structures were characterized by elemental analysis, FT‐IR, ¹H NMR, and ¹³C NMR spectroscopy. Single crystals of the title salts were cultured and their structures were determined by X‐ray single‐crystal diffraction. Both salts belong to the triclinic space group P1 with density values of 1.764 and 1.751 g · cm^–3, respectively. The thermal decomposition behaviors of both salts were investigated by differential scanning calorimetry (DSC), the non‐isothermal kinetic parameters and the critical temperature of thermal explosion were calculated. The heats of formation for the salts were also determined through the combustion heats date measured by using the oxygen bomb calorimetry. In addition, the detonation pressure (P) and detonation velocities (D) of the salts were predicted by using the K‐J equations, and their sensitivities towards impact and friction were tested. The results indicated that the title salts have potential applications in the field of energetic materials.     

Magnesium Azotetrazole‐1,1′‐dioxide: Synthesis and Promising Properties of Green Insensitive Energetic Materials

Magnesium azotetrazole‐1,1′‐dioxide ( 1 ) was first prepared and intensively characterized by single‐crystal X‐ray diffraction, IR spectroscopy, mass spectrometry, elemental analysis, and DSC measurements. The heat of formation was calculated using the atomization energy method based on quantum chemistry and the heat of detonation was also predicted. The NBO analysis was performed for inspecting charge distributions. The sensitivities towards impact and friction were tested using the BAM standard. The high detonation performance (5289 kJ · kg^–1), good thermal stabilities (245.5 °C) and excellent insensitivity (39.2 J and >360 N) as well as clean decomposition products supports it of great interest as a promising candidate of green insensitive energetic materials.     

Nitroguanidine‐Fused Bicyclic Guanidinium Salts: A Family of High‐Density Energetic Materials

A series of nitroguanidine‐fused bicyclic guanidinium energetic salts paired with inorganic energetic anions, mono‐ and di‐tetrazolate anions were synthesized through simple metathesis reactions of 2‐iminium‐5‐nitriminooctahydroimidazo[4,5‐d]imidazole chloride and sulfate with the corresponding silver and barium salts, respectively, in aqueous solution. Key physical properties, such as melting point, thermal stability, and density were measured. The relationship between the structures of the salts and these properties was determined. The salts exhibit thermal stability and density (>1.60 g cm^?3) that are comparable to currently used explosives The structures of the nitrate salt 1 and the dinitrocyanomethanide salt 4 were confirmed by single‐crystal X‐ray analysis. Densities, heats of formation, detonation pressures and velocities, and specific impulses were calculated. All of the salts possess positive calculated heats of formation and most of them exhibit promising energetic performance that is comparable with those of 1,3,5‐trinitrobenzene (TNT), 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB), and cyclotrimethylenetrinitramine (RDX). The effect of the fused bicycle 2‐iminium‐5‐nitriminooctahydroimidazo[4,5‐d]imidazole on these physicochemical properties was examined and discussed.     

New theoretically predicted RDX‐ and β‐HMX‐based high‐energy‐density molecules

Theoretically new high‐energy‐density materials (HEDM) in which the hydrogens on RDX and β‐HMX (hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine and octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine, respectively) were sequentially replaced by (N NO₂)x functional groups were designed and evaluated using density functional theory calculations in combination with the Kamlet–Jacobs equations and an atoms‐in‐molecules (AIM) analysis. Improved detonation properties and reduced sensitivity compared to RDX and β‐HMX were predicted. Interestingly, the RDX and β‐HMX derivatives having one attached N NO₂ group [RDX‐(NNO₂)1 and HMX‐(NNO₂)1] showed excellent detonation properties (detonation velocities: 9.529 and 9.575 km·s⁻¹, and detonation pressures: 40.818 and 41.570 GPa, respectively), which were superior to the parent compounds. Sensitivity estimations obtained by calculating impact sensitivities and HOMO‐LUMO gaps indicated that RDX‐(NNO₂)1 and HMX‐(NNO₂)1 were less stable than RDX and HMX but more stable than any of the other derivatives. This method of sequential NNO₂ group attachment on conventional HEDMs offers a firm basis for further studies on the design of new explosives. Furthermore, the newly found structures may be promising candidates for better HEDMs.