Energetic Ethylene‐ and Propylene‐Bridged Bis(nitroiminotetrazolate) Salts

High energy density materials with ethylene‐ and propylene bis(5‐nitroiminotetrazolate) as the anions are reported; all salts were fully characterized by IR, and ¹H, ¹³C, and ¹⁵N NMR spectroscopy as well as elemental analyses. In addition, the heats of formation (ΔH_f) and the detonation pressures (P) and velocities (D) were calculated.

     

Energetic Hydrazine‐Based Salts with Nitrogen‐Rich and Oxidizing Anions

1,1,1‐Trimethylhydrazinium iodide ([(CH₃)₃N? NH₂]I, 1 ) was reacted with a silver salt to form the corresponding nitrate ([(CH₃)₃N? NH₂][NO₃], 2 ), perchlorate ([(CH₃)₃N? NH₂][ClO₄], 3 ), azide ([(CH₃)₃N? NH₂][N₃], 4 ), 5‐amino‐1H‐tetrazolate ([(CH₃)₃N? NH₂][H₂N? CN₄], 5 ), and sulfate ([(CH₃)₃N? NH₂]₂[SO₄]?2H₂O, 6 ?2H₂O) salts. The metathesis reaction of compound 6 ?2H₂O with barium salts led to the formation of the corresponding picrate ([(CH₃)₃N? NH₂][(NO₂)₃Ph ‐ O], 7 ), dinitramide ([(CH₃)₃N? NH₂][N(NO₂)₂], 8 ), 5‐nitrotetrazolate ([(CH₃)₃N? NH₂][O₂N? CN₄], 9 ), and nitroformiate ([(CH₃)₃N? NH₂][C(NO₂)₃], 10 ) salts. Compounds 1 – 10 were characterized by elemental analysis, mass spectrometry, infrared/Raman spectroscopy, and multinuclear NMR spectroscopy (¹H, ¹³C, and ¹⁵N). Additionally, compounds 1 , 6 , and 7 were also characterized by low‐temperature X‐ray diffraction techniques (XRD). Ba(NH₄)(NT)₃ (NT=5‐nitrotetrazole anion) was accidentally obtained during the synthesis of the 5‐nitrotetrazole salt 9 and was also characterized by low‐temperature XRD. Furthermore, the structure of the [(CH₃)₃N? NH₂]⁺ cation was optimized using the B3LYP method and used to calculate its vibrational frequencies, NBO charges, and electronic energy. Differential scanning calorimetry (DSC) was used to assess the thermal stabilities of salts 2 – 5 and 7 – 10 , and the sensitivities of the materials towards classical stimuli were estimated by submitting the compounds to standard (BAM) tests. Lastly, we computed the performance parameters (detonation pressures/velocities and specific impulses) and the decomposition gases of compounds 2 – 5 and 7 – 10 and those of their oxygen‐balanced mixtures with an oxidizer.     

Nitrogen‐Rich Energetic Monoanionic Salts of 3,4‐Bis(1 H‐5‐tetrazolyl)furoxan

3,4‐Bis(1H‐5‐tetrazolyl)furoxan (H₂BTF, 2 ) and its monoanionic salts that contain nitrogen‐rich cations were readily synthesized and fully characterized by multinuclear NMR (¹H, ¹³C) and IR spectroscopy, differential scanning calorimetry (DSC), and elemental analyses. Hydrazinium ( 3 ) and 4‐amino‐1,2,4‐triazolium ( 7 ) salts crystallized in the monoclinic space group P2(1)/n and have calculated densities of 1.820 and 1.764 g cm^?3, respectively. The densities of the energetic salts range between 1.63 and 1.79 g cm^?3, as measured by a gas pycnometer. Detonation pressures and detonation velocities were calculated to be 23.1–32.5 GPa and 7740–8790 m s^?1, respectively.     

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.     

Synthesis and Promising Properties of a New Family of High‐Nitrogen Compounds: Polyazido‐ and Polyamino‐Substituted N,N′‐Azo‐1,2,4‐triazoles

A new family of high‐nitrogen compounds, that is, polyazido‐ and polyamino‐substituted N,N′‐azo‐1,2,4‐triazoles, were synthesized in a safe and convenient manner and fully characterized. The structures of 3,3′,5,5′‐tetra(azido)‐4,4′‐azo‐1,2,4‐triazole ( 15 ) and 3,3′,5,5′‐tetra(amino)‐4,4′‐azo‐1,2,4‐triazole ( 23 ) were also confirmed by X‐ray diffraction. Differential scanning calorimetry (DSC) was performed to determine their thermal stability. Their heats of formation and density, which were calculated by using Gaussian 03, were used to determine the detonation performances of the related compounds (EXPLO 5.05). The heats of formation of the polyazido compounds were also derived by using an additive method. Compound 15 has the highest heat of formation (6933 kJ kg^?1) reported so far for energetic compounds and a detonation performance that is comparable to that of octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX), while compound 23 has a decomposition temperature of up to 290 °C.     

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.     

Energetic Oxygen‐Containing Tetrazole Salts Based on 3,4‐Diaminotriazole

Energetic mono‐ and dicationic 3,4‐diaminotriazolium salts have been prepared by combining stoichiometric amounts (1:1 or 2:1 molar ratio) of 3,4‐diaminotriazole with various oxygen‐containing tetrazoles, and the structures have been confirmed by single‐crystal XRD for the first time. All structures are dominated by a strong hydrogen‐bond network owing to both amino groups and oxygen in the molecule. All salts, except 7 , exhibit excellent thermal stabilities with decomposition temperatures over 200 °C. Based on experimental densities and theoretical calculations carried out by using the Gaussian 03 suite of programs, all salts have calculated detonation pressures (20.3–33.9 GPa) and velocities (7095–8642 m s^?1).     

Energetic 2,2‐Dimethyltriazanium Salts: A New Family of Nitrogen‐Rich Hydrazine Derivatives

Amination of 1,1‐dimethylhydrazine with NH₂Cl or hydroxylamine‐O‐sulfonic acid yields 2,2‐dimethyltriazanium (DMTZ) chloride ( 3 ) and sulphate ( 4 ), respectively. The DMTZ cation was paired with the nitrogen‐rich anions 5‐aminotetrazolate ( 5 ), 5‐nitrotetrazolate ( 6 ), 5,5′‐azobistetrazolate ( 7 ), and azide ( 8 ), yielding a new family of energetic salts. The synthesis was carried out by metathesis reactions of salts 3 or 4 and a suitable silver or barium salt. To minimize the risks involved when using heavy metal salts, we used electrodialysis for the synthesis of azide 8 , which avoids the use of highly sensitive species. The DMTZ derivatives were characterized by IR and multinuclear NMR spectroscopy, elemental analysis, and X‐ray diffraction. Thermal stabilities were measured using DSC analysis and their sensitivities towards classical stimuli were determined using standard tests. Lastly, the relationship between hydrogen bonding in the solid state and sensitivity is discussed.     

Energetic N‐Trinitroethyl‐Substituted Mono‐, Di‐, and Triaminotetrazoles

A series of dense energetic N‐trinitroethyl‐substituted mono‐, bis‐, and tri‐5‐aminotetrazoles were obtained by reacting primary amines with in situ generated cyanogen azide, followed by the trinitroethyl functionalization that involves a condensation of a hydroxymethyl intermediate (prepared by a reaction with formaldehyde) with trinitromethane. These compounds were fully characterized by using multinuclear NMR spectroscopy, IR, elemental analysis, differential scanning calorimetry (DSC), and, in one case with 9 , with single‐crystal XRD analysis. The heats of formation for all compounds were calculated with Gaussian 03 and then combined with experimental densities to determine the detonation pressures (P) and velocities (D_v) of the energetic materials. Interestingly, most of them exhibited high density, good thermal stability, acceptable oxygen balance, positive heat of formation, low impact sensitivity, and excellent detonation properties, which highlighted their practical application potentials as a fascinating class of highly energetic materials.     

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.     

Highly Dense Nitranilates‐Containing Nitrogen‐Rich Cations

High density energetic salts containing nitrogen‐rich cations and the nitranilic anion were readily synthesized in high yield by metathesis reactions of sodium nitranilate 2 and an appropriate halide. All of the new compounds were fully characterized by elemental, spectral (IR, ¹H, ¹³C NMR), and thermal (DSC) analyses. The structure of hydrazinium nitranilate ( 4 ) was also determined by single‐crystal X‐ray analysis. The high symmetry and oxygen content of the anion give these salts extensive hydrogen bonding capability which further results in the high densities, low water solubilities, and high thermal stabilities (T_d> 200 °C) of these compounds. Theoretical performance calculations were carried out by using Gaussian 03 and Cheetah 5.0. The calculated detonation pressures (P) for these new salts fall between 17.5 GPa ( 10 ) and 31.7 GPa ( 4 ), and the detonation velocities (νD) range between 7022 m s^?1 ( 13 ) and 8638 m s^?1 ( 4 ).     

Synthesis of Thermally Stable Energetic 1,2,3‐Triazole Derivatives

Various thermally stable energetic polynitro‐aryl‐1,2,3‐triazoles have been synthesized through Cu‐catalyzed [3+2] cycloaddition reactions between their corresponding azides and alkynes, followed by nitration. These compounds were characterized by analytical and spectroscopic methods and the solid‐state structures of most of these compounds have been determined by using X‐ray diffraction techniques. Most of the polynitro‐bearing triazole derivatives decomposed within the range 142–319 °C and their heats of formation and crystal densities were determined from computational studies. By using the Kamlet–Jacobs empirical relation, their detonation velocities and pressures were calculated from their heats of formation and crystal densities. Most of these newly synthesized compounds exhibited high positive heats of formation, good thermal stabilities, reasonable densities, and acceptable detonation properties that were comparable to those of TNT.     

Energetic bicyclic azolium salts

Bicyclic azoles, 2-methyl-5-(imidazol-1-yl)-2H-tetrazole (1), 2-methyl-5-(1,2,4-triazol-1-yl)-2H-tetrazole (4), 1-methyl-5-(imidazol-1-yl)-1H-tetrazole (7), 1-methyl-5-(1,2,4-triazol-1-yl)-1H-tetrazole (10), 1-methyl-4-nitro-2-(imidazol-1-yl)-1H-imidazole (13), and 1-methyl-4-nitro-2-(1,2,4-triazol-1-yl)-1H-imidazole (16) were prepared. Their thermally stable azolium salts, 3, 6, 9, 12, 15, and 18-21, with densities ranging between 1.519-1.674 g cm-3, were synthesized by quaternization with nitric or perchloric acid or with iodomethane followed by metathesis reactions with silver nitrate and silver perchlorate. The structures of 12 b and 21 b were confirmed by single-crystal X-ray analysis. The standard enthalpies of formation for some of the new salts were calculated by using the computationally feasible DFT(B3LYP) and MP2 methods in conjunction with an empirical approach based on densities of salts. The calculated values range from DeltaHdegreef=209.9 (21 a) to 412.3 (12 b) kJ mol-1 in which the experimental densities are >1.515 g cm-3.     

1,2,4‐Triazole Links and N‐Azo Bridges Yield Energetic Compounds

Triazole links and polynitropyrazole rings give rise to compounds with energetic properties. These materials were fully characterized by NMR and infrared spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). In addition, the structures of compounds 5 and 8 were confirmed by single‐crystal X‐ray diffraction analysis. Detonation properties, calculated from heats of formation and experimental densities, thermal stabilities, and impact and friction sensitivities support the potential use of these materials for explosive applications.     

Fully C/N‐Polynitro‐Functionalized 2,2′‐Biimidazole Derivatives as Nitrogen‐ and Oxygen‐Rich Energetic Salts

Through the use of a fully C/N‐functionalized imidazole‐based anion, it was possible to prepare nitrogen‐ and oxygen‐rich energetic salts. When N,N‐dinitramino imidazole was paired with nitrogen‐rich bases, versatile ionic derivatives were prepared and fully characterized by IR, and ¹H, and ¹³C NMR spectroscopy and elemental analysis. Both experimental and theoretical evaluations show promising properties for these energetic compounds, such as high density, positive heats of formation, good oxygen balance, and acceptable stabilities. The energetic salts exhibit promising energetic performance comparable to the benchmark explosive RDX (1,3,5‐trinitrotriazacyclohexane).     

Energetic Salts Based on an Oxygen‐Containing Cation: 2,4‐Diamino‐1,3,5‐triazine‐6‐one

A family of energetic salts with high thermal stability and low impact sensitivity based on an oxygen‐containing cation, 2,4‐diamino‐1,3,5‐triazine‐6‐one, were synthesized and fully characterized by IR and multinuclear (¹H, ¹³C) NMR spectroscopy, elemental analysis, and differential scanning calorimetry. Insights into their sensitivities towards impact, friction, and electrostatics were gained by submitting the materials to standard tests. The structures of 2,4‐diamino‐1,3,5‐triazine‐6‐one nitrate, 2,4‐diamino‐1,3,5‐triazine‐6‐one sulfate, 2,4‐diamino‐1,3,5‐triazine‐6‐one perchlorate, 2,4‐diamino‐1,3,5‐triazine‐6‐one 5‐nitrotetrazolate were determined by single‐crystal X‐ray diffraction; their densities are 1.691, 1.776, 1.854, and 1.636 g cm^?3, respectively. Most of the salts decompose at temperatures over 180 °C; in particular, the salts 2,4‐diamino‐1,3,5‐triazine‐6‐one nitrate and 2,4‐diamino‐1,3,5‐triazine‐6‐one perchlorate, which decompose at 303.3 and 336.4 °C, respectively, are fairly stable. Furthermore, most of the salts exhibit excellent impact sensitivities (>40 J), friction sensitivities (>360 N), and are insensitive to electrostatics. The measured densities of these energetic salts range from 1.64 to 2.01 g cm^?3. The detonation pressure values calculated for these salts range from 14.6 to 29.2 GPa, and the detonation velocities range from 6536 to 8275 m s^?1; these values make the salts potential candidates for thermally stable and insensitive energetic materials.