Synthesis of Thermally Stable and Insensitive Energetic Materials byIncorporating the Tetrazole Functionality into a Fused-Ring 3,6-Dinitropyrazolo-[4,3‑c]Pyrazole FrameworkHonglei Xia, Wenquan Zhang,* Yunhe Jin, Siwei Song, Kangcai Wang, and Qinghua Zhang*

Institute of Chemical Materials, China Academy of Engineering Physics (CAEP), Mianyang 621900, China

*S Supporting Information

ABSTRACT: A series of fused-ring energetic materials, i.e.,3,6-dinitro-1,4-di(1H-tetrazol-5-yl)-pyrazolo[4,3-c]pyrazole(DNTPP, compound 2) and its ionic derivatives (compounds3−8), were designed and synthesized in this study. Themolecular structures of compounds 2, 3, 6, 7·2H2O, and 8were confirmed using single-crystal X-ray diffraction. Theirphysicochemical and energetic properties, such as density,thermal stability, heat of formation, sensitivity, and detonationproperties (e.g., detonation velocity and detonation pressure),were also evaluated. The results indicate that DNTPP andmost of its ionic derivatives are extremely thermally stable andinsensitive toward mechanical stimuli. In particular, thethermal decomposition temperature of compound 3 is up to329 °C, while compounds 7 and 8 are very insensitive (impact sensitivity: >20 J; friction sensitivity: >360 N). Compounds 2, 3,and 6 possess good comprehensive properties, including excellent thermal stability, remarkable low sensitivities, and favorabledetonation performance. These features show that DNTPP and its ionic derivatives have considerable promise as thermallystable and insensitive energetic materials.

KEYWORDS: energetic materials, fused ring, thermal stability, detonation, sensitivity

■ INTRODUCTION

Energetic materials are a class of special energy materials thatare extensively used in both military and civilian fields. In thepast few decades, the development of new energetic materialshas attracted considerable interest1−5 and various high-performance energetic materials have been developed.6−8

Although high energy is always the primary requirement,there has been increased interest in the molecular stability ofenergetic materials because of the increase in the number ofsecurity-related issues in practical applications.9,10 However,high energy is always accompanied by reduced molecularstability of energetic materials; therefore, a major challenge isto balance the incompatible energy and stability of energeticmaterials. Thus, there is considerable demand to develop high-performance energetic materials that have a good balancebetween energy and stability.Note that nitrogen-rich fused-ring compounds with

conjugated structures exhibit excellent molecular stability andlow mechanical sensitivities; therefore, they are promisingskeletons for developing novel high-performance energeticmaterials.11−15 Compared with single-ring skeletons, fused-ringenergetic materials may possess a larger planar conjugatestructure and more varieties of chemical modification sites.Furthermore, the ring strain energy stored in the fused ring isuseful for improving their positive heats of formation, thereby

enhancing the detonation performance of fused-ring energeticmaterials.16−19 Although the fused-ring skeleton shows certainadvantages for solving the contradiction between energy andmolecular stability of energetic materials, the design andsynthesis of new fused-ring energetic materials is a significantchallenge. The primary limitation is the design method and thesynthesis technology.As a promising fused-ring energetic compound, 3,6-

dinitropyrazolo[4,3-c]pyrazole (DNPP), which was firstsynthesized by Russian researchers, shows excellent thermalstability (the decomposition temperature (Td) is 336 °C) andlow sensitivities (the impact sensitivity (IS) is 15 J; the frictionsensitivity (FS) is 160 N).20,21 Therefore, DNPP is potentiallyuseful as a thermally stable and insensitive energetic material.Because of the energy and stability properties of DNPP, severalresearchers have focused on its structural modification usingvarious N-functionalization strategies.22−24 Chemical struc-tures and properties of DNPP and its typical energeticderivatives are shown in Scheme 1. Obviously, although manyenergetic derivatives based on DNPP exhibit preferabledetonation properties compared to DNPP, their molecular

Received: September 25, 2019Accepted: November 1, 2019Published: November 13, 2019

Research Article

www.acsami.orgCite This: ACS Appl. Mater. Interfaces 2019, 11, 45914−45921

© 2019 American Chemical Society 45914 DOI: 10.1021/acsami.9b17384ACS Appl. Mater. Interfaces 2019, 11, 45914−45921

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stabilities are considerably decreased in most cases, which isreflected by the decreased thermal decomposition temper-atures and higher sensitivities (Scheme 1). Therefore, after N-functionalization reactions, the special advantages of DNPP,such as excellent thermally stability and low sensitivities tomechanical stimuli, are weakened. Thus, identifying newDNPP derivatives with high energy and good stability isdifficult.As a typical nitrogen-rich heterocyclic backbone, tetrazole

has the highest positive enthalpy of formation (4.77 kJ g−1)among common single-ring azole compounds, except forpentazole.25 Furthermore, because of tetrazole’s aromaticity,multiple tetrazole-based energetic compounds show desirablethermal stability.26 In our continued efforts toward thermallystable and insensitive energetic compounds, a highly energeticcompound, DNTPP, was readily synthesized by incorporatingtwo tetrazole moieties into the DNPP framework. Further-more, we prepared a series of nitrogen-rich energetic saltsderived from DNTPP. All new energetic compounds werecharacterized using nuclear magnetic resonance (NMR)spectroscopy, infrared (IR) spectroscopy, elemental analysis,and single-crystal X-ray diffraction (XRD) analysis, respec-tively. Moreover, their physicochemical and energetic proper-ties, such as density, thermal stability, heat of formation,sensitivity, and calculated detonation performance (e.g.,

detonation velocities and detonation pressures), were inves-tigated.

■ RESULTS AND DISCUSSION

Synthesis. The synthesis route of 2 and its energetic salts isshown in Scheme 2. The fused-ring precursor, 3,6-dinitropyrazolo[4,3-c]pyrazole (DNPP), was synthesizedaccording to a previously reported method.21 Then, potassium3,6-dinitropyrazolo[4,3-c]pyrazole (1) was synthesized usingacid−base neutralization of DNPP and KOH. Cyanogen azideis a versatile substrate for introducing the tetrazole moiety intoheterocycles such as aliphatic amines,27−30 imidazoles,31

triazoles,32 tetrazoles,33 and nitrogen heterocyclic skeletons.34

Thus, compound 1 was treated with cyanogen azide in situsynthesized from CNBr and NaN3 and the resulting mixturewas acidified with HCl to obtain 2. Furthermore, a series ofenergetic ionic derivatives (compounds 3−8) were preparedby treating 2 with different nitrogen-rich bases. All of theenergetic salts are stable in air and can be stored for anextended time period.

Single-Crystal X-ray Diffraction. The crystals ofcompounds 2, 3, 6, 7·2H2O, and 8, which are suitable forsingle-crystal XRD analysis, were obtained by the slowevaporation of corresponding solutions at room temperature.Their crystallographic and structural refinement data are listed

Scheme 1. Comparison of Some Typical Energetic Derivatives of 3,6-Dinitropyrazolo[4,3-c]pyrazole (DNPP) in PreviousWork with Energetic Compounds Developed in this Work22−24

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in Table S1 (Supporting Information). The cif files aredeposited with CCDC Nos. 1889430 (2), 1947753 (3),1908667 (6), 1889431 (7·2H2O), and 1889078 (8).Compound 2 (DNTPP) crystallizes in the monoclinic P21/c

space group with a calculated density of 1.858 g cm−3 at 173 K,and the asymmetric unit of 2 contains a half energetic molecule(Figure 1a). The nitro groups are nearly coplanar with thepyrazolo[4,3-c]pyrazole ring and form a dihedral angle of8.012° with the C1−N7 length at 1.433(5) Å. The tetrazolerings and fused rings are connected by a C3−N5 bond with abond length of 1.399(5) Å, and the dihedral angle between thetetrazole rings and fused ring is 50.245°. When viewed along

the a-axis (Figure 1b), each energetic molecule interacts withtwo adjacent energetic molecules through π−π interactions.To gain insight into the interactions among the DNTPP

molecules contained in the single crystal, we studied the two-dimensional (2D)-fingerprint plot of the crystal and theassociated Hirshfeld surface. The results are demonstrated inFigure 2a−c. Figure 2a shows that the nitro groups are nearlycoplanar with the pyrazolo[4,3-c]pyrazole ring and they appearplate-shaped; however, the torsion angles between tetrazolerings and the fused ring can be obviously observed. The redand blue dots on the surface represent the high and lowintensities of close contacts, respectively. The red dotsprimarily indicate the O···H and N···H interactions in the

Scheme 2. Synthesis of DNPP-Derived Energetic Compound 2 (DNTPP) and Its Ionic Derivatives 3−821

Figure 1. (a) Molecular structure of compound 2 (DNTPP). (b) Unit cell of compound 2, as viewed along the a-axis.

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molecule, which can be confirmed by the two-dimensionalfingerprint plot. In Figure 2b, a pair of edged spikes at the leftbottom of the two-dimensional fingerprint plot of crystaldenotes the hydrogen bonds among molecules in the adjacentlayers. The atomic contact percentages of O···H and N···H are12 and 13.8%, respectively, as shown in Figure 2c. Note thatthe N···O, N···N, and N···C interactions occupy a largeproportion in the total weak interactions for DNTPP, whichare 27.2, 20.5, and 14.1%, respectively, i.e., the π−π interactionbetween molecular layers dominates in the intermolecularinteractions of the DNTPP crystal.

The single-crystal XRD pattern showed that compound 3crystallizes in the monoclinic P21/c space group with a highdensity of 2.061 g cm−3 at 173 K, as calculated from the single-crystal data. The asymmetric unit of compound 3 contains oneand a half energetic cations and three potassium ions.Compared to DNTPP, the structure of energetic ligands in 3is considerably different as the nitro groups and tetrazole ringsare both noncoplanar with the fused ring. The dihedral anglesbetween the nitro groups and the fused ring are 23.348°, whilethe dihedral angles between tetrazole groups and the fused ringare 32.073°. In the framework of 3, each deprotonatedenergetic ligand is connected to eight adjacent potassium ions

Figure 2. (a) Hirshfeld surface for compound 2 (DNTPP) (white, distance d equals the van der Waals distance; blue, d exceeds the van der Waalsdistance; and red, d is less than the van der Waals distance). (b) Two-dimensional fingerprint plot in crystal for compound 2. (c) Individual atomiccontacts percentage contribution to the Hirshfeld surface for compound 2.

Figure 3. (a) Connecting mode of the energetic ligand in compound 3. (b) Coordination environment of the potassium ion in compound 3. (c)3D framework of compound 3 along the a-axis.

Figure 4. (a) Unit cell of compound 6, as viewed along the b-axis. (b) Unit cell of compound 7·2H2O, as viewed along the a-axis. (c) Unit cell ofcompound 8, as viewed along the a-axis.

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via K−O and K−N bonds (Figure 3a). The bond lengths ofK−O and K−N are in the range of 2.774(4)−2.858(4) and2.829(5)−3.304(5) Å, respectively. Each K+ ion is coordinatedwith four adjacent atoms (two oxygen atoms and two nitrogenatoms) from four energetic ligands (Figure 3b). According tothis 6,4-connected mode, a three-dimensional (3D) structureof 3 is formed (Figure 3c). Note that, similar to 2, theenergetic ligands of compound 3 are connected with theirneighbors.The energetic salts 6, 7·2H2O, and 8 crystallize in the

monoclinic P21/c, P21/n, and P21/c space groups, respectively.In compound 6, the nitro groups and the fused ring areconnected in a nearly coplanar manner with a dihedral angle of10.014°. However, the nitro groups of compounds 7·2H2Oand 8 are obviously noncoplanar with the pyrazolo[4,3-c]pyrazole rings and form dihedral angles of 27.034 and24.588°, respectively. In the case of the tetrazole rings incompounds 6, 7·2H2O, and 8, they are twisted out of the fusedrings with dihedral angles of 37.895, 31.258, and 33.613°,respectively. Because of π−π interactions, the anions of thethree compounds interact with their adjacent anions, which isanalogous to 2 (Figure 4a−c).Physicochemical and Energetic Properties. The

physicochemical and energetic properties of the obtainedenergetic compounds were measured and calculated (Table 1).The thermal properties of compounds 2−8 were measuredwith differential scanning calorimetry (DSC) at a heating rateof 10 °C min−1 under N2 flow. Interestingly, none of thesynthesized compounds melted prior to decomposition. Exceptfor compound 5, most of the compounds show higher thermal

decomposition temperatures (Td) than RDX and FOX-7,indicating good thermally stability. These properties areattributed to the thermally stable tetrazole rings and π-conjugated structures in the compounds. Note that DNTPPexhibits very excellent thermal stability among the potentialenergetic materials of DNPP derivatives.22−24 In particular, thethermal decomposition temperatures of compounds 2, 3, 4,and 7 are even higher than 280 °C. Furthermore, compound 3has the highest thermal decomposition temperature of up to329 °C than others, which even exceeds that of traditionalheat-resistant energetic materials such as hexanitrostibene(HNS, Td = 316 °C).37 The detonation performance ofcompounds was evaluated using EXPLO5 version 6.02 withmeasured densities and calculated heats of formation in hand.The calculated detonation velocities of these energeticmaterials lie in the range from 8023 to 9082 m s−1, and thedetonation pressures of these energetic compounds fall in therange from 22.4 to 31.3 GPa. Furthermore, the detonationvelocity of neutral DNTPP is up to 8721 m s−1 andcomparable to that of RDX, which is ∼500 m s−1 higherthan that of DNPP (8250 m s−1). In other words, theintroduction of two tetrazole rings in DNTPP results in aremarkable increase in the detonation velocity. Moreover,compounds 3 and 6 possess favorable detonation velocities,8807 and 9082 m s−1, respectively, which are superior to thatof RDX (8748 m s−1). In fact, the detonation velocity ofcompound 6 even surpasses that of FOX-7 (8870 m s−1).The mechanical sensitivities of these energetic compounds

toward impact (IS) and friction (FS) were measured using thestandard BAM method. The samples used for measurements

Table 1. Physicochemical and Energetic Properties of Compounds 2−8 Compared with FOX-7 and RDX

compound formulaa Nb [%] Ωc [%] dd[g cm−3] ΔHff[kJ mol−1] Td

e [°C] Dg[m s−1] Ph [GPa] ISi [J] FSj [N]

2 C6H2N14O4 58.7 −14.4 1.79 1111.5 281 8721 30.9 15 1923 C6K2N14O4 47.8 −7.8 2.00 638.9 329 8807 28.5 25 2524 C6H8N16O4 60.9 −26.1 1.69 916.8 280 8404 26.2 19 >3605 C6H8N16O6 56.0 −16.0 1.61 1062.2 178 8237 26.0 27.5 3246 C6H10N18O4 63.3 −28.1 1.75 1223.0 221 9082 31.3 12 1447 C8H12N20O4 61.9 −35.4 1.62 926.9 299 8023 22.4 >60 >3608 C8H14N22O4 63.9 −36.5 1.64 1143.3 255 8396 24.9 35 >360RDX35 C3H6N6O6 37.8 0 1.81 70.3 205 8748 34.9 7 120FOX-736 C2H4N4O4 37.8 0 1.885 −130 219 8870 34.0 25 340

aMolecular formula. bNitrogen content. cOB for CaHbOcNd, 1600(c − a − b/2)/Mw (based on CO).dDensity measured using a gas pycnometer at

ambient temperature. eDecomposition temperature (onset temperature at a heating rate of 10 °C min−1). fHeat of formation. gDetonation velocity.hDetonation pressure. iImpact sensitivity. jFriction sensitivity.

Figure 5. Impact and friction sensitivities of DNPP and its typical energetic derivatives: (a) impact sensitivity (IS); (b) friction sensitivity (FS).

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were dried under vacuum at 80 °C for 6 h. The sensitivities ofcompounds 2−8 (IS: from 12 to >60 J, FS: from 144 to >360N) are all significantly lower than that of RDX (IS: 7 J, FS: 120J) and comparable to that of FOX-7 (IS: 25 J, FS: 340 J),whereas compounds 4, 5, 7, and 8 exhibit very low impact andfraction sensitivities (IF: from 19 to >60 J; FS from 324 to>360 N), which are even lower than DNPP itself and anyother derivatives of DNPP (as shown in Figure 5).The synthesis of energetic salts is an effective method to

prepare insensitive energetic materials, although there is still nosystematic explanation for the decreased sensitivities ofenergetic salts compared to neutral molecules.38−40 Thefactors affecting the sensitivities of energetic materials arevery complex. Herein, the DNTPP skeleton with its rotatableexplosive groups has offered us the opportunity to understandthe relationships between low sensitivity and ionic structure.Polycyclic energetic molecules with good aromaticity alwaysshow good stability and insensitive properties.41−43 As listed in

Table 2, the dihedral angle between the tetrazole ring andfused-ring skeleton of DNTPP (50.245°) is significantly higherthan that of other salts (31.258−37.895°), while the dihedralangle between the nitro group and fused ring (8.012°) inDNTPP is smaller than the others (10.014−27.034°). Thisindicates that the two dihedral angles show an oppositeinfluence on the anions, and the aromaticity of the DNTPPskeleton changed correspondingly. To evaluate the aromaticityof a neutral compound and its energetic salts, we calculated themulticenter bond orders for each heterocyclic atmosphere thatforms the DTNPP framework in the molecular structure basedon the obtained single-crystal parameters using Multiwfn3.5.44

As shown in Table 2, the multicenter bond orders of thepyrazolo[4,3-c]pyrazole ring and the two tetrazole rings inDTNPP (0.514/0.606/0.604) are smaller than those in theanions (0.518−0.562/0.624−0.630/0.624−0.630), which in-dicates that the newly synthesized energetic salts show betteraromaticity than neutral DTNPP. Furthermore, the Mayer

Table 2. Coplanar Properties and Sensitivities of Compounds 2, 3, 6, 7·2H2O, and 8

compound Dca[g cm−3] θ1

b [deg] θ2c[deg] B1/B2/B3

d BNe Pc

f [%] ISg [J] FSh [N]

2 (DNTPP) 1.859 8.012 50.245 0.514/0.606/0.604 0.779 72.09 15 1923 2.061 23.348 32.073 0.518/0.625/0.630 0.799 91.14 25 2526 1.762 10.014 37.895 0.562/0.630/0.630 0.806 73.94 12 1447·2H2O 1.677 27.034 31.258 0.533/0.624/0.624 0.792 72.84 >60 >3608 1.683 24.588 33.613 0.531/0.626/0.626 0.797 72.08 35 >360

aDensity of the single crystal at 173 K. bThe dihedral angle of the nitro groups and fused ring. cThe dihedral angle of the tetrazole rings and fusedring. dMulticenter bond orders of the pyrazolo[4,3-c]pyrazole ring and two tetrazole rings, respectively. eMayer bond order of the bond thatconnects the nitro groups and fused ring. fPacking coefficient of the single crystal. gImpact sensitivity. hFriction sensitivity.

Figure 6. Distance between the nitro groups and their nearest atoms in DNTPP (compound 2) (a), compound 6 (b), compound 7·2H2O (c), andcompound 8 (d).

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bond order of C−NO2 of compounds was also calculated usingthe same software because C−NO2 is always considered as thetrigger bond (i.e., the first bond to break in the molecule) thatcan cause explosions.45−48 As shown in Table 2, the Mayerbond order of C−NO2 in DTNPP (0.779) is smaller than thatof anions (0.792−0.806), indicating that the bond strength ofC−NO2 in DTNPP is poor. Because of the higher aromaticityand stronger bond strength of C−NO2 in molecular structures,most energetic salts show lower impact and friction sensitivitiesthan DNTPP, in addition to compound 6. Thus, we speculatethat the relatively high sensitivities of compound 6 areprimarily due to the more restricted space environment ofsensitive groups in its framework. The results in Table 2suggest a remarkably close stacking of compound 6 than otherorganic energetic salts in the solid state. Moreover, it isconsistent with the distance between the nitro group and itsnearest atom in crystals provided in Figure 6. That is to say,the anions in compound 6 are more spatially restricted thanother organic salts and might play an important role in therelatively high sensibilities of compound 6. The highestpacking coefficient of compound 3 is attributed to the metalcations and three-dimensional metal−organic framework(MOF) structure. Overall, the configuration and stackedstructure of energetic anions have important effects on thesensitivities of energetic salts. Thus, synthesizing ionic saltsfrom the neutral energetic compound sDNTPP is an effectivestrategy for constructing insensitive energetic materials.

■ CONCLUSIONS

To summarize, a thermally stable and insensitive energeticcompound, DNTPP, was synthesized by incorporating twotetrazole groups into the DNPP framework, followed by thepreparation of six energetic salts (compounds 3−8). All newenergetic compounds were characterized using various spec-troscopy techniques. The molecular structures of compounds2, 3, 6, 7·2H2O, and 8 were further confirmed by single-crystalXRD analysis. The physicochemical and energetic propertieswere measured and calculated, and the results indicate thatDNTPP and its nitrogen-rich energetic salts are thermallystable and insensitive toward mechanical stimuli. Among them,energetic salt 3 possesses the highest thermal stability (Td: 329°C) and low sensitivities (IS: 25 J, FS: 252 N). Note that, toour knowledge, compound 7 possesses optimal mechanicalsensitivities than any other energetic materials derived fromDNPP (IS: >60 J, FS: >360 N). Among them, compounds 2,3, and 6 possess good comprehensive properties, includingremarkable thermal decomposition temperature, excellentinsensitivity, and favorable detonation performance. Thesefeatures suggest that DNTPP and its energetic salts havepotential to be used as thermally stable and insensitiveenergetic materials.

■ ASSOCIATED CONTENT

*S Supporting InformationThe Supporting Information is available free of charge athttps://pubs.acs.org/doi/10.1021/acsami.9b17384.

Experimental procedures and characterization, X-raydiffraction details, calculation details, NMR spectra, anddetailed properties of DNPP and its typical energeticderivatives (PDF)

Crystallographic data: compound 2 (CIF), compound 3(CIF), compound 6 (CIF), compound 7·2H2O (CIF),and compound 8 (CIF)

■ AUTHOR INFORMATIONCorresponding Authors*E-mail: zhangwq_cn@caep.cn (W.Z.).*E-mail: qinghuazhang@caep.cn (Q.Z.).ORCIDQinghua Zhang: 0000-0002-4162-7155Author ContributionsThe manuscript was written through contributions of allauthors. All authors have given approval to the final version ofthe manuscript.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThis work was supported by the National Natural ScienceFoundation of China (Nos. 21875228, 21975231, and21602211).

■ REFERENCES(1) Klapotke, T. M.; Krumm, B.; Ilg, R.; Troegel, D.; Tacke, R. TheSila-Explosives Si(CH2N3)4 and Si(CH2ONO2)4: Silicon Analoguesof the Common Explosives Pentaerythrityl Tetraazide, C(CH2N3)4,and Pentaerythritol Tetranitrate, C(CH2ONO2)4. J. Am. Chem. Soc.2007, 129, 6908−6915.(2) Belanger-Chabot, G.; Rahm, M.; Haiges, R.; Christe, K. O.Ammonia-(Dinitramido)boranes: High-Energy-Density Materials.Angew. Chem., Int. Ed. 2015, 54, 11730−11734.(3) Vo, T. T.; Parrish, D. A.; Shreeve, J. M. TetranitroacetimidicAcid: a High Oxygen Oxidizer and Potential Replacement forAmmonium Perchlorate. J. Am. Chem. Soc. 2014, 136, 11934−11937.(4) Zhang, W.; Zhang, J.; Deng, M.; Qi, X.; Nie, F.; Zhang, Q. APromising High-Energy-Density Material. Nat. Commun. 2017, 8,No. 181.(5) Chen, D.; Yang, H.; Yi, Z.; Xiong, H.; Zhang, L.; Zhu, S.; Cheng,G. C8N26H4: An Environmentally Friendly Primary Explosive withHigh Heat of Formation. Angew. Chem., Int. Ed. 2018, 57, 2081−2084.(6) Archibald, T. G.; Gilardi, R.; Baum, K.; George, C. Synthesis andX-ray Crystal Structure of 1,3,3-Trinitroazetidine. J. Org. Chem. 1990,55, 2920−2924.(7) Zhang, M. X.; Eaton, P. E.; Gilardi, R. Hepta- andOctanitrocubanes. Angew. Chem., Int. Ed. 2000, 39, 401−404.(8) Fischer, N.; Fischer, D.; Klapotke, T. M.; Piercey, D. G.;Stierstorfer, J. Pushing the Limits of Energetic Materials − theSynthesis and Characterization of Dihydroxylammonium 5,5′-Bistetrazole-1,1′-Diolate. J. Mater. Chem. 2012, 22, 20418−20422.(9) Klapotke, T. M.; Witkowski, T. G. Covalent and IonicInsensitive High-Explosives. Propellants, Explos., Pyrotech. 2016, 41,470−483.(10) Tian, Y.; Han, Y.; Yang, G. Some Understanding and Thinkingof Insensitive High Explosive. Chin. J. Energ. Mater. 2016, 24, 1132−1135.(11) Chavez, D. E.; Parrish, D. A.; Mitchell, L.; Imler, G. H. Azidoand Tetrazolo 1,2,4,5-Tetrazine N-Oxides. Angew. Chem., Int. Ed.2017, 56, 3575−3578.(12) Dharavath, S.; Zhang, J.; Imler, G. H.; Parrish, D. A.; Shreeve, J.M. 5-(Dinitromethyl)-3-(Trinitromethyl)-1,2,4-Triazole and its De-rivatives: a New Application of Oxidative Nitration towards Gem-Trinitro-based Energetic Materials. J. Mater. Chem. A 2017, 5, 4785−4790.

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DOI: 10.1021/acsami.9b17384ACS Appl. Mater. Interfaces 2019, 11, 45914−45921

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(13) Tang, Y.; He, C.; Imler, G. H.; Parrish, D. A.; Shreeve, J. M.Aminonitro Groups Surrounding a Fused Pyrazolotriazine Ring: aSuperior Thermally Stable and Insensitive Energetic Material. ACSAppl. Energy Mater. 2019, 2, 2263−2267.(14) Schulze, M. C.; Scott, B. L.; Chavez, D. E. A High DensityPyrazolo-triazine Explosive (PTX). J. Mater. Chem. A 2015, 3,17963−17965.(15) Piercey, D. G.; Chavez, D. E.; Scott, B. L.; Imler, G. H.; Parrish,D. A. An Energetic Triazolo-1,2,4-Triazine and its N-Oxide. Angew.Chem., Int. Ed. 2016, 55, 15315−15318.(16) Li, W.; Wang, K.; Qi, X.; Jin, Y.; Zhang, Q. Construction of aThermally Stable and Highly Energetic Metal−Organic Framework asLead-free Primary Explosives. Cryst. Growth Des. 2018, 18, 1896−1902.(17) Hu, L.; Yin, P.; Zhao, G.; He, C.; Imler, G. H.; Parrish, D. A.;Gao, H.; Shreeve, J. M. Conjugated Energetic Salts based on FusedRings: Insensitive and Highly Dense Materials. J. Am. Chem. Soc.2018, 140, 15001−15007.(18) Wang, Q.; Shao, Y.; Lu, M. Amino-Tetrazole FunctionalizedFused Triazolo-Triazine and Tetrazolo-Triazine Energetic Materials.Chem. Commun. 2019, 55, 6062−6065.(19) Tang, Y.; Kumar, D.; Shreeve, J. M. Balancing ExcellentPerformance and High Thermal Stability in a Dinitropyrazole Fused1,2,3,4-Tetrazine. J. Am. Chem. Soc. 2017, 139, 13684−13687.(20) Shevelev, S. A.; Dalinger, L. L.; Shkineva, T. K.; Ugrak, B. L.;Gulevskaya, E. L.; Kanishchev, M. L. Nitropyrazoles 1. Synthesis,Transformations, and Physicochemical Properties of Nitro Derivativesof IH,4H-Pyrazolo[4,3-c]pyrazole. Russ. Chem. Bull. 1993, 42, 1063−1068.(21) Zhang, J.; Parrish, D. A.; Shreeve, J. M. Thermally Stable 3,6-Dinitropyrazolo[4,3-c]pyrazole-based Energetic Materials. Chem. -Asian J. 2014, 9, 2953−2960.(22) Yin, P.; Zhang, J.; Mitchell, L. A.; Parrish, D. A.; Shreeve, J. M.3,6-Dinitropyrazolo[4,3-c]pyrazole-based Multipurpose EnergeticMaterials through Versatile N-Functionalization Strategies. Angew.Chem., Int. Ed. 2016, 55, 12895−12897.(23) Zhang, J.; Yin, P.; Mitchell, L. A.; Parrish, D. A.; Shreeve, J. M.N-functionalized Nitroxy/Azido Fused-ring Azoles as High-perform-ance Energetic Materials. J. Mater. Chem. A 2016, 4, 7430−7436.(24) Li, Y.; Shu, Y.; Wang, B.; Zhang, S.; Zhai, L. Synthesis,Structure and Properties of Neutral Energetic Materials based on N-Functionalization of 3,6-Dinitropyrazolo[4,3-c]pyrazole. RSC Adv.2016, 6, 84760−84768.(25) Gutowski, K. E.; Rogers, R. D.; Dixon, D. A. AccurateThermochemical Properties for Energetic Materials Applications. I.Heats of Formation of Nitrogen-containing Heterocycles andEnergetic Precursor Molecules from Electronic Structure Theory. J.Phys. Chem. A 2006, 110, 11890−11897.(26) Joo, Y. H.; Shreeve, J. M. Energetic Mono-, Di-, andTrisubstituted Nitroiminotetrazoles. Angew. Chem., Int. Ed. 2009,48, 564−567.(27) Fischer, D.; Klapotke, T. M.; Stierstorfer, J. 1,5-Di(nitramino)-tetrazole: High Sensitivity and Superior Explosive Performance.Angew. Chem., Int. Ed. 2015, 54, 10299−10302.(28) Joo, Y. H.; Twamley, B.; Garg, S.; Shreeve, J. M. EnergeticNitrogen-Rrich Derivatives of 1,5-Diaminotetrazole. Angew. Chem.,Int. Ed. 2008, 47, 6236−6239.(29) Joo, Y. H.; Shreeve, J. M. High-Density Energetic Mono- orBis(oxy)-5-Nitroiminotetrazoles. Angew. Chem., Int. Ed. 2010, 49,7320−7323.(30) Joo, Y. H.; Shreeve, J. M. Nitroimino-Tetrazolates and Oxy-Nitroimino-Tetrazolates. J. Am. Chem. Soc. 2010, 132, 15081−15090.(31) Joo, Y. H.; Shreeve, J. M. Functionalized Tetrazoles fromCyanogen Azide with Secondary Amines. Eur. J. Org. Chem. 2009,2009, 3573−3578.(32) Bian, C.; Zhang, M.; Li, C.; Zhou, Z. 3-Nitro-1-(2H-Tetrazol-5-yl)-1H-1,2,4-Triazol-5-Amine (HANTT) and its Energetic Salts:Highly Thermally Stable Energetic Materials with Low Sensitivity. J.Mater. Chem. A 2015, 3, 163−169.

(33) Wang, B.; Qi, X.; Zhang, W.; Wang, K.; Li, W.; Zhang, Q.Synthesis of 1-(2H-Tetrazol-5-yl)-5-Nitraminotetrazole and itsDerivatives from 5-Aminotetrazole and Cyanogen Azide: a PromisingStrategy Towards the Development of C−N Linked BistetrazolateEnergetic Materials. J. Mater. Chem. A 2017, 5, 20867−20873.(34) Li, W.; Wang, Y.; Qi, X.; Song, S.; Wang, K.; Jin, Y.; Liu, T.;Zhang, Q. Design and Synthesis of Polycyclic DFP−based Low−sensitivity Energetic Materials with Excellent Thermal Stability. Chin.J. Energ. Mater. 2018, 26, 0901−0909.(35) Yin, P.; He, C.; Shreeve, J. M. Fused Heterocycle-basedEnergetic Salts: Alliance of Pyrazole and 1,2,3-Triazole. J. Mater.Chem. A 2016, 4, 1514−1519.(36) Anniyappan, M.; Talawar, M. B.; Gore, G. M.; Venugopalan, S.;Gandhe, B. R. Synthesis, Characterization and Thermolysis of 1,1-Diamino-2,2-Dinitroethylene (FOX-7) and its Salts. J. Hazard. Mater.2006, 137, 812−819.(37) Shipp, K. G. Reactions of α-Substituted Polynitrotoluenes. I.Synthesis of 2,2’,4,4′,6,6′-Hexanitrostilbene. J. Org. Chem. 1964, 29,2620−2623.(38) Wang, R.; Guo, Y.; Zeng, Z.; Twamley, B.; Shreeve, J. M.Furazan-Functionalized Tetrazolate-based Salts: a New Family ofInsensitive Energetic Materials. Chem. - Eur. J. 2009, 15, 2625−2634.(39) Gao, H.; Shreeve, J. M. Azole-based Energetic Salts. Chem. Rev.2011, 111, 7377−7436.(40) Wang, R.; Xu, H.; Guo, Y.; Sa, R.; Shreeve, J. M. Bis[3-(5-Nitroimino-1,2,4-Triazolate)]-based Energetic Salts: Synthesis andPromising Properties of a New Family of High-Density InsensitiveMaterials. J. Am. Chem. Soc. 2010, 132, 11904−11905.(41) Snyder, C. J.; Wells, L. A.; Chavez, D. E.; Imler, G. H.; Parrish,D. A. Polycyclic N-oxides: High Performing, Low sensitivity EnergeticMaterials. Chem. Commun. 2019, 55, 2461−2464.(42) Ma, Y.; Zhang, A.; Xue, X.; Jiang, D.; Zhu, Y.; Zhang, C. CrystalPacking of Impact-Sensitive High-Energy Explosives. Cryst. GrowthDes. 2014, 14, 6101−6114.(43) Ma, Y.; Zhang, A.; Zhang, C.; Jiang, D.; Zhu, Y.; Zhang, C.Crystal Packing of Low-Sensitivity and High-Energy Explosives. Cryst.Growth Des. 2014, 14, 4703−4713.(44) Lu, T.; Chen, F. Multiwfn: a Multifunctional WavefunctionAnalyzer. J. Comput. Chem. 2012, 33, 580−592.(45) Cao, C.; Gao, S. Two Dominant Factors Influencing the ImpactSensitivities of Nitrobenzenes and Saturated Nitro Compounds. J.Phys. Chem. B 2007, 111, 12399−12402.(46) Harper, L. K.; Shoaf, A. L.; Bayse, C. A. Predicting TriggerBonds in Explosive Materials through Wiberg Bond Index Analysis.ChemPhysChem 2015, 16, 3886−3892.(47) Shoaf, A. L.; Bayse, C. A. Trigger Bond Analysis ofNitroaromatic Energetic Materials using Wiberg Bond Indices. J.Comput. Chem. 2018, 39, 1236−1248.(48) Zhang, C.; Shu, Y.; Huang, Y.; Zhao, X.; Dong, H. Investigationof Correlation between Impact Sensitivities and Nitro Group Chargesin Nitro Compounds. J. Phys. Chem. B 2005, 109, 8978−8982.

ACS Applied Materials & Interfaces Research Article

DOI: 10.1021/acsami.9b17384ACS Appl. Mater. Interfaces 2019, 11, 45914−45921

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