Nitrogen-rich energetic salts of 1: H,1′ H -5,5′-bistetrazole-1,1′-diolate: Synthesis, characterization, and thermal behaviors

Article abstract of DOI:10.1039/c6ra10108a

A series of nitrogen-rich heterocyclic 1H,1′H-5,5′-bistetrazole-1,1′-diolate salts, namely, 1,2,4-triazolium (2), 3-amino-1,2,4-triazolium (3), 4-amino-1,2,4-triazolium (4), 3,5-diamino-1,2,4-triazolium (5), 2-methylimidazolium (6), imidazolium (7), pyrazolium (8), 3-amino-5-hydroxypyrazolium (9), dicyandiamidine (10), and 2,4-diamino-6-methyl-1,3,5-triazin (11), was synthesized with cations. These energetic salts were fully characterized through FT-IR, ¹H NMR, ¹³C NMR, and elemental analysis. The structures of 2, 3·7H₂O, 6·2H₂O, 8, and 10·4H₂O were further confirmed through single crystal X-ray diffraction. Their thermal stabilities were investigated through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results indicated that all of the salts possess excellent thermal stabilities with decomposition temperatures ranging from 225.7 °C to 314.0 °C. On the basis of the Kamlet-Jacobs formula, we carefully calculated their detonation velocities and detonation pressures. All of the salts, except 11, exhibit promising detonation performances with a detonation pressure of 20.23-28.69 GPa and a detonation velocity of 7050-8218 m s^-1. These values are much higher than those of TNT. The impact sensitivities of the compounds were determined via a Fall hammer test. All of the compounds show excellent impact sensitivities of >50 J, and this finding is higher than that of TATB (50 J). Therefore, these ionic salts with excellent energetic properties could be applied as new energetic materials.

Full text of DOI:10.1039/c6ra10108a

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Nitrogenꢀrich Energetic Salts of 1H,1′Hꢀ5,5′ꢀBistetrazoleꢀ1,1′ꢀdiolate: Synthesis,
Characterization, and Thermal Behaviors
Yu Shanga, Bo Jina*, Rufang Penga*, Zhicheng Guob, Qiangqiang Liua, Jun Zhaoa, Qingchun Zhanga
aState Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University of Science and Technology,
Mianyang 621010, China
bSchool of Nation Defence Science and Technology，Southwest University of Science and Technology, Mianyang 621010, China
Abstract: A series of nitrogenꢀrich heterocyclic 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate salts, namely, 1,2,4ꢀtriazolium (2), 3ꢀ
aminoꢀ1,2,4ꢀtriazolium (3), 4ꢀaminoꢀ1,2,4ꢀtriazolium (4), 3,5ꢀdiaminoꢀ1,2,4ꢀtriazolium (5), 2ꢀmethylimidazolium (6),
imidazolium (7), pyrazolium (8), 3ꢀaminoꢀ5ꢀhydroxypyrazolium (9), dicyandiamidine (10), and 2,4ꢀdiaminoꢀ6ꢀmethylꢀ
1,3,5ꢀtriazin (11), was synthesized with cations. These energetic salts were fully characterized through FTꢀIR, 1H NMR, 13C
NMR, and elemental analysis. The structures of 2, 3·7H2O, 6·2H2O, 8, and 10·4H2O were further confirmed through single
crystal Xꢀray diffraction. Their thermal stabilities were investigated through differential scanning calorimetry (DSC) and
thermogravimetric analysis (TGA). Results indicated that all of the salts possess excellent thermal stabilities with
decomposition temperatures ranging from 225.7 °C to 314.0 °C. On the basis of Kamlet–Jacobs formula, we carefully
calculated their detonation velocity and detonation pressure. All of the salts, except 11, exhibit promising detonation
performances with a detonation pressure of 20.23–28.69 GPa and a detonation velocity of 7050–8218 m s−1. These values
are much higher than those of TNT. The impact sensitivities of the compounds were determined via Fall hammer test. All of
the compounds show excellent impact sensitivities of >50 J, and this finding is higher than that of TATB (50 J). Therefore,
these ionic salts with excellent energetic properties could be applied as new energetic materials.
Introduction
Energetic materials, including explosives, propellants, and pyrotechnics, are widely used in various military and
civilian fields.1ꢀ3 To satisfy the requirements of improved energetic materials, researchers synthesized highꢀenergyꢀdensity
materials with decreased sensitivity to thermal shock and friction and with enhanced detonation performances, including
detonation velocity and detonation pressure.4 Nitrogenꢀrich energetic salts with high energy and low sensitivity play an
important role in energetic materials because of their high heat of formation (HOF), density, thermal stability, good oxygen
balance, and environmental greenness.5ꢀ14
Tetrazole moiety is a promising energetic building block in this research area because it contains a large number of
energetic N–N and C–N bonds, exhibits extensive hydrogen bonding, and decomposes to produce a high percentage of
dinitrogen.15ꢀ18 The introduction of Nꢀoxides to tetrazoles and bitetrazoles results in greater energetic performances, such as
high densities and low sensitivities, than the introduction of tetrazoles without Nꢀoxides does.12, 19ꢀ21 Thomas M. Klapötke22
reported that 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate (BTO) is a good energetic building block that presents various properties.
BTO exhibits excellent thermal stabilities but shows comparative insensitivity, although it contains a very high amount of
nitrogen that reaches 66.7%. Therefore, BTO is a good candidate of energetic anions. Recently, a family of energetic salts
based on BTO salts were synthesized as potential energetic materials 22ꢀ26. Triazolium
, limidazolium and dicyandiamidine
cations are important nitrogenꢀrich cations used to construct highꢀperformance energetic materials27ꢀ33. The combination of
the nitrogenꢀrich cations and BTO anion would be expected to possess both high nitrogen concomitant high energetic
properties and desired remarkable sensitivities.
Herein, we aimed to design and synthesize bitetrazoleꢀderived compounds based on BTO with a high percentage of
nitrogen content and thus develop powerful and ecoꢀfriendly energetic materials with enhanced thermal stability. In this
study, a series of energetic salts was designed and synthesized (Scheme 1) on the basis of BTO. These salts were fully
characterized through multinuclear NMR spectroscopy, IR spectroscopy, elemental analysis (EA), differential scanning

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calorimetry (DSC), and thermogravimetric analysis (TGA). As expected, several ionic salts exhibited potentially useful
thermal stabilities, detonation properties, and low sensitivities; therefore, these salts can be applied as energetic materials.
Results and Discussion
Syntheses
1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate (BTO) was synthesized in accordance with a previously described procedure.22
BTO was synthesized starting from glyoxal, which was treated with hydroxylamine to form glyoxime. Glyoxime was then
chlorinated with Cl2 gas in ethanol; chloro/azido exchange occurred and yielded diazidoglyoxime, which was cyclized
under acidic conditions (HCl gas in diethyl ether) to produce 1. All of the compounds except dicyandiamidine salt 10 were
synthesized after 1 was treated with stoichiometric amounts of the respective free base. Dicyandiamidine salt 10 was
isolated from a reaction mixture containing the barium salt of 1 and dicyandiamidine sulfate after the poorly soluble barium
sulfate was removed through filtration. The formation of nitrogenꢀrich salts (2–11) is straightforward, as shown in Scheme
1.
Scheme 1. Synthesis of energetic salts based on 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate (BTO).
Spectroscopy
1
The structures of these prepared energetic compounds are supported by their corresponding FTꢀIR, H NMR, 13C
NMR, and elemental analysis. The data are listed in the Experimental Section. In the IR spectra, the investigated
compounds reveal a number of bands between 1540 and 700 cm−1; the bands show a characteristic pattern of ν(NN),
ν(NCN), γ(CN), and aromatic ring vibrations of the tetrazole in the vibrational spectra22. The characteristic absorption of N–
H bonds was observed in all of the compounds at 3100–3500 cm−1; the bands at 3300–3500 cm−1 are attributed to the amino
group of the energetic salts. In the 13C NMR spectra, all of the signals, except a signal associated with the anion at δ =
134.84–135.69 ppm, are assigned to the energetic cations.
Xꢀray crystallography
Suitable crystals (2, 3·7H2O, 6·2H2O, 8, and 10·4H2O) were obtained by slowly evaporating water at room
temperature and then subjected to single crystal Xꢀray analysis. The selected crystallographic data are summarized in Table
1. The structures of 2, 6·2H2O, and 8 are displayed in Figs. 1–3. The structures of 3·7H2O and 10·4H2O are presented in

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Figs. S1 and S2.† Additional information regarding crystalꢀstructure determinations are provided in ESI.† In this paper,
only three examples of the determined crystal structures are discussed. The solidꢀstate structures of the remaining
compounds are described in Supporting Information.
Table 1. Crystal data and structure refinement parameters of 2, 3·7H2O, 6·2H2O, 8 and 10·4H2O.
Compound
Empirical formula
Formula weight
CCDC number
Crystal size [mm3]
Crystal system
Space group
a [Å]
2
3·7H2O
C30H63N80O17
1816.60
6·2H2O
C10H18N12O4
370.36
8
10·4H2O
C6H20N16O6
412.38
C6H8N14O2
308.26
1435484
C5H6N10O2
238.20
1435486
1444741
1435485
1441695
0.65×0.25×0.15 0.80×0.70×0.20 0.20×0.19×0.12 0.20×0.18×0.12 0.21×0.20×0.19
Monoclinic
C2/c
15.2410(12)
10.5185(8)
7.7546(7)
90
100.767(8)
90
Monoclinic
P21/c
19.0634(3)
11.83085(18)
32.1874(7)
90
95.3131(17)
90
7228.2(2)
4
Triclinic
Pꢀ1
Monoclinic
P21/c
10.042(2)
13.882(2)
6.7012(12)
90
98.155(4)
90
924.8(3)
4
1.711
113(2)
488
0.0483
2122
Triclinic
P1
5.3860(5)
7.2676(6)
11.1149(11)
106.362(7)
92.344(13)
104.613(9)
401.00(6)
1
1.534
113
194.0
0.0147
1800
3.5356(14)
13.300(5)
18.164(7)
72.222(4)
87.207(4)
86.316(4)
811.3(6)
2
1.688
100(2)
432
0.0327
5081
b [Å]
c [Å]
α[°]
β[°]
γ[°]
V [Å 3]
1221.26(18)
8
Z
ρcalcd[g·cmꢀ3]
T[K]
1.688
293
640.0
0.0329
1093
1.670
293K
3756.0
0.0291
12900
F(000)
Rint.
Data
Restraints
parameters
R1 (I > 2σ (I))
ωR2 (I > 2σ (I))
R1(all data)
ωR2(all data)
0
108
0.0474
0.1247
0.0522
0.1331
1
1189
0.0637
0.1790
0.0886
0.2054
5
133
0.0313
0.0893
0.0329
0.0904
3
163
0.0422
0.1191
0.0442
0.1213
9
506
0.0927
0.2447
0.0955
0.2473
Compound 2 crystallizes in the monoclinic space group C2/c with a calculated density of 1.688 g cm−3. Fig. 2 shows
that the molecular unit of crystalline 2 consists of one anion and two 1,2,4ꢀtriazolium cations. The selected data and
parameters from their Xꢀray structures are listed in Table 1. All of the atoms of BTO anion are almost coplanar, and the
largest torsion angle is 179.6(2)°. This angle is located at N006ꢀN002ꢀC009ꢀC0091. The N–N bond lengths in the tetrazolate
of BTO anion vary from 1.304(2) Å to 1.340(2) Å, which are between N–N single bonds (1.454 Å) and N=N double bonds
(1.245 Å).34 Furthermore, the C–C bond connecting the two tetrazole moieties and the N–O bonds are found between a C–C
single bond and a C=C double bond (d(C0090ꢀC0091) = 1.437(3) Å) and between a N–O single bond and a N=O double
bond (d(O001ꢀN002) = 1.3209(17) Å), respectively. This finding indicates the conjugation of the negative charge
throughout the aromatic rings, as seen in other tetrazolate salts.35, 36 One bis(tetrazoleꢀ1ꢀoxide) anion, whose packing is
affected by several strong hydrogen bonds, is coordinated by four additional 1,2,4ꢀtriazolium cations. Strong hydrogen
bonds between N003ꢀH003···O001 (1.830 Å) and N004ꢀH004···O001 (1.616 Å) are also illustrated in Fig. 1(a). The
packing structure of 2 was built and linked to a 2D layer by various hydrogen bonds. After the layer was assembled, further
interlinking of the 2D layers to 3D supramolecules was stimulated by πꢀstacked or other weak interactions, as shown along
the b axis in Fig. 1(b).

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Figure 1. Molecular structure (a) and packing diagram in the unit cell (b) of 2.
Compound 6·2H2O crystallizes in the triclinic space group Pꢀ1 with two H2O per molecule and exhibits a density of
1.534 g cm−3 at 113 K. Its crystallographic data are summarized in Table 1. As shown in Fig. 2(a), all of the atoms of BTO
anion are almost coplanar, with the largest torsion angle of 179.73(8)° in O(1)ꢀN(1)ꢀN(2)ꢀN(3). The bond lengths, bond
angles, and torsion angles of anions are similar to those of compound 2. For example, the bond lengths of C–C, which
connects two tetrazole moieties, range from 1.437(3) Å to 1.4393(19) Å; this value indicates a delocalization effect. This
length is significantly shorter than that of a typical C–C single bond of 1.54 Å. Hydrogen bond interactions between cations
and anions are provided in ESI.† In Fig. 2(a), one anion is coordinated by two 2ꢀmethylimidazolium cations and two
hydrate water molecules to form four strong intermolecular hydrogen bonds [N(6)ꢀH(6) ··N(4)#2 (1.978 Å), O(2)ꢀH(2B)
··O(1)#5 (1.855 Å)]. The 2D layer structure is formed by intermolecular hydrogen bonds, and the 2D layer stacks are
parallel to the crystallographic c axis in Fig. 2(b).
Figure 2. Molecular structure (a) and packing diagram in the unit cell (b) of 6·2H2O.
In Table 1, 8 crystallizes in the monoclinic space group P21/c with four molecules per unit cell and exhibits a crystal
density of 1.711 g cm−3 at 113 K. Fig. 3(a) shows the presence of two asymmetric units. Each unit contains one BTO anion
and one limidazolium cation. For the anion, a small torsion angle of the two tetrazoleꢀoxide rings at N(1)ꢀC(1)ꢀC(2)ꢀN(8) of
−8.6(2)° is detected. The bond lengths are similar to those of compound 2 and 6·2H2O. The N–N bond lengths in the
tetrazolium ring range from 1.3027(15) Å to 1.35 594(15) Å, which are between the lengths of N–N single bonds (1.454 Å)
and N=N double bonds (1.24 Å). The C–N bond lengths in the tetrazolium ring vary from 1.3311(15) Å to 1.3448(14) Å,
which are between the lengths of C–N single bonds (1.470 Å) and C=N double bonds (1.220 Å). This result also
demonstrates the conjugation of the negative charge throughout the aromatic rings. Among the bonds in the crystals of 8,
the intermolecular hydrogen bonds of tetrazole [O(2)ꢀH(2) ··O(1)#1 (1.637 Å), N(9)ꢀH(9) ··O(1) (1.945 Å)] are the
strongest. Hydrogen bond interactions between cations and anions are provided in ESI.† In Fig. 3(b), the supercell
consisting of layers of 8 are arranged in a waveꢀlike layer structure along the a axis.

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Figure 3. Molecular structure (a) and packing diagram in the unit cell (b) of 8.
Thermal behavior
Thermal stability is a key factor of energetic materials because unacceptable thermal stabilities strictly limit their
applications. Compounds 2–11 were examined through DSC and TGA at a heating rate of 10 °C/min in flowing high purity
nitrogen (ESI,† Figs. S1–S10). In Table 2, the decomposition peak temperatures (Td) of the compounds are higher than that
of RDX (230.0 °C) except compound 8 (Td = 228 °C); Td of some compounds (5,11) is even higher than that of TNT (295.0
°C). Td of all of the products range from 228 °C (8) to 413 °C (11); this value indicates that these compounds are promising
energetic materials that exhibit good thermal stability. In all of the salts, the exothermic temperature range agrees with that
of weight loss. In these energetic materials, the least mass loss of 53.7% can be observed in the exothermic temperature
range of 3; this phenomenon can be attributed to its low oxygen content. In particular, salt 2 decomposes with the highest
mass loss of 90.8% at the exothermic temperature range.
Energetic Properties
The heat of formation (HOF) is an important parameter used to evaluate the performance of energetic compounds; this
parameter was calculated by using Gaussian 09 program 37. The calculated HOFs are summarized in Table 2. All of the
compounds exhibit positive HOFs ranging from 120.1 kJ/mol (10·4H2O) to 1385.3 kJ/mol (9), which are higher than those
of HMX (104.8 kJ/mol), TNT (95.3 kJ/mol), and RDX (83.8 kJ/mol).
On the basis of the calculated density and calculated HOFs, we determined the detonation properties of 2–11 by using
the empirical Kamlet–Jacobs (K–J) equations. In Table 2, the detonation pressures of the salts ranged from 19.76 GPa (11)
to 28.69 Gpa (4), which are comparable to those of TNT (19.5 GPa) and RDX (34.9 GPa). Their detonation velocities range
from 6820 m/s (11) to 8218 m/s (4), which are also comparable to those of TNT (6881 m/s) and RDX (8748 m/s). The
detonation velocities of the salts except 11 were higher than that of TNT. These properties suggest that these energetic salts
may be used as environmentally friendly and nitrogenꢀrich energetic materials.
Sensitivity should be extensively investigated because this parameter is closely linked with the safety of handling and
applying explosives. In this work, the impact sensitivities were determined using a BAM Fallhammer apparatus with a 10
kg drop weight. These sensitivities were >50 J (Table 2). This result indicates that all of the energetic salts are more
sensitive than RDX (7.4 J), HMX (7 J), TNT (15 J), and TATB (50 J).
Table 2. Properties of compounds 2ꢀ11 compared with TNT/RDX
[a]
[d]
[e]
[f]
[g]
Tdec
ρ[b]
N+O[c] ꢁfHcation
ꢁfHanion
ꢁHL
ꢁf Hsalt
[ kJ/mol] [GPa] [m/s]
P[h]
vD[i]
IS[j]
[J]
[°C]
[g/cm3]
[%]
[ kJ/mol]
[ kJ/mol]
[ kJ/mol]
246.7
1.688
1.670
1.667
1.650
1.534
74.00
838.5
802.0
936.3
764.0
672.4
587.7
1301.70
956.00
1548.67
885.00
906.21
751.13
24.49 7577
21.05 7050
28.69 8218
23.05 7405
20.23 7142
2
＞60
＞50
＞50
＞50
＞60
282.7
243.0
303.0
269.0
75.71
79.38
77.15
62.67
587.7
420.7
587.7
587.7
643.027
472.00
3·7H2O
4
5
1209.49
1173.72
6·2H2O

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262.0
225.7
273.0
254.0
314.0
295.0
230.0
324.0
1.715
1.711
1.702
1.688
1.678
1.648
1.806
1.930
65.33
72.24
70.62
78.05
67.59
18.50
37.84
69.74
723.0
587.7
420.7
587.7
587.7
587.7
－
1316.05
491.02
1223.81
1168.85
1130.96
－
717.64
751.13
1385.29
120.05
752.74
95.3
22.03 7151
7
8
＞50
821. 5
1010.7
350.6
648.0
－
25.45 7693
＞50
28.48 8151
9
＞60
25.41 7720
10·4H2O
＞50
19.76 6820
11
＞60
TNT[k]
RDX[k]
TATB[l]
19.5
34.9
6881
8748
15
7.5
50
83.8
－
－
－
ꢀ139.7
31.15 8114
－
－
－
[a] Decomposition peak temperature. [b] Calculated density. [c] Nitrogen and Oxygen content. [d] Calculated enthalpy of formation of cations,
Reference. 32, 38[e] Calculated molar enthalpy for the formation of the anion, Reference.22 [f] The lattice energy of the ionic salts. [g] Calculated
molar enthalpy for the formation of the salts. [h] Detonation pressure. [i] Detonation velocity. [j] Impact sensitivity. [k] Reference.38 [l]
Reference.9
Conclusions
A series of BTOꢀbased nitrogenꢀrich energetic salts were synthesized and fully characterized through multinuclear
NMR spectroscopy, IR spectroscopy, elemental analysis (EA), DSC, and TGA. The structures of 2, 3·7H2O, 6·2H2O, 8,
and 10·4H2O were further confirmed through singleꢀcrystal Xꢀray diffraction characterization. The DSC results revealed
that all of the energetic salts exhibit excellent thermal stabilities with decomposition temperatures ranging from 225.7 (8) °C
to 314 °C (11). All of the salts are insensitive to impact (>50 J); as such, these salts can be safely handled and can be
applied to specific areas. Furthermore, the calculated detonation parameters of the new energetic compounds yield
detonation pressures and velocities ranging from 19.76 GPa (11) to 28.69 GPa (4) and from 6820 m/s (11) to 8218 m/s (4),
respectively. On the basis of reasonable detonation properties, excellent impact sensitivities, and superior stabilities, we can
use these compounds as potential “green” energetic materials in commercial applications.
Experimental Section
Safety Precautions! Although we experienced no difficulties in the synthesis and characterization of these materials,
smallꢀscale syntheses are strongly encouraged. All of the compounds should be handled with extreme care, and eye
protection and gloves must be worn at all times.
General Methods: Chemical reagents and solvents were purchased from Aladdin (Shanghai, China) and used as
1
supplied without further purification. H NMR and 13C NMR spectra were obtained using a JEOL GSX 600 MHz nuclear
magnetic resonance (NMR) spectrometer in a DMSO solution by using tetramethylsilane as an internal standard. Fourier
transform infrared (FTꢀIR) spectra were recorded on a Nicoletꢀ5700 FTIR spectrometer by using pressed KBr pellets to
evaluate the chemical bonding of the samples from 4000 cm−1 to 400 cm−1. Elemental analyses (C, H, and N) were
conducted using a Vario EL CUBE device. DSC was performed by a Q200 DSC instrument (TA Instruments, United
States) at a heating rate of 10 °C/min in flowing highꢀpurity nitrogen. TGA was performed with an SDT Q600 TGA
instrument (TA Instruments, United States) at a heating rate of 10 °C/min in flowing highꢀpurity nitrogen.
Xꢀray Crystallography: The single crystals of 2, 3·7H2O, 6·2H2O, 8, and 10·4H2O were cultured via a slow solvent
evaporation method. Data were collected using a threeꢀcircle Bruker platform diffractometer equipped with a SMART
APEX II CCD detector. All calculations were performed using the Crystal Structure39 crystallographic software package
except for refinement, which was performed using SHELXL201440. Hydrogen atoms were added theoretically and refined
with riding model position parameters and fixed isotropic thermal parameters. The details of the data collection and
refinement are presented in Table 1.
Computational details: Computations were performed in Gaussian 09 Suite.37 The structures were geometrically
optimized and the frequency was analyzed using a B3LYP function with a 6ꢀ31+G** basis set41. Singleꢀpoint energies were

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calculated at the MP2(full)/6ꢀ311++G** level. All of the optimized structures were characterized as true local energy
minima on the potentialꢀenergy surface without imaginary frequencies.
Figure 4. Born–Haber circle of ionic salt
According to the Born–Haber42 (m, n, o, and p respectively stand for the factor of C, H2, N2, and O2) energy cycle
(Figure 4), the standard HOF of a salt can be simplified in Eq. (1):
H0 (Salt,298K) =Δ
f
H0 (Cation,298K) +Δ
f
H0 (Anion,298K)−ΔH
L
(1)
Δ
f
where ꢁHL is the lattice energy of the salts, which can be predicted by the formula proposed by Jenkins et al.42, 43 [Eq.
(2)]
(2)
where nM and nX depend on the nature of the ions Mp+ and Xq−, respectively; these parameters are equal to 3 for
ΔH =UPOT+[ p( nM / 2- 2) +q( nX / 2- 2) ] RT
L
monatomic ions, 5 for linear polyatomic ions, and 6 for nonlinear polyatomic ions. Lattice potential energy (UPOT) is
expressed as follows [Eq. (3)]
POT/ kJ·molꢀ1= m / Mm )1/3 +
γ(ρ δ
(3)
U
where ρm is the density, Mm is the chemical formula mass of the ionic material, and γ and δ are coefficients, whose
values are described in previous studies.42, 43
HOF is an important parameter that represents the energy content of a material. Positive values correspond to enhanced
detonation properties. The enthalpies of BTO− and BTO2− are 420 and 587.7 kJ/mol, respectively. The HOF of the gas
phase of the selected cations were obtained through isodesmic reactions.44, 45 The representative reactions are shown in
Scheme 2. The calculated total energy (E0), zeroꢀpoint energy (ZPE), and other thermal factors are obtained in ESI.† The
HOFs of the cations and the anion are listed in Table 2.
Detonation velocity (D) and detonation pressure (P) were evaluated by the empirical K–J equations, as shown in Eqs.
(4) and (5):43,46,47
1/2
1/2
D=1.01(NM Q )1/2(1+1.3
ρ)
(4)
P =1.558ρ
2NM1/2Q1/2
(5)
where D is the detonation velocity (km/s), P is the detonation pressure (GPa), N is the explosive detonation that
−1
M
generates gas moles per gram (mol/g), is the gaseous product with an average molecular weight (g·mol ), Q is the
explosive detonation chemical energy (kJ/g) per gram, and ρ is the density (g·cm−3). Q should be calculated before D and P
M
are determined. Q is also determined by ꢁHf of the detonation reactant and product. In this study, N, , and Q are
calculated on the basis of the chemical composition of each explosive.47

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Scheme 2. Isodesmic reaction schemes for selected compounds
Synthesis of 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate Dihydrate: 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate dihydrate was
synthesized according to a procedure reported in the literature.22
Bisꢀ1,2,4ꢀtriazolium 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate (2): 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate dihydrate (206 mg, 1
mmol) was dissolved in 5 mL distilled water, and 1,2,4ꢀtriazolium (138.1 mg, 2 mmol), previously dissolved in 3 ml water
was added. The mixture was heated and filtered. After cooling to room temperature, 2 crystallized as colorless blocks to
yield 249.4 mg (0.81 mmol, 81%). DSC (10 °C/min): 227 °C (m.p), 246.7 °C (dec.). IR (KBr) v/cmꢀ1: 3495 (vs), 3412 (vs),
3140 (s), 2923 (s), 1891 (w), 1636 (w), 1570 (w), 1428 (s), 1384 (m), 1227 (s), 1166 (w), 1040 (s), 951 (w), 906 (s), 730
(m), 637 (w), 520 (m). 1H NMR (600 MHz, [D6]DMSO, 25 °C) δ/ppm: 8.89. 13C NMR (150 MHz, [D6]DMSO, 25 °C)
δ/ppm: 145.39, 135.63. elemental analysis (%) calcd for C6H10N14O2 (308.17): C, 23.38; H, 2.62; N, 63.62; found: C, 23.26;
H, 2,51; N, 63.62.
Bisꢀ3ꢀaminoꢀ1,2,4ꢀtriazolium 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate (3): 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate dihydrate
(206 mg, 1 mmol) was dissolved in 3 mL distilled water, and 3ꢀaminoꢀ1,2,4ꢀtriazole (168.2 mg, 2 mmol), previously
dissolved in 4 ml water was added. The mixture was briefly heated to reflux and filtered. After cooling to room temperature,
3 crystallized as colorless needles, yield 256.9 mg (0.76 mmol, 76%). DSC (10 °C/min): 282.7 °C (dec.). IR (KBr) v/cmꢀ1:
3400 (s), 3151 (s), 2698 (w), 1808 (w), 1696 (s), 1630 (w), 1571 (w), 1506 (w), 1419 (m), 1360 (w), 1319 (w), 1234 (m),
1173 (w), 1064 (w), 948 (m), 784 (w), 717 (w), 519 (w). 1H NMR (600 MHz, [D6]DMSO, 25 °C) δ/ppm: 7.91. 13C NMR
(150 MHz, [D6]DMSO, 25 °C) δ/ppm: 154.67, 143.81, 135.61. elemental analysis (%) calcd for C30H64N80O17 (338.20): C,
21.31; H, 2.98; N, 66.25; found: C, 21.06; H, 3.01; N, 66.20.
4ꢀaminoꢀ1,2,4ꢀtriazolium 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate (4): 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate dihydrate (206
mg, 1 mmol) was suspended in a few milliliters of water, and 4ꢀaminoꢀ1,2,4ꢀtriazole (168.2 mg, 2 mmol) was added. After
boiling and stirring the mixture for a few minutes, 4 precipitated as thin, colorless plates upon cooling the solution to room
temperature, yield 174.1 mg (0.64 mmol, 64%). DSC (10 °C/min): 213 °C (m.p.) 243 °C (dec.). IR (KBr) v/cmꢀ1: 3497 (s),
3408 (s), 3178 (w), 3129 (w), 2926 (w), 1637 (w), 1424 (w), 1365 (w), 1271 (vw), 1241 (w), 1072 (w), 1031 (w), 668 (w).
1H NMR (600 MHz, [D6]DMSO, 25 °C) δ/ppm: 9.19, 7.57. 13C NMR (150 MHz, [D6]DMSO, 25 °C) δ/ppm: 144.62,
135.63, 119.08. elemental analysis (%) calcd for C4H8N12O3 (272.1): C, 17.65; H, 2.94; N, 61.77; found: C, 17.91; H, 2.37;
N, 61.44.
Bisꢀ3,5ꢀdiaminoꢀ1,2,4ꢀtriazolium
1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate
(5):
1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate
dihydrate (206 mg, 1 mmol) was dissolved in 3 mL distilled water, and 3,5ꢀdiaminoꢀ1,2,4ꢀtriazole (198.2 mg, 2 mmol),
previously dissolved in 4 ml water was added dropwise resulting in the formation of a white precipitate at room
temperature. The solution was stirred for a few minutes, and then filtered, washed with cold water and dried in vacuo to
afford 331.4 mg of 5 as a white powder in a yield of 90%. DSC (10 °C/min): 303 °C (dec.). IR (KBr) v/cmꢀ1: 3418 (vs),
1
3117 (m), 1700 (m), 1652 (s), 1419 (m), 1230 (w), 1169 (vw), 1050 (w), 1010 (w), 733 (w). H NMR (600 MHz,
[D6]DMSO, 25 °C) δ/ppm: 7.15. 13C NMR (150 MHz, [D6]DMSO, 25 °C) δ/ppm: 155.07, 135.55. elemental analysis (%)
calcd for C6H12N18O2 (368.2): C, 19.57; H, 3.261; N, 68.48; found: C, 19.73; H, 3.17; N, 69.28.

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Bisꢀ2ꢀmethylimidazolium 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate (6): 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate dihydrate (206
mg, 1 mmol) was suspended in a few milliliters of water, and 2ꢀmethylimidazole (164.2 mg, 2 mmol) was added. After
boiling and stirring the mixture for a few minutes, After cooling, the precipitate was collected by filtration, and then 315 mg
of 6 was obtained as white solid in a yield of 85%. DSC (10 °C/min): 240 °C (m.p.) 269 °C (dec.). IR (KBr) v/cmꢀ1: 3430
(s), 3129 (s), 2917 (s), 2713 (s), 1955 (w), 1621 (m), 1420 (s), 1406 (s), 1349 (w), 1330 (w), 1303 (w), 1230 (s), 1168 (m),
1116 (w), 1086 (w), 1051 (w), 999 (w), 890 (w), 769 (m), 665 (w), 501 (m). 1H NMR (600 MHz, [D6]DMSO, 25 °C)
δ/ppm: 7.29, 2.45. 13C NMR (150 MHz, [D6]DMSO, 25 °C) δ/ppm: 144.33, 135.31, 119.89, 12.41. elemental analysis (%)
calcd for C10H18N12O4 (370.29): C, 32.42; H, 4.90; N, 45.38; found: C,32.30; H, 4.92; N, 45.40.
Bisꢀimidazolium 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate (7): 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate dihydrate (206 mg, 1
mmol) was dissolved in 3 mL distilled water, and imidazole (136.2 mg, 2 mmol), previously dissolved in 4 ml water was
added. The mixture was briefly heated to reflux and filtered. After cooling to room temperature, 7 crystallized as colorless
needles, yield 233 mg (0.76 mmol, 76%). DSC (10 °C/min): 258 °C (m.p.) 262 °C (dec.). IR (KBr) v/cmꢀ1: 3410 (s), 3145
(m), 1631 (m), 1574 (w), 1425 (m), 1288 (w), 1169 (w), 1080 (m), 927 (w), 757 (m), 627 (w). 1H NMR (600 MHz,
[D6]DMSO, 25 °C) δ/ppm: 9.09, 7.70. 13C NMR (150 MHz, [D6]DMSO, 25 °C) δ/ppm: 135.62, 119.77. elemental analysis
(%) calcd for C8H10N12O2 (306.20): C, 31.38; H, 3.29; N, 54.88; found: C,31.30; H, 3.32; N, 54.79.
Pyrazolium 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate (8): 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate dihydrate (206 mg, 1 mmol)
was dissolved in 3 mL distilled water, and 1,2ꢀdiazole (138.16 mg, 2 mmol), previously dissolved in 4 ml water was added
dropwise resulting in the formation of a white precipitate at room temperature. The solution was stirred for a few minutes,
and then filtered, washed with cold water and dried in vacuo to afford 207 mg of 8 as a white powder in a yield of 87%.
DSC (10 °C/min): 225.7 °C (dec.). IR (KBr) v/cmꢀ1: 3496 (s), 3410 (s), 3145 (s), 3090 (s), 1624 (m), 1533 (m), 1413 (m),
1395 (m), 1356 (m), 1312 (w), 1218 (s), 1176 (s), 1128 (m), 1097 (s), 1064 (m), 1015 (w), 996 (w), 806 (m), 612 (w), 774
(m), 486 (m). 1H NMR (600 MHz, [D6]DMSO, 25°C) δ/ppm: 14.11, 8.14, 6.62. 13C NMR (150 MHz, ([D6]DMSO, 25°C)
δ/ppm: 135.69, 134.13. elemental analysis (%) calcd for C5H6N10O2 (238.13): C, 25.22; H, 2.54; N, 58.81; found: C, 25.10;
H, 2.56; N, 58.90.
Bisꢀ3ꢀaminoꢀ5ꢀhydroxypyrazole 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate (9): 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate dihydrate
(206 mg, 1 mmol) was dissolved in 3 mL distilled water, and 3ꢀaminoꢀ5ꢀhydroxypyrazole (198.2 mg, 2 mmol), previously
dissolved in 4 ml water was added. After boiling and stirring the mixture for a few minutes, water was removed by filtrate,
and then 316.68 mg of 9 was obtained as light yellow solid in a yield of 86%. DSC (10 °C/min): 233 °C (m.p.) 273 °C
(dec.). IR (KBr) v/cmꢀ1: 3411 (s), 3198 (s), 2308 (vw), 1635 (w), 1401 (s), 1231 (m), 1165 (w), 1046 (w), 998 (w), 727 (w),
501 (w). 1H NMR (600 MHz, [D6]DMSO, 25 °C) δ/ppm: 12.76, 7.03, 4.90. 13C NMR (150 MHz, [D6]DMSO, 25 °C) δ/ppm:
160.76, 155.01, 135.52, 74.41. elemental analysis (%) calcd for C8H12N14O4 (368.23): C, 26.10; H, 3.28; N, 53.24; found:
C, 25.870; H, 3.56; N, 53.90.
Bisꢀdicyandiamidine 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate (10): 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate dihydrate(206 mg, 1
mmol) was suspended in a few milliliters of water. Ba(OH)2·8H2O (316 mg, 1 mmol) was added to the clear solution, and
the mixture was heated until boiling to obtain a white, poorly soluble deposit. The white barium salt was filtered off under
vacuum and dried. The substance was proved to be anhydrous by elemental analysis. Afterwards, the white powder was
suspended in water to mix it with dicyandiamidine sulfate (504.54 mg, 2 mmol). BaSO4 was filtered off and water was
removed by evaporating the filtrate, and then 313 mg of 10 was obtained as white solid in a yield of 76%. DSC (10 °C/min):
230 °C (m.p.) 254 °C (dec.). IR (KBr) v/cmꢀ1: 3368 (vs), 1750 (m), 1700 (m), 1606 (m), 1420 (m), 1354 (w), 1241 (w),
1084 (w), 625 (w), 458 (w). 1H NMR (600 MHz, [D6]DMSO, 25 °C) δ/ppm: 8.04, 7.18. 13C NMR (150 MHz, [D6]DMSO,
25 °C) δ/ppm: 156.30 155.63,134.84. elemental analysis (%) calcd for C6H20N16O6 (412.38): C, 17.48; H, 4.89; N, 54.35;
found: C, 17.30; H, 4.90; N, 54.50.
Bisꢀ2,4ꢀdiaminoꢀ6ꢀmethylꢀ1,3,5ꢀtriazin 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate (11): 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate
dihydrate (206 mg, 1 mmol) was dissolved in 3 mL distilled water, and 2,4ꢀdiaminoꢀ6ꢀmethylꢀ1,3,5ꢀtriazin (250.26 mg, 2

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mmol), previously dissolved in 4 ml water was added dropwise resulting in the formation of a white precipitate at room
temperature. The solution was stirred for a few minutes, and then filtered, washed with cold water and dried in vacuo to
afford 378.3 mg of 11 as a white powder in a yield of 90%. DSC (10 °C/min): 314 °C (dec.). IR (KBr) v/cmꢀ1: 3291 (s),
3116 (s), 2324 (vw), 1685 (s), 1623 (m), 1550 (w), 1463 (w), 1398 (m), 1241 (m), 1174 (w), 1104 (w), 1065 (w), 1006 (w),
906 (w), 792 (w), 742 (m), 552 (m). 1H NMR (600 MHz, [D6]DMSO, 25 °C) δ/ppm: 7.44, 2.18. 13C NMR (150 MHz,
[D6]DMSO, 25 °C) δ/ppm: 171.03, 164.28, 135.60,23.39. elemental analysis (%) calcd for C10H16N18O2 (420.29): C, 28.57;
H, 3.81; N, 60.00; found: C, 29.02; H, 4.19; N, 60.15.
Acknowledgments
We are grateful for financial support from the National Natural Science Foundation of China (project no.51372211),
Open Project of State Key Laboratory Cultivation Base for Nonmetal Composites and Functional (project no. 14zdfk05),
Southwest University of Science and Technology Outstanding Youth Fundation (project no. 13zx9107).
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A series of nitrogenꢀrich heterocyclic 1H,1′Hꢀ5,5′ꢀbistetrazoleꢀ1,1′ꢀdiolate salts was synthesized.
Results indicated that all of the salts possess excellent thermal stabilities with decomposition
temperatures ranging from 225 °C to 314 °C. All of the compounds show excellent impact
sensitivities of >50 J and promising detonation performances with a detonation pressure of 20.23–
28.69 GPa and a detonation velocity of 7050–8218 m/s. Therefore, these ionic salts with excellent
energetic properties could be applied as new energetic materials.