Synthesis and properties of novel nitrogen- and oxygen-enriched dicationic 3,4-diaminotriazolium salts as attractive energetic materials

Article abstract of DOI:10.1016/j.molstruc.2020.129536

The incorporation of both fuel and oxidizer properties into a single molecule to effectively improve the oxygen balance of energetic compounds has become one of the most acceptable strategies for the design of modern high-energy-density materials (HEDMs). To identify more powerful and less sensitive HEDMs with favorable oxygen balance, novel nitrogen- and oxygen-enriched dicationic 3,4-diaminotriazolium salts were prepared via the quaternization of 3,4-diamino-triazole with 4,4′-bis(nitramino)azofurazan and 4,4′-bis(nitramino)azoxyfurazan, and then fully characterized. These compounds exhibited favorable thermal stabilities with decomposition temperatures up to 216°C, high densities over 1.82 g·cm^?3 as well as acceptable sensitivities. In addition, the two-dimensional fingerprint spectra based on Hirshfeld surface analysis were adopted to illustrate structure–property relationships. Based on the combination of experimentally determined densities and heats of formation calculated with Gaussian 03, the energetic properties were determined using the EXPLO5 v6.02 program. The newly synthesized ionic salts displayed excellent detonation properties (V_d, 9115-9220 m·s^?1; P, 33.9-35.4 GPa), comparable to those of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX), thus highlighting their potential in energetic material applications.

Full text of DOI:10.1016/j.molstruc.2020.129536

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Synthesis and Properties of Novel Nitrogen- and Oxygen-Enriched
Dicationic 3,4-diaminotriazolium Salts as Attractive Energetic
Materials
Mi Wang , Zhenyuan Wang , Binshen Wang , Jichuan Zhang ,
Jiaheng Zhang
PII:
S0022-2860(20)31851-2
DOI:
Reference:
https://doi.org/10.1016/j.molstruc.2020.129536
MOLSTR 129536
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Accepted date:
23 July 2020
27 October 2020
27 October 2020
Please cite this article as: Mi Wang , Zhenyuan Wang , Binshen Wang , Jichuan Zhang ,
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diaminotriazolium Salts as Attractive Energetic Materials, Journal of Molecular Structure (2020), doi:
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Highlights



Novel dicationic 3,4-diaminotriazolium salts were designed and synthesized.
These salts displayed superb physicochemical properties and acceptable sensitivities.
These salts exhibited excellent detonation properties comparable to those of HMX.
1

Synthesis and Properties of Novel Nitrogen- and Oxygen-Enriched Dicationic
3,4-diaminotriazolium Salts as Attractive Energetic Materials
Mi Wang‡[a,b], Zhenyuan Wang‡[a,b], Binshen Wang[a,b], Jichuan Zhang*[c]
and Jiaheng Zhang*[a,b,c]
,
aState Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology,
Shenzhen 518055, China.
bResearch Centre of Printed Flexible Electronics, School of Materials Science and Engineering,
Harbin Institute of Technology, Shenzhen 518055, China.
cZhuhai Institute of Advanced Technology Chinese Academy of Sciences, Zhuhai, 519000,
China
Corresponding Author: *E-mail: zhangjiaheng@hit.edu.cn.
Author Contributions: ‡These authors contributed equally.
2

Abstract: The incorporation of both fuel and oxidizer properties into a single molecule to
effectively improve the oxygen balance of energetic compounds has become one of the most
acceptable strategies for the design of modern high-energy-density materials (HEDMs). To
identify more powerful and less sensitive HEDMs with favorable oxygen balance, novel
nitrogen- and oxygen-enriched dicationic 3,4-diaminotriazolium salts were prepared via the
quaternization
of
3,4-diamino-triazole
with
4,4′-bis(nitramino)azofurazan
and
4,4′-bis(nitramino)azoxyfurazan, and then fully characterized. These compounds exhibited
favorable thermal stabilities with decomposition temperatures up to 216°C, high densities over
1.82 g·cm-3 as well as acceptable sensitivities. In addition, the two-dimensional fingerprint
spectra based on Hirshfeld surface analysis were adopted to illustrate structure–property
relationships. Based on the combination of experimentally determined densities and heats of
formation calculated with Gaussian 03, the energetic properties were determined using the
EXPLO5 v6.02 program. The newly synthesized ionic salts displayed excellent detonation
properties (Vd, 9115-9220 m·s-1; P, 33.9-35.9 GPa), comparable to those of
1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX), thus highlighting their potential in
energetic material applications.
Keywords: Ionic salt; oxygen balance; energetic material; detonation properties.
3

1. Introduction
In recent years, research on energetic materials (explosives, propellants, and pyrotechnics) has
attracted considerable interest owing to their continuously growing applications in civilian as
well as military areas [1-5]. Desirable characteristics for modern energetic materials include high
energetic performance, mechanical insensitivity, thermal stability, along with environmental and
toxicological acceptability [6-10]. Unfortunately, it is well known that excellent detonation
properties in energetic materials are rarely accompanied by low sensitivities. Hence, designing
and synthesizing novel high-energy-density materials (HEDMs) with an appropriate balance
between sensitivity and energetic properties still represents an important and challenging
research subject [11-14].
A favorable oxygen balance (OB) is one of the desirable characteristics of modern HEDMs,
and exercises great influence upon the sensitivity, strength, and brisance of an explosive [15, 16].
To achieve a favorable oxygen balance, incorporating both fuel and oxidizer properties into a
single molecule is one of the most effective strategies, which should enhance the combustion and
therefore support release of large amounts of energy [17-22]. The replacement of a nitrogen atom
in triazole ring with an oxygen atom gives rise to the well-known family of energetic
oxadiazoles, which are increasingly being used as key moieties for improving oxygen balance in
HEDMs [23, 24]. Comparing the density, thermal stability and heat of formation of the possible
oxadiazoles, 1,2,5-oxadiazole (furazan) is the best choice as an effective building block for the
generation of HEDMs [17]. In addition, the azo linkage is another important energetic moiety,
whose presence not only increases the heat of formation of the energetic compounds, but also
decreases the sensitivity. In particular, high nitrogen content compounds containing furazan rings
linked with an azo group show particularly desirable energetic properties, insensitivity and
4

thermal stability arising from the aromaticity [25]. Furthermore, the incorporation of the
nitramino (–NHNO2) moiety in the furazan ring can provide an acidic proton and enable the
molecule to serve as an anion, which has been used as an effective strategy to construct advanced
energetic salts [26]. Therefore, the combination of furazan rings, an azo bridge, and a nitramino
group in a molecule should lead to interesting results with respect to various energetic properties.
Recently, 4,4′-bis(nitramino)-azofurazan, 4,4′-bis(nitramino)-azoxyfurazan, as well as their ionic
derivatives were synthesized and showed superior detonation performances [17, 27-32].
As a general principle, the presence of amino groups in triazolium cations is advantageous for
the development of intramolecular and intermolecular hydrogen bond interactions with an anion
containing nitro or nitramine groups, which is in favour of improving density, sensitivity and
stability of energetic salts [32, 33]. Therefore, the readily available and relatively inexpensive
3,4-diamino-triazole (DATr) is a good candidate as an energetic cation [34]. Herein, with our
continuing efforts to seek more powerful, less sensitive HEDMs, two kinds of energetic salts
were designed and synthesized, using DATr as the cation, combined with energetic anions of
4,4′-bis(nitramino)-azofurazan and 4,4′-bis(nitramino)-azoxyfurazan. These compounds were
fully characterized by single-crystal X-ray diffraction analysis, elemental analysis, differential
scanning calorimetry (DSC), multinuclear NMR and IR spectroscopy. In addition, experimental
and theoretical analyses were conducted to evaluate the potential applications of these
compounds as energetic materials. Compared to previous work, the newly prepared energetic
salts exhibit excellent integrated properties, including superb detonation performance, high
thermal stability, and simultaneously low sensitivity.
5

2. Experimental section
2.1. General methods
Analytical-grade reagents were purchased from Aladdin and Aldrich and used as received. 1H
and 13C spectra were recorded with a Bruker AVANCE 400 nuclear magnetic resonance
spectrometer. Dimethyl sulfoxide d6 (d6-DMSO) was used as a locking solvent unless otherwise
1
13
stated, and H and C chemical shifts were reported relative to Me4Si. Elemental analysis was
conducted on a CE-440 Elemental Analyzer. Melting and decomposition points were recorded
on a differential scanning calorimeter (DSC, TA Instruments Q20) at a heating rate of 5°C·min-1.
Impact and friction sensitivity were measured on a standard BAM Fallhammer and a BAM
friction tester, respectively. Density measurements were performed at 25°C using a
Micromeritics AccuPyc 1330 gas pycnometer.
2.2. X-ray crystallography
A yellow plate crystal of dimensions 0.124 × 0.115 × 0.026 mm3 for 1a·2H2O and a pale
yellow plate crystal of dimensions 0.400 × 0.360 × 0.210 mm3 for 2a·2H2O were used for
single-crystal X-ray diffraction analysis. The X-ray intensity data were collected on a Bruker
three-circle platform diffractometer equipped with a Smart Apex II charge-coupled detector
(CCD). The crystals were irradiated using graphite monochromated Mo Kα radiation (λ =
0.71073 Å). The frames were integrated using the Bruker SAINT software package with a
narrow-frame algorithm, and data were corrected for absorption effects by the multiscan method
(SADABS) [35, 36]. The obtained structures were solved and refined with the aid of the Bruker
SHELXTL software package [37]. The full-matrix least-squares refinement on F2 included
6

atomic coordinates and anisotropic thermal parameters for all non-H atoms, while the H atoms
were included based on a riding model.
2.3. Syntheses
2.3.1. 4,4′-Bis(nitramino)-azofurazan (1)
Compound 1 was prepared according to a method reported in literature [30] and obtained as a
yellow solid (0.72g, 76%). 1H NMR: δ 10.3 (s, 2H, N-NO2) ppm; 13C NMR: δ 159.5, 148.0 ppm;
Elemental analysis calcd (%) for C4H2N10O6 (286.12): C, 16.79; H, 0.70; N, 48.95; Found: C,
16.61; H, 0.75; N, 49.12.
2.3.2. 4,4′-Bis(nitramino)-azoxyfurazan (2)
Compound 2 was prepared according to a previously reported method [17] and obtained as an
1
ivory solid (0.81g, 82%). H NMR: δ 13.6 (s, 2H, N−NO2) ppm; 13C NMR: δ 155.2, 153.1,
150.8, 148.3 ppm; Elemental analysis calcd (%) for C4H2N10O7: C, 15.90; H, 0.67; N, 46.36;
Found: C, 15.63; H, 0.69; N, 45.47.
2.3.3. Di(3,4-diamino-1,2,4-triazolium) 4,4′-bis(nitramino)-azofurazanate (1a)
3,4-Diamino-1,2,4-triazole (0.40 g, 4 mmol) was added to a solution of 1 (0.57 g, 2 mmol) in a
minimum amount of ethanol. The mixture was heated at 50°C for 1 h. After cooling to room
temperature, the precipitate was collected by filtration to give 1a (0.76g, 78%) as a yellow solid.
1H NMR: δ 8.4 (s, 2H, CH), 8.2 (s, 4H, NH2), 6.1 (s, 4H, NH2) ppm; 13C NMR: δ 161.3, 154.0,
152.0, 143.2 ppm; IR (KBr): 3415, 3332, 3219, 1701, 1661, 1559, 1490, 1425, 1388, 1276, 1055,
997, 810, 778 cm-1; Elemental analysis calcd (%) for C8H12N20O6: C, 19.84; H, 2.50; N, 57.84;
Found: C, 19.82, H, 2.54, N, 57.55.
7

2.3.4. Di(3,4-diamino-1,2,4-triazolium) 4,4′-bis(nitramino)-azoxyfurazanate (2a)
3,4-Diamino-1,2,4-triazole (0.40 g, 4 mmol) was added to a solution of 2 (0.60 g, 2 mmol) in
minimum ethanol. The mixture was heated at 50°C for 1 h. After cooling to room temperature,
1
the precipitate was collected by filtration to give 2a (0.79g, 79%) as a light yellow solid. H
NMR: δ 8.4 (s, 2H, CH), 8.1 (s, 4H, NH2), 6.1 (s, 4H, NH2) ppm; 13C NMR: δ 156.4, 156.3,
155.2, 152.5, 152.0, 143.1 ppm; IR (KBr): 3358, 3282, 3124, 2752, 1707, 1626, 1566, 1502,
1302, 1010, 955, 849, 771, 708 cm-1; Elemental analysis calcd (%) for C8H12N20O7: C, 19.21, H,
2.42, N, 55.99; Found: C, 18.61, H, 2.41, N, 55.39.
3. Results and discussion
3.1. Synthesis
Some readily available starting materials were used for the synthesis of the energetic salts via
a straightforward three-step procedure as illustrated in Scheme 1. In the first step,
3,4-diaminofurazan was reacted with either hypochlorite or oxone in aqueous solution to form
azo and azoxy aminofurazans, respectively. Subsequently, the azo and azoxy nitraminofurazans
(1 and 2) were obtained by nitration of the corresponding aminofurazans in 100% HNO3 at 0–5℃
for
2
h, followed by quenching with ice water. Finally, energetic salts of
4,4′-bis(nitramino)-azofurazanate (1a) and
di(3,4-diamino-1,2,4-triazolium)
di(3,4-diamino-1,2,4-triazolium) 4,4′-bis(nitramino)-azoxyfurazanate (2a) were generated via
deprotonation of the azo and azoxy nitraminofurazans (1 and 2) with 3,4-diamino-1,2,4-triazole.
Both salts were isolated as crystalline solids in good yields. The structure of resulting salts was
13
confirmed by 1H and C NMR spectroscopy, X-ray crystallography, infrared spectroscopy, and
elemental analysis, showing a high purity level of all synthesized ionic structures.
8

Scheme 1. Synthesis of the energetic salts investigated in this study.
3.2. Single crystal X-ray structure analysis
Single crystals of di(3,4-diamino-1,2,4-triazolium) 4,4′-bis(nitramino)-azofurazanate with two
water molecules (1a·2H2O) and di(3,4-diamino-1,2,4-triazolium)
4,4′-bis(nitramino)-azoxyfurazanate with two water molecules (2a·2H2O) were obtained through
slow recrystallization from aqueous solutions at room temperature and ambient pressure, and the
suitable crystals were selected for crystal-structure analysis. The structures of compounds
1a·2H2O and 2a·2H2O are shown in Fig. 1 and 2, respectively. As can be seen in Table 1, both of
1a·2H2O and 2a·2H2O crystallized in the triclinic system with P-1 space group. Due to the
presence of water molecules in the unit cell, low calculated densities of 1.670 and 1.729 g·cm−3
were obtained for crystals 1a·2H2O and 2a·2H2O, respectively. As reported in a previous work,
the two furazan rings, azo or azoxy linkage, and the N-nitro moieties are coplanar for the neutral
compounds 1 and 2 [17]. However, it is interesting to note that one of the furazan rings is bent
away from the azo or azoxy linkage and the other ring in 1a·2H2O (torsion angle
N8−C9−N10−N10A, -167.0°) and 2a·2H2O (torsion angle N6−C4−N10−N10A, 147.5°). This
9

may be due to the intramolecular hydrogen bond between cations and anions present in the ionic
salts. As shown in Fig.1 and 2, the crystal structures of compounds 1a·2H2O and 2a·2H2O were
built up by several hydrogen bonds, which use hydrogen atoms of the DATr cation and water
molecule as donor atoms. For compound 1a·2H2O, H···A lengths of hydrogen bonds were in the
range of 1.77-2.59 Å, with the strongest contact supported by O1S with the N11···H11. With
respect to compound 2a·2H2O, H···A lengths of hydrogen bonds lay within the range of
1.71-2.56 Å, with the strongest contact supported by O5 with the N1···H1. For both compounds
1a·2H2O and 2a·2H2O, the DATr cations, azo- or azoxy anions and water molecules were linked
through hydrogen bonds and constituted a dense 3D interspace network. The details can be found
in the ESI.
Fig. 1. (a) Single-crystal X-ray structure and (b) Packing diagram of 1a·2H2O.
10

Fig. 2. (a) Single-crystal X-ray structure and (b) Packing diagram of 2a·2H2O.
Table 1 Crystallographic data for 1a·2H2O and 2a·2H2O.
1a·2H2O
2a·2H2O
Compound
Formula
Formula weight
CCDC number
Crystal size (mm3)
Crystal system
Space group
a (Å)
C8H16N20O8
520.41
C8H16N20O9
536.41
1999077
0.124×0.115×0.026
Triclinic
P-1
1999078
0.400×0.360×0.210
Triclinic
P-1
6.183(14)
7.082(18)
12.947(3)
98.831(9)
91.346(9)
111.936(9)
517.6(2)
1
6.168(2)
7.010(2)
13.087(4)
99.061(10)
91.215(10)
112.201(10)
515.3(3)
1
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
Z
ρcalc(g·cm-3)
μ (mm-1)
F (000)
1.670
1.729
0.146
0.153
268
276
θ (°)
1.598 to 26.456
3.165 to 28.636
11

-7<=h<=7;
-8<=k<=8;
-16<=l<=16
-8<=h<=8;
-9<=k<=9;
-17<=l<=17
Index ranges
Reflections collected
Independent reflections (Rint)
Data/restraints/parameters
GOF on F2
5000
2114 (0.0307)
2114/0/184
1.043
14296
2626 (0.0419)
2626/0/204
1.035
R1 (I>=2σ(I))
0.0358
0.0330
wR2 (I>=2σ(I))
0.082
0.0916
R1 (all data)
0.0592
0.0380
wR2 (all data)
0.1025
0.0938
Largest diff. peak/hole (e Å-3)
0.193/-0.187
0.345/-0.306
3.3. Thermal stability and sensitivity
The thermal properties are among the most important properties of energetic materials. The
phase transition temperature (Tg/Tm) and thermal decomposition temperature (Td) were
determined by means of differential scanning calorimetric (DSC) measurements (Table 2). It
should be noted that neither of the synthesized compounds melts prior to decomposition. As
expected, the Td values of 1a (216°C) and 2a (191°C) were more than 100°C higher than those of
the corresponding neutral compounds 1 (100°C) and 2 (90°C), indicating much higher thermal
stabilities. In addition, the anions were found to have a significant effect on Td. In the case of the
same cation, the azofurazan-based ionic salt 1a showed a higher decomposition temperature than
the azoxyfurazan-based ionic salt 2a, with the same trend exhibited by their neutral anion
precursors.
Moreover, the impact and friction sensitivities were determined by using standard BAM
procedures. As shown in Table 2, both synthesized ionic salts displayed superior sensitivities to
their neutral anion precursors whose impact and friction sensitivities were 2 J and 10 N,
12

respectively, as those of salt 1a were 22 J and 160 N, respectively, while those of salt 2a were 26
J and 160 N, respectively. Meanwhile, it is clear that both the azo and azoxy salts are less
sensitive
than
cyclo-1,3,5-trimethylene-2,4,6-trinitamine
(RDX)
and
1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX), which highlights their promising potential
as safe energetic materials.
With the aim of gaining a deep insight into the weak interactions of the obtained compounds,
Hirshfeld surfaces analyses were conducted for crystals 1a·2H2O, 2a·2H2O, as well as 1 and 2
obtained from our previous work. The two-dimensional (2D) fingerprint spectra of crystals
derived from Hirshfeld surfaces and the percentage of contribution for each type of interaction to
the total weak interactions are shown in Fig. 3 and 4, respectively. The hydrogen bonds
indicators of O···H and N···H interactions accounted for 60.3% and 58.6% of the total weak
interactions for 1a·2H2O and 2a·2H2O, respectively, which were nearly three times as high as
those of their neutral anion precursors. At the same time, the percentages of O···O interactions in
1a·2H2O and 2a·2H2O showed a sharp decrease from 25.6% and 22.8% to 1.8% and 5.2%,
respectively, compared to those of 1 and 2. This indicates that 1a·2H2O and 2a·2H2O may be less
sensitive than 1 and 2, as the O···O interactions reflecting the possibility of unexpected
explosion. Furthermore, the N···O interactions in 1 and 2 were higher than those in 1a·2H2O and
2a·2H2O, showing a higher percentage of interlayer contact. Based on the above analysis, the
results of the Hirshfeld surfaces appear to support the higher stability and lower sensitivity of the
ionic salts compared to their neutral anion precursors.
13

Fig. 3. Two-dimensional fingerprint plots for 1, 2, 1a·2H2O and 2a·2H2O.
14

Fig. 4. Individual atomic contact percentage contribution to the Hirshfeld surface for 1, 2, 1a·2H2O and
2a·2H2O.
N···H,
O···H,
O···O,
N···O,
N···C,
other
3.4. Density
In addition to thermal properties and sensitivities, density is another vital parameter for
evaluating energy level of energetic materials. In general, the higher density usually means the
higher mole number of energetic materials that can be packed into a limited volume, thereby
providing higher energy and combustion contribution to the explosive composition. As shown in
Fig. 5 and Table 2, the synthesized ionic salts 1a and 2a showed favorable densities of 1.82 and
1.85 g·cm-3, respectively, both of which were higher than those of TNT (1.65 g·cm-3) and RDX
(1.81 g·cm-3). As described in our previous work, the higher density of azoxy salt 2a than azo salt
15

1a could be attributed to the participation of the N-oxide and the nitrogen-rich cations being
involved in multiple intermolecular hydrogen-bonding interactions. In addition, the advantages
of introducing the N-oxide moiety into the azo linkage were further confirmed by the observed
density increase.
Fig. 5. Comparison of density values of synthesized salts, neutral anion precursors, and traditional energetic
materials.
3.5. Heat of formation
The heat of formation (HOF, ΔfHo) is one of the key properties of energetic compounds, and is
closely related to the energy and the prediction of the detonation performance. For both energetic
salts investigated in this work, the solid-phase HOFs can be simplified by Eq. (1) on the basis of
Born-Haber energy cycle (Scheme 2) [38]. The HOFs of the cation and anions were determined
according to the literature [39] or our previous work [30], in which these values were calculated
using the Gaussian 03 suite of programs.
16

Scheme 2. Born-Haber cycle for the formation of energetic salts.
ΔfHo(salt, 298 K) = ΣΔfHo(cation, 298 K) + ΣΔfHo(anion, 298 K) - ΔHL
(1)
The lattice energy ΔHL in Eq. (1) was predicted using Eq. (2) [38], as suggested by Jenkins et
+
-
al. In this equation, the parameters nM and nX depend on the nature of the ions Mp and Xq ,
respectively.
ΔHL = UPOT + [p(nM/2-2) + q(nx/2-2)]RT
(2)
The lattice-potential energy (UPOT) was calculated according to Eq. (3):
UPOT = γ(ρm/Mm)1/3 + δ
(3)
in which ρm and Mm represent the density and chemical formula mass of the ionic compound,
respectively, while the γ and δ coefficients were obtained from the literature [38].
As shown in Table 2, the HOFs estimated for both energetic salts (1a and 2a) were greater
than those of currently used explosives such as TNT (-67.0 kJ·mol-1, -0.30 kJ·g-1), RDX (80
kJ·mol-1, 0.36 kJ·g-1) and HMX (74.8 kJ·mol-1, 0.25 kJ·g-1). This is due to the presence of a large
number of N−N or N=N bonds within the molecules, and in particular to the introduction of azo
or azoxy linkages. Among the present materials, the azo salt 1a exhibited a much higher HOF
(1444.7 kJ·mol-1, 2.98 kJ·g-1) than the azoxy salt 2a (1374.5 kJ·mol-1, 2.75 kJ·g-1).
17

Table 2 Physicochemical properties of the energy salts.
a
d
Td
ρb
g·cm-3
1.89
1.82
1.96
1.85
1.65
1.81
1.90
ΔfHc
Vd
Pe
ISf
J
FSg
N
OBh
%
ILs
°C
kJ·mol-1/kJ·g-1
820.2/2.86
1444.7/2.98
730.0/2.42
1374.5/2.75
-67.0/-0.30
80/0.36
m·s-1
9517
9115
9746
9220
6881
8748
9144
GPa
41.1
33.9
44.1
35.4
19.5
34.9
39.2
1
1a
100
216
90
2
10
-16.7
-52.9
-10.6
-48.0
-24.7
-21.6
-21.6
22
2
160
10
2
2a
191
295
205
280
26
15
7.4
7.4
160
353
120
120
TNT
RDX
HMX
74.8/0.25
[a] Decomposition temperature (onset); [b] Density measured by using a gas pycnometer at 25°C; [c] Calculated heat of
formation in the solid state; [d] Detonation velocity; [e] Detonation pressure; [f] Impact sensitivity; [g] Friction sensitivity; [h]
Oxygen balance for CaHbOcNd, 1600(c-2·a-b/2)/Mw; Mw = molecular mass.
3.6. Energetic properties
Using the calculated HOFs and the experimentally measured densities, the values of
detonation properties were calculated with Explo5 v6.02 software [40]. Table 2 shows that 1a
and 2a exhibit favorable detonation properties, with detonation velocities of 9115 and 9220 m·s−1
and detonation pressures of 33.9 and 35.4 GPa, respectively, thus outperforming TNT and RDX,
while showing performances comparable with those of HMX. It is not surprising that the azoxy
salt (2a) showed better performances than the azo salt (1a), due to its relatively higher density.
The oxygen balance (OB) is used to represent the deficiency or excess of oxygen in an energetic
compound required to be oxidized. In general, the OB value can be calculated based on the
molecular formula needed to convert all carbon into carbon dioxide and all hydrogen into water
[41]. Furthermore, the sensitivity and detonation properties of an explosive directly relate to the
oxygen balance and tend to reach their maxima as the oxygen balance approaches zero [15, 16].
In this study, the azoxy salt 2a showed a higher oxygen balance than the azo salt 1a, as the
addition of the single oxygen atom to the azo linkage improved the oxygen balance.
18

4. Conclusion
In summary, two types of novel nitrogen- and oxygen-enriched dicationic
3,4-diaminotriazolium salts were designed and synthesized, in combination with
4,4′-bis(nitramino)azofurazan and 4,4′-bis(nitramino)azoxyfurazan anions. These compounds
displayed excellent physiochemical properties including high thermal stability, high density, as
well as low sensitivities. Furthermore, theoretical analyses showed that the calculated detonation
properties of the newly prepared ionic salts were superior to those of RDX and comparable to
those of HMX, which highlights their promising potential as ingredients in energetic materials
applications.
Supplementary data
Crystal structure data, Infrared Spectra, 1H-NMR and 13C-NMR Spectra.
Notes
The authors declare no competing financial interest.
Acknowledgment
This work was supported by the Basic and Applied Basic Research Foundation of Guangdong
(2019A1515110754), the National Natural Science Foundation of China (21905069, 21703218),
the Shenzhen Science and Technology Innovation Committee (JCYJ20180507183907224,
KQTD20170809110344233), Economic, Trade and Information Commission of Shenzhen
Municipality through the Graphene Manufacture Innovation Center (201901161514).
19

Credit Author Statement
Mi Wang and Zhenyuan Wang contribute equally to this work, they performed the IR, NMR,
physicochemical and energetic properties experiments. Mi Wang, Zhenyuan Wang and Jiaheng
Zhang wrote the paper. Jichuan Zhang and Binshen Wang performed the theoretical calculations.
Jiaheng Zhang and Jichuan Zhang conceived and designed the project.
Conflict of Interest
The authors declare that they have no conflict of interest to this work.
Graphical abstract
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