The enhanced properties of energetic materials through ring replacement strategy

Article abstract of DOI:10.1016/j.molstruc.2019.127358

In order to meet the high demands of modern energetic materials, numerous routes have been explored by the researchers. In this study, a ring replacement strategy was designed to enhance the energetic properties. The ring replacement compounds 11 (N,N′-methylenebis (N-(4-(2H-tetrazol-5-yl)-1,2,5-oxadiazol-3-yl)- nitramide) and 15 (N,N′-ethylenebis (N-(4-(2H-tetrazol-5-yl)-1,2,5-oxadiazol-3-yl)- nitramide), in which the oxadiazole rings connected to the furazan backbone were replaced by tetrazole rings were characterized by x-ray single crystal diffraction and NMR (¹H, ¹³C, ¹⁵N). The results compounds show that the heats of formation and detonation performance of the replacement compounds were significantly better than those of the precursor compounds, and the nitrogen content of compounds 11 and 15 were improved from 41.18% and 39.81% to54.9% and 53.08%, respectively, which belongs to the category of high nitrogen compounds. In a word, the ring replacement strategy in this work offers fresh routes for the improvement in properties of energetic materials.

Full text of DOI:10.1016/j.molstruc.2019.127358

Journal of Molecular Structure xxx (xxxx) xxx
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
The enhanced properties of energetic materials through ring
replacement strategy
Jichuan Zhang a
Jiaheng Zhang
a
,
b
,
c
,
1
, Guangxing Pan b , Haifeng Huang , Jun Yang a
,
c
,
1
a
, **
,
b, c, d, *
CAS Key Laboratory of Energy Regulation Materials, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai,
00032, China
State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Shenzhen, 518055, China
Research Centre of Flexible Printed Electronic Technology, Harbin Institute of Technology, Shenzhen, 518055, China
School of Material Sciences and Engineering, Harbin Institute of Technology, Shenzhen, 518055, China
2
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 August 2019
Received in revised form
In order to meet the high demands of modern energetic materials, numerous routes have been explored
by the researchers. In this study, a ring replacement strategy was designed to enhance the energetic
0
properties. The ring replacement compounds 11 (N,N -methylenebis (N-(4-(2H-tetrazol-5-yl)-1,2,5-
1
November 2019
0
oxadiazol-3-yl)- nitramide) and 15 (N,N -ethylenebis (N-(4-(2H-tetrazol-5-yl)-1,2,5-oxadiazol-3-yl)-
Accepted 2 November 2019
Available online xxx
nitramide), in which the oxadiazole rings connected to the furazan backbone were replaced by tetrazole
1
13
15
rings were characterized by x-ray single crystal diffraction and NMR ( H, C, N). The results com-
pounds show that the heats of formation and detonation performance of the replacement compounds
were significantly better than those of the precursor compounds, and the nitrogen content of compounds
Keywords:
High nitrogen content
Ring replacement
Energetic materials
Tetrazole ring
11 and 15 were improved from 41.18% and 39.81% to54.9% and 53.08%, respectively, which belongs to the
category of high nitrogen compounds. In a word, the ring replacement strategy in this work offers fresh
routes for the improvement in properties of energetic materials.
© 2019 Elsevier B.V. All rights reserved.
Oxadiazole ring
1. Introduction
packaging via hydrogen-bonding interactions [12e14], as well as
anion exchange in metal-organic framework [15]. Nevertheless,
Energetic materials play a significant role in both military and
civilian fields, since Nobel invented dynamite. It has been attracting
considerable interest over the past two centuries [1]. Generally
speaking, the energy density higher, the volume of the energetic
materials needed for application is smaller, therefore, endowing
energetic materials with improved detonation properties has al-
ways been the developmental theme of energetic materials [2e4].
In the past decades, many strategies have been employed to
improve the properties of energetic materials, for instance, intro-
duction of more powerful energetic groups to replace original
groups as substituents on the backbone [5e7], employing cage or
ring with strain as the energetic backbone [8e11], and close
due to the increasing development and modern demands of ener-
getic materials, more approaches to improve the energetic prop-
erties are desired.
Among the numerous heterocyclic compounds proposed for
energetic materials, oxadiazole compounds, due to higher densities
and better oxygen balance of their derivatives compared to those of
imidazole, pyrazole and triazole, make them better choice (Fig. 1a)
[16,17]. Especially for the bis-oxadiazole derivatives, which display
very promising as alternative to replace current explosive. Such as
0
0
the 3,3 -dinitramino-4,4 -bifurazane and its derivatives [18], de-
rivatives of 3-nitroamino-4-(5-nitroamino-1,2,4-oxadiazol-3-yl)
furazan [6]. On the other hand, tetrazole has a higher heat of for-
mation and nitrogen content than other types of heterocycle-based
compounds, which would lead to relatively environmentally
benign decomposition products [19e21], and some compounds
based on tetrazole have favorable energetic properties [22].
Therefore, one ring of the bis-oxadiazole compounds was replaced
by tetrazole, the heat of formation, oxygen balance and density
*
Corresponding author. State Key Laboratory of Advanced Welding and Joining,
Harbin Institute of Technology, Shenzhen, 518055, China.
** Corresponding author.
E-mail address: zhangjiaheng@hit.edu.cn (J. Zhang).
Jichuan Zhang and Guangxing Pan contributed equally to this work.
1
https://doi.org/10.1016/j.molstruc.2019.127358
022-2860/© 2019 Elsevier B.V. All rights reserved.
0
Please cite this article as: J. Zhang et al., The enhanced properties of energetic materials through ring replacement strategy, Journal of Molecular
Structure, https://doi.org/10.1016/j.molstruc.2019.127358

2
J. Zhang et al. / Journal of Molecular Structure xxx (xxxx) xxx
Fig. 1. (a) The calculated gas-phase heats of formation for small ring compounds; (b) The ring replacement strategy was employed in this work.
would reach up to be an excellent combination, and some of these
reported compounds’ properties do satisfy modern demand of
energetic materials [23e25]. However, there are seldom reports
employing ring replacement to introduce tetrazole into oxadiazole,
and none of them studied the energetic properties between the
precursor and replaced compounds comprehensively [26,27].
What’s more, most of the tetrazole-oxadiazole compound were
synthesized from the cyano-oxadiazole compound, which almost
has no power, it limits the investigation of structure-property
relationship between precursor and resulted compounds.
Recently, our group successfully incorporated 1,2,4-oxadiazole,
a five-membered heterocyclic ring, into a furan ring and synthe-
sized compounds with modest energetic performance [28]. To
continue further exploration, we envisage that if the 1,2,4-
oxadiazole rings are replaced by tetrazole rings (Fig. 1b), the ni-
trogen content can be further improved. Moreover, the heat of
formation of 1,2,4-oxadiazole is lower than 1,2,5-oxadiazole ring,
and the heat of formation of tetrazole is higher than that of 1,2,5-
oxadiazole. Hence, the heat of formation, nitrogen content, and
the properties of replaced compounds would be improved greatly
compared to their precursors. The energetic properties of resulted
compounds were investigated and compared with their precursors
comprehensively in this study.
investigated are potentially explosive materials. Therefore, ma-
nipulations must be carried out in a hood behind a safety shield.
Eye protection and leather gloves must be worn all the time. During
synthesis and characterization, mechanical actions involving
scratching or scraping must be avoided. All of the energetic com-
pounds must be synthesized only in small amounts.
2.2. General methods
1
H spectra were recorded on a 300 MHz nuclear magnetic
13
resonance spectrometer operating at 300 MHz C NMR spectra
were recorded on a 400 MHz nuclear magnetic resonance spec-
trometer operating at 100 MHz. The solvent were [d6]dime-
3
thylsulfoxide ([d6]DMSO) and [d4]methanol ([d4]CH DO) unless
15
otherwise specified. N NMR spectra was recorded on a 400 MHz
nuclear magnetic resonance spectrometer operating at 40.5 MHz.
The melting and decomposition points were recorded on a
ꢀ
ꢁ1
NETZSCH STA 449F3 equipment at a scan rate of 5 C min
,
respectively. Infrared spectra were recorded by using KBr pellets.
Densities were measured at toom temperature using a Micro-
meriticsAccupyc
п 1340 gas pycnometer. Elemental analyses were
obtained on an ElementarVario MICRO CUBE (Germany) elemental
analyser. Impact and friction-sensitivity measurements were tested
by employing a standard BAM Fallhammer and a BAM friction
tester. The acknowledgements come at the end of an article after
the conclusions and before the notes and references.
2
. Experimental
2.1. Safety precautions
2.3. X-ray crystallography
Although we have experienced no difficulties in the synthesis
and characterization of these compounds, all the compounds
3
The single-crystal X-ray diffraction data of 5 and 15$CH OH
Please cite this article as: J. Zhang et al., The enhanced properties of energetic materials through ring replacement strategy, Journal of Molecular
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J. Zhang et al. / Journal of Molecular Structure xxx (xxxx) xxx
3
were collected at 293 K using graphite-monochromated MoK
diation (
a
ra-
calculated: C: 19.68, H: 0.55, N: 53.55; found: C: 19.63, H: 0.85, N:
53.89.
l
¼ 0.71073 Å) using omega scans from a Bruker CCD area
detector diffractometer. Data collection and reduction were per-
formed and the unit cell was initially refined using Bruker SMART
software. The reflection data were also corrected for LP factors. The
structure was solved by direct methods and refined by a least-
0
0
2.5.3. N,N - dinitro-N,N -bis[5-(tetrazol)furazan-4-yl]
methylenediamine (11)
The synthesis of compound 11 is similar to compound 3, ac-
2
0
0
squares method on F using the Bruker SHELXTL program. In
cording to the literature [26]. N,N -Dinitro-N,N -bis [3-hydrazino
(imino)methyl-furazan-4-yl]methylenediamine (0.386 g, 1 mmol)
these structures, the value of the Flack parameter did not allow the
direction of the polar axis to be determined and Friedel reflections
were then merged for the final refinement. Details of the data
collection and refinement are given in Table S1.
ꢀ
was added into AcOH (5 ml), the reaction system was cooled to 5 C,
vigorously stirred at this temperature and treated with by dropwise
addition of NaNO
2
(0.152 g, 2.2 mmol), and then the reaction
ꢀ
mixture was stirred for 1 h at 10e15 C, acidified with conc. HCl to
pH 1, the solvent was removed in vacuo, and the residue was taken
up in 10 ml of ethanol, the precipitate that formed was filtered off
and recrystallized from ethanol twice. Yield 0.265 g (65%), light
grown solid, Dec 148.9 C. H NMR (DMSO‑d
CH2, 4.98 (s, 2H, NH); C NMR (DMSO‑d
2.4. Computational method
The gas phase heats of formation for all new neutral compounds
ꢀ
1
were obtained using isodesmic reactions. The geometric optimi-
zation and frequency analysis of the structures were calculated
using B3LYP function with 6-31 þ G** basis set. All of the optimized
structures were checked to be true local energy minima on the
potential energy surface without imaginary frequencies. Single-
point energies based on the optimized structures were calculated
at the MP2/6-311þþG** set. Atomization energies for the frame
molecules or ions were obtained by employing the G2 ab initio
method. The conversion of gas phase enthalpies to solid phase
values for the neutral compounds was done by subtracting the
empirical heat of sublimation obtained based on Trouton’s rule.
Detonation properties of new compounds were calculated by using
EXPLO5 program. More calculation details can be found in the
Electronic Supporting Information.
6
, ppm):
d
6.69 (s, 2H,
151.05, 148.93,
42.6,
1
3
6
, ppm):
d
1
5
145.86,
67.61;
N
NMR
(DMSO‑d
6
):
d
31.9, ꢁ33.7, ꢁ41.3, ꢁ75.8, ꢁ206.9 ppm. IR (KBr) ṽ: 3630, 3039, 2924,
ꢁ
1
2854, 1592, 1407, 1279, 1104, 1021, 996, 897, 751, 733, 647 cm
Elemental analysis (%) for C (408.05): calculated: C: 20.60,
H: 0.99, N: 54.90; found: C: 20.39, H: 0.85, N: 54.71.
.
7 4 16 6
H N O
0
0
2.5.4. N, N - dinitro-N, N -bis[5-(tetrazol) furazan-4-yl]
ethylenediamine (15)
The synthesis of compound 15 is similar to compound 11. It was
recrystallized from MeOH twice. Yield (63%), light grown solid, Dec
ꢀ
1
163.4 C. H NMR (DMSO‑d
6
, ppm):
NH); C NMR (d4-MeOH, ppm): 152.60, 150.43, 143.75, 51.78;
NMR (d4-MeOH):
41.8, 26.9, ꢁ32.9, ꢁ38.5, ꢁ77.2, ꢁ214.1 ppm. IR
(KBr) ṽ: 3636, 3318, 3037, 1625, 1576, 1455, 1348, 1280, 1195, 1044,
2
d6.74 (s, 4H, CH ), 4.74 (s, 2H,
1
3
15
d
N
d
2
2
.5. Synthesis
ꢁ1
1
8 6 16 6
028, 1000, 757, 545 cm . Elemental analysis (%) for C H N O
.5.1. 4-Hydrazinofurazan-3-carboxylic acid (5)
(422.07): calculated: C: 22.76, H: 1.43, N: 53.08; found: C: 22.63, H:
1.23, N: 53.01. CCDC number: 1567536.
The synthesis of compound 5 is similar to compound 2 [26]. 3-
nitro-4-(1,2,4-oxadiazol-3-yl)furazan (5), (1.83 g, 10 mmol) was
ꢀ
dissolved in MeOH (20 ml), the mixture was heated to 40e45 C
3. Results and discussion
2 4 2
and treated with 80% N H $H O(1.02 ml, 21 mmol) at this tem-
perature, accompanying the reaction mixture becoming cloudy
from transparent solution, after the exothermic effect ended, the
mixture was stirred at 40e45 C for 1 h, cooled to room tempera-
3.1. Synthesis
ꢀ
According to the literature [26,28] and synthesis route depicted
in Fig. 2, 4-(1,2,4-oxadiazol-3-yl)furazan-3-amine (1), a luminous
yellow solid, was synthesized with high yield and then treated with
80% hydrazine hydrate in methanol at 50 C for 30 min. Hence,
amidrazone of 4-aminofurazan-3-carboxylic acid (2) was obtained
as faint yellow solid with high yield. Thereafter compound 2 was
treated with AcOH again at 5 C, and NaNO
the reaction mixture at 10e15 C for 30min, 4-(Tetrazol-5-yl)fur-
azan-3-aminie (3) was obtained as white solid.
ture and the precipitate was filtered off and recrystallized from
1
H
2
O. Yield in 80%, light brown needles. For compound 5. H NMR
ꢀ
(
DMSO‑d
6
, ppm):
C NMR (DMSO‑d
335, 3155, 1664, 1564, 1603, 1464, 1320, 1288, 1192, 955, 853, 802,
d
7.23 (s,1H), 5.84 (s, 2H), 5.72 (s, 2H), 4.47 (s, 2H);
1
3
6
, ppm): 158.52, 140.18, 136.37. IR (KBr) ṽ: 3379,
d
3
6
ꢁ
1
ꢀ
51, 418 cm . Elemental analysis (%) for C
H
3 7
N
7
O (183): calculated:
2
was slowly added into
ꢀ
C 22.93; H 4.49; N 62.40; found: C 22.41; H 3.89; N 62.44. CCDC
number: 1567538.
Similarly, 3-nitro-4-(1,2,4-oxadiazol-3-yl) furazan (4) was pre-
pared via the method used to synthesize 7. Due to the reducibility of
hydrazine and the nitro group of 4 was replaced by hydrazine
group, and the oxadiazole ring reacted with hydrazine to change
into amidrazone, compound 5 was obtained instead of compound
6. Compound 5 can act as an energetic dication, which would have
potential applications in energetic salts. Although compound 5 had
been reported by Stepanov [27], its single crystal structure has not
been reported. Finally, the ring replaced compound 3-nitro-4-
(Tetrazol-5-yl) furazan (7) was finally synthesized via treating
2
.5.2. 3-Nitro-4-(tetrazol-5-yl) furazan (7)
4
-(Tetrazol-5-yl)furazan-3-aminie (3) (3) (0.765 g, 5 mmol) was
added into the oxidation mixture of H
phuric acid at 50e60 C, attention please, this step is exothermic
and the temperature stay 50e60 C not easily. After the exothermic
effect ended, the reaction mixture was stirred at this temperature
for 1 h, cooled to room temperature and treated with Н
5
was washed with saturated brines two times, dried with anhydrous
sodium sulphate evaporated in vacuum, the solid residue was
recrystallized from
2
O
2
and concentrated sul-
ꢀ
ꢀ
2
О (about
0 ml). The product was extracted with CH Cl , the organic extract
2
2
compound 3 with classic oxidation mixture of H
trated sulphuric acid at 50e55 C. Compounds 8, 9, 10 and 12, 13, 14
2
O
2
and concen-
ꢀ
М
еОН. Yield 0.76 g (83%), white round-shaped
ꢀ
1
13
0
crystals, Dec 215 C. H NMR (DMSO‑d
6
, ppm):
155.43, 147.78, 136.35. IR (KBr) ṽ: 3459,
357, 3122, 3029, 2939, 2840, 2777, 2725, 2629, 2575, 2483, 1699,
641, 1622, 1503, 1450, 1408, 1392, 1187,1086, 1034, 996, 982, 883,
d
10.08 (s, 1H);
C
were prepared as described in our previous work. N,N -dinitro-
0
NMR (DMSO‑d
6
, ppm):
d
N,N -bis [5-(tetrazol)furazan-4-yl] methylene diamine (11) and
0
0
3
1
N,N -
dinitro-N,N -bis
[5-(tetrazol)furazan-4-yl]
ethylene
diamine(15) were obtained as maple solid by successfully
employing the same method of synthesis as compound 3;
ꢁ
1
3 7 3
516, 481, 419 cm . Elemental analysis (%) for C HN O (144.08):
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4
J. Zhang et al. / Journal of Molecular Structure xxx (xxxx) xxx
Fig. 2. Synthesis route of various compounds.
compound 15 could be recrystallized from the mixture of methanol
and water as white diamond crystals.
methylene protons in compound 11 were 6.69 and 4.98 ppm,
respectively, which are also similar to the reported data [33]. For
compound 15, the signals of H NMR spectra were 6.74 and
1
4
.74 ppm, which correspond to the tetrazole protons and ethylene
3
.2. Spectroscopy and X-ray crystallography
1
protons, respectively. The H NMR signals of ethylene group of 15
were slightly upshifted compared to methylene group of com-
pound11 which is because the ethylene group can provide more
electrons than methylene group. The C NMR signals of tetrazole
rings and furazan ring are similar (
The novel 15 was characterized by 1H and 13C NMR spectra; the
15
compounds 11 and 15 were further characterized using N NMR
spectra (Fig. 3, and Figs. S10eS12). The protons of compound 5 were
consistent with compound 2 and other reported data in the liter-
13
d
¼ 151.05, 148.93, and 145.86 for
compound 11;
d
¼ 152.60, 150.43, and 143.75 for compound 15) for
1
ature. The signals in the H NMR spectra of tetrazole protons and
Fig. 3. 15N NMR spectra of compounds 11 and 15.
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J. Zhang et al. / Journal of Molecular Structure xxx (xxxx) xxx
5
both the compounds 11 and 15. The signal of 13C NMR for the
methylene group of compound 11 was 67.29, which is different
ethyl group are nearly coplanar (torsion of N1eC1eC2eN5: 9.19 )
and the torsion (C2eC3eN7eN8) between nitramino and furazan
ꢀ
ꢀ
from that of compound 15 (
of compound 15 is poor in DMSO‑d
were obtained in d4-MeOH. The N NMR spectra of compounds 11
and 15 are also similar, only the position of N5 was slightly
different, this is because the ethylene group can provide more
electrons than methylene group.
d
¼ 51.78), this is because the solubility
ring was 63.69 . There are two kinds of hydrogen bonds extensively
13
6
, the C signals of compound 15
throughout the crystal. The first hydrogen bond of NeH/O with
bond length 1.717 Å where the hydrogen atom is from the tetrazole
ring while the oxygen atom is from molecular methanol. The sec-
ond hydrogen bond OeH/N of bond length 2.012 Å where the
hydrogen atom is from the methanol while the nitrogen atom is
from the tetrazole ring. As to crystal 13, it crystallized with
monoclinic (P21/n) symmetry with two molecules in each lattice
15
The light brown needle crystals of compound 5 were slowly
recrystallized from water. The compound 5 crystallized with
monoclinic (P 121/c1) symmetry with eight molecules in each
ꢁ3
cell (Z ¼ 2) and a density of 1.750 g cm at 150 K, its density in
ꢁ
3
ꢁ3
lattice cell (Z ¼ 8) and the density of 1.603 g cm at 296 K. The
room temperature is 1.68 g cm . The atoms in the furazan core and
atoms which from furazan ring, amino group, and hydrazine group
1,2,4-oxadiazole are nearly coplanar with a torsion angle close to
zero. The nitramine moieties in this crystal are also considerably
twisted to the furazan and 1,2,4-oxadiazole plane with torsion
ꢀ
are nearly coplanar accompanying torsions (N7eN6eC1eC2:4.79 ;
ꢀ
ꢀ
N5eN4eC3eC2:3.64 ; N5eN4eC3eN3:3.73 ) close to zero. An
intramolecular hydrogen bond formed between hydrogen atoms
connecting N6 and N4, which is repeated throughout the crystal.
ꢀ
angles 118.41 . After calculation of packing coefficient by MolInfo,
the packing coefficients of compounds 13 and 15 are 55.45% and
74.32%, respectively. It is clear that the packing mode of 15 is closer
than that of 13, which lead to a higher density of 15.
(Fig. 4a and b, and Figs. S6eS7).
The white block crystal 15 recrystallized slowly from the
mixture of H
2
O and methanol with triclinic (P ꢁ1) symmetry
having one compound 15 molecule and two methanol molecules in
3
.3. Physicochemical and energetic properties
each lattice cell (Z ¼ 1) (Fig. 4c and d, and Figs. S8eS9) and the
ꢁ3
density of 1.62 g cm at 296 K. It was put in infrared oven for 24 h,
in order to remove the methanol molecular exited in compounds
Thermal stability is one of the most vital physicochemical pa-
ꢁ
3
rameters of energetic compounds; hence, all the newly synthesized
compounds were measured at 5 C min in the nitrogen envi-
ronment (Table 1). The decomposition temperatures of compound
completely, and then its measured is 1.77 g cm at room temper-
ature by gas pycnometer. The crystal structure of 15 was symmet-
rical with two 3-nitramino-furazantetrazole anions bridged by
ethyl group. The furazan ring and the tetrazole ring for both sides of
ꢀ
ꢁ1
ꢀ
ꢀ
5
and 7 were 198.8 C and 215 C, respectively. Also, the decom-
position temperatures of compounds 11 and 15 were 149 and
Fig. 4. (a): Single-crystal X-ray structure of compound 5; (b): the package structure of compound 5 from the view of b-axis; (c): Single-crystal X-ray structure of compound 15; (d):
the package structure of compound 15 from the view of b-axis.
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6
J. Zhang et al. / Journal of Molecular Structure xxx (xxxx) xxx
Table 1
Physicochemical and detonation parameters of the synthesized compounds.
a
ꢀ
b
ꢀ
c
dd (g cmꢁ3
e
ꢁ1
ꢁ1
f(m sꢁ1
Pg(GPa)
22.63
h
i
Compound
T
m
( C)
T
d
( C)
N (%)
)
D
f
H [kJ mol (kJ g )]
v
D
)
IS (J)
FS (N)
2
4
5
7
9
169.4
58.31
38.3
62.4
53.6
41.2
50.8
54.9
39.8
49.0
53.1
18.5
32.6
37.8
1.60
e
246.4/1.71
327.1/1,79
352/2.24
8201
>40
>360
55
198.8
215
149
138
149
175
145
163
295
160
205
1.60
1.75
1.77
1.64
1.82
1.75
1.60
1.77
1.65
1.77
1.81
8090
8585
8182
8126
8874
8185
7914
8589
7459
8564
8748
22.44
30.55
27.70
25.3
33.86
27.9
23.3
30.51
23.5
>40
6
>360
112
240
>360
96
240
>360
144
353
60
120
124
115
96
142
128
97
486/2.91
586.2/1.44
810.7/2.10
1249.4/3.06
785.8/1.88
797.6/1.99
1239.8/2.94
55.7/0.25
27
>40
11
31
>40
17
15
3
1
1
1
1
1
0
1
3
4
5
j
TNT
81
j
PETN
RDX
141
ꢁ502.8/-1.59
31.3
34.9
j
79.2/0.36
7
120
a
Melting temperature.
b
c
d
e
f
ꢀ
ꢁ1
Thermal decomposition temperature (onset) under nitrogen gas (DSC, 5 C min ).
Nitrogen content.
Density measured by gas pycnometer (25 C).
Calculated heat of formation.
Detonation velocity.
Detonation pressure.
Impact sensitivity.
Friction sensitivity.
Ref [30e32].
ꢀ
g
h
i
j
ꢀ
1
63 C (Figs. S1eS5), respectively, which are similar to their
tetrazole ring, the enthalpies of formation of the ring-replaced
ꢁ
1
precursors.
The enthalpies of formation of all the resultant compounds were
calculated using isodesmic equations and G03 software program
29] (see Electronic Supplementary Information). Compound 4 has
the enthalpy of formation of 327.1 kJ mol /1.79 kJ g . As the oxa-
diazole ring was replaced by tetrazole ring, the enthalpy of for-
mation of compound 7 improved significantly up to 486 kJ mol
.91 kJ g . In the case of compounds 11 and 15, owing to a high
enthalpy of formation of tetrazole, their enthalpies of formation
reached up to 1249.4 kJ mol /3.06 kJ g
.94 kJ g , respectively. Additionally, their nitrogen contents were
improved to 54.90 and 53.08%, respectively, which are clearly
higher than their precursors and place them in the category of high
nitrogen content energetic materials.
compounds 11 and 15 were improved to 3.06 kJ mol
and
ꢁ
1
2.94 kJ mol , respectively, while the nitrogen content of these two
compounds reached up to 54.90% and 53.08%, respectively. The
detonation properties of the resultant two compounds were
[
ꢁ1
ꢁ1
ꢁ1
improved to 8874, 8589 m s and 33.86, 30.51 GPa, respectively,
showing comprehensive compared to the detonation properties of
RDX and PETN, and are higher than those of original compounds. 3-
nitro-4-tetrazolefurazan (7) has excellent energetic performance
relative to PETN and may act as a potential replacement for PETN.
To summarize, the ring replacement strategy was designed and
implemented successfully and offers fresh routes for the improve-
ment in properties of energetic materials.
ꢁ1
/
ꢁ
1
2
ꢁ
1
ꢁ1
ꢁ1
/
and 1239.8 kJ mol
ꢁ1
2
With the measured densities and calculated enthalpies of for-
mation in hand, the detonation properties of the synthesized
compounds were determined by EXPLO5 v6.01 version. We can
observe from Table 1 that the detonation velocity and pressure of
Author contributions
Jichuan Zhang and Guangxing Pan contribute equally to this
work, they performed the NMR, physicochemical and energetic
properties experiments. Jichuan Zhang, Jiaheng Zhang and
Guangxing Pan wrote the paper. Jun Yang, Jiaheng Zhang and Hai-
feng Huang performed the theoretical calculations. Jiaheng Zhang
and Jun Yang conceived and designed the project.
ꢁ
1
compound 7 were estimated to be 8585 m s
and 30.55 GPa,
respectively. A relatively simple synthesis route and excellent per-
formance make it comparable to PETN. Compound 5 can act as a
potential dication of energetic salt, although its density of
ꢁ
3
1
.60 g cm is lower than that of TNT, because of its higher heat of
formation, which also leads to markedly better detonation prop-
erties than TNT [30e32]. In the case of compounds 11 and 15, owing
to the higher heats of formation brought by tetrazole ring as
compared to their precursors, the detonation velocities and pres-
sure increased remarkably relative to those of compounds 9,10 and
Declaration of competing interest
The authors declare no competing interests.
ꢁ1
13,14, reaching to 8874, 8589 m s and 33.86, 30.51 GPa, respec-
tively, and showing comprehensive comparative to the detonation
properties of RDX and PETN, respectively. Hence, this ring
replacement strategy has opened novel avenues to improve prop-
erties of energetic compounds.
Acknowledgements
The authors acknowledge financial support from the Shenzhen
Science
and
Technology
Innovation
Committee
(JCYJ20151013162733704), and the Thousand Talents Plan (Youth).
4
. Conclusions
This work was also financially supported by National Natural Sci-
ence Foundation of China (NSFC, Grant. No. 21602241). X-ray single
crystal structure determinations have been deposited with the
Cambridge Crystallographic Data Centre with CCDC numbers
(1567538 and 1567536).
In this work, we employed ring replacement strategy to replace
the oxadiazole rings of the original compounds with tetrazole rings.
Due to the high heat of formation and high nitrogen content of
Please cite this article as: J. Zhang et al., The enhanced properties of energetic materials through ring replacement strategy, Journal of Molecular
Structure, https://doi.org/10.1016/j.molstruc.2019.127358

J. Zhang et al. / Journal of Molecular Structure xxx (xxxx) xxx
Di(nitramino)furazan, J. Am. Chem. Soc. 137 (2015) 15984e15987.
7
Appendix A. Supplementary data
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Supplementary data to this article can be found online at
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Structure, https://doi.org/10.1016/j.molstruc.2019.127358