Energetic salts based on 1-amino-1,2,3-triazole and 3-methyl-1-amino-1,2,3- triazole

Article abstract of DOI:10.1039/c1jm14322k

High-density energetic salts that contain nitrogen-rich anions and the 1-amino-1,2,3-triazole (ATZ) or 3-methyl-1-amino-1,2,3-triazole (MAT) cation were synthesized. All salts were fully characterized by IR spectroscopy, multinuclear (¹H, ¹³C) NMR spectroscopy, differential scanning calorimetry (DSC), and impact sensitivity. 1-Amino-1,2,3-triazolium 5-nitrotetrazolate, 3-methyl-1-amino-1,2,3-triazolium 5-nitrotetrazolate, and 3-methyl-1-amino-1,2,3-triazolium azotetrazolate crystallize in the triclinic space group P1, as determined by single-crystal X-ray diffraction. Their densities are 1.688, 1.588, and 1.550 g cm^-3, respectively. The measured densities of the other organic energetic salts range between 1.56 and 1.86 g cm^-3. The detonation pressure (P) values calculated for these salts range from 21.2 to 37.3 GPa, and the detonation velocities (D) range from 7239 to 9082 m s^-1, making the salts potentially energetic materials.

Full text of DOI:10.1039/c1jm14322k

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PAPER
Energetic salts based on 1-amino-1,2,3-triazole and 3-methyl-1-amino-1,2,3-
triazole†
*
Qiu-Han Lin, Yu-Chuan Li, Ya-Yu Li, Zhu Wang, Wei Liu, Cai Qi and Si-Ping Pang
Received 2nd September 2011, Accepted 10th October 2011
DOI: 10.1039/c1jm14322k
High-density energetic salts that contain nitrogen-rich anions and the 1-amino-1,2,3-triazole (ATZ) or
3-methyl-1-amino-1,2,3-triazole (MAT) cation were synthesized. All salts were fully characterized by
IR spectroscopy, multinuclear (1H, 13C) NMR spectroscopy, differential scanning calorimetry (DSC),
and impact sensitivity. 1-Amino-1,2,3-triazolium 5-nitrotetrazolate, 3-methyl-1-amino-1,2,3-
triazolium 5-nitrotetrazolate, and 3-methyl-1-amino-1,2,3-triazolium azotetrazolate crystallize in the
ꢀ
triclinic space group P1, as determined by single-crystal X-ray diffraction. Their densities are 1.688,
1.588, and 1.550 g cmꢀ3, respectively. The measured densities of the other organic energetic salts range
between 1.56 and 1.86 g cmꢀ3. The detonation pressure (P) values calculated for these salts range from
21.2 to 37.3 GPa, and the detonation velocities (D) range from 7239 to 9082 m sꢀ1, making the salts
potentially energetic materials.
protonated triazole cations paired with percholate, nitrate, or
dinitramide anions were initially synthesized.19,21
Introduction
As controllable storage systems for relatively large amounts of
chemical energy, energetic materials are widely applied in mili-
tary and industrial venues. In the last decade, a unique class of
high energetic compounds composed of nitrogen-containing
heterocyclic anions and/or cations has been developed to meet
the continuing need for improved energetic materials.1–5
Recently, salt-based molecules have been reported to display
attractive energetic properties because of special properties of
ionic compounds, such as lower vapor pressures and higher
densities compared with those of their atomically similar
nonionic analogues.6–14 The present research is mainly directed
toward the synthesis of new organic cations and anions, which
exhibit high safety, performance, density, and stability.
The incorporation of amino groups into a heterocyclic triazole
ring is one of the simplest routes for enhancing thermal
stability.22 The N-amino group behaves as an electron-with-
drawing group in these high-nitrogen heterocycles when forming
energetic salts. Many 4-amino-1,2,4-triazole and 1-methyl-4-
amino-1,2,4-triazole salts have already been reported.23–25
Meanwhile, salts based on 1,2,3-triazole series may possess more
positive heats of formation than do salts of 1,2,4-triazole series.
Studies on the chemistry and properties of energetic salts con-
taining the former are limited possibly because of the difficulty in
the purification of 1-amino-1,2,3-triazole. Although Drake
et al.26 reported the preparation of 3-methyl-1-amino-1,2,3-tri-
azolium nitrate, neither the detonation performance nor impact
sensitivity of the compounds were provided. A simplified process
for purification of 1-amino-1,2,3-triazole (ATZ) was developed
in our previous studies,27,28 then we investigated the energetic
salts based on ATZ.
Five-membered nitrogen-containing heterocycles are tradi-
tional sources of energetic materials; energetic salts based on C/N
heteroaromatic rings with high nitrogen content (such as triazole
and tetrazole) are at the forefront of high energy research.15–18
1H-1,2,4-Triazole, 4-amino-1,2,4-triazole, and 1H-1,2,3-triazole
were utilized to produce energetic ionic salts.19,20 1,2,3-Triazole
(272 kJ molꢀ1) and 1,2,4-triazole (109 kJ molꢀ1) have positive
heats of formation. Respectively, the salts comprising
ATZ may be protonated by strong mineral acids, an
approach that has been employed using classic energetic and
oxidizing anions, such as NO3ꢀ (a) (Scheme 1). ATZ can also be
quaternized at N-3 by reaction with equivalent amounts of
methyl iodides under neat conditions to produce 3-methyl-1-
amino-1,2,3-triazole (MAT). Compared with ATZ, MAT has
an extra methyl group. Particularly, the introduction of
a methyl group decreases the enthalpies of formation and
densities of such compounds, as well as desensitizes them. In the
present work, a series of high-nitrogen salts based on ATZ and
MAT were prepared and characterized. Their thermal stabili-
ties, detonation performance, and impact sensitivities were also
investigated.
State Key Laboratory of Explosion Science and Technology, School of
Materials Science
& Engineering, School of Life Science and
Technology, Beijing Institute of Technology, Beijing, P.R. China. E-mail:
pangsp@bit.edu.cn; Fax: +86-010-68913038
† Electronic supplementary information (ESI) available. CCDC
reference numbers 842816, 837299 and 837300. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c1jm14322k
666 | J. Mater. Chem., 2012, 22, 666–674
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Scheme 1 The anions we choose to pair with ATZ and MAT.
Results and discussion
Synthesis
As shown in Scheme 2, compounds 2 and 5 were prepared by
treating 1-amino-1,2,3-triazole with nitric acid and nitroform (d),
respectively. Given that 5-nitro-tetrazole (b) and 5-nitroimino-
tetrazole (c) (Scheme 1) are strong acids (c was characterized as
a dibasic acid with pKa values of 2.5 and 6.1),29 they can easily
protonate ATZ and form energetic nitrogen rich salts. We also
attempted to synthesize salt 6 by anion exchange between 1-
amino-1,2,3-triazolium sulfate and barium azotetrazolate or
anion exchange between 1-amino-1,2,3-triazolium hydrochloride
and silver azotetrazolate, but no desired product was formed
possibly because barium azotetrazolate or silver azotetrazolate
decomposes in acidic media.30
Scheme 3 Synthesis of the energy salts based on 3-methyl-1-amino-
1,2,3-triazole.
X-Ray crystallography
Compounds 3, 9, and 12 have been characterized using single
crystal X-ray structure determination. Data collection was
performed, and the unit cell was initially refined using APEX2
[v2.1-0].31 Data reduction was performed using SAINT [v7.34A]32
and XPREP [v2005/2].33 Corrections were applied for Lorentz,
polarization, and absorption effects using SADABS [v2004/1].34
Thestructures weresolvedandrefinedwith theaidof the programs
in the SHELXTL-plus [v6.12] system of programs.35 The full-
matrixleast-squaresrefinementonF2includedatomiccoordinates
and anisotropic thermal parameters for all non-H atoms. The H
atoms were included using a riding model. Table 1 summarizes
a selection of crystallographic data and refinement details. A
comparison of selected bond lengths and angles of compounds 3, 9
and 1-amino-1,2,3-triazole is given in Table 2. Selected bond
lengths and angles of compound 12 are given in Table 3.
Synthesis of the salts based on 3-methyl-1-amino-1,2,3-triazole
was performed according to Scheme 3. Compounds 8–11 were
prepared from the anion exchange of silver nitrate, silver 5-
nitrotetrazolate, silver 5-nitroiminotetrazolate and silver nitro-
formate with 1-amino-1,2,3-triazolium iodide in methanol.
Compound 12 was synthesized by anion exchange between 3-
methyl-1-amino-1,2,3-triazolium sulfate and barium azote-
trazolate in methanol.
As expected and found in several selected structures including
1-amino-1,2,3-triazole36 and its salts (3) and 3-methyl-1-amino-
1,2,3-triazole salts (9 and 12) discussed in this work, the triazole
ring is nearly planar, building an aromatic system, which can be
seen at the torsion angle of triazole ring between ꢀ0.247(192)ꢁ
and 0.611(131)ꢁ. The ring moieties of 3, 9 and 12 are in agreement
with the geometry observed for 1,2,3-triazole. The N–N bond
lengths in triazole ring of all structures of 3, 9, 12 lie between
ꢁ
1.314 and 1.334 A, which are typical values observed for the
1,2,3-triazole and their cations. We observed that, for the N–N
bond lengths, neutral compounds 1-amino-1,2,3-triazole (1.316
A)36 are slightly shorter than their salts and their methylated salts
ꢁ
ꢁ
(between 1.319 and 1.331 A).
Compound 3 crystallizes in the monoclinic space group P2(1)
with eight molecules in the unit cell (Fig. 1a), and has a density of
1.688 g cmꢀ3 (at 93(2) K) (Table 2). The C–N and N–N bonds of
the triazole ring are in a range similar to that observed in 1,2,3-
ꢁ
triazole. The N1–NH2 distances (1.3372 A) in compound 3 are
ꢁ
found to be shorter than the N1–NH2 distances (1.398 A) in
1-amino-1,2,3-triazole. The triazole ring [torsion angle N11–
N12–N13–C4 0.176(185)ꢁ] is planar. In contrast to this, the
amino unit [torsion angle N11–N12–N13–N14 ꢀ172.435(141)ꢁ]
Scheme 2 Synthesis of the energy salts based on 1-amino-1,2,3-triazole.
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Table 1 Crystal data and structure refinement details of 3, 9, and 12
Crystal
3
9
12
Empirical formula
Temperature/K
C3H5N9O2
93(2)
0.71073
Monoclinic
P2(1)
C4H7N9O2
93(2)
0.71073
Triclinic
ꢀ
P1
C8H14N18
133(2)
0.71073
Monoclinic
P2(1)/c
ꢁ
Wavelength/A
Crystal system
Space group
Unit cell dimensions
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
a ¼ 9.813(2) A, a ¼ 90
a ¼ 7.736(7) A, a ¼ 100.16(1)
a ¼ 5.681(16) A, a ¼ 90
ꢁ
ꢁ
ꢁ
b ¼ 10.246(2) A, b ¼ 90.405(4)
b ¼ 9.684(9) A, b ¼ 98.07(1)
b ¼ 7.222(2) A, b ¼ 97.778(4)
ꢁ
ꢁ
ꢁ
ꢁ
c ¼ 15.592(4) A, g ¼ 90
c ¼ 12.512(11) A, g ¼ 100.74(1)
c ¼ 19.096(6) A, g ¼ 90
3
ꢁ
Volume/A
1567.6(6)
8
1.688
891.8(14)
4
1.588
776.3(4)
2
1.550
Z
Calculated density/g cmꢀ3
Absorption coefficient/mmꢀ1
F(000)
0.142
816
0.131
440
0.117
376
Crystal size/mm
q range for data collection
Limiting indices
0.37 ꢃ 0.27 ꢃ 0.08
0.30 ꢃ 0.17 ꢃ 0.09
3.15ꢁ to 27.48ꢁ
ꢀ9 # h # 9, ꢀ11 # k # 8,
ꢀ14 # l # 14
6375/3388 [R(int) ¼ 0.0436]
0.40 ꢃ 0.33 ꢃ 0.20
3.15ꢁ to 27.48ꢁ
3.15ꢁ to 27.48ꢁ
ꢀ12 # h # 12, ꢀ12 # k # 13,
ꢀ15 # l # 20
ꢀ7 # h # 7, ꢀ9 # k # 8,
ꢀ24 # l # 24
Reflections collected/unique
Completeness to q ¼ 27.73
Max. and min. transmission
Reflections with I > 2s(I)
Goodness-of-fit on F2
Final R indices (I > 2s(I))
R indices (all data)
12 990/3774 [R(int) ¼ 0.0292]
5842/1760 [R(int) ¼ 0.0236]
99.2%
0.9887 and 0.9496
3160
0.998
R1 ¼ 0.0453, wR2 ¼ 0.0910
R1 ¼ 0.0538, wR2 ¼ 0.0956
842816
—
2052
0.999
—
1489
1.002
R1 ¼ 0.0472, wR2 ¼ 0.0995
R1 ¼ 0.0765, wR2 ¼ 0.1054
837299
R1 ¼ 0.0353, wR2 ¼ 0.0884
R1 ¼ 0.0450, wR2 ¼ 0.0935
837300
CCDC
ꢁ
ꢁ
Table 3 Selected bond lengths (A) and bond angles ( ) of compound 12
ꢁ
ꢁ
Table 2 Selected bond lengths (A) and bond angles ( ) of compounds 3,
9 and 1-amino-1,2,3-triazole(ATZ)
Bond lengths
N(1)–C(1)
N(1)–N(2)
N(2)–N(3)
N(3)–N(4)
N(4)–C(1)
N(5)–C(1)
N(5)–N(5)
1.3352
1.3373
1.3324
1.3414
1.3392
1.4059
1.2629
N(6)–C(3)
N(6)–N(7)
N(7)–N(8)
N(8)–N(9)
N(8)–C(2)
C(2)–C(3)
C(4)–N(6)
1.3374
1.3343
1.3141
1.3938
1.3471
1.3624
1.4602
3
9
ATZ
Bond lengths
N(1)–C(1)
N(1)–N(2)
N(2)–N(3)
N(3)–N(4)
N(4)–C(1)
N(5)–C(1)
N(5)–O(1)
N(5)–O(2)
C(3)–C(4)
C(3)–N(11)
N(11)–N(12)
N(12)–N(13)
N(13)–N(14)
N(13)–C(4)
Bond angles
1.3242
1.3346
1.3277
1.3417
1.3186
1.4426
1.2374
1.2169
1.3591
1.3433
1.3305
1.3156
1.3772
1.3590
1.3300
1.3419
1.3388
1.3511
1.3166
1.4472
1.228
1.2296
1.3693
1.3480
1.3190
1.3264
1.4038
1.3469
Bond angles
N(1)–N(2)–N(3)
N(2)–N(3)–N(4)
N(3)–N(4)–C(1)
N(4)–C(1)–N(1)
C(1)–N(1)–N(2)
N(1)–C(1)–N(5)
C(1)–N(5)–N(5)
109.175
109.761
103.892
112.616
104.555
118.962
112.845
C(2)–C(3)–N(6)
C(3)–N(6)–N(7)
N(6)–N(7)–N(8)
N(7)–N(8)–C(2)
N(8)–C(2)–C(3)
N(7)–N(8)–N(9)
N(7)–N(6)–C(4)
105.868
112.627
103.156
113.423
104.921
118.743
119.745
1.359
1.363
1.316
1.345
1.398
1.343
is slightly bent from the ring plane. The packing of 3 is also
characterized by a three-dimensional network. The packing
structure of 3 is shown in Fig. 1b.
C(1)–N(1)–N(2)
N(1)–N(2)–N(3)
N(2)–N(3)–N(4)
N(3)–N(4)–C(1)
N(1)–C(1)–N(4)
N(5)–C(1)–N(4)
O(2)–N(5)–C(1)
O(2)–N(5)–O(1)
C(4)–C(3)–N(11)
C(3)–N(11)–N(12)
N(11)–N(12)–N(13)
N(12)–N(13)–C(4)
N(13)–C(4)–C(3)
N(12)–N(13)–N(14)
N(13)–N(14)–H(14A)
N(13)–N(14)–H(14B)
103.629
109.065
109.969
102.900
114.435
123.875
118.638
124.952
106.273
112.454
103.458
113.244
104.571
119.091
107.824
110.084
102.744
109.711
109.237
102.947
115.358
122.175
117.108
124.480
105.631
113.024
103.211
113.468
104.655
121.441
107.497
107.483
The colorless crystals of 9 were grown by slow evaporation of
a diethyl ether solution. The unit cell of 9 crystallizes with
a calculated density of 1.588 g cmꢀ3 (93(2) K) in the triclinic space
ꢀ
group P1. The triazole ring of 9 is nearly planar and four similar
ꢁ
bond lengths are observed [N11–N12 1.319 A, N12–N13 1.326
ꢁ
ꢁ
ꢁ
A, N11–C3 1.348 A, N13–C4 1.347 A] and shows the delocal-
ization of the positive charge from the ring (Fig. 2). The main
change observed is the bond length of C3–C4 which corresponds
to the N3.
Nitrogen atom undergoes protonation in 1-amino-1,2,3-tri-
azole. Protonation results in a shortening of the C3–N11
ꢁ
distances (ꢂ0.015 A) and a lengthening of the C3–C4 bond
668 | J. Mater. Chem., 2012, 22, 666–674
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Fig. 2 (a) View of the molecular unit of 9. Thermal ellipsoids represent
50% probability. (b) Unit cell packing of 9 (MAT.NT 1-amino-1,2,3-
triazolium 5-nitrotetrazolate).
Physicochemical properties
Fig. 1 (a) View of the molecular unit of 3. Thermal ellipsoids represent
50% probability. (b) Unit cell packing of 3 (ATZ.NT 1-amino-1,2,3-tri-
azolium 5-nitrotetrazolate).
The melting points, thermochemical, and energetic data of 2–5
and 8–12 are summarized in Table 4. The melting points of these
ꢁ
new compounds (except for 4, 5, and 12) are below 100 C, the
accepted boundary between ionic liquids and melting salts.38 The
ꢁ
(ꢂ0.01 A). These distances are considerably longer than C3–C4
ꢁ
double bonds (1.326 A) but significantly shorter than the N13–
ꢁ
N14 (1.404 A) single bond. The amino and methyl unit lies in the
plane of the triazole ring as clearly shown by the N11–N12–N13–
N15 torsion angle of ꢀ177.43ꢁ and N13–N12–N11–C5 torsion
angle of 179.27ꢁ.
3-Methyl-1-amino-1,2,3-triazolium azotetrazolate 12 crystal-
lizes in the monoclinic crystal system in the space group P2(1)/c.
By including two molecular moieties in the unit cell, the calcu-
lated density is 1.550 g cmꢀ3. In general, the azo-tetrazolate
anions have geometries found in dihydrazinium azotetrazolate.37
Two tetrazole anions in the molecule exhibit coplanar geometry
with torsion angle C1–N5–N5–C1 180.00 (99)ꢁ. This cation is
nearly planar with torsion angle (N6–N7–N8–C2 ꢀ0.694(131)ꢁ)
and C–N and N–N bond lengths observed between 1.314 and
ꢁ
1.347 A (Fig. 3a). The negative charge is delocalized as supported
ꢁ
by similar C–N bond lengths C1–N1 ¼ 1.335(16) A, C1–N4
ꢁ
1.339(17) A and a planar system, and shows the delocalization of
the negative charge from the ring (Fig. 3a). Delocalization results
in a shortening of the N5–N5 distances. The distances are
ꢁ
considerably longer than N–N double bonds (1.232 A) but
ꢁ
significantly shorter than the N8–N9 (1.3938 A) single bond. The
Fig. 3 (a) View of the molecular unit of 12. Thermal ellipsoids represent
50% probability. (b) Unit cell packing of 12 (MAT.NT 1-amino-1,2,3-
triazolium 5-nitrotetrazolate).
packing structure of 12 is shown in Fig. 3b.
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Table 4 The physicochemical properties of 2–5 and 8–12 compared with TNT and RDX
Salt
Tm
OBe
Nf
DHocg
DHoah
DHoLi
DHof j/DHomk
Pl
Dm
ISn
a
b
Td
c
dc /dm
d
2
3
4
5
8
9
10
11
12
98.6
98.8
112.2
132.6
87.0
92.6
89.6
82.2
177.7
200.8
162.8
152.3
241.8
224.3
197
176.5
182.9
295
1.64/1.75
1.69/1.69
1.60/1.72
1.77/1.86
1.59/1.59
1.59/1.59
1.56/1.57
1.57/1.70
1.56/1.56
1.65
ꢀ16
ꢀ28
ꢀ43
47.6
63.3
65.8
41.7
43.5
59.2
60.1
39.4
69.6
18.5
37.8
972.1
972.1
972.1
972.1
951.6
951.6
951.6
951.6
951.6
—
ꢀ306.4
112.8
386.1
ꢀ247.7
ꢀ306.4
112.8 (ref. 60)
386.1
546.5
507.8
1287.6
492.1
528.8
490.4
1232.4
469.8
1184.0
—
119.3/0.81
577.1/2.90
1042.7/3.50
232.3/0.99
116.4/0.72
574.0/2.70
1056.8/3.24
234.1/0.94
1463.7/4.04
95.3/0.42
30.5
27.0
28.9
37.3
23.7
23.1
23.0
29.7
21.2
19.5
35.2
8366
7948
8187
9082
7596
7509
7524
8320
7239
6881
8977
21.5
3.1
5.7
—
28.9
3.4
6.9
—
3.4
ꢀ35
ꢀ41
ꢀ59
ꢀ10
ꢀ66
ꢀ25
0
ꢀ247.7
144.6
80.4
204.1
744.6
—
—
28.2
15
7.4
TNT61
RDX62
230
1.82
—
—
83.8/0.38
a
b
c
d
Melting point (ꢁC). Decomposition temperature (ꢁC). Calculated density (g cmꢀ3). Measured density (g cmꢀ3), using an ULTRAPYC 1200,
Automatic Density Analyzer. CO oxygen balance (OB) is an index of the deficiency or excess of oxygen in a compound required to convert all C
e
into CO and all H into H2O. For a compound with the molecular formula of CaHbNcOd (without crystal water), OB (%) ¼1600[(d ꢀ a ꢀ b/2)/Mw],
f
g
h
Mw molecular weight of the salt. Nitrogen content (%). Molar enthalpy of the formation of cation (kJ molꢀ1). Molar enthalpy of the formation
i
j
k
of anion (kJ molꢀ1). Lattice energy (kJ molꢀ1). Molar enthalpy of the formation of salt (kJ molꢀ1). Enthalpy of the formation of salt per gram
(kJ gꢀ1). l Detonation pressure (GPa). m Detonation velocity (m sꢀ1). Impact sensitivity (J).
n
low melting point salts show good liquid state characteristics
(compounds 2, 3, 8, 9, 10, and 11; Table 4). Ionic liquids 2–5 have
a similar 1-amino-1,2,3-triazolium cation and compounds 8–12
have a similar 3-methyl-1-amino-1,2,3-triazolium cation. Nitro-
tetrazolate samples 3 and 9 melt at 98.8 and 92.6 ꢁC, respectively.
For the salts with the same cations, the melting points of MAT
ionic liquids (8–12) are generally lower than those of ATZ ionic
liquids (2–5). The methyl group clearly helps to decrease the
melting point. In comparison with 1,2,3-triazolium nitrate (Mp
110 ꢁC),19 1-amino-1,2,3-triazolium nitrate has lower melting
point (98.8 ꢁC). Therefore, incorporating amino groups as well as
a methyl group into a heterocyclic triazole ring can decrease
melting point.
the salts can be calculated with good accuracy (including the heat
of formation of the cation and anion, and the lattice energy of
salts).41–45 The heats of formation of these MAT and ATZ anions
were calculated. Calculations were carried out using the
Gaussian 03 suite of programs.46 The geometric optimization of
the structures and frequency analyses were carried out using B3-
LYP functional with the 6-31 + G** basis set,47 and single-point
energies were calculated at the MP2/6-311++G** level. All of the
optimized structures were characterized to be true local energy
minima on the potential-energy surface without imaginary
frequencies.
Based on the Born–Haber energy cycle, heats of formation of
ionic salts can be simplified by eqn (1):
Except for compound 5, which begins to decompose at 152.3
ꢁC, the decomposition temperatures of the other salts are higher
than 160 ꢁC, showing that they are thermally stable energetic
materials.39 Their possible liquid ranges may reach 100 ꢁC. In
comparison with 1,2,3-triazolium nitrate, 1-amino-1,2,3-tri-
azolium nitrate is more thermally stable (the decomposition
temperature of 1,2,3-triazolium nitrate iꢁs 125 ꢁC19 and that of 1-
amino-1,2,3-triazolium nitrate is 177.7 C). These indicate that
incorporating amino groups into a heterocyclic triazole ring can
also enhance thermal stability.
DHof (ionic salts, 298 K) ¼ SDHfo (cation, 298 K) + SDHof (anion,
298 K) ꢀ DHL
(1)
in which DHof is the lattice energy of the ionic salts, which could
be predicted by using the formula suggested by Jenkins et al.48
DHL ¼ UPOT + [p(nM/2 ꢀ 2) + q(nX/2 ꢀ 2)]RT
(2)
in which nM and nX depend on the nature of the ions Mp+ and
Xqꢀ, respectively, and are equal to 3 for monoatomic ions, 5 for
linear polyatomic ions, and 6 for nonlinear polyatomic ions. The
equation for lattice potential energy Upot has the form [eqn (3)]:
One of the most important physical properties of a solid
energetic material is its density. The calculated and measured
densities are summarized in Table 4. The densities of the ATZ
and MAT salts range from 1.56 to 1.86 g cmꢀ3 while salt 5
exhibiting the highest value. The measured density of 3-methyl-1-
amino-1,2,3-triazolium nitrate is 1.59 g cmꢀ3 while that of 1-
UPOT (kJ molꢀ1) ¼ g(rm/Mm)1/3 + d
(3)
in which rm is the density (g cmꢀ3) and Mm is the chemical
formula mass of the ionic material (g), and the coefficients g (kJ
molꢀ1 cm) and d (kJ molꢀ1) are assigned literature values.48 The
heats of formation of the cations were computed by using iso-
desmic reactions.49 The heats of formation of the anion and the
parent ions in the isodesmic reactions were calculated from
protonation reactions (DHof (H+) ¼ 1528 kJ molꢀ1).49–51
methyl-4-amino-1,2,4-triazolium nitrate is 1.55 g cmꢀ3 23
The
.
physical densities of 1-amino-1,2,3-triazolium salts are also
higher than those of 4-amino-1,2,4-triazolium salts; for example,
the density of 4-amino-1,2,4-triazolium nitrate is 1.60 g cmꢀ3 19
whereas that of 1-amino-1,2,3-triazolium nitrate is 1.75 g cmꢀ3
,
.
The density of 1-amino-1,2,3-triazolium nitroformate (1.86 g
cmꢀ3) is higher than that of 4-amino-1,2,4-triazolium nitro-
The enthalpies of the isodesmic reactions (DHor298) were
obtained by combining the MP2/6-311++G** energy differences
for the reactions, the scaled zero-point energies (B3LYP/6-31 +
G**), and other thermal factors. The calculated heats of
formation are summarized in Table 4. Salt 12 has the highest
25
formate (1.62 g cmꢀ3
)
possibly because 1,2,3-triazole contains
more inherently energetic N–N bonds.28,40
The heat of formation is another important parameter in
evaluating the performance of energetic salts. This property of
670 | J. Mater. Chem., 2012, 22, 666–674
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value at 1463.7 kJ mo1ꢀ1. The calculated heat of formation of the
ATZ anion is 972.1 kJ molꢀ1 and that of the MAT anion is 951.6
kJ molꢀ1. All of the ATZ and MAT salts exhibit positive heats of
formation, with 12 having the highest at 4.04 kJ gꢀ1 (RDX: 0.42
kJ gꢀ1; HMX: 0.38 kJ gꢀ1). For salts with the same anions, the
ATZ salts show higher heats of formation than do the MAT salts
(e.g., 3, 577.1 kJ molꢀ1 versus 9, 574 kJ molꢀ1).
Experimental
Caution: although we experienced no difficulties in handling
these materials, with such high positive heats of formation some
could be unstable. Therefore, all of them should be treated with
care and with appropriate safety precautions.
General methods
The detonation parameters were calculated by Kamlet–Jacobs
(K–J) equations.40,49,52,53 Table 4 shows that for salts 2–5 and
8–12, the calculated detonation pressures (P) fall in the range
21.2–37.3 GPa, which is comparable to that of TNT (19.5 GPa)
and RDX (35.2 GPa). The detonation velocities (D) range from
7239 m sꢀ1 (comparable to TNT, 6881 m sꢀ1) to 9082 m sꢀ1
(comparable to RDX, 8977 m sꢀ1).
All materials were commercially available and used as received.
Melting point was determined using an XT4 microscope melting
point apparatus. IR spectra were recorded by using KBr pellets
for solids on a Bruker tensor 27 spectrometer. 1H and 13C NMR
spectra were recorded on a Bruker 400 MHz spectrometer
operating at 400 MHz, respectively, with [D6]-DMSO as the
locking solvent unless otherwise stated. 1H and 13C NMR
chemical shifts are reported in ppm relative to TMS. DSC
measurements were performed on a TA-DSC Q2000 calorimeter
equipped with an Autocool accessory, and calibrated by usꢁing
indium. Measurements were carried out by heating from 50 C.
Densities were measured by using an Automatic Density
Analyzer, ULTRAPYC 1200. Detonation pressure and velocity
were predicted by the Kamlet–Jacobs equations. Computations
were performed by using the Gaussian 03 (Revision D.01) suites
of programs.46 We used the B3LYP/6-31G** method to calculate
the molecular volumes for the energetic triazolium salts. The
volume of each ion was defined as inside a contour of 0.001
electrons bohrꢀ3 density that was evaluated using a Monte Carlo
integration. The geometric optimization and the frequency
analyses were carried out using B3LYP functional analyses with
the 6-311 + G** basis set.47 Single energy points were calculated
at the MP2/6-311++G** level. All of the optimized structures
were characterized to be true local energy minima on the
potential energy surface without imaginary frequencies.
Sensitivity deserves closer attention by researchers because this
is closely linked with the safety of handling and applying
explosives. In the present study, impact sensitivity was tested on
a type 12 tooling according to the ‘‘up and down’’ method. Listed
in Table 4 are the impact sensitivities of sensitive compounds 3, 4,
9, and 10 (ranging between 3 and 6 J) as well as those of relatively
less sensitive compounds 2, 8, and 12 (between 20 and 30 J).
Because of the extremely deliquescent nature of compounds 5
and 11, the sensitivity tests could not be carried out with accuracy
given that water is extremely efficient at reducing the sensitivity
of energetic materials. The properties of the new ATZ and MAT
salts were compared; ATZ salts have superior detonation prop-
erties because methyl groups have a significant negative effect on
density. Incorporating methyl groups into 1-amino-1,2,3-triazole
rings can also lead to enhanced thermal stability and lower
impact sensitivity compared with that observed for 1-amino-
1,2,3-triazolium salts.
These ATZ and MAT compounds have high nitrogen content,
some of them exceeding 50% and reaching as high as 60%. Pol-
ynitrogen compounds are of significant interest as high-energy
materials for propulsion or explosive applications.54–59 In the
past several years, a large number of salts with polyazide cations
have presented considerable competitiveness as materials with
the highest nitrogen content.3,54–59 Compared with such
compounds, however, the ATZ and MAT salts have superior
thermal stabilities, suggesting promise for practical applications.
X-Ray crystallography
Crystals suitable for X-ray crystallographic analysis were
obtained as mentioned above. The crystal structure was deter-
mined by a Rigaku RAXIS IP diffractometer and SHELXTL
crystallographic software package of molecular structure. The
single crystals of compounds 3, 9, and 12 were mounted on
a Rigaku RAXIS RAPID IP diffractometer equipped with
Conclusions
ꢁ
a graphite-monochromatized MoKa radiation (l ¼ 0.71073 A).
A family of energetic salts based on nitrogen-rich anions and the
ATZ or MAT cation were prepared and fully characterized. The
structures of 3, 9, and 12 were confirmed by single-crystal X-ray
diffraction, which showed that there are extensive hydrogen-
bonding interactions between the cation and anion in these salts.
The densities of the ATZ and MAT salts, measured with an auto-
matic density analyzer (ULTRAPYC 1200), fall within the range
1.56(12) to 1.86 g cmꢀ3 (5), which places them in a class of relatively
dense compounds. Using K–J equations, we calculated their
detonationpressures andvelocities;these fallin the range 21.2–37.3
GPa and 7239–9082 m sꢀ1, respectively. Salt 5, with a detonation
pressure and velocity of 37.3 GPa and 9082 m sꢀ1, is comparable to
HMX(35.2GPaand8977 msꢀ1).Exceptfor theimpactsensitivities
of 5 and 11, those of the ATZ and MAT salts range from 3 to 30 J.
Based on rather high detonation properties and superior stabilities,
the ATZ and MAT salts have potential as energetic materials.
Data were collected by the u scan technique. The structure was
solved by direct methods with SHELXS-97 and expanded by
using the Fourier technique. The non-hydrogen atoms were
refined anisotropically. The hydrogen atom was determined with
theoretical calculations and refined with an isotropic vibration
factor.
1-Amino-1,2,3-triazole (1)
In a 500 mL round-bottom flask equipped with an over-head
stirrer, 14.46 g (168 mmol) of glyoxal bishydrazone was dispersed
in 225 mL acetonitrile at 20 ꢁC. Manganese dioxide 30.00 g (348
mmol) was added portion-wise over a few minutes to the vigor-
ously stirred solution. The reaction was stirred for 40 min while
additional manganese dioxide 20.00 g (232 mmol) was added.
Thin layer chromatography revealed through a plug of Celite.
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The filtrate was stripped down under reduced pressure leaving
a viscous oil that was sublimed, yielding 12.30 g (88%) of highly
pure 1-amino-1,2,3-triazole (yield: 79.8%). Mp 49–50 ꢁC; IR
(KBr) n: 3292, 3123, 1624, 1482, 1319, 1224, 1171 cmꢀ1; 1H NMR
3-Methyl-1-amino-1,2,3-triazolium iodide (7)
1-Amino-1,2,3-triazole 5.00 g (59.5 mmoles) was dissolved and
stirred vigorously in 100 mL of acetonitrile at 20 ꢁC, whereupon
methyl iodide 50 g (352 mmoles) was added. The reaction was
stirred in darkness, being periodically monitored by thin layer
chromatography until all 1-amino-1,2,3-triazole was consumed.
As the reaction progressed, white crystals of 1-amino-3-methyl-
1,2,3-triazolium iodide precipitated. The product salt was filtered
and washed with several aliquots (120 mL total) of diethyl ether.
The mother liquor was concentrated by distillation under
reduced pressure resulting in a second crop of crystals that were
filtered, washed with diethyl ether combined with first crop and
dried under high vacuum, resulting in a good yield 12.1 g (93%)
of 1-amino-3-methyl-1,2,3-triazolium iodide. Mp 146–147 ꢁC; 1H
NMR (DMSO-d6) d: 8.71 (s, 1H), 8.76 (s, 1H), 8.27 (s, 2H), 4.23
ppm (s, 3H); 13C NMR (DMSO-d6) d: 131.4, 126.9, 39.7 ppm.
Anal. calcd for C3H7N4I: C 15.94, H 3.12, N 24.79; found: C
16.22, H 3.20, N 24.66%.
(acetonitrile-d6) d: 7.65 (s, 1H), 7.56 (s, 1H), 5.97 ppm (s, 2H); 13
C
NMR (acetonitrile-d6) d: 132.2, 124.0 ppm; Anal. calcd for
C2H4N4: C 28.57, H 4.80, N 66.64; found C 28.56, H 4.75, N
67.07%.
1-Amino-1,2,3-triazolium nitrate (2)
Acetonitrile (20 mL) was mixed with 1-amino-1,2,3-triazole
(1.72 g, 20 mmol) and nitric acid (30 wt%, 4.2 g, 30 mmol). The
mixture was stirred for 30 min at room temperature; the solvent
was evacuated under vacuum to produce a white solid (2) (2.56
g), 87% yield. Mp 98.6 ꢁC; IR (KBr): 3297, 3166, 2823, 2703,
1614, 1572, 1443, 1384, 1311, 1163, 1119, 1089, 1037, 932, 791,
1
691, 629 cmꢀ1; H NMR (DMSO-d6): d: 8.12 (s, 1H), 7.72 (s,
1H), 9.7 ppm (s, 3H); 13C NMR (DMSO-d6) d: 132.44, 124.61
ppm.
3-Methyl-1-amino-1,2,3-triazolium nitrate (8)
Compound 7 (2.26 g, 10 mmol) was dissolved in 15 mL distilled
water. While stirring, a solution of 1.72 g (10 mmol) of silver
nitrate in 10 mL distilled water was added dropwise. The pale
yellow suspension was stirred for 30 min, filtered, and rinsed with
10 mL distilled water. The solvent was removed under reduced
pressure to produce a white solid (8) at 91% yield (1.47 g). Mp
87.0 ꢁC; IR (KBr): 3151, 3070, 3014, 2935, 1762, 1629, 1538,
1485, 1386, 1323, 1241, 1188, 1081, 1050, 987, 825, 815, 713, 626
1-Amino-1,2,3-triazolium 5-nitro-tetrazolate (3)
A 50 mL beaker was charged with 1-amino-1,2,3-triazole (0.50 g,
6 mmol), ether (20 mL), and 5-nitrotetrazole (0.68 g, 6 mmol).
The mixture was stirred for 30 min at room temperature. The
solvent was evacuated under vacuum to produce a white solid (3)
ꢁ
in 97% yield (1.15 g). Mp 98.8 C; IR (KBr): 3427, 3281, 3155,
3119, 1633, 1540, 1446, 1420, 1318, 1188, 1168, 1029, 924, 837,
800, 670 cmꢀ1; 1H NMR (DMSO-d6): d: 8.75 (s, 1H), 8.58 (s, 1H),
8.28 (s, 1H), 4.23 ppm (s, 2H); 13C NMR (DMSO-d6) d: 185.24,
131.98, 127.32 ppm.
cmꢀ1; H NMR (DMSO-d6) d: 4.21 (s, 3H), 8.29 (s, 2H), 8.60
(s, 1H), 8.75 ppm (s, 1H); 13C NMR (DMSO-d6) d: 133.45, 126.93
1
ppm.
1-Amino-1,2,3-triazolium 5-nitroiminotetrazolate (4)
3-Methyl-1-amino-1,2,3-triazolium 5-nitro-tetrazolate (9)
5-Nitroiminotetrazole (390 mg, 3 mmol) was dissolved in 20 mL
ether, and 1-amino-1,2,3-triazole (504 mg, 6 mmol) was added to
the solution. The mixture was stirred for 60 min at room
temperature. After evaporation of the ether in vacuum, a poorly
water-soluble white powder was obtained, which could be
recrystallized from methanol to produce 861 mg of (2.89 mmol,
Silver 5-nitro-tetrazolate (2.44 g, 11 mmol) was added to a solu-
tion of 2.26 g (10 mmol) of compound 7 dissolved in 70 mL
distilled water. The solution was stirred for 2 h, filtered in the
dark, and then rinsed with 25 mL distilled water. The resulting
solid was recrystallized from methanol, yielding 1.81 g of 9 at
91%. Mp 92.6 ꢁC; IR (KBr): 3284, 3260, 3166, 3153, 3024, 2838,
1620, 1538, 1438, 1417, 1373, 1316, 1266, 1229, 1200, 1158, 1095,
1023, 993, 839, 802, 672, 630, 548 cmꢀ1; 1H NMR (DMSO-d6) d:
8.76 (s, 1H), 8.62 (s, 1H), 8.30 (s, 2H), 4.23 ppm (s, 3H); 13C
NMR (DMSO-d6) d: 188.08, 132.01, 127.32, 42.37 ppm.
ꢁ
96% yield) 4. Mp 112.2 C; IR (KBr): 3279, 3189, 3151, 3097,
2986, 1614, 2886, 2842, 2750, 1535, 1489, 1433, 1389, 1348, 1325,
1230, 1157, 1091, 1029, 932, 867, 809, 690 cmꢀ1 1H NMR
;
(acetone-d6) d: 7.23 (s, 6H), 7.75 (s, 2H), 7.87 ppm (s, 2H); 13C
NMR (DMSO-d6) d: 179.32, 132.51, 120.76 ppm.
3-Methyl-1-amino-1,2,3-triazolium 5-nitroiminotetrazolate (10)
1-Amino-1,2,3-triazolium nitroformate (5)
A mixture of compound 7 (2.26 g, 10 mmol) and silver 5-nitro-
iminotetrazolate (10 mmol) in water (70 mL) was stirred for 60
min at room temperature. The AgI was filtered and rinsed with
25 mL distilled water. The clear filtrate was evaporated to
dryness under reduced pressureꢁto produce a pale yellow solid
product, at 88% yield. Mp 89.6 C; IR (KBr): 3417, 3318, 3150,
3124, 3070, 3014, 1619, 1537, 1485, 1399, 1300, 1241, 1222, 1188,
A 50 mL beaker was charged with 1-amino-1,2,3-triazole (0.50 g,
6 mmol), methanol (20 mL), and nitroform (0.39 g, 3 mmol). The
mixture was stirred for 30 min at room temperature. The solvent
was evacuated under vacuum to yield a yellow solid, which could
be recrystallized from methanol to produce compound 5 at 89%
ꢁ
yield (0.87 g). Mp 132.6 C; IR (KBr): 3407, 3252, 3142, 2807,
1
1621, 1547, 1465, 1403, 1192, 1084, 1050, 1032, 795, 697, 601, 509
1
1140, 1081, 1028, 986, 816, 763, 730, 633, 483 cmꢀ1; H NMR
cmꢀ1; H NMR (acetone-d6) d: 9.21 (s, 3H), 8.14 (s, 1H), 8.09
(DMSO-d6) d: 8.32 (s, 6H), 8.13 (s, 2H), 7.82 (s, 2H), 4.52 ppm
(s, 3H, CH3); 13C NMR (DMSO-d6) d: 182.27, 133.46, 126.27,
42.62 ppm.
ppm (s, 1H); 13C NMR (DMSO-d6): d: 150.36, 130.83, 125.31
ppm.
672 | J. Mater. Chem., 2012, 22, 666–674
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17 G. H. Tao, Y. Guo, D. A. Parrish and J. M. Shreeve, J. Mater. Chem.,
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Compound 7 (1356 mg, 6 mmol) was dissolved in 20 mL meth-
anol. While stirring, a solution of 1548 mg (6 mmol) of silver
nitroformate dissolved in 10 mL methanol was added dropwise.
The pale yellow suspension was stirred for 30 min, filtered, and
then rinsed with 20 mL methanol. The yellow solvent was
removed under reduced pressure to provide a yellow solid (11) at
82% yield (1.22 g). Mp 82.2 ꢁC; IR (KBr): 3178, 3152, 3124, 3105,
3070, 3015, 2865, 1697, 1630, 1537, 1513, 1422, 1384, 1323, 1279,
1147, 1107, 984, 815, 794, 733, 631, 483 cmꢀ1; 1H NMR (DMSO-
d6) d: 9.10 (s, 2H), 8.63 (s, 1H), 8.50 (s, 1H), 4.23 ppm (s, 3H); 13
C
NMR (DMSO-d6) d: 150.53, 131.68, 127.36, 49.01 ppm.
25 Y. G. Huang, H. X. Gao, B. Twamley and J. M. Shreeve, Eur. J.
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A mixture of 3-methyl-1-amino-1,2,3-triazolium sulfate salt (1.47
g, 5 mmol) and barium azotetrazole (1.81 g, 6 mmol) in methanol
(100 mL) was stirred at room temperature. BaSO4 was filtered and
rinsed with 25 mL methanol. The clear filtrate was evaporated to
dryness under reduced pressure to obtain a yellow solid product at
90% yield. Mp 144.6 ꢁC; IR (KBr) n: 3426, 3248, 3148, 3124, 3063,
2930, 2808, 1627, 1548, 1486, 1389, 1315, 1250, 1196, 1180, 1106,
1029, 800, 729, 628, 560, 482 cmꢀ1; 1H NMR (DMSO-d6) d: 8.77 (s,
28 Y. C. Li, C. Qi, S. H. Li, H. J. Zhan, C. H. Sun, Y. Z. Yu and
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31 APEX2 v2.1 0, Bruker AXS Inc., Madison, Wisconsin, USA, 2006.
32 SAINT v7.34 A, Bruker AXS Inc., Madison, Wisconsin, USA, 2005.
33 XPREP v2005/2, Bruker AXS Inc., Madison, Wisconsin, USA, 2004.
34 SADABS v2004/1, Bruker AXS Inc., Madison, Wisconsin, USA,
2004.
1H), 8.62 (s, 1H), 8.32 (s, 2H, NH2), 4.22 ppm (s, 3H, CH3); 13
C
35 SHELXTL v6.12, Bruker AXS Inc., Madison, Wisconsin, USA, 2000.
36 G. Kaplan, G. Drake, K. Tollison, L. Hall and T. Hawkins, J.
Heterocycl. Chem., 2005, 42, 19–27.
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37 A. Hammerl, T. M. Klapotke, H. Noth, M. Warchhold, G. Holl,
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38 P. Wasserscheid and T. Welton, Ionic Liquids in Synthesis, Wiley-
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Acknowledgements
This work was supported by the Program for New Century
Excellent Talents in University no. NCET-09-0046 and the
National Natural Science Foundation of China under Grant no.
11176004.
40 C. Qi, S. H. Li, Y. C. Li, Y. Wang, X. K. Chen and S. P. Pang, J.
Mater. Chem., 2011, 21, 3221–3225.
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