Green Energetic Nitrogen-Rich Salts of 1,1′-Dinitramino-5,5′-bistetrazolate

Article abstract of DOI:10.1002/chem.201702759

A series of nitrogen-rich energetic salts of 1,1′-dinitramino-5,5′-bistetrazolate (DNABT) guanidinium (1), aminoguanidinium (2), diaminoguanidinium (3), triaminoguanidinium (4), diaminouronium (5), 3,4-diamino-1,2,4-triazolium (6), and ethylenediammonium (7) was synthesized by a metathesis strategy and characterized by elemental analysis, mass spectrometry, and IR spectroscopy as well as single-crystal X-ray diffraction and differential scanning calorimetry (DSC). The natural bond orbitals (NBOs) and electrostatic potentials (ESPs) were further computed for a better understanding of the structures of the DNABT molecule. The heats of formation were calculated based on the Born–Haber energy cycle. The detonation parameters were evaluated by using the EXPLO5 program, and the sensitivities were measured according to BAM standers. These new salts exhibit highly positive heats of formation (407.0–1377.9 kJ mol^?1) and good thermal stabilities (180–211 °C). Most of these compounds possess detonation velocities comparable to RDX and acceptable detonation pressures. The high volumes of explosion gases of the salts 3 and 4 (921 and 933 L kg^?1, respectively) further support their power as explosives. The enhancing performances, the fact of being free of metals, and the more moderate sensitivities than K₂DNABT, suggest that the salts 4 (D=8851 m s^?1, P=29.0 GPa), 5 (D=9053 m s^?1, P=32.3 GPa), and 6 (D=8835 m s^?1, P=30.2 GPa) might be potential environmentally friendly energetic materials.

Full text of DOI:10.1002/chem.201702759

A Journal of
Accepted Article
Title: Green Energetic Nitrogen-rich Salts of 1,1'-Dinitramino-5,5'-
Bistetrazolate
Authors: Piao He, Le Wu, Jinting Wu, Qianyou Wang, Zhimin Li,
Michael Gozin, and Jianguo Zhang
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To be cited as: Chem. Eur. J. 10.1002/chem.201702759
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Chemistry - A European Journal
10.1002/chem.201702759
Green Energetic Nitrogen-rich Salts of 1,1’-Dinitramino-5,5’-Bistetrazolate
a
a
a
a
b
c
*a
Piao He , Le Wu , Jinting Wu , Qianyou Wang, Zhimin Li , Michael Gozin , Jianguo Zhang
a
b
c
State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081 P. R. China
Department of Chemical and Biomolecular Engineering, The Hong Kong University of Science and Technology, Hong Kong, China.
School of Chemistry, Faculty of Exact Science, Tel Aviv University, Tel Aviv, 69978, Israel.
Abstract:
A series of nitrogen-rich energetic salts of 1,1’-dinitramino-5,5’-bistetrazolate (DNABT)
guanidinium (1), aminoguanidinium (2), diaminoguanidinium (3), triaminoguanidinium (4),
diaminouronium (5), 3,4-diamino-1,2,4-triazolium (6) and ethylenediammonium (7) were
synthesized by a metathesis strategy, and characterized by elemental analysis, MS and IR
spectroscopy, single crystal X-ray diffraction and differential scanning calorimetry (DSC). The
natural bond orbitals (NBO) and electrostatic potential (ESP) were further computed for a better
understanding of the structures for DNABT molecule. The heats of formation were calculated based
on the Born-Haber energy cycle. The detonation parameters were evaluated using the EXPLO5
program, and sensitivities were measured according to BAM standers. These new salts exhibit
-1
highly positive heats of formation (407.0 to 1377.9 kJ·mol ) and good thermal stabilities (180 to
11 °C). Most of these compounds possess detonation velocities comparable to RDX and
acceptable detonation pressures. The high volumes of explosion gases of salts 3 and 4 (921 and 933
2
-1
L·kg ) further support their power of explosives. Enhancing performances, free of metal and more
-1
moderate sensitivities than K DNABT, suggest salts 4 (D=8851 m·s , P=29.0 GPa), 5 (D=9053
2
-1
-1
m·s , P=32.3 GPa) and 6 (D=8835 m·s , P=30.2 GPa) might be for potential environmentally
friendly energetic materials.
Key words: energetic materials; nitrogen-rich salt; 1,1’-dinitramino-5,5’-bistetrazole; detonation
performance; sensitivities
*
Corresponding authors: Jianguo Zhang, Tel & Fax: +86 10 68918091.
E-mail: zjgbit@bit.edu.cn
1
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1
. Introduction
The research of Energetic Materials (EMs) encompassing explosives, propellants and
pyrotechnics is of both academic and general interest owing to their continuously growing
[
1-2]
applications.
Desirable characteristics for new EMs include increased performance, high stability,
ease and efficiency of synthesis, safe handling and transportation, environmental and toxicological
[
3-4]
acceptability.
However, the requirements of high energy and low sensitivity are often
contradictory. The approaches of achieving a workable balance between these two properties
[
5-9]
include co-crystals, metal organic frameworks and energetic salts.
Energetic salts have been proved to possess advantages over conventional nonionic molecules,
[10]
such as low vapor pressures, which eliminate the risk of exposure through inhalation. They also
mostly have a higher density and stability than their neutral analogues as a result of the high lattice
[
11]
energy. Compared with alkali metals as cations, nitrogen-rich cations are more popular because
[12]
of a potential hydrogen bond network and a high positive heat of formation. Additionally, their
properties could be readily optimized and improved via the judicious combination and the
independent modification of different cations and anions components. Versatile energetic ionic salts
have been well documented and potentially used in explosives, gas generators, smoke-free
pyrotechnic fuels, solid fuels in micro-propulsion system, effective precursors for carbon nitride
[
1, 13-19]
nanomaterials and pharmaceutical field.
Among the nitrogen-rich heterocycles, tetrazoles occupy an intermediate position on the
[20]
‘stability versus performance’ continuum,
thereby offer intriguing structural backbones for
design and construction of new high-energy density materials (HEDMs). The introduction of
hydroxyl or nitramino units into tetrazole chemistry is an effective strategy to synthesize highly
[
20-22]
energetic tetrazole derivatives.
A few typical examples are given in Scheme 1. Incorporating
the high energy groups into the bistetrazole could straightforwardly achieve an enhanced level in
detonation performance due to the significant improvement in high density and oxygen balance of
frames. 1,1’-Dinitramino-5,5’-bistetrazole (DNABT) was shown to be a promising building block
in the development of new HEDMs. Klapötke et al firstly reported new primary explosive
[
21]
[22]
potassium 1,1’-dinitramino-5,5’-bistetrazolate (K DNABT)
and its neutral compound.
2
However, they are extremely sensitive to external stimuli (IS < 1 J, FS ≤1 N, ESD = 0.003 J),
which might hinder their practical applications.
2
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10.1002/chem.201702759
NO2
NO2
OH
HN
N
HN
N
OH
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
HO
NH
HO
O2N
NH
O N
2
N,N'-(Diazene-1,2-diylbis-
5
,5'-(Diazene-1,2-diyl)- [5,5'-Bitetrazole]-
1H-tetrazole-5,1-diyl))dinitramide N,N'-(1H,1'H-[5,5'-bitetrazole]-
bis(1H-tetrazol-1-ol)
1,1'-diol
(
1
,1'-diyl)-dinitramide
DNABT
Scheme 1. Selected tetrazoles substituted with hydroxyl or nitramino moieties.
Continuing our efforts in seeking new eco-friendly energetic materials with good performance
and stabilities, we combined the nitramino-functionalized tetrozole anion and abundant
nitrogen-rich cations. A new series of DNABT-based energetic salts were prepared to adjust
sensitivity and performance values (Scheme 2). Obtained compounds were comprehensively
characterized and their physicochemical and energetic properties were investigated. Density
functional theory (DFT) calculation was also performed to assist in the understanding of their
unique structures and properties.
Scheme 2. Versatile structures and properties of energetic ionic salts.
2
. Results and Discussion
2
.1 Synthesis
Potassium 1,1’-dinitramino-5,5’-bistetrazolate (K DNABT) was obtained in six
2
synthetic steps from commercially available methyl carbazate (Scheme 3). The reaction with
glyoxal results in condensation product, and subsequent chlorination with NCS
(
N-chlorosuccinimide) offers the corresponding chloride. Substitution with sodium azide
affords the diazide, then cyclized under acidic conditions (HCl gas in diethyl ether) to form
3
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N-methoxycarbonyl protected DNABT. The pivotal nitration is gently performed with N O5
2
in dry acetonitrile below 0 °C, then quenching with an alkaline aqueous KOH precipitates
dipotassium K DNABT. The silver salt was prepared by reacting with a solution of AgNO3
2
and simultaneously the KNO including the dipotassium salt was removed as expected.
3
The preparation of these new salts was achieved by straightforward metathesis reactions
that used DNABT silver salt with the corresponding nitrogen-rich hydrochlorides in water.
After filtration of the silver chloride and evaporation of the filtrate, these nitrogen-rich salts
based on DNABT anion were isolated in good yields, and elemental analysis indicated all
were pure. With regard to the stoichiometry, we anticipated the isolation of 2:1 compounds
so the 2:1 stoichiometry was used in the respective reactions in the cases of guanidinium (
aminoguanidinium ( ), diaminoguanidinium ( ), triaminoguanidinium ( ), diaminouronium
), and 3,4-diamino-1,2,4-triazolium salt ( ). We also observed the crystallization of
compound with a 1:1 stoichiometry and double protonated cations in the case of
ethylenediammonium salt ( ).
1),
2
3
4
(
5
6
7
1
.glyoxal
.NCS
NO2
K
N
NO2 Ag
N
NO2 Cation
N
N
N
N
N
2
Nitrogen-rich salt
hydrochloride
O
3.NaN3
N
AgNO3
N
N
N
N
N
N
N
N
N
N
N
H C
NH2
3
O
N
4
5
.HCl / Et O
.N O
N
- AgCl
N
N
H
2
N
N
N
N
N
N
N
2
5
N
Methyl carbazate
6.KOH
K
O N
2
Ag O N
O N
2
Cation
2
K DNABT
2
Ag2DNABT
Compounds 1 - 7
NH2
NH2
NH2
NH2
NH2
HN
Cation
NH2
H N
NH2
H N
NH2
2
2
H N
H2N
N
H
N
N
H
N
H
N
2
H
H
Guanidine (G)
1
Aminoguanidine (AG)
2
Diaminoguanidine (DAG)
3
Triaminoguanidine (TAG)
4
NH2
O
N
NH2
H N
2
NH3
NH3
N
N
H3N
NH
N
H
H
-
1
Diaminourea (DAU)
5
3,4-Diamino ,2,4-triazole (DAT)
6
Ethylenediamine (EDA)
7
Scheme 3. Synthetic pathway towards energetic salts (1-7).
2
.2 Single Crystal X-ray Structure
Crystals were obtained by slow evaporation of aqueous solutions at room
1-7
temperature, as colourless blocks or plates (Figure. 1). All compounds have been fully
4
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characterized by X-ray crystallography. (Figure. 2-6) The crystallographic data and
refinement details, selected bond lengths, angles, and hydrogen bonds are given in Table S1,
S2 and S3 (Supporting Information).
Figure 1. Crystal morphologies of compounds.
Compound
in the unit cell and a density of 1.620 g·cm (Figure 2a). The tetrazole rings are coplanar
N4-C1-C1ʹ-N4ʹ 180.0°), and two nitramino groups are twisted out from the plane with a
1 crystallizes in monoclinic space group P 21/c with two molecular moieties
-
3
(
torsion angle C1-N1-N5-N6 of 84.4°. Molecules are stacked along a axis forming
three-dimensional network like a spider web (Figure 2b). The angle of DNABT anion plane
and the guanidinium cation plane is 135°. The crystal structure of 1 is built up by seven
hydrogen bonds (Figure 2c), which use only the hydrogen of amine group as donor atoms.
Four hydrogen bonds can be considered moderately strong hydrogen bonds, with H···A
distances of 2.15, 2.38, 2.49 and 2.23 Å, respectively, for N7-H7A···O2, N8-H8A···N4,
N9-H9A···O2 and N9-H9A···N5. They are directed with D-H···A angles of 169, 151, and
1
31 and 167°, respectively. The other three hydrogen bonds are formed by the donor atoms
N7-H7B···N2, N8-H8B···N3 and N9-H9B···O1 with H···A distances of 2.30, 2.30, 2.12 Å,
and with D-H···A angles of only 160, 167, and 148°, respectively.
5
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Figure 2. (a) A view of the molecular unit of 1. (b) Unit cell view along a axis. (c) Hydrogen bonds (shown as
dotted lines).
Compound
2 crystallizes in monoclinic space group P2(1)/n with two molecular
-
3
moieties in the unit cell and with density of 1.688 g·cm (Figure 3a). Two tetrazole rings are
almost planar to each other. The nitramino groups are twisted out of this plane by a torsion
angle C1-N1-N5-N6 of -94.9°. The DNABT anion plane goes perpendicular with the
aminoguanidinium cation plane. Compound
3 crystallizes in the triclinic space group P-1
with only one molecular moiety in the unit cell (Figure 3b). There is a torsion angle
C2-N6-N10-N11 of 85.5° between the tetrazole ring and nitramino groups. The density of
3
-
3
is 1.644 g·cm , which is lower than that of
2
. The DNABT plane and diaminoguanidinium
plane is approximately parallel. Both for
2
and 3, the molecular moieties in the crystal
structure are controlled by an extensive hydrogen-bonding network since both O and N
atoms have sites capable of forming different kinds of hydrogen bonds. The details can be
found in the Electronic Supplementary Information (ESI).
6
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Figure 3. (a) Crystal structure of 2 (b) Crystal structure of 3.
Compound 4 crystallizes in triclinic space group P-1 with one molecule in the unit cell and
-3
remarkably lower density of 1.594 g·cm (Figure 4a). The structure of 4 consists of one DNABT
anion, two cations and two molecules of crystal water. Due to the different positions of the
nitramino moiety, there is twisted by the torsion angle of the nitramino groups toward the tetrazole
ring (C1-N4-N5-N6, -81.1°), and therefore form an extended 3D “spider-web” network. The
structure of 4·2H O is strongly influenced by hydrogen bonds via triaminoguanidinium protons and
2
water molecules. Compound 7 could be obtained in the crystalline state with one molecule of
crystal water as a compound with 1:1 stoichiometry (Figure 4b). It crystallizes in the monoclinic
space group P1211 with two molecules in the unit cell and a density of 1.721 g·cm-3. The nitramino
groups are twisted out of the tetrazole ring plane with a torsion angle C1–N1–N9–N10 of -80.2°.
The packing of 7·H O is also stabilized by hydrogen bonds involving intermolecular and
2
intramolecular interactions. Additional information can be found in the ESI.
7
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Figure 4. (a) Crystal structure of 4·2H O (b) Crystal structure of 7·H O.
2
2
Compound
5, as colorless crystalline plates, crystallizes in the monoclinic space group
P2(1)/c with two molecules per unit cell (Figure 5a). It has the highest density of 1.769
-
3
g·cm at 298(2) K among DNABT salts in this work. The lengths of CN and NN bonds
within the tetrazole rings of these compounds are located between the values f of formal
single and double bonds (C-N 1.47, C=N 1.22; N-N 1.48, N=N 1.20). Two nitramino groups
are located on each side of the tetrazole plane with deviation of -82.0° (C1-N1-N5-N6). The
structure of
5 presents a dense 3D hydrogen-bonded network (Figure 5b). Some hydrogen
bonds (N7-H7···O3, N8-H8A···N3, N8-H8A···O2, N8-H8B···N5, N8-H8C···N5,
N9-H9···O1 and N10-H10C···O1) are moderately strong with a D···A distance of 2.792(4)
~
3.036(4) Å, which are shorter than the sum of van der Waals radii (rw(N)+rw(N)=3.10 Å;
[
23]
rw(N)+rw(O)=3.07 Å).
Other three hydrogen bonds show an electrostatic nature in the
cases of N9-H9···N10, N10-H10B···N7 and N10-H10C···O3.
8
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Figure 5. (a) Crystal structure of
5
(b) Packing diagram of
5
viewed along b axis, dashed
lines represent hydrogen bonding.
Compound
6 crystallizes in the triclinic crystal system in the space group P-1 with one
-
3
molecular moiety in the unit cell and a density of 1.747 g·cm at 298(2) K (Figure 6a). The
nitramino groups are twisted out of the tetrazole plane by an angle of -85.2°
(C3-N6-N10-N11). And the DNABT anion plane is almost paralleled with the cation plane.
The C-C bond length of 1.450 Å is found to be shorter than a typical C-C single bond (1.54
Å). Deprotonation results in a elongating of the N6-N10 distances (1.396 Å) compared with
[
22]
the bond length of DNABT molecule (1.3735 Å).
The packing structure of 6 is
characterized by a three-dimensional network along a axis (Figure 6b). These hydrogen
bonds could be divided into two categories according to comparison of the D···A distance
and the sum of van der Waals radii. One category include seven moderately strong hydrogen
bonds for instance N2-H2···N1, N4-H4B···O1, N5-H5A···O2, N5-H5B···N4 and
N5-H5B···N11. Remaining hydrogen bonds such as N2-H2···N8, N4-H4A···N9 and
9
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N5-H5B···O1 are more of an electrostatic nature and not as strong as those bonds mentioned
above.
Figure 6 (a) Crystal structure of
6 (b) Packing diagram of 6 viewed along a axis, dashed
lines represent hydrogen bonding.
2
.3 Spectroscopy
Compounds 1-7 were characterized by using mass spectrometry and IR spectroscopy. In its
mass spectrum, DNABT anion has the strongest peak (m/z 256.75), corresponding to this
anion molecular weight. The IR spectra of all compounds were recorded and the frequencies
were assigned according to the literature. In DNABT anion moiety (Figure 7), the nitramino
-
1
group shows the asymmetric stretching vibration at 1713 cm and the symmetric stretching
-
1
-1
vibration at 1282 cm . The absorption bands in the range of 1149, 1117, 1009 and 979 cm
can be attributed to the vibrations of the CN and NN bonds in the tetrazole unit. The spectra
of the guanidine derivatives show absorption bands of valence vibrations of the amino
groups at 3000-3500 cm [ν (NH ), ν (NH )]. And the deformation vibrations of the
1-4
–
1
sym
2
asym
2
–
1
amino groups can be found at 1500-1700 cm [δ (NH ), δ (NH )]. Moreover, the
sym
2
asym
2
10
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–
1
carbonyl of the diaminourea cation of
5 reveals a sharp absorption band at 1713 cm . The
–
1
diamino-substituted cation in
6 exhibits a broadened signal at 1557-1694 cm because of
the existence of two amino groups. Also, the valence vibrations of C-H bond of the –CH2
–
1
part in
7 appear at 2920 (νasym(CH )), 2645 (ν (CH )) and 1429 cm (scissoring vibration),
2 sym 2
respectively.
Figure 7 The IR (left) and MS (right) spectra for DNABT anion.
2
.4 Thermal Behaviour
The thermal behaviours were investigated by differential scanning calorimetry (DSC)
-
1
measurements at a heating rate of 10 °C·min . Comparative thermograms are illustrated in
Figure 8. A detailed description of the setup in presented in the Table S4. Compounds
exhibit high decomposition temperatures at or above 180 °C, and compound and
comparable to RDX (204 °C). Salt , and show direct exothermic peaks indicating
extremely fast decomposition without the melting. And the highest onset decomposition
temperature is observed for the guanidinium salt (211 °C), which could be attributed to the
dense hydrogen bond network. In the cases of salt and , the materials melt before
decomposing as evidenced by endothermic steps (159 °C and 172°C). For dihydrate , a
dehydration temperature of 74 °C and a decomposition temperature of 181 °C were recorded.
The only exception is another hydrated salt with missing endothermic event in the DSC
1-7
1
,
3
7 are
1
,
5
6
1
2
3
4
7
curves. This may indicate that either standing at ambient temperatures over time lead to lose
the crystal water or it is released during the decomposition process. The decomposition
11
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temperatures of these salts prepared are significantly higher than that of the free acid
1
,1’-dinitramino-5,5’-bitetrazole (107 °C), which supports their better thermal stabilities.
Figure 8. DSC thermograms obtained for compounds 1-7
.
2
.5 Heats and Energies of Formation
The heats of formation of new EMs are frequently calculated theoretically, avoiding
synthesis of these materials on a multigram-scale and related experimental complications.
The heats of formation of all cations and anions were computed using the Gaussian 09 suites
[
24]
[25]
of programs
by the isodesmic reaction method
. The lattice energy (U ) and lattice
L
[
26]
enthalpy (ΔH ) were calculated by the equation provided by Jenkins and Glasser
.
L
[
27]
According to the Born-Haber energy cycles
(Scheme 4), the heats of formation of
energetic salts can be obtained by Eq.1. And the heats of formation (ΔH ) for solid state
m
were used to calculate the energies of formation (ΔU ) according to Eq. 2.
m
Hfo

Cation Anion (Solid)
aC(s) + bH (g) + cN (g) + dO (g)
2 2 2

HL
o


H (anion)
f
Cation (gas)
+
Anion (gas)
o
H (cation)
f
Scheme 4. Born-Haber Cycle for the formation of DNABT-based energetic salts.
12
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º
º
f
º
∆
∆
H (ionic salt, 298 K)=∆H (cation, 298 K)+∆H (anion, 298 K)−∆H (1)
f
f
L
U =∆H −∆nRT
m
(2)
m
As shown in Table 1, nitrogen-rich salts
1
-
7
are all formed endothermically and exhibit
has the lowest value
407.0 kJ·mol ) because of its large lattice energy. The highest positive value is for the
strongly positive heats of formation. The ethylenediammonium salt
7
-
1
(
-
1
triaminoguanidinium salt
4 (1377.9 kJ·mol ), which has lots of inherently energetic NN
bonds in molecules. Among the guanidine derivatives, there is an increase of heats of
formation by the number of the substituted amino in the cases of salts
1
-
4
. Additionally, the
-
1
-1
solid-state energies of formation vary between 2821.3 kJ·kg (
4
) and 1154.3 kJ·kg (
7
),
which may be the result of the high lattice enthalpy (1:1 compound with double-charged
cation) and hydrate formation.
Table 1 Heats of formation of compounds 1-7
a
b
c
d
e
f
Density
Cation
Anion
∆ H(cation)
f
∆ H(anion)
f
∆HL
∆ H (298K)
∆ U (298K)
f
∆n
f
m
-
3
-1
-1
-1
-1
-1
[
g·cm ]
1.62
1.69
1.64
1.64
1.77
1.75
1.76
[kJ·mol ]
[kJ·mol l]
711.8
[kJ·mol ]
1191.1
1175.0
1131.9
1101.0
1162.1
1138.8
1956.7
[kJ·mol ]
671.5
[kJ·kg ]
+
2-
2-
2-
2-
2-
2-
2-
1
2
3
4
5
6
G
DNABT
DNABT
DNABT
DNABT
DNABT
DNABT
575.4
671.6
796
1659.2
2037.5
2554.9
2821.3
1646.2
2777.0
1154.3
19
21
23
25
21
23
16
+
AG
711.8
880.0
+
DAG
711.8
1171.9
1377.9
773.6
+
TAG
883.6
611.9
875.7
1651.9
711.8
+
DAU
711.8
+
DAT
711.8
1324.3
407.0
2
+
7
EDA
DNABT
711.8
a
b
c
Heats of formation for cation. Heats of formation for anion. Lattice energy calculated by Jenkins and Glasser
d
e
f
equations. Standard solid state heats of formation. Solid state energies of formation. Change in moles of
gaseous components.
2
.6 Energetic Properties
Physiochemical and energetic properties of compounds 1-7 are summarized in Table 2,
alongside a comparison with common explosives. These DNABT based compounds have
high nitrogen content (exceeding 60%) and negative oxygen balances. These energetic salts
also possess superior thermal stabilities (180.0~210.5 °C). The decomposition temperature
of salt
1 is the highest and that of salts 3 and 7 are slightly higher than that of K DNABT
2
(200 °C) and RDX (204 °C). The measured densities of these salts range from 1.62 to 1.77
13
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10.1002/chem.201702759
-
3
g·cm . Some salts have a comparatively higher density than that of TNT and salt
highest one comparable to RDX, which could be explained by the stronger attractive ionic
forces. All of the salts investigated exhibit positive heats of formation varying 407.0 (
5 is the
7
)
-
1
between 1377.9 kJ·mol (
4) and are significantly greater than those of K DNABT, TNT and
2
RDX.
[
28]
Detonation performance was predicted by using the EXPLO5 6.01code
based on
calculated heats of formation and measured densities. The heats of detonation of salts
3-6
-
1
are slightly higher than that of K DNABT (4959 kJ·kg ), but lower than RDX (5845
2
-
1
-1
kJ·kg ). The detonation velocities of salts
4, 5 and 6 are 8851, 9053 and 8835 m·s
-
1
respectively, which are higher than that of RDX (8748 m·s ). The other DNABT derivatives
-
1
have moderate detonation velocities ranging from 8184 (
1
) to 8712 m·s (
2), and several
-
1
overmatch K DNABT (8330 m·s ). The detonation pressures are found in the range from
2
2
4.3 (
1
) to 32.3 GPa (
5
), which are superior to TNT (19.5 GPa). It is worth mentioning that
and have
values of 906, 921, 933and 907 L·kg , which overmatch other reported explosives.
these energetic salts exhibit all-right volume of detonation gases, and salts
2
,
3
,
4
5
-
1
Impact and friction sensitivities of these synthesized salts were measured by standard BAM
techniques and classified according to the “U.N. Recommendations on the Transport of Dangerous
[
29]
Goods” . All salts are expectedly less sensitive than K DNABT (IS < 1 J, FS ≤ 1 N), and can be
2
classified as sensitive (IS ≥ 4 J, FS ≥ 80 N). Furthermore, these salts are more sensitive towards
impact compared to RDX (7.4 J), whereas salt 1 and 4 show friction sensitivities of 120 and 144 N,
which are comparable with RDX (120 N).
Among all the salts synthesized in this work, there are many salts have physiochemical and
detonation properties superior to TNT. The diaminouronium salt 5 possesses best detonation
-1
performance with a detonation pressure of 32.3 GPa and a detonation velocity of 9053 m·s . When
-1
taking the sensitivities into consideration, triaminoguanidinium salt 4 (D = 8851 m·s , P = 29.0
-1
GPa) and 3,4-diamino-1,2,4-triazolium salt 6 (D = 8835 m·s , P = 30.2 GPa) could be possible
candidates to replace RDX. (Figure 9)
14
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Figure 9. Overall performances of compounds 1-7 compared with RDX.
Table 2. Physiochemical and energetic properties of compounds 1-7
p
q
r
Compound
1
2
3
4
5
6
7
K DNABT
2
TNT
RDX
a
[30]
IS [J]
4.9
3.9
3.9
3.9
2.5
4.9
3.9
1
39
7.4
b
FS [N]
120
80
96
144
40
96
96
≤1
353
120
0
c
Ω co [%]
-25.5
-42.5
66.9
83.9
211
-27.5
-43.3
68.9
84.6
180
1.69
880.0
-29.3
-44.0
70.5
85.2
205
-28.6
-41.4
66.8
85.9
181
-18.2
-32.8
63.8
85.7
185
-28.0
-49.0
67.5
81.5
183
-23.7
-42.8
58.3
82.1
209
4.8
-24.7
-74.0
18.5
d
Ω co [%]
-4.8
50.3
69.4
200
2.11
326.4
1036.1
-21.6
37.8
81.0
204
1.80
70.3
417.0
2
e
N [%]
f
N + O [%]
60.79
295
g
Tdec [°C ]
-
3 h
ρ [g·cm ]
1.62
671.5
1.64
1171.9
2554.9
1.64
1377.9
2821.3
1.77
773.6
1646.2
1.75
1324.3
2777.0
1.76
407.0
1154.3
1.65
-
1
i
∆fH ° [kJmol ]
-67.0
-415.2
m
-
1 j
∆fU° [kJ·kg ]
EXPLO5 6.01
values:
1659.2 2037.5
-
1
k
-
∆ H°[kJ·kg ]
4525
3146
24.3
4802
3170
28.2
8712
906
5200
3341
28.0
5378
3374
29.0
8851
933
5122
3373
32.3
9053
907
5160
3445
30.2
8835
842
4434
3028
28.6
8648
870
4959
3424
31.7
8330
489
5042
--
5845
--
Ex
l
Tdet
m
PCJ[GPa]
19.5
6881
825
34.9
8748
903
-
1 n
V [m·s ]
8184
8711
det
-
1 o
V [L·kg ]
893
921
0
a
b
c
d
Impact sensitivity. Friction sensitivity. Oxygen balance for CaHbOcNd: 1600(c-a-b/2)/MW. Oxygen balance for CaHbOcNd:
e
f
g
h
i
1
600(c-2a-b/2)/MW. Nitrogen content. Nitrogen and oxygen content. Decomposition temperature. Density at RT. Heat of
j
k
l
m
n
o
formation. Energy of formation. Heat of detonation. Detonation temperature.
Volume of detonation gases (assuming only gaseous products). MW=molecular weight. Ref. 21. Ref. 2. Ref. 4, Ref. 11.
Detonation velocity. Detonation pressure.
p
q
r
15
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2
.7 Computational Structural Considerations
To better understand the electronic structural properties for target compounds, natural bond orbitals
NBO) and electrostatic potential (ESP) of DNABT molecule were calculated using the density
(
functional theory with B3LYP/6-311++G** method based upon the optimized geometry.
Figure 10. NBO and ESP analysis of DNABT molecule
DNABT shows a bitetrazole linked by the C-C bond and two nitramino groups twisted out
from the tetrazole plane with a torsion angle. (Figure 10a) The optimized geometrical parameters
are similar to the experimental values and tabulated in Table S5. The calculated NBO charges for
DNABT are listed in Table S6. There appears a symmetric charge distribution in the terms of entire
molecule. Both carbon and hydrogen atoms are positively charged, while the oxygen atoms have the
most negative charges. All nitrogen atoms of the ring show negative charges except N6 atom of the
nitro groups with positive charges. The HOMO of the molecule is localized approximately on the
tetrazole ring, while the LUMO is distributed on the ring as well as the C=C bond. (Figure 10b) The
16
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Chemistry - A European Journal
10.1002/chem.201702759
energy gap between the HOMO and LUMO is 0.19831 eV, which shows molecular unstable nature.
[
31]
The quantitative molecular surface analysis was performed by using the Multiwfn program
,
and the extreme value points of ESP on molecular surface are plotted in Figure 10c. The surface
local minima and maxima are blue and red point respectively, and only global minima and maxima
are labelled. The positive and negative potential are distributed inside and outside the bitetrazole
ring. The surface maxima naturally present near H atoms, and the surface minima of ESP present
near the N3 atom, which may be primary electrophilic site. Surface areas in each ESP range are
visualized in Figure 10d. DNABT molecule unit has surface of ESP value within -25 to +65
-1
-1
kcal·mol , and the value on biggest area is about -10 kcal·mol . The areas of negative ESP are
larger than that of positive ESP, which may because of the effect of electron-attracting groups.
3
. Conclusions
A family of 1,1’-dinitramino-5,5’-bistetrazole energetic salts were synthesized with
cations of guanidinium (
triaminoguanidinium ( ), diaminouronium (
ethylenediammonium ( ). All of the compounds were fully characterized by analytical and
1
), aminoguanidinium (
2
), diaminoguanidinium (
3),
4
5
), 3,4-diamino-1,2,4-triazolium (
6
) and
7
spectroscopic methods (elemental analysis, MS and IR spectroscopy). Single-crystal X-ray
diffraction indicates the presence of complex 3D networks of hydrogen bonds in these new
salts. The detonation performances and sensitivities of the salts were calculated by the
EXPLO5 program and tested by BAM methods, respectively. DNABT nitrogen-rich salts
exhibit good thermal stabilities (180-211 °C) and have highly positive heats of formation
-
1
(
407.0-1377.9 kJ·mol ). The high volumes of explosion gases of salts
3
and
4 (921 and 933
-
1
L·kg ) support their power of explosives. Several compounds show detonation properties
-
1
-1
comparable to RDX, such as salt
2.3 GPa) and
4
(D = 8851 m·s , P = 29.0 GPa), 5 (D = 9053 m·s , P =
-
1
3
6
(D = 8835 m·s , P = 30.2 GPa). Enhancing performances and more
moderate sensitivities than K DNABT, as well as free of metal, suggest that they may have
2
value to the field of environmentally friendly energetic materials. Additionally, the NBOs
and ESPs of DNABT molecule were calculated based on quantum chemistry and analysed
for a better understanding of the structures for salts studied in this work.
17
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Experimental Section
General Procedures
All chemical reagents and solvents were obtained from Sinopharm Chemical Reagent
Co., Ltd. Infrared spectra were recorded on a Bruker Equinox 55 spectrometer. Mass spectra
were measured at an Agilent 500-MS. Elemental analysis was performed on an Elementar
Vario El III analyzer. Decomposition point was determined by differential scanning
calorimetry (DSC) on a model Pyris-1 at a heating rate of 10 °C . The impact and friction
sensitivities were tested on a BAM fall hammer BFH-10 and a BAM friction apparatus
FSKM-10, respectively. Collection of XRD data was performed on a Rigaku Saturn 724+
CCD diffractometer equipped with graphite monochromatized MoKα radiation. The
[
32]
[33]
structure was solved with SHELXS-97 refined with SHELXL-97) . The non-hydrogen
atoms were refined anisotropically and the hydrogen atoms were located and freely refined.
CCDC-1492723 (
CCDC-1492727 (
1
), CCDC-1492724 (
2
), CCDC-1492725 (
3), CCDC-1492726 (4),
5
), CCDC-1492728 ( ), CCDC-1492729 (7
6
) contain the supplementary
crystallographic data, which can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Caution! All of these investigated compounds are potentially explosive energetic materials.
Specifically, silver salt is extremely sensitive and have to be handled very carefully. This
necessitates additional meticulous safety precautions (ear plugs, face shield and Kevlar
gloves etc).
Bis(guanidinium) 1,1’-dinitramino-5,5’-bitetrazolate (1)
All syntheses described in this work start from commercially available methyl carbazate
(
Scheme 3). K DNABT was obtained in six complicated steps according to the literature
2
[
21]
procedure
. Powdered colourless K DNABT (0.16 g, 0.48 mmol) was dissolved in
2
enough deionized water (K DNABT shows low water solubility). The silver salt was
2
immediately precipitated by adding a solution of silver nitrate (0.16 g, 0.96 mmol). Caution!
Silver salt is extremely sensitive and never let the filter paper dry out when filtrate the
suspension. Silver 1,1’-diamino-5,5’-bistetrazolate (0.23 g, 0.48 mmol) was added to an
18
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aqueous solution (5 mL) of guanidinium chloride (0.09 g, 0.96 mmol). After the mixture had
been stirred overnight, the solids were removed by filtration. The filtrate was slowly
evaporated to leave solid product
1
as colourless crystals in good yield (89%).
-
1
DSC (10 °C·min ): 211 °C (dec.); IR (KBr): v = 3442 (vs), 3367 (s), 3275 (s), 3208 (s),
2
1
919 (w), 2850 (w), 2287 (w), 1657 (vs), 1571 (m), 1432 (s), 1364 (w), 1295 (vs), 1256 (s),
161 (m), 1127 (m), 1031 (w), 996 (w), 876 (m), 774 (w), 547 (w), 520 (w), 456 (w); MS
+
+
-
-
(
ESI ): m/z: 59.95 (CH N ); MS (ESI ): m/z: 256.80 (C N O ); EA (C H N O , 376.32):
6 3 2 12 4 4 12 18 4
calc: C 12.77%, N 67.01%; found: C 12.75% , N 67.00 %; BAM drop hammer: 4.9 J;
friction tester: 120 N.
Bis(aminoguanidinium)
1,1’-dinitramino-5,5’-bitetrazolate
(2).
Silver
1
,1’-diamino-5,5’-bistetrazolate (0.23 g, 0.48 mmol) was suspended in a few millilitres of
water (5 mL), and aminoguanidinium chloride (0.10 g, 0.96 mmol) was added. The mixture
was stirred overnight and then filtered. The filtrate was slowly evaporated to leave the
colourless crystals
2
in good yield (87%).
-
1
DSC (10 °C·min ): 180 °C (dec.); IR (KBr): v = 3845 (w), 3457 (vs), 3328 (s), 3051 (m),
2
1
8
918 (m), 2300 (w), 2118 (w), 1676 (vs), 1644 (s), 1610 (s), 1494 (w), 1450 (w), 1408 (w),
388 (w), 1361 (w), 1293 (m), 1259 (m), 1161 (w), 1125 (m), 1036 (w), 1004 (w), 938 (w),
+
98 (w), 876 (m), 774 (w), 727 (w), 675 (w), 623 (w), 548 (w), 495 (m), 462 (w); MS (ESI ):
+
-
-
m/z: 75.1 (CH N ); MS (ESI ): m/z: 256.75 (C N O ); EA (C H N O , 406.35): calc: C
7
4
2
12
4
4
14 20
4
1
8
1.82%, N 68.95%; found: C 11.80% , N 68.92 %; BAM drop hammer: 3.9 J; friction tester:
0 N.
Bis(diaminoguanidinium)
,1’-diamino-5,5’-bistetrazolate (0.23 g, 0.48 mmol) was suspended in a few milliliters of
water (5 mL), and diaminoguanidinium chloride (0.12 g, 0.96 mmol) was added. After the
1,1’-dinitramino-5,5’-bitetrazolate
(3).
Silver
1
mixture had been stirred overnight, the solids were removed by filtration. Compound
obtained as colorless crystalline residue in good yield (83%).
3 was
-
1
DSC (10 °C·min ): 205 °C (dec.); IR (KBr): v = 3440 (m), 3357 (s), 3316 (s), 3263 (s),
1
679 (vs), 1622 (m), 1511 (w), 1428 (m), 1359 (w), 1293 (m), 1252 (w), 1194 (w), 1161 (w),
19
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1
126 (w), 1077 (w), 996 (w), 956 (w), 878 (m), 776 (w), 723 (w), 562 (m), 432 (w); MS
+
+
-
-
(
ESI ): m/z: 90.15 (CH N ); MS (ESI ): m/z: 256.95 (C N O ); EA (C H N O , 436.39):
8 5 2 12 4 4 16 22 4
calc: C 11.01%, N 70.63%; found: C 11.03% , N 70.64 %; BAM drop hammer: 3.9 J;
friction tester: 96 N.
Bis(triaminoguanidinium) 1,1’-dinitramino-5,5’-bitetrazolate dehydrate (4). Silver
1
,1’-diamino-5,5’-bistetrazolate (0.23 g, 0.48 mmol) was suspended in a few milliliters of
water (5 mL), and triaminoguanidinium chloride (0.13 g, 0.96 mmol) was added. The
mixture was stirred overnight and filtered. The solvent was evaporated from the filtrate to
yield compound
4 as colorless crystalline blocks in good yield (91%).
-
1
DSC (10 °C min ): 181 °C (dec.); IR (KBr): v = 3451 (m), 3319 (s), 3210 (vs), 2918 (w),
2
1
858 (w), 2302 (w), 1700 (vs), 1613 (m), 1519 (w), 1493 (w), 1444 (s), 1363 (m), 1299 (s),
256 (m), 1163 (w), 1127 (s), 1032 (w), 949 (s), 872 (m), 774 (w), 728 (w), 715 (w), 638
+
+
-
-
(
m), 608 (m), 456 (w); MS (ESI ): m/z: 104.85 (CH N ); MS (ESI ): m/z: 256.75 (C N O );
9 6 2 12 4
EA (C H N O , 502.46): calc: C 9.56%, N 66.91%; found: C 9.58% , N 66.95 %; BAM
4
22 24
6
drop hammer: 3.4 J; friction tester: 144 N.
Bis(diaminouronium)
,1’-diamino-5,5’-bistetrazolate (0.23 g, 0.48 mmol) was added to an aqueous solution (5
mL) of diaminouronium chloride (0.12 g, 0.96 mmol). After the mixture had been stirred
1,1’-dinitramino-5,5’-bitetrazolate
(5).
Silver
1
overnight, the solids were removed by filtration. Compound
crystalline plates in good yield (90%).
5 was obtained as colorless
-
1
DSC (10 °C·min ): 185 °C (dec.); IR (KBr): v = 3332 (vs), 3108 (s), 2922 (s), 2708 (m),
1
1
5
713 (s), 1633 (w), 1545 (w), 1469 (m), 1438 (w), 1383 (w), 1282 (s), 1267 (m), 1149 (w),
117 (m), 1009 (m), 979 (w), 950 (w), 880 (w), 778 (w), 758 (w), 671 (w), 617 (w), 582 (m),
+
+
-
56 (m), 472 (w), 417 (w); MS (ESI ): m/z: 90.85 (CH N ); MS (ESI ): m/z: 256.75
7
4
-
(
C N O ); EA (C H N O , 438.35): calc: C 10.96%, N 63.92%; found: C 10.93% , N
2 12 4 4 14 20 6
6
3.91 %; BAM drop hammer: 2.5 J; friction tester: 40 N.
20
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Bis(3,4-diamino-1,2,4-triazolium)
1,1’-dinitramino-5,5’-bitetrazolate
(6).
Silver
1
,1’-diamino-5,5’-bistetrazolate (0.23 g, 0.48 mmol) was added to an aqueous solution (5
mL) of 3,4-diamino-1,2,4-triazolium chloride (0.13 g, 0.96 mmol). After the mixture had
been stirred overnight, the solids were removed by filtration. Compound
colourless plates in good yield (85%).
6 was obtained as
-
1
DSC (10 °C·min ): 183 °C (dec.); IR (KBr): v = 3396 (s), 3338 (s), 3281 (s), 3254 (s), 2919
(w), 2854 (w), 1694 (vs), 1637 (w), 1570 (w), 1557 (w), 1409 (m), 1387 (w), 1360 (w),
1
8
4
295 (s), 1249 (w), 1207 (w), 1159 (w), 1121 (w), 1049 (w), 1035 (w), 1018 (w), 967 (m),
72 (w), 836 (w), 777 (w), 690 (w), 615 (w), 594 (w), 560 (w), 526 (w), 471 (w), 449 (w),
+
+
-
-
32 (w), 413 (w); MS (ESI ): m/z: 99.85 (C H N ); MS (ESI ): m/z: 256.75 (C N O ); EA
2
6
5
2
12
4
(
C H N O , 456.38): calc: C 15.79%, N 67.53%; found: C 15.77% , N 67.52 %; BAM
6 12 22 4
drop hammer: 4.9 J; friction tester: 96 N.
Ethylenediammonium 1,1’-dinitramino-5,5’-bitetrazolate monohydrate (7). Silver
1
,1’-diamino-5,5’-bistetrazolate (0.45 g, 0.96 mmol) was added to an aqueous solution (5
mL) of ethylenediammonium chloride (0.13 g, 0.96 mmol). After the mixture had been
stirred overnight, the solids were removed by filtration. Compound
agglomerates in good yield (81%).
7 was obtained as white
-
1
DSC (10 °C·min ): 209 ºC (dec.); IR (KBr): v = 3239 (s), 2920 (s), 2645 (w), 2529 (w),
2
1
427 (w), 2294 (w), 1961 (w), 1733 (w), 1615 (m), 1501 (m), 1429 (m), 1364 (m), 1293 (s),
257 (m), 1162 (w), 1124 (m), 1064 (w), 1031 (m), 1008 (m), 879 (s), 771 (s), 722 (w), 712
+
(
w), 671 (w), 525 (w), 481 (w), 459 (m), 426 (w), 413 (w); MS (ESI ): m/z: 62,08
+
-
-
(
C H N ); MS (ESI ): m/z: 256.70 (C N O ); EA (C H N O , 336.28): calc: C 14.29%,
2
10 22
2
12
4
4
12 14
5
N 58.32%; found: C 14.26%, N 58.31 %; BAM drop hammer: 3.9 J; friction tester: 96 N.
Acknowledgements
The support of the National Natural Science Foundation of China (10776002), the project of
State Key Laboratory of Explosion Science and Technology (YBKT16-15 and YBKT16-04)
and Graduate student science and technology innovation activities plan project (2016CX10006) are
gratefully acknowledged. We are indebted to Prof. Yanqiang Zhang, Dr. Long Liu and thank
21
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Chemistry - A European Journal
10.1002/chem.201702759
Institute of process engineering, Chinese Academy of Sciences for considerable assistance
with sensitivities test.
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