Energetic derivatives of 5-(5-amino-2H-1,2,3-triazol-4-yl)-1H-tetrazole

Article abstract of DOI:10.1039/c5dt03044g

This study presents the preparation of the novel nitrogen-rich compound 5-(5-amino-2H-1,2,3-triazol-4-yl)-1H-tetrazole (5) from commercially available chemicals in a five step synthesis. The more energetic derivatives with azido (6) and nitro (7) groups, as well as a diazene bridge (8) were also successfully prepared. The energetic compounds were comprehensively characterized by various means, including vibrational (IR, Raman) and multinuclear (¹H, ¹³C, ¹⁴N, ¹⁵N) NMR spectroscopy, mass spectrometry and differential thermal analysis. The sensitivities towards important outer stimuli (impact, friction, electrostatic discharge) were determined according to BAM standards. The enthalpies of formation were calculated on the CBS-4M level of theory, revealing highly endothermic values, and were utilized to calculate the detonation parameters using EPXLO5 (6.02).

Full text of DOI:10.1039/c5dt03044g

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Energetic Derivatives of
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DOI: 10.1039/C5DT03044G
5-(5-Amino-2H-1,2,3-triazol-4-yl)-1H-tetrazole
Dániel Izsák, Thomas M. Klapötke,* and Carolin Pflüger
Department of Chemistry, Ludwig–Maximilian University of Munich, Butenandtstr. 5–13 (D),
81377 Munich, Germany
(Fax: +49-89-2180-77492, E-Mail: tmk@cup.uni-muenchen.de)
Abstract: This study presents the preparation of the novel nitrogen-rich compound 5-(5-amino-2H-
1,2,3-triazol-4-yl)-1H-tetrazole (5) from commercially available chemicals in a five step synthesis.
The more energetic derivatives with azido (6) and nitro (7) groups, as well as a diazene bridge (8)
were also successfully prepared. The energetic compounds were comprehensively characterized by
various means, including vibrational (IR, Raman) and multinuclear (1H, 13C, 14N, 15N) NMR
spectroscopy, mass spectrometry and differential thermal analysis. The sensitivities towards
important outer stimuli (impact, friction, electrostatic discharge) were determined according to
BAM standards. The enthalpies of formation were calculated on the CBS-4M level of theory,
revealing highly endothermic values, and were utilized to calculate the detonation parameters using
EPXLO5 (6.02).
Keywords: Energetic materials; Heterocycles; Triazoles; Tetrazoles;
Supporting Information: Crystallographic data, refinement parameters and additional figures.
CCDC reference numbers: 1406925 (2) and 1413469 (5). Parts of this study have been presented at
the 18th Seminar on New Trends in Research of Energetic Materials, Pardubice, Czech Republic,
April 15–17, 2015.

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Introduction
Poly-azole compounds have been the focus of several research groups world-wide working in the
field of energetic materials in the recent years. These feature two, or even more, linked azoles
(furazan, 1,2,4-triazole, tetrazole, etc.), which can be either directly linked,[1–6] or through energetic
bridging moieties like a diazene bridge.[7–11] The detonation performance of energetic compounds
depends strongly on the enthalpy of formation and the density, with higher values resulting in more
powerful explosives. The high nitrogen content of azole based compounds results in high positive
enthalpies of formation due to the large number of inherent N-N and C-N bonds and thereby
showing high potential as explosive.[12] Furthermore, the nitrogen-rich heterocycles mainly release
nontoxic dinitrogen gas upon decomposition, whereby the environmental pollution might be
diminished. The design of new high explosives should consider improved thermal and mechanical
sensitivities as well as an increased detonation performance, but unfortunately, these parameters
often have contradictory impact to each other.[13] The combination of multiple different
heterocycles is advantageous due to the vast possibilities of tailoring the energetic performances.
An interesting example combining the frequently utilized tetrazole and 1,2,4-triazole moieties are
the derivatives of 5-(5-amino-1H-1,2,4-triazol-3-yl)tetrazole with the energetic azido, nitro and
nitramino groups, which have been investigated recently.[14] This C-C linkage of the two
heterocycles benefits from the energetic tetrazole ring, the higher stability of the triazole ring and
the second carbon atom of the triazole which carries various energetic groups. Another option
would be the utilization of a 1,2,3-triazole instead of the 1,2,4-triazole, which should result in
higher enthalpies of formation and thus improved energetic performances, although potentially at
the expense of thermal and mechanical stability. A suitable nitrile precursor had already been
reported in 1956,[15] but no studies concerning the binary combination of a tetrazole and a 5-amino-
1,2,3-triazole by means of a C-C link could be found.
The goal of this study has therefore been the synthesis of the novel 5-(5-amino-2H-1,2,3-triazol-
4-yl)-1H-tetrazole (5) and its derivatives with azido (6) and nitro (7) groups as well as diazene

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bridging (8), their comprehensive characterization and the comparison of the compounds with the
respective 1,2,4-triazole isomers and analogues.
Results and Discussion
Synthesis: There are two possible routes to the intermediate 5-amino-1-benzyl-1,2,3-triazole-4-
carbonitrile (3). The first one is the direct synthesis from benzyl azide (1) and malononitrile with
sodium in ethanol,[15] but this reaction suffers from low yields and the formation of 5-amino-l-
benzyl-4-carbiminoethoxy-1,2,3-triazole as a byproduct, due to the presence of the second nitrile
which can react with the formed ethoxide. The second option is the well working synthesis (80 %)
of 5-amino-1-benzyl-1,2,3-triazole-4-carboxamide (2) from benzyl azide (1) and cyanoacetamide
with sodium in ethanol,[15] which can then be further processed in two different ways. The first one
would be the debenzylation to 4-amino-2H-1,2,3-triazole-5-carboxamide with sodium in liquid
ammonia,[15] followed by the dehydration of the amide to a nitrile. Although the debenzylation is
working well (96 %), the dehydration did not result in a complete conversion with various reagents
(phosphorus pentoxide, phosphoryl chloride, phosphorus pentachloride, thionyl chloride).
Therefore, the benzyl protective group was left on the triazole and thus enabling the use of
trifluoroacetic anhydride by protecting the ring from its acylation properties, resulting in a complete
conversion of 2 into 3 in high yields (86 %). The next step, the formation of 5-(5-amino-1-benzyl-
1,2,3-triazol-4-yl)tetrazole (4) from 3 and sodium azide, proved to be quite difficult due to the
frequent hydrolysis of the nitrile, in addition to the desired product, when zinc chloride was
employed in a protic solvent (water, ethanol, methanol). Hydrochloric acid and ammonium chloride
in the same solvents did not result in partial hydrolysis, but also did not yield any product, and
neither did acetic acid (both as acid and as solvent). Utilization of the polar, aprotic tetrahydrofuran
and zinc chloride finally yielded pure 4 (97 %). Debenzylation was again carried out with sodium in
liquid ammonia to obtain the title compound 5-(5-amino-2H-1,2,3-triazol-4-yl)-1H-tetrazole (5) in
high yield (95 %). The optimized route is shown in Scheme 1.

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The amine of 5 was then converted into different energetic moieties as illustrated in Scheme 1.
The azido derivative 6 was obtained in high yield (87 %) by diazotation with sodium nitrite in
sulfuric acid, followed by a diazo azide exchange with sodium azide. The nitro derivative 7 could
not be obtained by the common reaction with an excess of sodium nitrite in sulfuric acid, a method
which works well with 5-(5-amino-1H-1,2,4-triazol-3-yl)tetrazole for example,[14] but it was
obtained by oxidation of the amine with potassium superoxide in tetrahydrofuran in a fair yield
(68 %). Azo coupling with potassium permanganate in water yielded 1,2-bis(4-(1H-tetrazol-5-yl)-
2H-1,2,3-triazol-5-yl)diazene (8) also only in a fair yield (48 %) as a dihydrate.

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Scheme 1:
Synthetic route towards 5-(5-amino-2H-1,2,3-triazol-4-yl)-1H-tetrazole (5) from
commercially available benzyl chloride, and its energetic derivatives 5-(5-azido-2H-
1,2,3-triazol-4-yl)-1H-tetrazole (6), 5-(5-nitro-2H-1,2,3-triazol-4-yl)-1H-tetrazole (7)
and 1,2-bis(4-(1H-tetrazol-5-yl)-2H-1,2,3-triazol-5-yl)diazene (8).
Crystal Structures: The precursor molecule 5-amino-1-benzyl-1,2,3-triazole-4-carboxamide (2)
crystallized in the monoclinic space group P21/c with four formula units per unit cell. The
molecular unit is depicted in Figure 1. The bond lengths of the 1,2,3-triazole ring are between the

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length of the corresponding single and double bonds,[16] with the N1–N2 bond being significantly
longer (1.376(1) Å) than the N2–N3 bond (1.304(1) Å), which is quite common for 1,4,5-
substituted 1,2,3-triazoles.[17] The bond lengths of the amino group attached to the triazole
(1.351(2) Å), as well as the amide N4–C3 bond (1.346(2) Å) are considerably shorter than the
corresponding single bonds, caused by an involvement of the non-bonding electron pair of the
nitrogen atoms, with both groups being almost planar. The amide group and the triazole ring are
practically in plane (C2–C1–C3–O1: 1.66(2)°). The molecule features one weak and undirected
intramolecular hydrogen bond between the ring amine and the amide oxygen as N5–H3ꢀꢀꢀO1 (DꢀꢀꢀA:
2.956(1) Å; D–HꢀꢀꢀA: 125(1)°), and a long but directed intermolecular hydrogen bond N4–H2ꢀꢀꢀO1i
(DꢀꢀꢀA: 3.070(2) Å; D–HꢀꢀꢀA: 171(2)°) resulting in dimers (see Figure 2 for both). The dimers are
connected by undulated ribbons through a π-π stacking interaction of the phenyl groups, depicted in
Figure 2. The distance between the two aromatic moieties is 3.531(2) Å, which is characteristic for
these interactions.[18] The second intermolecular interaction which connects the ribbons is formed
by a very long but directed hydrogen bond N5–H4ꢀꢀꢀN2ii between the amino moiety and a nitrogen
atom of a neighboring triazole (DꢀꢀꢀA: 3.128(2) Å; D–HꢀꢀꢀA: 164(1)°), slightly above the sum of the
van der Waals radii (
∑
rw(N,N) = 3.10 Å).[19] The resulting crystal structure, presented in Figure 3,
has two areas which are either dominated by polar hydrogen bonds or by nonpolar
π-π
stacking
interactions. The parameters of the described hydrogen bonds are summarized in Table 1. Further
information regarding the crystal structure determination has been compiled in the Supplementary
Information (Table S1).

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Figure 1:
Molecular structure of 5-amino-1-benzyl-1,2,3-triazole-4-carboxamide (2). Thermal
ellipsoids at 50 % probability.
Figure 2:
Hydrogen bonds and π-π stacking interactions of 2. Thermal ellipsoids at 50 %
probability. Symmetry code: (i) −x+1, −y+3, −z+1.

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Figure 3:
Table 1:
Unit cell of 2 along the (010) axis, illustrating the intermolecular N5–H4···N2ii
hydrogen bond. Thermal ellipsoids at 50 % probability.
Hydrogen bonds present in 2.
D–H···A
D–H / Å
0.88(2)
0.90(2)
0.91(2)
H···A / Å
2.36(1)
2.17(2)
2.24(2)
D···A / Å
2.956(1)
3.070(2)
3.128(2)
D–H···A / °
125(1)
N5–H3···O1
N4–H2···O1i
N5–H4···N2ii
171(2)
164(1)
Symmetry codes: (i) −x+1, −y+3, −z+1; (ii) x, −y+1.5, z−0.5.
The title compound 5-(5-amino-2H-1,2,3-triazol-4-yl)-1H-tetrazole (5) crystallized in the
monoclinic space group P21/n with four formula units per unit cell and a calculated density of
1.705 g cm−3 at 100 K. The molecular unit is depicted in Figure 4. The bond lengths are again
between formal single and double bonds. The triazole ring is more symmetrical than that of 2 with
N1–N2 and N2–N3 bond lengths of 1.350(2) and 1.311(2) Å, respectively. The length of the C1–C3
bond (1.442(2) Å) is comparable to similar bisazole compounds.[14] Both rings form an almost

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planar system with a N3–C1–C3–N4 torsion angle of −1.1(2)°. The amino group is similar to that of
2 and is also in plane with both rings, leading to the assumption of a conjugated π-system across the
whole molecule. Additionally, the molecule features an intramolecular N8–H4···N7 hydrogen bond
between the amino group and the tetrazole ring. The structure is dominated by an extensive
hydrogen bonding network involving all eight nitrogen atoms, which is illustrated in Figure 5. The
strong and quite directed N2–H1···N6i hydrogen bond (D···A: 2.875(2) Å; D–H···A: 163(1)°)
results in the formation of a chain (A), which is connected to the anti-parallel chain (B) through the
N4–H2···N1ii, N8–H3···N3iii and N8–H4···N5iv contacts (see Figure 5 and Table 2). The
arrangement of the anti-parallel chains overall results in a layer structure with no special
interactions between the layers.
Figure 4:
Molecular structure of 5-(5-amino-2H-1,2,3-triazol-4-yl)-1H-tetrazole (5). Thermal
ellipsoids at 50 % probability.

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Figure 5:
Table 2:
Hydrogen bonds of 5, illustrating the two anti-parallel chains (A) and (B). Thermal
ellipsoids at 50 % probability. Symmetry codes: (i) x, y, z+1; (ii) –x+0.5, y+0.5,
−z+0.5; (iii) –x+0.5, y–0.5, −z+0.5; (iv) –x+0.5, y–0.5, −z–0.5.
Hydrogen bonds present in 5.
D–H···A
D–H / Å
0.90(2)
0.91(2)
0.89(2)
0.88(3)
0.88(3)
H···A / Å
2.00(2)
1.98(2)
2.12(2)
2.41(2)
2.42(2)
D···A / Å
2.875(2)
2.891(2)
3.011(2)
3.004(2)
3.081(2)
D–H···A / °
163(1)
N2–H1···N6i
N4–H2···N1ii
N8–H3···N3iii
N8–H4···N7
N8–H4···N5iv
178(2)
175(2)
125(2)
131(2)
Symmetry codes: (i) x, y, z+1; (ii) –x+0.5, y+0.5, −z+0.5; (iii) –x+0.5, y–0.5, −z+0.5; (iv) –x+0.5, y–0.5, −z–0.5.
Multinuclear NMR Spectroscopy: All compounds prepared herein were investigated by
multinuclear NMR spectroscopy (1H and 13C, some additionally 14N and 15N). 13C NMR
spectroscopy is well suited to differentiate between the precursor molecules 2–4, the title compound
5 and its further derivatives 6–8. While 2–4 all show the signals of the benzyl group (phenyl:
135.2–136.0, 128.7, 127.8–127.9, 127.4–127.5 ppm; methylene: 48.4–48.8 ppm), those are

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completely gone in the spectrum of 5. The signal of the triazole carbon atom attached to the
exocyclic carbon is at 121.8 (2), 113.7 (3) and 114.4 ppm (4). The carbon atom carrying the amine
shows a signal at 144.9 (2), 148.0 (3) and 148.6 ppm (4). While the spectrum of 2 shows a signal at
164.5 ppm, stemming from the amide, 3 has the signal of the nitrile at 101.3 ppm and shows no
signs of the former. Pure 4 finally exhibits a new signal at 142.9 ppm, belonging to the newly
14
formed tetrazole. The signals of compounds 5–8 (1H, 13C and N) are compiled in Table 3. While
6–8 show three sharp signals for the two triazole and one tetrazole carbon atoms in their
corresponding 13C NMR spectra, 5 shows only one sharp signal at 149.0 ppm, attributed to the
tetrazole, and two small and broad signals at 147.6 and 111.6 ppm, attributed to the triazole. The
carbon resonances of the rings are assigned due to their signal shapes and intensities, and in
comparison to 13C NMR spectra of corresponding salts. The corresponding 14N NMR spectra show
the signals of the central azide nitrogen atom (Nβ) of 6 at −138 ppm as a broad signal and the nitro
group of 7 at −21 ppm. Compounds 6 and 7 were further investigated by 15N and 15N{1H} NMR
spectroscopy. The proton coupled 15N NMR spectra are depicted in Figure 6. The proton decoupled
15N NMR spectra can be found in the Supporting Information (Figure S1). All nitrogen atoms
display clearly visible resonances in the 15N NMR spectra of both 6 (eight signals) and 7 (six
signals). The tetrazole emits only two signals due to the enabled proton exchange in DMSO-d6,
equalizing the four nitrogen atoms to one protonated (−101.9 ppm in 6, −65.4 ppm in 7) and one
non-protonated (−11.1 ppm in 6, −14.4 ppm in 7), similar to 5-(5-azido-1H-1,2,4-triazol-3-
yl)tetrazole and 5-(3-nitro-1H-1,2,4-triazol-5-yl)-2H-tetrazole for example.[14] The triazole shows
three signals in both compounds, with one being strong and sharp (−74.1 ppm in 6, −51.1 ppm in 7)
and the other two being weaker and broad (−55.7 and −126.3 ppm in 6, −65.4 and −97.2 ppm in 7).
The 15N{1H} NMR spectra confirm that the signals at −126.3 and −97.2 ppm carry the proton, in
addition to their high field shift. The signal of the protonated nitrogen atom of the tetrazole ring is
in all spectra broader than that of the triazole. The remaining signals are belonging to the azide
(−143.2, −148.6 and −303.3 ppm) of 6 and the nitro group (−27.5 ppm) of 7. While the signal at
−303.3 ppm in the spectrum of 6 can be clearly attributed to the alpha nitrogen atom of the azide,

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the signals at −143.2 and −148.6 ppm have nearly identical intensities and are thus preventing an
unambiguous assignment to the beta and gamma nitrogen atoms.
Table 3:
NMR signals of 5–8 in DMSO-d6 at room temperature.
δ
1H
13C{1H}
(triazole)
13C{1H}
(tetrazole)
14N
16.19, 14.64, 6.03
147.6, 111.6
147.7, 123.0
151.1, 127.7
153.7, 126.6
149.0
143.1
147.7
147.2
—
−138
−21
—
5
6
7
8
15.81
9.93
10.09
Figure 6:
15N NMR spectra of 5-(5-azido-2H-1,2,3-triazol-4-yl)-1H-tetrazole (6) and 5-(5-
nitro-2H-1,2,3-triazol-4-yl)-1H-tetrazole (7) in DMSO-d6 at room temperature.
Theoretical Calculations, Performances and Stabilities: The thermal behaviors of the
synthesized compounds were investigated by differential thermal analysis (DTA). The amino

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derivative 5 displays, as expected, the highest thermal stability of the neutral compounds (241 °C),
while the nitro derivative 7 (188 °C), azido derivative 6 (152 °C) and especially the diazene bridged
derivative 8 (128 °C) are significantly less thermally stable. It is interesting to note that, while the
isomer 5-(5-amino-1H-1,2,4-triazol-3-yl)tetrazole (347 °C) and its nitro derivative (211 °C) display
higher thermal stabilities than 5 and 7,[14] respectively, due to the 1,2,4-triazole, the azido derivative
exhibits the same decomposition temperature as 6, as does the third isomer 1-(5-azido-1H-1,2,4-
triazol-3-yl)tetrazole.[20] The azo bridged 1,2-bis(4-(1H-tetrazol-5-yl)-2H-1,2,3-triazol-5-yl)diazene
(8), which was obtained as a dihydrate according to elemental analysis, shows no sign of water loss
before decomposition at 128 °C. Dehydration thus proved to be unsuccessful at 100 °C and high
vacuum for two days. Higher temperatures were not desirable due to the low decomposition point.
For initial safety testing the impact and friction sensitivities as well as the electrostatic discharge
sensitivities were determined and assigned according to the UN recommendations on the transport
of dangerous goods.[21] The parent compound 5 is the least sensitive of the neutral compounds,
although it is still sensitive to impact (10 J), but insensitive to friction (360 N). While the azido
derivative 6 is very sensitive to impact (3 J) and to friction (10 N), the nitro derivative 7 is only
sensitive to impact (4 J) and to friction (108 N). Interestingly, the diazene 8 is very sensitive to both
impact (2 J) and friction (28 N), although it is a dihydrate. 5-(5-Amino-1H-1,2,4-triazol-3-
yl)tetrazole and its derivatives show the same trends, although the amine itself is additionally
insensitive to impact, while its nitro derivative displays likewise lower sensitivities (25 J, 288 N)
than its isomer 7.[14]
The enthalpies and energies of formation were calculated on the CBS-4M level of theory as
implemented in Gaussian 09,[22,23] using the atomization energy method and utilizing experimental
data.[24,25] Gas phase enthalpies were transformed to solid state enthalpies by using Trouton's rule
for neutral compounds.[26] The complete method is extensively described in the literature.[27]
Calculations with the various isomers regarding the position of the proton revealed the 1H-tetrazole
to be the most stable, albeit the difference to the 2H-tetrazole is only marginally. Detonation
parameters of the neutral compounds were calculated with EXPLO5 6.02.[28] The program is based

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on the steady-state model of equilibrium and uses the Becker–Kistiakowsky–Wilson equation of
state (BKW EOS) for gaseous detonation products and the Murnaghan EOS for both solid and
liquid products. The parameters of the BKW EOS in EXPLO5 6.02 are calibrated particularly for
the formation of nitrogen gas, which is the main detonation product for compounds with a high
nitrogen content. It is designed to enable the calculation of detonation parameters at the Chapman–
Jouguet point. The calculations were performed using the maximum densities at room temperature,
measured with a helium pycnometer. The calculated detonation performances of 5–7 and RDX are
summarized in Table 4. The calculated detonation velocities range from 7963 m s−1 (6) up to
8397 m s−1 (5). The calculated detonation pressures are in the range of 237 to 263 kbar and the
volume of gaseous reaction products amounts up to 772 L kg−1 (5). The detonation temperature of 7
(3816 K) is similar to RDX. The parameters of compound 8 were not calculated due to the
unsuccessful dehydration.
Table 4: Energetic properties and detonation parameters of 5–7 and RDX.
6
7
RDX
C6H5N7O4
222.12
37.84
7.4
5
C3H2N10
178.13
78.64
3
C3H2N8O2
182.11
61.53
4
Formula
C3H4N8
152.13
73.66
10
FW / g mol−1
N / % [a]
IS / J [b]
FS / N [c]
ESD / mJ [d]
Tm / °C [e]
Td / °C [f]
> 360
800
—
241
−84.1
1.66
10
250
108
250
120
200
—
152
−60.0
1.56
846
180
188
−43.9
1.69
516
—
204
−21.6
1.80
85
Ω
ρ
/ % [g]
/ g cm−3 [h]
ꢁfH° / kJ mol−1 [i] 460
3120
Calculated detonation parameters (EXPLO5 6.02)
ꢁfU°/ kJ kg−1 [j]
4833
2915
481
−ꢁexU / kJ kg−1 [k] 3481
4929
3678
220
7963
758
5064
3816
263
8251
753
5903
3849
347
8854
785
Tdet / K [l]
2479
237
pCJ / kbar [m]
D / m s−1 [n]
V0 / L kg−1 [o]
8397
772
[a] Nitrogen content; [b] impact sensitivity (BAM drophammer, 1 of 6); [c] friction sensitivity (BAM friction tester, 1 of 6); [d]
sensitivity to electrostatic discharge; [e] melting point; [f] decomposition temperature; [g] oxygen balance (CO2); [h] density at
room temperature; [i] calculated enthalpy of formation; [j] calculated energy of formation; [k] heat of explosion; [l] explosion
temperature; [m] detonation pressure; [n] detonation velocity; [o] volume of gaseous detonation products.

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Conclusions
The goal of this study has been the preparation and thorough characterization of the novel nitrogen-
rich compound 5-(5-amino-2H-1,2,3-triazol-4-yl)-1H-tetrazole (5) and the further derivatization of
the amino moiety into the more energetic azido (6) and nitro (7) groups, as well as the connection
by means of a diazene bridge (8). Low temperature single crystal X-ray diffraction revealed the
position of the benzyl group of the precursor molecule 5-amino-1-benzyl-1,2,3-triazole-4-
carboxamide (2), and likewise the position of the protons of the title compound 5. The compounds
were comprehensively characterized by multinuclear NMR (including 15N for 6 and 7) as well as
vibrational spectroscopy and mass spectrometry. While the amino derivate exhibits a very good
thermal stability (241 °C), as evidenced by DTA, the more energetic derivatives 6–8 are less
thermally stable (128 to 188 °C). With the exception of the friction insensitive 5, the main
compounds 5–8 all have to be classified as sensitive to both impact and friction, as determined by
BAM standards. Although, compounds 5–7 are superior to the commonly used TNT regarding their
calculated detonation parameters (EPXLO5, 6.02), the performance of RDX is not reached. On the
other hand, taking into account the high nitrogen contents of 73.66 (5), 78.64 (6) and 61.53 % (7)
and high enthalpies of formation the compounds might be of interest as anions for primary as well
as secondary explosives, or gun propellants in combination with metal (6) or nitrogen-rich cations
(5 and 7), respectively.[29]
Experimental Section
All chemicals were used as supplied (ABCR, Acros Organics, AppliChem, Sigma-Aldrich, VWR),
if not stated otherwise.
NMR spectra were recorded using the spectrometers JEOL Eclipse 270, JEOL Eclipse 400,
JEOL ECX 400 and Bruker Avance III 400. The measurements were conducted in regular glass
NMR tubes (Ø 5 mm) and, if not stated otherwise, at 25 °C. Tetramethylsilane (1H, 13C) and
nitromethane (14/15N) were used as external standards. As additional internal standard the reference

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values of the partially deuterated solvent impurity (1H) and the fully deuterated solvent (13C) were
used.[30] 13C{1H} and 14N{1H} NMR spectra are simplified as 13C and 14N NMR spectra,
1
respectively. The routinely performed H broad band decoupling is not mentioned explicitly.
Infrared (IR) spectra were recorded on a PerkinElmer BX FT IR spectrometer equipped with a
Smiths DuraSamplIR II diamond ATR unit with pure samples. Transmittance values are
qualitatively described as “very strong” (vs), “strong” (s), “medium” (m) and “weak” (w). Raman
spectra were recorded on a Bruker RAM II spectrometer equipped with a Nd:YAG laser operating
at 1064 nm and a reflection angle of 180°. The intensities are reported as percentages of the most
intense peak and are given in parentheses. Low resolution mass spectra were recorded on a JEOL
MStation JMS-700. Determination of the carbon, hydrogen and nitrogen contents was carried out
by combustion analysis using an Elementar Vario EL (the determined nitrogen values are often
lower than the calculated ones, which is common with nitrogen-rich compounds and cannot be
avoided). Differential thermal analysis was conducted with an OZM Research DTA 552-Ex in open
glass tubes (diameter 4 mm, length about 47 mm) at a heating rate of 5 °C min−1. The temperatures
are given as onset temperatures. Melting points were checked with a Büchi Melting Point B-540 in
open glass capillaries.
Sensitivities to impact (IS) and friction (FS) were determined according to BAM standards,[31]
using a BAM drop hammer and a BAM friction apparatus.[32] The compounds were classified in
compliance with UN guidelines.[21] Impact: insensitive > 40 J, less sensitive ≥ 35 J, sensitive ≥ 4 J,
very sensitive ≤ 3 J; Friction: insensitive > 360 N, less sensitive = 360 N, sensitive < 360 N and
> 80 N, very sensitive ≤ 80 N, extremely sensitive ≤ 10 N. Sensitivities to electrostatic discharge
(ESD) were determined with an OZM Research ESD 2010 EN. The compounds were sieved to
determine the grain size (< 100 µm, 100 to 500 µm, > 500 µm).
The crystal structures of 2 and 5 were determined by single crystal X-ray diffraction on an
Oxford Diffraction Xcalibur 3 or a Bruker D8 Venture diffractometer. Both devices work with
graphite-monochromated molybdenum Kα radiation (λ = 71.073 pm). Data collection and reduction
were performed with CrysAlisPro,[33] or SAINT.[34] The structures were solved with SIR97,[35]

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refined with SHELXL-97,[36] or SHELXL-2013,[37] and finally checked with PLATON,[38] all
integrated into the WinGX software suite.[39] The finalized CIF files were checked with
checkCIF,[40] and deposited at the Cambridge Crystallographic Data Centre as supplementary
publications 1406925 (2) and 1413469 (5).[41] Intra- and intermolecular contacts were analyzed with
Mercury.[42] The illustrations of molecular structures were drawn with ORTEP-3.[43]
Caution! Most compounds prepared herein are energetic compounds sensitive to impact, friction
and electrostatic discharge. Although there were no problems in handling the compounds, proper
protective measures (ear protection, Kevlar® gloves, face shield, body armor and earthed
equipment) should be used.
Benzyl azide (1): Benzyl chloride (106 g, 840 mmol) and sodium azide (82.0 g, 1.26 mol) were
stirred in a mixture of ethanol (400 mL) and water (50 mL) for 20 hours at 95 °C. The suspension
was afterwards poured in water (2 L), divided into four portions and each was extracted with diethyl
ether (2 × 200 mL). The combined organic phases were dried over magnesium sulfate and
evaporated under reduced pressure at 50 °C to obtain a clear, yellow liquid (106 g, 796 mmol,
1
95 %). H NMR (DMSO-d6):
δ
= 7.44–7.34 (m, 5H, CH), 4.44 (s, 2H, CH2). 13C NMR (DMSO-
= −127, −164, −300.
d6):
δ
= 135.6, 128.7, 128.4, 128.1, 53.6 (CH2). 14N NMR (DMSO-d6):
δ
5-Amino-1-benzyl-1,2,3-triazole-4-carboxamide (2): Cyanoacetamide (16.8 g, 200 mmol) and
1 (26.6 g, 200 mmol) were added to sodium (4.60 g, 200 mmol) in ethanol (500 mL) and the
mixture was refluxed for one hour. The precipitate was filtered off and washed with water and
ethanol, then suspended in ethanol/water (4:1, 500 mL) and heated for half an hour. The precipitate
was filtered off again, washed with water, ethanol and diethyl ether to yield a colorless solid
1
(34.5 g, 159 mmol, 80 %). H NMR (DMSO-d6):
δ
= 7.50 (br, 2H, NH2), 7.39–7.20 (m, 5H, CH),
5.45 (s, 2H, CH2). 13C NMR (DMSO-d6):
δ = 164.5 (CONH2), 144.9 (Ctri), 136.0, 128.7, 127.8,
127.4, 121.8 (Ctri), 48.4 (CH2). MS (DEI+): m/z = 217.2 ([M]+). EA (C10H11N5O): calcd. C 55.29, H
5.10, N 32.24 %; found C 55.17, H 4.93, N 32.11 %.

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5-Amino-1-benzyl-1,2,3-triazole-4-carbonitrile (3): Trifluoroacetic anhydride (26.0 mL,
184 mmol) was carefully added to a suspension of 2 (20.0 g, 92.1 mmol) in dry pyridine (210 mL),
while cooled with an ice/water bath. The flask was sealed and the deep red solution was stirred for
16 hours without removing or refreshing the cooling bath. The reaction mixture was poured on ice
(250 g) and stirred for about 24 hours at room temperature. Concentrated hydrochloric acid
(220 mL) was added dropwise, then stirred for about 48 hours at room temperature until a
completely homogenized, light brown suspension was obtained. The precipitate was filtered off,
washed with diluted hydrochloric acid and water, then suspended in toluene and stirred for one
hour. The solvent was removed under reduced pressure and the residue was suspended in n-pentane,
filtered off and washed with n-pentane to yield a pale brownish powder (15.7 g, 78.8 mmol, 86 %).
1H NMR (DMSO-d6):
(s, 2H, CH2). 13C NMR (DMSO-d6):
δ = 7.40–7.30 (m, 3H, CH), 7.25–7.23 (m, 2H, CH), 7.18 (s, 2H, NH2), 5.43
δ
= 148.0 (Ctri), 135.2, 128.7, 127.9, 127.5, 113.7 (Ctri), 101.3
(CN), 48.8 (CH2). MS (DEI+): m/z = 199.1 ([M]+). EA (C10H9N5): calcd. C 60.29, H 4.55, N
35.16 %; found C 60.29, H 4.47, N 34.97 %.
5-(5-Amino-1-benzyl-1,2,3-triazol-4-yl)tetrazole (4): A suspension of 3 (15.9 g, 80.0 mmol),
sodium azide (10.4 g, 160 mmol) and zinc chloride (13.6 g, 100 mmol) in dry tetrahydrofuran
(250 mL) was stirred for 16 hours at 70 °C. Concentrated hydrochloric acid (14 mL) was added to
the cooled down solution, which was then stirred for half an hour. The solvent was removed under
reduced pressure and the residue was suspended in half concentrated hydrochloric acid (300 mL)
and stirred for several hours. The precipitate was filtered off and washed with diluted hydrochloric
acid and water to yield a pale yellow powder (18.8 g, 77.6 mmol, 97 %). 1H NMR (DMSO-d6):
7.37–7.26 (m, 5H, CH), 6.61 (s, 2H, NH2), 5.55 (s, 2H, CH2). 13C NMR (DMSO-d6):
δ =
δ
= 148.6
(Ctri), 142.9 (Ctet), 135.8, 128.7, 127.9, 127.5, 114.4 (Ctri), 48.8 (CH2). MS (DEI+): m/z = 242.2
([M]+). EA (C10H10N8): calcd. C 49.58, H 4.16, N 46.26 %; found C 48.95, H 4.05, N 45.32 %.
5-(5-Amino-2H-1,2,3-triazol-4-yl)tetrazole (5): Sodium was added in small pieces to a clear
red solution of 4 (37.6 g, 155 mmol) in liquid ammonia (about 150 mL) until a deep blue
suspension was obtained, carefully followed by ammonium chloride until the blue color was

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completely gone. The solvent was allowed to slowly evaporate and the residue was dissolved in
water (about 200 mL), then filtered. The filtrate was evaporated under reduced pressure and the
residue was dissolved again in water (200 mL), then acidified with concentrated hydrochloric acid
(40 mL). The precipitate was filtered off and washed with water to yield a yellow powder (22.5 g,
1
148 mmol, 95 %). H NMR (DMSO-d6):
δ
= 16.19 and 14.64 (br, 2H, NH), 6.03 (br, 2H, NH2).
13C NMR (DMSO-d6):
δ
= 149.0 (Ctet), 147.6 (br, Ctri), 111.6 (br, Ctri). IR (ATR): = 3437 (m),
ν
3317 (m), 3227 (w), 3138 (m), 3036 (m), 2976 (m), 2895 (m), 2796 (m), 2700 (m), 2553 (m), 1624
(vs), 1564 (s), 1503 (m), 1467 (m), 1404 (w), 1372 (m), 1332 (w), 1250 (w), 1240 (s), 1214 (m),
1185 (m), 1145 (m), 1090 (s), 1019 (m), 1003 (s), 971 (vs), 866 (vs), 764 (m), 749 (vs), 691 (m)
cm−1. Raman (300 mW):
ν = 1646 (24), 1627 (100), 1571 (8), 1474 (5), 1406 (21), 1250 (8), 1178
(6), 1151 (9), 1104 (13), 1020 (23), 747 (9), 421 (12), 334 (15), 172 (14), 140 (24), 121 (31), 63
(10) cm−1. MS (DEI+): m/z = 152.1 ([M]+). EA (C3H4N8): calcd. C 23.69, H 2.65, N 73.66 %;
found C 24.07, H 2.76, N 73.29 %. DTA (5 °C min−1): Td = 241 °C. Sensitivities (grain size
< 100 µm): IS 10 J, FS 360 N, ESD 800 mJ.
5-(5-Azido-2H-1,2,3-triazol-4-yl)tetrazole (6): Sodium nitrite (2.07 g, 30.0 mmol) was added
to a suspension of 5 (3.04 g, 20.0 mmol) in sulfuric acid (20 %, 200 mL) at 0 °C. The cooling was
removed and the yellow reaction mixture was stirred for three hours at room temperature. Sodium
azide (2.60 g, 40.0 mmol) was then added in small portions and stirred for 30 minutes at room
temperature. The resulting colorless foamy suspension was refluxed until a clear solution was
obtained. The resulting suspension after cooling down was extracted with ethyl acetate (4 ×
150 mL). The combined organic phases were dried over magnesium sulfate and evaporated under
reduced pressure. The residue was suspended in toluene, evaporated again and washed with n-
1
pentane to yield a colorless solid (3.08 g, 17.3 mmol, 87 %). H NMR (DMSO-d6):
δ = 15.81 (br,
NH). 13C NMR (DMSO-d6):
δ δ =
= 147.7 (Ctri), 143.1 (Ctet), 123.0 (Ctri). 14N NMR (DMSO-d6):
−138 (Nβ). 15N NMR (DMSO-d6):
δ
= −11.1 (Ntet), −55.7 (Ntri), −74.1 (Ntri), −101.9 (NHtet), −126.3
(NHtri), −143.2 (Nγ), −148.6 (Nβ), −303.3 (Nα). N{1H} NMR (DMSO-d6):
15
δ = −11.1 (Ntet), −55.4
(Ntri), −74.0 (Ntri), −102.1 (NHtet), −126.1 (NHtri), −143.2 (Nγ), −148.6 (Nβ), −303.3 (Nα). IR

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(ATR): ν = 3524 (w), 3227 (w), 3132 (w), 2923 (w), 2800 (w), 2677 (w), 2426 (w), 2331 (w), 2147
(vs), 1915 (w), 1628 (s), 1525 (vs), 1407 (w), 1356 (w), 1345 (w), 1322 (m), 1308 (w), 1295 (w),
1250 (w), 1209 (s), 1160 (w), 1121 (w), 1103 (w), 1067 (m), 1019 (s), 1006 (m), 977 (s), 835 (m),
795 (m), 769 (m), 757 (s), 717 (w), 703 (w), 694 (w) cm−1. Raman (300 mW): 2163 (12), 1631
(100), 1534 (22), 1445 (5), 1409 (17), 1357 (18), 1326 (9), 1299 (5), 1252 (8), 1219 (11), 1168
(17), 1126 (5), 1022 (16), 978 (9), 797 (6), 760 (11) cm−1. MS (DEI+): m/z = 178.1 ([M]+). EA
(C3H2N10): calcd. C 20.23, H 1.13, N 78.64 %; found C 19.83, H 1.89, N 73.11 %. DTA
(5 °C min−1): Td = 152 °C. Sensitivities (grain size < 100 µm): IS 3 J, FS 10 N, ESD 250 mJ.
5-(5-Nitro-2H-1,2,3-triazol-4-yl)tetrazole (7): Potassium superoxide (4.75 g, 66.9 mmol) and 5
(1.00 g, 6.57 mmol) were stirred in tetrahydrofuran (50 mL) for 72 hours at 60 °C. The solvent was
removed under reduced pressure and ice (80 g) was added to the dry residue, followed by sulfuric
acid (11 mL). The resulting yellow suspension was stirred for one hour, then extracted with methyl
ethyl ketone (5 × 75 mL). The combined organic phases were washed with a saturated sodium
chloride solution (2 × 50 mL), dried over magnesium sulfate and removed under reduced pressure.
The resulting green solid was dried in fine vacuum overnight, pestled, resuspended in
dichloromethane, sonicated for a few minutes and filtered off to yield a pale green solid (814 mg,
4.47 mmol, 68 %).
1H NMR (DMSO-d6):
127.7 (Ctri). 14N NMR (DMSO-d6):
(NO2), −51.1 (Ntri), −65.4 (Ntri), −89.6 (NHtet), −97.2 (NHtri). 15N{1H} NMR (DMSO-d6): −14.8
δ
= 9.93 (br, NH). 13C NMR (DMSO-d6):
δ = 151.1 (Ctri), 147.7 (Ctet),
δ
= −21 (NO2). 15N NMR (DMSO-d6): −14.4 (Ntet), −27.5
(Ntet), −27.9 (NO2), −51.5 (Ntri), −65.8 (Ntri), −90.2 (NHtet), −97.4 (NHtri). IR (ATR): ν = 3221 (w),
3113 (w), 3055 (w), 2908 (w), 1630 (w), 1547 (vs), 1500 (vw), 1472 (w), 1383 (s), 1350 (m), 1244
(w), 1197 (vw), 1138 (m), 1097 (m), 1065 (s), 1021 (w), 1008 (s), 991 (m) 845 (m), 835 (vs), 744
(m), 726 (m), 707 (m) cm−1. Raman (300 mW):
ν = 1652 (12), 1630 (100), 1546 (6), 1470 (16),
1414 (7), 1387 (23), 1340 (23), 1284 (8), 1244 (6), 1201 (7), 1014 (11), 987 (8), 833 (5), 504 (7),
383 (5), 166 (5), 137 (9), 92 (40), 79 (24) cm−1. MS (DEI+): m/z = 182.2 (12 %, [M+]), 30.1
(100 %, [NO+]). EA (C3H2N8O2): calcd. C 19.79, H 1.11, N 61.53 %. found C 19.88, H 1.63, N

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59.98 %. DTA (5 °C min−1): Tmelt = 180 °C, Td = 188 °C. Sensitivities (grain size < 100 µm): IS
4 J, FS 108 N, ESD 250 mJ.
1,2-Bis(4-(tetrazol-5-yl)-1,2,3-triazol-5-yl)diazene dihydrate (8): Potassium permanganate
(1.05 g, 6.67 mmol) was added in small portions to 5 (1.52 g, 10.0 mmol) in aqueous sodium
hydroxide (10 %, 40 mL) at 70 °C. After stirring for two hours at 100 °C, ethanol (10 mL) was
added and stirred for further 15 minutes. The suspension was filtered through kieselgur and washed
until the filtrate was colorless. The combined filtrates were evaporated under reduced pressure, the
residue was suspended in hydrochloric acid (2 M, 100 mL) and stirred for several hours. The
precipitate was filtered off and washed with diluted hydrochloric acid and water to yield a yellow
1
solid (700 mg, 2.08 mmol, 42 %). H NMR (DMSO-d6):
δ
= 10.09 (br, NH). 13C NMR (DMSO-
d6):
δ
= 153.7, 147.2, 126.6. IR (ATR):
ν
= 3522 (w), 3422 (w), 3232 (s), 2824 (w), 2748 (w), 2613
(w), 2501 (m), 2360 (m), 2000 (vw), 1877 (w), 1637 (m), 1611 (m), 1498 (m), 1428 (vw), 1406
(m), 1369 (s), 1344 (m), 1298 (vw), 1245(w), 1220 (w), 1207 (w), 1178 (w), 1143 (w), 1125 (vs),
1076 (vs), 1030 (vs), 1004 (s), 977 (s), 960 (s), 903 (m), 822 (vs), 772 (w), 726 (m), 672 (vw) cm−1.
Raman (300 mW):
ν = 1638 (37), 1613 (16), 1503 (16), 1492 (17), 1469 (100), 1432 (21), 1404
(8), 1369 (56), 1344 (69), 1329 (31), 1298 (10), 1245 (7), 1200 (14), 1182 (5), 1151 (4), 1125 (6),
980 (14), 903 (8), 621 (7), 353 (4) cm−1. MS (FAB−): m/z = 299.1 ([M]+). EA (C3H4N8·2H2O):
calcd. C 21.43, H 2.40, N 66.65 %; found C 22.68, H 2.32, N 66.07 %. DTA (5 °C min−1):
Td = 128 °C. Sensitivities (grain size < 100 µm): IS 2 J, FS 28 N, ESD 700 mJ.
Acknowledgement
The Konrad Adenauer Foundation is gratefully acknowledged for the award of a Ph.D. scholarship
(Carolin Pflüger). Financial support of this work by the Ludwig–Maximilian University of Munich
(LMU), the U.S. Army Research Laboratory (ARL), the Armament Research, Development and
Engineering Center (ARDEC), the Office of Naval Research (ONR) under grant no. ONR.N00014-
12-1-0538, and the Bundeswehr – Wehrtechnische Dienststelle für Waffen und Munition (WTD 91)
under grant no. E/E91S/FC015/CF049 is gratefully acknowledged. The authors acknowledge

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collaborations with Dr. Mila Krupka (OZM Research, Czech Republic) in the development of new
testing and evaluation methods for energetic materials and with Dr. Muhamed Su eska (Brodarski
ć
Institute, Croatia) in the development of new computational codes to predict the detonation and
propulsion parameters of novel explosives. We are indebted to and thank Drs. Betsy M. Rice, Jesse
Sabatini and Brad Forch (ARL, Aberdeen, Proving Ground, MD) for many inspired discussions.
Stefan Huber is thanked for assistance during sensitivity measurements.
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