Preparation and characterization of 3,5-dinitro-1H-1,2,4-triazole

Article abstract of DOI:10.1039/c5dt00888c

Neat 3,5-dinitro-1H-1,2,4-triazole was obtained in quantitative yield from potassium 3,5-dinitro-1,2,4-triazolate and sulfuric acid. The compound was purified by sublimation in vacuo at 110 °C. Pure HDNT is a hygroscopic white solid that is impact and friction sensitive and decomposes explosively upon heating to 170 °C. However, the presence of impurities might lower the decomposition temperature and increase the sensitivity of the material. Potassium 3,5-dinitro-1,2,4-triazolate was prepared from commercially available 3,5-diamino-4H-1,2,4-triazole with sodium nitrite and sulfuric acid. The synthesis of HDNT from 2-cyanoguanidine and hydrazine hydrate without isolation and purification of the 3,5-diamino-4H-1,2,4-triazole intermediate can result in the formation of azidotriazole impurities. A triclinic and a monoclinic polymorph of 3,5-dinitro-1H-1,2,4-triazole were found by X-ray structure determination. In addition, the crystal structure of the hydrate (HDNT)₃·4H₂O, as well as those of several HDNT impurities and decomposition products were obtained.

Full text of DOI:10.1039/c5dt00888c

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Preparation and characterization of 3,5-dinitro-
1H-1,2,4-triazole†
Cite this: DOI: 10.1039/c5dt00888c
R. Haiges,* G. Bélanger-Chabot, S. M. Kaplan and K. O. Christe*
Neat 3,5-dinitro-1H-1,2,4-triazole was obtained in quantitative yield from potassium 3,5-dinitro-1,2,4-
triazolate and sulfuric acid. The compound was purified by sublimation in vacuo at 110 °C. Pure HDNT is a
hygroscopic white solid that is impact and friction sensitive and decomposes explosively upon heating to
170 °C. However, the presence of impurities might lower the decomposition temperature and increase
the sensitivity of the material. Potassium 3,5-dinitro-1,2,4-triazolate was prepared from commercially
available 3,5-diamino-4H-1,2,4-triazole with sodium nitrite and sulfuric acid. The synthesis of HDNT from
2-cyanoguanidine and hydrazine hydrate without isolation and purification of the 3,5-diamino-4H-1,2,4-
triazole intermediate can result in the formation of azidotriazole impurities. A triclinic and a monoclinic
polymorph of 3,5-dinitro-1H-1,2,4-triazole were found by X-ray structure determination. In addition, the
crystal structure of the hydrate (HDNT)3·4H2O, as well as those of several HDNT impurities and decompo-
sition products were obtained.
Received 4th March 2015,
Accepted 16th March 2015
DOI: 10.1039/c5dt00888c
www.rsc.org/dalton
As part of our research on energetic materials, we investi-
gated the preparation of neat HDNT. Herein we report the syn-
Introduction
In recent years, much effort has been devoted to the develop- thesis and purification of HDNT together with the structural
ment of environmentally friendly, green energetic materials characterization of two of its polymorphs, as well as of a
(GEM).1 Important building blocks for energetic materials are HDNT hydrate. We also identified and structurally character-
nitrogen-rich cyclic compounds, such as triazoles and tetra- ized several impurities that were found in HDNT, which was
zoles, which can be further functionalized with explosophore prepared according to literature methods.
groups, such as nitro, N-nitro, azo, or azido. 3-Nitro-1H-1,2,4-
triazole2–5
and
especially
3,5-dinitro-1H-1,2,4-triazole
(HDNT)6,7 have attracted considerable interest for energetic
material and high oxygen carrier applications. A significant
number of compounds containing the 3,5-dinitro-1,2,4-tri-
azolate anion have been prepared and characterized.5,8–16 The
synthesis of HDNT was first described in the 1960s8,9 but the
neat compound has not been isolated. Instead, the compound
has been handled in solution only and subsequently been con-
verted into salts containing the 3,5-dinitro-1,2,4-triazolate
anion. Although related compounds, such as 3-amino-5-nitro-
Experimental part
Caution! The compounds of this work are energetic materials
that might explode under certain conditions (e.g., elevated
temperature, impact, friction or electric discharge). Appropri-
ate safety precautions,20 such as the use of shields or barri-
cades in a fume hood and personal protection equipment
(safety glasses, face shields, ear plugs, as well as gloves and
suits made from leather and/or Kevlar) should be taken all the
time when handling these materials. Pure HDNT decomposes
explosively when heated above 160 °C, and certain impurities
might further lower the decomposition temperature. The subli-
mation of HDNT should be carried-out behind a blast shield
and only on a small scale. Ignoring safety precautions may
lead to serious injuries!
1H-1,2,4-triazole,17
5-azido-3-nitro-1,2,4-1H-triazole18
and
3-nitro-1-(2H-tetrazol-5-yl)-1H-1,2,4-triazol-5-amine19 have been
structurally characterized, to the best of our knowledge, the
crystal structure of HDNT has not been reported so far.
Materials and apparatus
Loker Hydrocarbon Research Institute, University of Southern California,
Los Angeles, CA 90089-1661, USA. E-mail: haiges@usc.edu; Tel: +1-213-7403197
†Electronic supplementary information (ESI) available: Vibrational data and
All chemicals and solvents were obtained from Sigma-Aldrich
or Alfa-Aesar and were used as supplied. NMR spectra were
recorded at 298 K on Bruker AMX500 or Varian VNMRS-600s
spectrometers using (CD3)2CO or D2O solutions in standard
crystallographic reports including packing diagrams. CCDC 1009538,
1013935–1013938 and 1045452. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c5dt00888c
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5 mm o.d. glass tubes. Chemical shifts are given relative to through the addition funnel while the reaction mixture was
neat tetramethylsilane (1H, 13C) or neat CH3NO2 (14N, 15N). stirred vigorously. Immediately, the reaction mixture turned
Raman spectra were recorded at ambient temperatures in red, foamed and formed some dark red precipitate. In
Pyrex glass tubes in the range of 4000–80 cm−1 on a Bruker addition, brown-orange fumes of nitrogen dioxide were pro-
Equinox 55 FT-RA spectrometer using a Nd-YAG laser at duced. After about one to two hours, the addition was com-
1064 nm or a Cary 83 spectrometer using an Ar laser at pleted and 80% sulfuric acid (220 mL) was added carefully
488 nm. Infrared spectra were recorded in the range while the reaction mixture was stirred vigorously in order to
4000–400 cm−1 on a Midac, M Series spectrometer using KBr avoid excessive foam formation. The reaction mixture was then
pellets or on a Bruker Optics Alpha FT-IR ATR spectrometer. refluxed for about 60 minutes and then allowed to cool to
KBr pellets were prepared very carefully using an Econo mini- 40–50 °C. Activated decolorizing charcoal (10 g) was added and
press (Barnes Engineering Co.). Differential thermal analysis the mixture stirred at ambient temperature for eight hours. The
(DTA) curves were recorded with a purge of dry nitrogen gas reaction mixture was then filtered over Celite 545 and the fil-
and a heating rate of 5 °C min−1 on an OZM Research DTA552- trate extracted six times with ethyl acetate (150 mL each). The
Ex instrument with the Meavy 2.2.0 software. The sample sizes combined organic phases were dried over magnesium sulphate
were 3–15 mg. The impact and friction sensitivity data were and the solvent removed immediately using a rotary evaporator
determined with an OZM Research BAM Fall Hammer BFH-10 without (!) heating of the sample. The obtained yellow to orange
and an OZM Research BAM Friction apparatus FSKM-10, oil or paste was dissolved immediately in acetone (200 mL) and
respectively, through five individual measurements that were the yellow solution poured onto potassium carbonate (60 g).
averaged. Both instruments were calibrated using RDX. The Immediately, a gas was evolved and the mixture was stirred at
samples were finely powdered materials that were not sifted.
ambient temperature. After about two hours, the mixture was
filtered and the orange solid residue was washed extensively
with acetone. The combined yellow filtrates were taken to
X-ray crystal structure determination
The single crystal X-ray diffraction data for HDNT-1, HDNT-2, dryness on a rotary evaporator leaving behind a yellow solid.
3, 3·4 (co-crystals), and 5·H2O were collected on a Bruker Recrystallization from water resulted in the isolation of
SMART diffractometer, equipped with an APEX CCD detector, yellow crystals of KDNT·2H2O that were dried in vacuo at 50 °C
using Mo Kα radiation (graphite monochromator) from a fine- for eight hours, resulting in colourless to pale yellow KDNT16
focus tube. The single crystal X-ray diffraction data for the (yield: 52.5 g, 65.9%). DTA: 265 °C decomposition; NMR
remaining structures were collected on a Bruker SMART APEX (CD3CN) δ(ppm): 13C (125.76 MHz) 164.3 (C-NO2);14N
DUO diffractometer, equipped with an APEX II CCD detector, (36.14 MHz) −20.3 (s, ν1/2 = 65 Hz, 2N, C-NO2), −52 (s, ν1/2
=
using Mo Kα radiation (TRIUMPH curved-crystal monochroma- 500 Hz, DNT−).
tor) from a fine-focus tube or Cu Kα from a IμS micro-source.
Synthesis of potassium 3,5-dinitro-1,2,4-triazolate (method 2)27
The frames were integrated using the SAINT algorithm to give
the hkl files corrected for Lp/decay.21 The absorption correc-
In a 1000 mL three-necked round-bottom flask that was cooled
by a water bath, concentrated nitric acid (80 mL) was slowly
added to hydrazine hydrate (20.0 g, 0.40 mol). Water (140 mL)
and 2-cyanoguanidine (33.6 g, 0.40 mol) was added and the
reaction mixture heated to 50 °C for one hour. A solution of
concentrated sulfuric acid (35 mL) in water (300 mL) was
added, and the resulting DAT solution transferred into an
addition funnel from which it was added carefully to a vigor-
ously stirred solution of sodium nitrite (220 g, 3.28 mol) in
water (350 mL) at 50 °C. The procedure was continued as
described above for method 1. A yellow-orange solid was
obtained. Recrystallization from water resulted in the isolation
of yellow crystals that were dried in vacuo at 50 °C for eight
hours, resulting in yellow KDNT containing various impurities
(yield: 54.3 g, 69% based on KDNT).
tion was performed using the SADABS program. The structures
were solved and refined on F2 using the Bruker SHELXTL Soft-
ware Package.22–25 Non-hydrogen atoms were refined aniso-
tropically. ORTEP drawings were prepared using the ORTEP-III
for Windows V2.02 program.26 Further crystallographic details
can be obtained from the Cambridge Crystallographic Data
Centre (CCDC, 12 Union Road, Cambridge CB21EZ, UK (Fax:
(+44) 1223-336-033; e-mail: deposit@ccdc.cam.ac.uk) on
quoting the deposition no. CCDC 1009538, 1013935–1013938
and 1045452, and from the Fachinformationszentrum Karls-
ruhe, 76344 Eggenstein-Leopoldshafen, Germany (Fax: (+49)
7247-808-666, e-mail: crysdata@fiz-karlsruhe.de, http://www.
fiz-karlsruhe.de/request_for_deposited_data.html) on quoting
the deposition numbers CSD 427861–427864.
Synthesis of potassium 3,5-dinitro-1,2,4-triazolate (method 1)27
Synthesis of 3,5-dinitro-1H-1,2,4-triazole (HDNT)
In a 2000 mL three-necked round-bottom flask, equipped with
a reflux condenser, an addition funnel and a mechanical A solution of KDNT (5.937 g, 30.11 mmol) in water (20 mL)
stirrer, a mixture of sodium nitrite (220 g, 3.28 mol) in water was acidified with 20% sulfuric acid (50 mL) and the resulting
(350 mL) was heated to 50 °C using a water bath until all yellow solution extracted four times with ethyl acetate (50 mL
sodium nitrite had dissolved. A solution of 3,5-diamino-1,2,4- each). The combined organic phases were washed with water
triazole (DAT) (40.0 g, 0.404 mol) in water (500 mL) and con- (50 mL), dried over magnesium sulfate and the solvent
centrated sulfuric acid (36 mL) was added slowly and carefully removed using a rotary evaporator. The resulting yellow oil was
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further dried in a high vacuum at 50–60 °C for eight hour, lation of crude HDNT as yellow to dark orange oil or paste.
resulting in light-yellow, solid HDNT (yield: 4.502 g, 93.0%). This crude product contained various acidic impurities, which
HDNT of high-purity was obtained as a white solid through rendered it prone to decomposition. On several occasions,
careful sublimation of the crude HDNT at 100–105 °C in a samples of crude HDNT started to decompose exothermically
vacuum of less than 0.1 mTorr. The temperature was carefully within minutes once the solvent had been removed. These
monitored in order to avoid a potentially explosive decompo- samples started to heat up very fast, reaching temperature in
sition of the HDNT.
excess of 60 °C and released large quantities of brown NO2
DTA: 170 °C (onset) explosive decomposition; friction sensi- gas. It was possible to quench this potentially dangerous
tivity: 144 N; Impact sensitivity: 35 J; NMR (CD3CN) δ(ppm): decomposition reaction through the addition of large amounts
1H (500.13 MHz) 13.6 (ν1/2 = 100 Hz); 13C (125.76 MHz) 157.1 of water. The resulting aqueous HDNT solutions contained
(C-NO2);14N (36.14 MHz) −32.4 (s, ν1/2 = 20 Hz C-NO2).
various amounts of decomposition products and were dis-
carded. The decomposition of the crude HDNT was avoided by
immediately re-dissolving the dark orange evaporation residue
in acetone. When the resulting yellow acetone solution was
treated with an excess of potassium carbonate, carbon dioxide
was evolved and the mixture turned orange. After filtration and
evaporation of the solvent a yellow to orange solid was
obtained. Recrystallization of the solid from water resulted in
the isolation of the dihydrate KDNT·2H2O as a crystalline solid
which could be dried at 50 °C in vacuo.16
Results and discussion
Synthesis of HDNT
The synthetic route for the preparation of HDNT is shown in
Scheme 1.
Potassium 3,5-dinitro-1,2,4-triazolate (KDNT) was prepared
from 3,5-diamino-1,2,4-triazole (DAT, guanazole) through a
Sandmeyer reaction28 according to a modified literature pro-
cedure.27 While the DAT starting material required for the syn-
thesis of HDNT is commercially available, it can be prepared
in high yield from 2-cyanoguanidine (dicyandiamide) and
hydrazine hydrate.29 The addition of a sulfuric acid solution of
DAT to a vigorously stirred aqueous solution of excess sodium
nitrite at 50–60 °C results in nitration of the triazole. It was
found that the yield of the synthesis and the purity of the
resulting KDNT were highly dependent on the addition rate of
the DAT solution as well as the speed at which the solution
was stirred. Low addition rates coupled with vigorous stirring
with a mechanical stirrer instead of a magnetic stirrer resulted
in higher yields and higher purity of the resulting KDNT and,
subsequently, HDNT.
Potassium 3,5-dinitro-1,2,4-triazolate was dissolved in 5 M
sulfuric acid and the solution extracted with ethyl acetate. The
solvent was removed using a rotary evaporator, leaving behind
yellow, very hygroscopic and deliquescent HDNT. According to
1
its H and 13C NMR spectra, the HDNT prepared in this way
contains various amounts of impurities. As already described
before, it was possible to minimize the amount of impurities
through careful control of the reaction condition in the KDNT
synthesis. In addition, it was also noted that the amount of
impurities increases the longer HDNT remains dissolved in
ethyl acetate. HDNT is strongly acidic and catalyses the clea-
vage of ethyl acetate, resulting in the formation of acetic acid
which in turn appears to promote the decomposition of
HDNT. It is therefore recommended to remove the ethyl
acetate solvent immediately after each extraction step.
The crude yellow HDNT was further purified by sublimation
in vacuo at 100–110 °C. Very pure 3,5-dinitro-1H-1,2,4-triazole
was obtained as an off-white amorphous or colourless crystal-
line solid that is hygroscopic and deliquescent. The sublima-
tion of HDNT should only be attempted on a small scale and
behind blast shields. In addition, it is necessary to carefully
monitor and control the temperature during the sublimation
in order to avoid a possible explosion as pure HDNT decom-
poses explosively upon heating to 170 °C (DTA onset). The fric-
tion and impact sensitivity of HDNT was determined as 144 N
and 35 J, respectively. However, it was found that certain impu-
rities might increase the sensitivity of the material and also
lower its explosion temperature. For example, one sample of
crude HDNT showed an explosion temperature of 150 °C with
friction and impact sensitivities of 130 N and 30 J, respectively.
The isolation of DAT prepared from 2-cyanoguanidine and
hydrazine hydrate is complicated and labour intensive.29 Cher-
nyshev et al. developed a procedure for the synthesis of HDNT
from 2-cyanoguanidine and hydrazine hydrate without iso-
lation of the DAT intermediate.27 Following this procedure, we
found it very difficult to obtain pure HDNT. Even after repeated
Extraction of the reaction mixture with ethyl acetate, fol-
lowed by the immediate evaporation of the solvent using a
rotary evaporator at ambient temperature resulted in the iso-
Scheme 1 Synthesis of HDNT.
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sublimation, the resulting HDNT always had a greenish to
light yellow-orange colour and contained various unidentified
impurities. A major concern is that HDNT prepared according
to this procedure showed significantly lower explosion temp-
eratures and higher impact sensitivities than HDNT that was
prepared from commercial DAT. The 14N NMR and vibrational
spectra of these samples indicated the presence of azido com-
pounds and single crystals of 5-azido-3-nitro-1H-1,2,4-triazo-
late were obtained from such an HDNT sample.
Impurities and decomposition products of HDNT
During the course of this work, several HDNT impurities and/
or decomposition products have been identified by their X-ray
crystal structures. However, no efforts were made to purify and
further characterize these compounds other than by their
X-ray crystal structure. From various batches of HDNT that
have been prepared by nitration of DAT, crystals of 5-ethoxy-1-
methyl-3-nitro-1H-1,2,4-triazole 1, 1-acetyl 3,5-diamino-1H-
1,2,4-triazole 2, 1-(i-propyl)-3,5-dinitro-1H-1,2,4-triazole 3 and
a co-crystal of 1-(i-propyl)-3,5-dinitro-1H-1,2,4-triazole 3 and
3-nitro-1H-1,2,4-triazole 4 were obtained. The crystals of these
compounds were generally obtained through recrystallization
of crude HDNT from acetonitrile, ethanol, ethyl acetate, or
acetone. A small amount of crystals of sodium 3-nitro-1,2,4-
triazol-5-olate 5 were obtained when a batch of crude HDNT
was treated with NaBH4,10 and the resulting product was
recrystallized from acetonitrile. The formation of compounds
1–5 can be rationalized through a radical decomposition of
HDNT under the formation of NO2, followed by reaction of the
resulting radical with the solvents ethyl acetate, water or
acetone (Scheme 2). This is consistent with the observation
that the exothermic decomposition of crude HDNT involves
the release of large quantities of brown NO2/N2O4 gas.
Scheme 3 Formation of azidotriazoles.
that had been prepared from 2-cyanoguanidine and hydrazine
hydrate consistently showed significantly lower explosion
temperatures and higher impact sensitivities than the one pre-
pared from commercial DAT. The 14N NMR spectra of HDNT
prepared from 2-cyanoguanidine showed weak resonances at
−146 ppm and −232 ppm and the vibrational spectra of this
HDNT showed bands at around 2100 cm−1. These spectro-
scopic data indicate the presence of azido compounds, which
would explain the increased sensitivity of the material. Con-
clusive evidence for the presence of an azido impurity was
found when an aqueous solution of HDNT, which had been
prepared from 2-cyanoguanidine was treated with PPN+Cl−,10
and the resulting precipitate was recrystallized from acetone
(PPN+ = bis(triphenylphosphine)iminium, ((Ph3P)2N+). The
X-ray structure determination of a resulting single crystal
resulted in the structure of PPN+ 3,5-dinitro-1H-1,2,4-triazolate
in which the anion showed a 25% substitution disorder with
5-azido-3-nitro-1,2,4-triazolate (AzNT). In another instance, the
structure of a crystal containing equal amounts of 5-azido-3-
nitro-1H-1,2,4-triazole (HAzNT) and PPN+ 5-azido-3-nitro-1,2,4-
triazolate (PPNAzNT) was obtained. The formation of the azido
compounds can be rationalized according to Scheme 3.
Batches of HDNT that had been prepared directly from
2-cyanoguanidine and hydrazine hydrate generally contained
more impurities than HDNT that had been prepared by
nitration of commercial DAT. It is troublesome that not even
through repeated sublimation it was possible to obtain pure
HDNT from these batches. It is important to note that HDNT
DAT, prepared through the reaction of 2-cyanoguanidine
and hydrazine hydrate (Scheme 1), which has not been iso-
lated and purified, contains small amounts of unreacted
hydrazine hydrate. The reaction of nitrous acid, formed from
sodium nitrite and sulfuric acid, with hydrazine hydrate
results in the formation of hydrazoic acid,30 which in turn will
form azidotriazoles in the Sandmeyer reaction.
X-ray crystal structures
Single crystals suitable for X-ray crystal structure determi-
nation were obtained for two polymorphs of neat HDNT and
the hydrate (HDNT)·4H2O. In addition, crystal structures were
obtained of the HDNT impurities or decomposition products
5-ethoxy-1-methyl-3-nitro-1H-1,2,4-triazole
1,
1-acetyl-3,5-
diamino-1H-1,2,4-triazole 2, 1-(i-propyl)-3,5-dinitro-1H-1,2,4-
triazole 3, a co-crystal of 1-(i-propyl)-3,5-dinitro-1H-1,2,4-tri-
azole 3 and 3-nitro-1H-1,2,4-triazole 4, sodium 3-nitro-1,2,4-
triazol-5-olate 5, as well as PPN+[H(AzNT)2]− 6 (AzNT = 5-azido-
Scheme 2 Possible pathways for the formation of the HDNT impurities
1–5.
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3-nitro-1,2,4-triazolate). The relevant data and parameters for Further crystallographic data and representations of the unit
the X-ray structure determinations and refinements of the cells for all crystal structures can be found in the ESI.†
investigated compounds are summarized in Tables 1–3.
Colourless crystals of 3,5-dinitro-1H-1,2,4-triazole that were
obtained by sublimation in vacuo belong to space group P21/c
(HDNT-1). The unit cell of this monoclinic modification con-
tains four molecules per unit cell (Z = 4). A triclinic modifi-
Table 1 Crystallographic data for the three HDNT crystal structures
ˉ
cation with six HDNT molecules per unit cell (space group P1)
HDNT-1
HDNT-2
(HDNT)3 4H2O
was obtained by recrystallization from anhydrous acetonitrile
(HDNT-2). The density of the triclinic modification (1.850 g
cm−3) is lower than the one of the monoclinic modification
(1.920 g cm−3). Crystals of the hydrate (HDNT)3·4H2O were
obtained by recrystallization of neat HDNT from moist
acetone. The hydrate crystallizes in the triclinic space group P1
with one formula unit per unit cell. Its density of 1.737 g cm−3
is lower than the one of the two polymorphs of pure HDNT.
The geometry of the HDNT molecule remains virtually
unchanged between the three different crystal structures.
Selected bond lengths and bond angles of the molecule are
listed in Table 2. The observed N–N bond distances range from
1.343(4) to 1.3471(13) Å and are shorter than the ones found
for the 3,5-dinitro-1,2,4-triazolate (DNT) anion (1.350(2) to
1.368(5) Å).16 The five-membered ring contains two shorter
C–N distances (C1–N2 and C2–N3) of 1.309(5) to 1.325(5) and
two longer C–N distances (C1–N3 and C2–N1) of 1.3267(13) to
1.3479(13) Å. This is consistent with the common description
of the 1H-1,2,4-triazole ring having double bonds between the
2–3 and 4–5 positions.
Formula
Mol wt [g mol−1
Temp [K]
λ [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C2HN5O4
159.08
140(2)
0.71073
Monoclinic
P21/c
6.1585(14)
9.083(2)
9.858(2)
90
93.892(3)
90
550.2(2)
4
1.920
0.183
320
11 484
1470
0.0308
103
0.0327
0.0831
1.050
C2HN5O4
159.08
140(2)
0.71073
Triclinic
ˉ
P1
8.7465(15)
8.9684(16)
11.942(2)
111.927(2)
96.726(3)
93.853(2)
856.7(3)
6
1.850
0.176
480
5462
C6H11N15O16
549.30
100(2)
0.71073
Triclinic
P1
6.1906(2)
9.5492(3)
9.5656(3)
111.377(2)
93.467(2)
90.765(3)°
525.22(4)
1
1.737
0.169
280
16 510
5371
0.0241
343
0.0251
0.0554
1.015
]
γ [°]
V [Å3]
Z
ρcalc [g cm−3
]
μ [mm−1
F(000)
]
Reflns collected
Ind reflns
Rint
No. of parameters
R1 [I > 2σ(I)]
wR2 [I > 2σ(I)]
GOF
3826
0.0196
302
0.0499
0.1170
1.036
In the solid-state structure of the monoclinic modification
HDNT-1, individual HDNT molecules are linked through
single N1–H1⋯N3 hydrogen bonds, resulting in chains in
which the individual HDNT molecules are rotated by 61° from
each other (Fig. 1). The chains are oriented along the c-axis of
the crystal.
Table 2 Selected bond lengths [Å] and angles [°] for HDNT in the
crystal structures
The hydrogen bonding of the triclinic polymorph HDNT-2
is more complex than the one of monoclinic HDNT-1. The
molecules form chains along the (011) direction of the crystal
in which units of two coplanar HDNT molecules are linked
through hydrogen bonds to other units that are rotated by 75°.
In addition, every HDNT molecule of a chain is linked to a
single HDNT molecule through a hydrogen bond at the nitro-
gen atom in the 4-position of the triazole ring (N3 and N13). A
part of the hydrogen bonding in the triclinic HDNT polymorph
is depicted in Fig. 2.
As expected, the solid-state structure of the hydrate
(HDNT)3·4H2O is dominated by hydrogen bonding. It is inter-
esting to note that all hydrogen bonds involve water molecules
and that no direct bonds between HDNT molecules can be
observed. A part of the hydrogen bonding in (HDNT)3·4H2O is
shown in Fig. 3.
The crystallographic data for 5-ethoxy-1-methyl-3-nitro-1H-
1,2,4-triazole 1, 1-acetyl-3,5-diamino-1H-1,2,4-triazole 2, 1-(i-
propyl)-3,5-dinitro-1H-1,2,4-triazole 3, sodium 3-nitro-1,2,4-
triazol-5-olate 5, as well as the co-crystals of 1-(i-propyl)-3,5-
dinitro-1H-1,2,4-triazole 3 and 3-nitro-1H-1,2,4-triazole 4, and
5-azido-3-nitro-1,2,4-triazole 6 and PPN+ 5-azido-3-nitro-1,2,4-
triazolate 7 are listed in Table 3. The crystallographic data for
HDNT-1
HDNT-2a
(HDNT)3 4H2Oa
N1–N2
N1–C2
N2–C1
N3–C1
N3–C2
C1–N4
C2–N5
N4–O1
N4–O2
N5–O3
N5–O4
N1–N2–C1
N2–C1–N3
C1–N3–C2
N3–C2–N1
C2–N1–N2
O1–N4–O2
O3–N5–O4
1.3471(13)
1.3267(13)
1.3169(13)
1.3479(13)
1.3118(13)
1.4544(14)
1.4520(14)
1.2191(13)
1.2260(12)
1.2221(12)
1.2204(13)
100.97(8)
117.43(9)
99.66(8)
1.346(3)
1.330(3)
1.313(3)
1.346(3)
1.312(3)
1.451(3)
1.445(3)
1.218(3)
1.221(3)
1.213(3)
1.223(3)
101.1(2)
118.0(2)
99.0(2)
1.343(4)
1.329(5)
1.325(5)
1.336(5)
1.309(5)
1.451(5)
1.452(5)
1.225(4)
1.221(4)
1.216(4)
1.228(4)
101.6(3)
117.3(3)
99.3(3)
112.82(9)
109.11(8)
125.87(10)
126.99(10)
113.3(2)
108.6(2)
125.7(2)
126.2(2)
117.3(3)
107.9(3)
125.8(3)
125.9(3)
a Values given for one of the independent molecules in the asymmetric
unit.
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Table 3 Crystallographic data for the crystal structures of the identified HDNT impurities and decomposition products
1
2
3
3·4
5·H2O
6
Formula
Mol wt [g mol−1
Temp [K]
λ [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C5H8N4O3
172.15
100(2)
1.54178
Triclinic
ˉ
P1
6.6336(8)
7.6993(8)
8.5129(9)
83.636(5)
73.035(5)
65.784(7)
379.25(7)
2
C4H7N5O
141.15
100(2)
0.71073
Triclinic
ˉ
P1
5.25150(10)
7.69060(10)
8.49150(10)
67.2290(10)
85.4460(10)
70.1300(10)
296.854(8)
2
C5H7N5O4
201.16
130(2)
0.71073
Orthorhombic
Pbca
9.4402(19)
10.611(2)
17.296(4)
90
90
90
1732.5(6)
8
1.542
C7H8N9O6
314.22
130(2)
0.71073
Orthorhombic
Pbca
9.467(2)
11.270(3)
23.865(6)
90
C2H3N4NaO4
170.07
140(2)
0.71073
Monoclinic
P21/c
10.7152(18)
8.3768(14)
6.7473(11)
90
97.084(2)
90
601.01(17)
4
C40H31N15O4P2
847.74
100(2)
]
0.71073
Triclinic
ˉ
P1
11.1121(11)
12.5247(12)
16.0476(16)
70.424(2)
72.600(2)
83.653(2)
2007.9(3)
2
90
90
γ [°]
V [Å3]
2546.2(10)
8
1.639
0.144
1288
Z
ρcalc [g cm−3
]
1.508
1.086
180
1.579
0.122
148
1.880
0.232
344
1.402
0.172
876
μ [mm−1
F(000)
]
0.134
832
Reflns collected
Ind reflns
Rint
No. of parameters
R1 [I > 2σ(I)]
wR2 [I > 2σ(I)]
GOF
8069
1315
0.0241
141
0.0300
0.0823
1.055
35 219
2865
0.0256
109
0.0288
0.0807
1.123
13 391
2124
0.0393
129
0.0435
0.0943
1.024
15 158
3102
0.0323
201
0.0551
0.1588
1.052
6577
1444
0.0417
112
0.0433
0.1008
1.055
48 323
12 028
0.0605
550
0.0692
0.1441
1.026
Fig. 1 Part of a chain made through hydrogen bonding in the monocli-
nic crystal structure HDNT-1. Thermal ellipsoids are shown at the 50%
probability level. Hydrogen atom positions were determined from the
electron density map and are depicted as spheres of arbitrary radius.
The N1–N3 distance is 2.837(1) Å.
the structure of PPN+ 3,5-dinitro-1H-1,2,4-triazolate that is
disordered with 5-azido-3-nitro-1,2,4-triazolate is given in
the ESI.†
5-Ethoxy-1-methyl-3-nitro-1H-1,2,4-triazole 1 crystallizes in
ˉ
the triclinic space group P1 with two molecules per unit cell.
In the solid-state structure, the molecules are aligned along
parallel planes. The shortest distances between molecules of
neighbouring planes are 3.007(2) Å (O2–O2′) and 3.299(2) Å
(C1–C2′) (Fig. 4).
In the solid-state structure of 1-acetyl 3,5-diamino-1H-1,2,4-
triazole 2, the molecules are associated by N–H⋯N and
N–H⋯O hydrogen bonds, forming planar layers (Fig. 5). The
shortest distances between molecules of neighbouring planes
are 3.1592(8) Å (C3–N4′) and 3.3351(2) Å (N3–N4′).
Fig. 2 Hydrogen bonding in the crystal structure of triclinic HDNT-2.
Thermal ellipsoids are shown at the 50% probability level. Some nitro
groups have been omitted for clarity. Hydrogen atoms are depicted as
spheres of arbitrary radius. The hydrogen atoms H1/H1a and H3/H3a
show a 1 : 1 positional disorder, only one of the disordered atoms is
shown per molecule. Selected distances (Å): N1–N12 2.959(2), N2–N2
2.975(3), N6–N13 2.858(3), N11–N11 2.971(3).
1-(i-propyl)-3,5-dinitro-1H-1,2,4-triazole 3 crystallizes in the
orthorhombic space group Pbca with eight symmetry related
molecules in the unit cell (Z = 8). The molecule is depicted in
Fig. 6. The five-membered ring is almost co-planar with both
nitro-groups (dihedral angles of 5.7° and 14.0°) and is perpen-
dicular to the plane of the isopropyl group.
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Fig. 6 Crystal structure of 1-(i-propyl)-3,5-dinitro-1H-1,2,4-triazole 3.
Thermal ellipsoids are shown at the 50% probability level. Hydrogen
atoms have been omitted for clarity. Selected distances (Å) and angles
(°): C2–N3 1.311(2), C1–N3 1.334(2), C2–N1 1.345(2), C1–N2 1.318(2),
N1–N2 1.349(2), C2–N5 1.456(2), C1–N4 1.451(2), N4–O1 1.219(2), N4–
O2 1.218 (2), N5–O3 1.2147(19), N5–O4 1.221 (2), N1–C3 1.491(2), N1–
N2–C1 101.75(13), N2–N1–C2 107.67(12), C2–N3–C1 99.91(13), N3–
C2–N1 113.05(14), N3–C1–N2 117.62(14), O1–N4–O2 124.94(14), O3–
N5–O4 125.38(15).
Fig. 3 Hydrogen bonding in the crystal structure of (HDNT)3·4H2O.
Thermal ellipsoids are shown at the 50% probability level. Hydrogen
atom positions were determined from the electron density map and are
depicted as spheres of arbitrary radius. Selected distances (Å): N1–O13
2.849(4), N7–O13 2.587(4), N8–O16 2.882(3), N13–O14 2.984(5), O3–
O16 2.927(4).
Similar to pure 1-(i-propyl)-3,5-dinitro-1H-1,2,4-triazole 3,
the compounds 1-(i-propyl)-3,5-dinitro-1H-1,2,4-triazole 3 and
3-nitro-1H-1,2,4-triazole 4 co-crystallize in the orthorhombic
space group Pbca with eight symmetry related formula units
per unit cell (Z = 8). However, the unit cell of the co-crystal 3·4
(V = 2546.2(10) Å3) is almost 50% larger than that of the neat 3
(V = 1732.5(6) Å3). The asymmetric unit of the crystal structure
3·4 is depicted in Fig. 7. The closest distances between mole-
cules 3 and 4 in the crystal structure are 2.820(3) and 2.854(3)
Å. The geometry of compound 3 remains virtually unchanged
going from the structure of the neat compound 3 to the co-
crystal 3·4.
Sodium 3-nitro-1,2,4-triazol-5-olate 5 crystallizes as mono-
hydrate in space group P21/c with four symmetry related
formula units in the unit cell (Z = 4). Not surprisingly, the
crystal structure does not consist of isolated ions but is domi-
nated by interactions between the sodium cation and the
Fig. 4 Crystal structure of 5-ethoxy-1-methyl-3-nitro-1H-1,2,4-triazole
1. Thermal ellipsoids are shown at the 50% probability level. Hydrogen
atoms have been omitted for clarity. Selected distances (Å) and angles
(°): C1–N1 1.351(2), C2–N1 1.326(2), N2–C2 1.346(2), N3–C1 1.311(2),
C1–N4 1.455(2), N2–N3 1.364(2), N2–C5 1.461(2), N4–O2 1.223(2), N4–
O3 1.227(2), C2–O1 1.321(2), C3–O1 1.467(2), C1–N1–C2 100.1(1), N1–
C2–N2 117.7(1), C2–N2–N3 109.1(1), N2–N3–C1 100.9(1), N3–C1–N1
118.2(1), O2–N4–O3 125.4(1).
Fig. 5 Intermolecular hydrogen bonding in the crystal structure of
1-acetyl 3,5-diamino-1H-1,2,4-triazole 2. Thermal ellipsoids are shown
at the 50% probability level. Some hydrogen atoms have been omitted
for clarity. Selected distances (Å): N2–N4’ 3.0771(5), N3–N5’ 3.0160(5),
N5–O1’ 3.0174(6).
Fig. 7 Asymmetric unit of the co-crystal of 1-(i-propyl)-3,5-dinitro-1H-
1,2,4-triazole 3 and 3-nitro-1H-1,2,4-triazole 4. Thermal ellipsoids are
shown at the 50% probability level. Some hydrogen atoms have been
omitted for clarity.
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triazol-5-olate anion as well as the water molecule. The solid-
state structure of 5·H2O is depicted in Fig. 8.
Conclusions
When a sample of HDNT, which had been prepared from The important energetic building block 3,5-dinitro-1H-1,2,4-
hydrazine hydrate, was reacted with PPN+Cl− and the resulting triazole (HDNT) was structurally characterized for the first
PPN+DNT− was recrystallized from acetone, single crystals of time. Neat HDNT was obtained in quantitative yield from pot-
PPN+[H(AzNT)2]− (AzNT = 5-azido-3-nitro-1,2,4-triazolate) were assium 3,5-dinitro-1,2,4-triazolate and sulfuric acid, followed
obtained. The solid-state structure of 6 contains isolated PPN+ by extraction with ethyl acetate. The compound was isolated as
cations and anions in which two AzNT− parts that are associ- a pale yellow solid, which can be further purified by sublima-
ated through a hydrogen bond between the N atoms in the tion to give colourless crystals. Pure HDNT is a hygroscopic
1-position of both triazole moieties (N–N distance: 2.655(3) Å). white solid that decomposes explosively upon heating to
Both 5-azido-3-nitro-1,2,4-triazolate moieties have essentially 170 °C. However, the presence of impurities might lower the
identical geometries and are depicted in Fig. 9. The H-atom decomposition temperature and increase the sensitivity of the
shows in a 1 : 1 positional disorder between both triazolate material.
moieties, occupying positions near N3 and N10.
Potassium 3,5-dinitro-1,2,4-triazolate was prepared from
commercially available 3,5-diamino-1,2,4-triazole through a
Sandmeyer reaction with sodium nitrite and sulfuric acid. The
synthesis of HDNT from 2-cyanoguanidine and hydrazine
hydrate in one step without isolation and purification of the
3,5-diamino-1,2,4-triazole intermediate is not recommended
as it might lead to the formation of very sensitive azidotriazole
impurities.
3,5-Dinitro-1H-1,2,4-triazole was characterized by its multi-
nuclear NMR and vibrational spectra, as well as its X-ray
crystal structure. The crystal structures of several HDNT impu-
rities and decomposition products were obtained.
Acknowledgements
The Office of Naval Research (ONR) and the Defence Threat
Reduction Agency (DTRA) financially supported this work. We
acknowledge NSF CRIF grant 1048807 for an X-ray diffracto-
meter. We thank Profs. G. K. S. Prakash and G. A. Olah for
their help and stimulating discussions. G.B.C. acknowledges
support from the Fonds de recherche du Québec-Nature et
technologies (FQRNT) and from the Natural Sciences and
Engineering Research Council of Canada (NSERC).
Fig. 8 Crystal structure of sodium 3-nitro-1,2,4-triazol-5-olate 5·H2O.
Thermal ellipsoids are shown at the 50% probability level. Hydrogen
atoms are depicted as spheres of arbitrary radius.
Notes and references
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