5-(Fluorodinitromethyl)-2H-tetrazole and its tetrazolates - Preparation and Characterization of New High Energy Compounds

Article abstract of DOI:10.1039/c5dt00291e

5-(Fluorodinitromethyl)-2H-tetrazole (HFDNTz) has been prepared by the cycloaddition reaction of HN₃ with F(NO₂)₂CCN, which in turn was prepared by aqueous fluorination of sodium dinitrocyanomethanide. HFDNTz was converted into the ammonium, silver and tetraphenylphosphonium 5-(fluorodinitromethyl)tetrazolates. While the reaction of trinitroacetonitrile with HBr, followed by the treatment with NaOH, resulted in the formation of sodium dinitrocyanomethanide, the reaction of trinitroacetonitrile with aqueous ammonia produced ammonium dinitrocyanomethanide. Hydrazinium dinitromethanide was obtained from trinitroacetonitrile and hydrazine hydrate. All compounds were fully characterized by multinuclear NMR spectroscopy, IR spectroscopy and X-ray crystal structure determinations. Initial safety testing (impact and friction sensitivity) and thermal stability measurements (DTA) were also carried out.

Full text of DOI:10.1039/c5dt00291e

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5-(Fluorodinitromethyl)-2H-tetrazole and its
tetrazolates – Preparation and Characterization of
New High Energy Compounds†
Cite this: DOI: 10.1039/c5dt00291e
Ralf Haiges* and Karl O. Christe
5-(Fluorodinitromethyl)-2H-tetrazole (HFDNTz) has been prepared by the cycloaddition reaction of HN3
with F(NO2)2CCN, which in turn was prepared by aqueous fluorination of sodium dinitrocyanomethanide.
HFDNTz was converted into the ammonium, silver and tetraphenylphosphonium 5-(fluorodinitromethyl)
tetrazolates. While the reaction of trinitroacetonitrile with HBr, followed by the treatment with NaOH,
resulted in the formation of sodium dinitrocyanomethanide, the reaction of trinitroacetonitrile with
aqueous ammonia produced ammonium dinitrocyanomethanide. Hydrazinium dinitromethanide was
obtained from trinitroacetonitrile and hydrazine hydrate. All compounds were fully characterized by multi-
nuclear NMR spectroscopy, IR spectroscopy and X-ray crystal structure determinations. Initial safety
testing (impact and friction sensitivity) and thermal stability measurements (DTA) were also carried out.
Received 21st January 2015,
Accepted 18th March 2015
DOI: 10.1039/c5dt00291e
www.rsc.org/dalton
under-oxidized. 5-Nitrotetrazolate12 has an OB of 14.0% for
combustion to CO but the recently investigated 5-(trinitro-
Introduction
Tetrazoles are a fascinating class of compounds. The parent methyl)tetrazolate5 has an OB of 29.4%. The general disadvan-
compound 1H-tetrazole has a nitrogen content of 80%, result- tage of most 5-(trinitromethyl)tetrazolates are their high
ing in a relatively high heat of formation of about 330 kJ impact (IS) and friction sensitivities (FS) (e.g. IS = 0.5 J and
mol−1 1–3
.
At the same time, tetrazoles can exhibit astonishing FS < 1 N for the rubidium and cesium salts).5
high thermal stabilities which results in a wide array of appli-
The instability of the trinitromethyl group toward cata-
cation in agriculture, medicine and biology.4 For energetic strophic decomposition is well established. It has been found
materials applications, tetrazole is usually further functiona- that the fluorodinitromethyl group –CF(NO2)2 is generally
lized with explosophore groups such as nitro, N-nitro, azo, or more stable than the trinitromethyl group –C(NO2)3 without
azido.5–15
incurring too much of a performance penalty. The 5-(fluoro-
In recent years, much effort in energetic materials research dinitromethyl)tetrazolate anion has an OB of 20.9% for
was dedicated to the synthesis of novel energetic highly over- combustion to N2, CO and CF4. Fluorine-containing com-
oxidized compounds that can be used to replace ammonium pounds such as Teflon or Viton are common ingredients
perchlorate as high-oxygen carrier in solid rocket propellant of metallized formulations for flares and pyrotechnics (e.g.
formulations. An expression that is often being used in order MTV: Mg/Teflon/Viton). The highly exothermic formation of
to indicate the degree of oxidation of a compound is the metal fluorides during combustion increases the flame
oxygen balance (OB). In its original form, the OB was defined temperature which in turn improves the performance of the
as percentage of oxygen required for complete conversion of a formulation.
molecule to carbon dioxide, water and metal oxide.16 Because
The synthesis of 5-(fluorodinitromethyl)-2H-tetrazole
if the usually high combustion temperatures in rocket engines, (HFDNTz) by reaction of fluorodinitroacetonitrile with sodium
it is more useful to calculate the OB of a rocket propellant azide or trimethylsilyl azide has been reported but the
based on combustion to carbon monoxide instead of carbon obtained tetrazole was not isolated and directly converted into
monoxide. While energetic, tetrazoles are usually notoriously the sodium or ammonium salt. The tetrazole and the salts
were identified only by IR and 19F NMR spectra and have not
been well characterized.17,18
Loker Hydrocarbon Research Institute, University of Southern California, Los
In this manuscript we report the synthesis and full charac-
Angeles, CA 90089-1661, USA. E-mail: haiges@usc.edu; Tel: +1-213-7403197
terization of 5-(fluorodinitromethyl)-2H-tetrazole and three
†Electronic supplementary information (ESI) available: Crystallographic reports
salts with the energetic 5-(fluorodinitromethyl)tetrazolate
including packing diagrams. CCDC 1044179–1044181. For ESI and crystallo-
anion.
graphic data in CIF or other electronic format see DOI: 10.1039/c5dt00291e
This journal is © The Royal Society of Chemistry 2015
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Synthesis of trinitroacetonitrile
Experimental part
Under an atmosphere of nitrogen, a mixture of cyanoaceta-
mide (16.8 g, 0.2 mol) and dichloromethane (50 mL) was
cooled to 0 °C. While stirring vigorously, 100% nitric acid
(32 mL) was added through an addition funnel within a time
period of 2 minutes. The cyanoacetamide dissolved and a
yellow two-layer mixture was obtained. While maintaining a
temperature of 0 °C, oleum (20% SO3) (38 mL) was slowly
added drop wise and the mixture then stirred vigorously at
ambient temperature for an additional 8–10 hours until all
gas-evolution stopped. The pale yellow two-phase mixture was
transferred into a separatory funnel and the upper organic
layer removed. The lower acid layer was extracted three times
with dichloromethane (30 mL each). The combined organic
layers were extracted twice with cold (−5 °C) concentrated sul-
phuric acid (15 mL each) and the obtained colourless solution
kept over magnesium sulfate.
Caution! The compounds of this work are energetic materials
that might explode under certain conditions (e.g. elevated
temperatures, impact, friction or electric discharge). Appro-
priate safety precautions,19 such as the use of shields or
barricades 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. Ignoring safety precau-
tions may lead to serious injuries!
Materials and apparatus
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
5 mm glass tubes. Chemical shifts are given relative to neat
tetramethylsilane (1H, 13C) or neat CH3NO2 (14N, 15N). Raman
spectra were recorded at ambient temperatures in Pyrex glass
tubes in the range of 4000–80 cm−1 on a Bruker Equinox 55
FT-RA spectrometer using a Nd-YAG laser at 1064 nm or a
Cary 83 spectrometer using an Ar laser at 488 nm. Infrared
spectra were recorded in the range 4000–400 cm−1 on Midac M
Series or Bruker Optics Alpha ATR FT-IR spectrometers.
Solid samples were recorded as KBr pellets or with an ATR
attachment. The KBr pellets were prepared using an Econo
mini-press (Barnes Engineering Co.). Gaseous samples were
kept in a 5 cm Pyrex glass cell that was equipped with AgCl
windows. Differential thermal analysis (DTA) curves were
recorded using a purge of dry nitrogen gas and a heating rate
of 5 °C min−1 on an OZM Research DTA552-Ex instrument
with the Meavy 2.2.0 software. The sample size was 3–15 mg.
The impact and friction sensitivity data were determined on
an OZM Research BAM Fall Hammer BFH-10 and an OZM
Research BAM Friction apparatus FSKM-10, respectively,
through five individual measurements that were averaged.
Both instruments were calibrated using RDX. The samples
were finely powdered materials that were not sifted.
Neat trinitroacetonitrile was obtained as a colourless solid
by removing the solvent from a cold dichloromethane solution
(−40 °C) on a vacuum line.
NMR (CDCl3) δ(ppm): 13C (100.54 MHz) 103.4 (s, CN), 112.1
1
(sept, J(13C14N) = 9.5 Hz, C(NO2)3); 14N (36.14 MHz) −45.4 (s,
1
1
ν = 20 Hz, NO2), −272 (s, ν = 350 Hz, CN); Raman (25 °C,
2
2
50 mW): 2265 (7.8), 1628 (1.9), 1623 (2.1), 1350 (1.4), 1344
(1.4), 1276 (3.1), 1164 (1.5), 943 (4.6), 856 (6.8), 801 (0.8), 657
(0.9), 477 (2.2), 444 (2.5), 380 (6.6), 360 (10.0), 200 (3.8), 151
(6.5), 110 (7.6) cm−1
.
Synthesis of sodium dinitrocyanomethanide27
The obtained solution of (NO2)3CCN in CH2Cl2 (100 mL) was
added drop wise to a stirred solution of methanol (50 mL) and
48% aqueous HBr (100 mL). The mixture was stirred at
ambient temperature for about 4 hours during which the solu-
tion gradually turned from colourless to reddish brown and
evolved brown fumes of bromine. The pH of the mixture was
then adjusted to pH 10 with 3 M NaOH in methanol. The now
milky, yellow mixture was taken to dryness on a rotary evapor-
ator. The yellow solid residue was extracted five times with
ethyl acetate (70 mL each). The combined organic phases were
carefully evaporated on a rotary evaporator without heating.
Pumping on a vacuum line at ambient temperature for
X-ray crystal structure determination
The single crystal X-ray diffraction data were collected on a 12 hours resulted in the isolation of a yellow solid residue
Bruker SMART APEX DUO diffractometer, equipped with an (yield: 18.2 g, 53.2% based on 0.2 mol cyanoacetamide). Single
APEX II CCD detector, using Mo Kα radiation (TRIUMPH crystals of Na[(NO2)2CCN]·H2O were obtained by recrystalliza-
curved-crystal monochromator) from
The frames were integrated using the SAINT algorithm20 to
give the hkl files corrected for Lp/decay. The absorption (100.54 MHz) 109.1 (s, CN), 157.0 (s, C(NO2)2); 14N (36.14 MHz)
a
fine-focus tube. tion from an ethanol–water solution.
DTA: 150 °C (exotherm); NMR (acetone-d6) δ(ppm): 13C
correction was performed using the SADABS program.21 The −20.6 (s, ν = 40 Hz, NO2), −88 (s, ν = 320 Hz, CN).
structures were solved and refined on F2 using the Bruker
Raman (25 °C, 20 mW): 2244 (7.7), 2226 (4.4), 1493 (1.0),
1
2
1
2
SHELXTL Software Package.22–25 Non-hydrogen atoms were 1442 (1.5), 1433 (2.1), 1377 (8.8), 1295 (1.3), 1260 (5.7), 1250
refined anisotropically. Unless noted otherwise, the positions (5.7), 1230 (10.0), 1159 (2.6), 1153 (1.8), 1070 (0.6), 1026 (0.2),
of hydrogen atoms attached to heteroatoms have been located 1004 (0.2), 921 (0.3), 883 (1.4), 865 (7.1), 858 (8.5), 778 (0.5),
from the difference electron density map. ORTEP drawings 769 (0.8), 753 (0.3), 731 (0.3), 577 (0.9), 515 (0.7), 505 (0.8), 469
were prepared using the ORTEP-III for Windows V2.02 (1.1), 440 (0.5), 408 (1.1), 273 (2.0), 217 (3.4), 212 (3.3), 151
program.26
(4.2), 117 (7.4), 98 (7.3) cm−1; IR (ATR): 3583 (m), 3511 (m),
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2230 (ms), 1631 (m), 1611 (m), 1498 (s), 1481 (s), 1424 (m), cooling the solution with an ice/water bath to 0 °C, a stream
1376 (w), 1224 (vs), 1150 (s), 861 (w), 855 (w), 792 (vw), 773 (w), of 10% fluorine in nitrogen was introduced at a rate of approx.
744 (m), 569 (vw), 497 (vw), 417 (vw) cm−1
.
10 l h−1. The off-gas was swept through four traps at −78 °C and
then vented through a bubbler that contained perfluorinated
Krytox GPL107 oil. After about 3 hours, the fluorine stream
Synthesis of ammonium dinitrocyanomethanide
A concentrated aqueous ammonia solution (5 mL) was added was stopped and replaced by a pure nitrogen stream. This
drop wise to a solution of (NO2)3CCN (400 mg, 2.28 mmol) in stream was maintained for an additional two hours in order to
CH2Cl2 (5 mL). Immediately, a yellow reaction mixture was sweep all fluorinated products into the traps. The content of
obtained that is weakly effervescent. After stirring for 12 hours all four traps was combined and fluorodinitroacetonitrile was
at ambient temperature, the reaction mixture was taken to obtained as a colourless liquid. The crude product was puri-
dryness on a vacuum line, resulting in a yellow solid (yield: fied by fractional condensation using cold traps at −31 °C,
314 mg, 93%.) Single crystals were obtained from an aqueous −78 °C and −196 °C. The −31 °C fraction consisted of water
solution by slow evaporation of the solvent.
and (NO2)3CF, and the −196 °C trap contained CO2, SiF4, and
DTA: 240 °C (exotherm); NMR (D2O) δ(ppm): 1H some NO2. The fluorodinitroacetonitrile (5.35 g, 55.2%)
(599.80 MHz) 7.2 (s br, NH4), δ(ppm): 13C (100.54 MHz) 111.8 stopped in the −78 °C trap.
14
2
NMR (CDCl3) δ(ppm): 13C (100.54 MHz) 104.8 (d, J(13C19F
1
(s, CN), 152.4 (s, C(NO2)2); N (36.14 MHz) −23.1 (s, ν = 50
2
14
Hz, NO2), −89 (s, ν = 300 Hz, CN), −363.4 (quint, J( H N) = = 35.3 Hz, CN), 105.5 (d, quint, 1J(13C19F) = 298.1 Hz, 1J
1
1
1
2
56.9 Hz, NH4); IR (ATR): 3500–2800 (br, s), 2224 (ms), 1791 (w), (13C14N) = 3.0 Hz, CF(NO2)2); 14N (36.14 MHz) −36.7 (d, 2J
1661 (m), 1610 (w sh), 1523 (w sh), 1477 (m sh), 1396 (s), 1341 ( N F) = 11.2 Hz, ν = 5 Hz, NO2), −95 (s, ν = 320 Hz, CN); 19F
14 19
1
2
1
2
(m sh), 1207 (vs), 1144 (s sh), 1110 (s), 852 (w), 827 (w), 788 (470.55 MHz) −90.8 (quint, J(14N19F) = 11.3 Hz, CF(NO2)2); IR
2
(w), 772 (m), 744 (s), 566 (m), 501 (m), 433 (w) cm−1
.
(gas-phase, 10 Torr): 2914 (vw), 2261 (m), 1632 (vs), 1297 (s),
1093 (m), 1022 (vw), 842 (w), 801 (s), 794 (s sh), 655 (w) cm−1
.
Synthesis of tetraphenylphosphonium dinitrocyanomethanide
Synthesis of HFDNTz
A solution of PPh4Cl (0.400 g; 1.07 mmol) in water (5 mL) was
added to a solution of Na[(NO2)2CCN] (0.153 g; 1.00 mmol) in In a 250 mL round bottom flask, a mixture of NaN3 (3.00 g,
water (5 mL). The precipitate was filtered off, washed with 46.0 mmol) and CCl4 (50 mL) was cooled to 0 °C using an ice
water (10 mL) and dried on a vacuum line resulting in a pale bath and acetic acid (15 mL) was added slowly. After
yellow solid (yield: 0.452 g; 96%). DTA: 180 °C (endotherm, 5 minutes, a solution of fluorodinitroacetonitrile (1.20 g,
melting), 240 °C (exotherm); IR (ATR): 3086 (vw), 3071 (vw), 8.76 mmol) in CCl4 was added slowly through an addition
2956 (vw), 2923 (vw), 2892 (vw), 1593 (s), 1480 (w), 1435 (s), funnel. When the addition was complete, the mixture was
1395 (vw), 1358 (vw), 1314 (m), 1215 (m), 1185 (vw), 1161 (m), stirred for 10 hours at ambient temperature. The solvent was
1106 (s), 1073 (m), 1025 (m), 1025 (vw), 996 (m), 970 (m), 937 removed using a rotary evaporator. The gel-like, colourless
(vw), 835 (m), 795 (m), 754 (m), 721 (s), 688 (s), 615 (w), 523 residue was dissolved in CH2Cl2 (20 mL) and 2 M H2SO4
(vs), 447 (w) cm−1
.
(10 mL). The organic phase was removed and the aqueous
phase extracted three times with CH2Cl2 (15 mL each). The
combined organic phases were dried over magnesium sul-
Synthesis of hydrazinium dinitromethanide
A solution of hydrazinium hydrate (1 mL) in water (1 mL) was phate. The solvent was carefully evaporated on a rotary evapor-
added drop wise to a solution of trinitroacetonitrile (200 mg, ator. The remaining colourless, oily liquid was dried by
1.14 mmol) in water (5 mL). The reaction was exothermic and pumping for several hours on a vacuum line at ambient tem-
a colourless gas was evolved. The orange reaction mixture perature, resulting in a colourless solid (yield: 1.42 g, 84.3%).
was allowed to evaporate under air, resulting in pale yellow
[N2H5][(NO2)2CH].
DTA: 110 °C (explosion); NMR (CDCl3) δ(ppm): 1H
(599.80 MHz) 14.0 (s, CN4H); 13C (150.84 MHz) 115.2 (d,
2
DTA: 134 °C (exotherm); NMR (DMSO-d6) δ(ppm): 1J(13C19F), = 290.1 Hz CF(NO2)2), 153.9 (d, J(13C19F = 25.9 Hz,
1H (599.80 MHz) 5.6 (s br, N2H5), 8.3 (s, (NO2)2CH); CN4); N (36.14 MHz) −27.3 (s, ν = 70 Hz, NO2), −50 (s, ν =
14
1
2
1
2
13C (150.84 MHz) 165.6 (s, CH(NO2)2); 14N (36.14 MHz) −24.1 350 Hz, CN4); 19F (564.33 MHz) −98.1 (s, CF(NO2)2); Raman
1
1
(s, ν = 100 Hz, NO2), −336 (s, ν = 600 Hz, N2H5); IR (DTA): (25 °C, 20 mW): 3100–2900 (3.9), 1701 (2.1), 1693 (2.0), 1611
2
2
3600–2800 (br, m), 1604 (w), 1585 (w), 1499 (vw), 1483 (w), (2.4), 1482 (5.7), 1424 (2.4), 1359 (4.2), 1313 (2.2), 1239 (1.6),
1459 (vw), 1436 (m), 1341 (w), 1298 (w), 1251 (vw sh), 1240 1210 (2.7), 1188 (2.0), 1104 (2.9), 1081 (2.0), 1057 (1.6), 1034
(vw sh), 1192 (m), 1105 (s), 1071 (m), 997 (m), 948 (w), 758 (m), (1.5), 982 (6.4), 956 (3.4), 837 (10.0), 801 (4.2), 544 (2.4), 539
719 (s), 687 (s), 615 (vw), 568 (vw), 522 (vs), 503 (m sh), 470 (2.3), 425 (3.1), 397 (3.7), 371 (8.6), 300 (2.6), 282 (2.8), 196
(m sh), 436 (w sh), 411 (vw) cm−1
Synthesis of fluorodinitroacetonitrile28
.
(3.3) cm−1; IR (KBr): 3072 (w), 3069 (vw), 3012 (w), 2911 (w),
2774 (w), 2682 (vw), 2593 (vw), 1694 (s), 1611 (vs), 1478 (w),
1422 (w), 1362 (m), 1307 (m), 1240 (s), 1211 (m), 1173 (m),
A solution of Na[(NO2)2CCN] (10.0 g, 65.5 mmol) in water 1093 (vw), 1078 (w), 1054 (m), 1031 (s), 980 (m), 883 (m),
(30 mL) was placed in a 1″ o.d. FEP reactor equipped with a 849 (m), 836 (s), 800 (s), 745 (w), 695 (vw), 663 (vw), 594 (m),
magnetic stirrer, a gas inlet and a gas outlet tube. After 582 (m), 549 (w), 459 (vw), 403 (vw) cm−1
.
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2
Synthesis of [NH4][FDNTz]
Hz, CN4); 150.8 (d, J(13C19F = 23.2 Hz, CN4); 14N (36.14 MHz)
1
1
−39.1 (s, ν = 50 Hz, NO2), −52 (s, ν = 380 Hz, CN4);
2
2
A solution of 20% NH3 in water (5 mL) was added to a solution
of HFDNTz (400 mg, 2.08 mmol). The resulting light yellow
solution was allowed to evaporate, resulting in crystalline
[NH4][FDNTz] (yield: 992 mg, 93.4%).
19F (564.33 MHz) −94.0 (s, CF(NO2)2); 31P (242.82 MHz) 23.14
(s, PPh4); IR (ATR): 3088 (vw), 3071 (vw), 2956 (vw), 2892 (vw),
1593 (s), 1480 (m), 1435 (s), 1395 (vw), 1358 (w), 1339 (vw),
1314 (m), 1215 (m), 1185 (w), 1161 (m), 1106 (s), 1073 (m),
1025 (w), 996 (m), 970 (m), 937 (vw), 835 (m), 795 (m), 754 (m),
721 (s), 688 (s), 645 (vw sh), 615 (w), 523 (vs), 447 (w), 436
DTA: 140 °C (explosion); NMR (D2O) δ(ppm): 1H (599.80 MHz)
1
7.04 (s, NH4); 13C (150.84 MHz) 117.9 (d, J(13C19F) = 290.1 Hz
CF(NO2)2), 150.8 (d, 2J(13C19F) = 23.2 Hz, CN4); 14N (36.14 MHz)
(vw sh), 404 (vw) cm−1
.
1
1
−38.2 (s, ν = 60 Hz, NO2), −52 (s, ν = 350 Hz, CN4), −362.3
2
2
(quint, 1J(1H14N) = 58.7 Hz, NH4); 19F (564.33 MHz) −98.5
(s, CF(NO2)2); Raman (25 °C, 40 mW): 3200–2800 (3.4), 1685
(1.3), 1609 (2.8), 1472 (8.9), 1364 (4.1), 1326 (1.8), 1320 (1.9),
1319 (1.9), 1313 (1.9), 1309 (1.8), 1191 (5.4), 1161 (1.7), 1153
(1.7), 1102 (4.4), 1071 (2.9), 1067 (3.0), 985 (6.9), 949 (7.8), 839
(9.1), 805 (1.7), 707 (1.3), 652 (2.2), 542 (1.9), 537 (2.1), 533
(2.2), 443 (3.6), 437 (3.3), 401 (3.7), 398 (3.7), 373 (10.0), 303
(3.2), 292 (2.9), 204 (5.8), 170 (6.3), 166 (6.3) cm−1; IR (ATR):
3600–3050 (s), 2977 (m), 2931 (w), 2901 (w), 1655 (w sh),
1606 (m), 1455 (w sh), 1401 (vs), 1320 (w), 1275 (vw), 1184 (vw),
1089 (s), 1049 (vs), 980 (w), 880 (m), 836 (w), 801 (w), 643 (vw),
Results and discussion
Synthesis
The synthetic route for the preparation of 5-(fluorodinitro-
methyl)-2H-tetrazole (HFDNTz) is shown in Scheme 1.
Nitration of cyanoacetamide with fuming nitric acid in 20%
oleum under anhydrous conditions resulted in the formation
of trinitroacetonitrile.5,29 Due to the compound’s reported
sensitivity and high reactivity, trinitroacetonitrile was rec-
ommended to be handled only in solution.27 As a result,
trinitroacetonitrile had not been fully characterized. We were
able to isolate the compound by careful evaporation of
the solvent from dichloromethane solutions in a vacuum at
−40° C as a moisture sensitive, wax-like colourless solid. It is a
very noxious lachrymator that slowly vaporizes in the air at
ambient temperature.
Treatment of a trinitroacetonitrile solution in methanol
with a 48% aqueous HBr solution resulted in gas evolution
and the slow formation of elemental bromine. When the
resulting reaction mixture was neutralized with sodium
hydroxide, sodium dinitrocyanomethanide could be isolated
in up to 53% yield. While this reaction had already been
described in the literature, its mechanism is unknown but was
assumed to involve the formation of N2O.27 Single crystals of
Na[(NO2)2CCN]·H2O were obtained from an aqueous solution
by slow evaporation of the solvent.
615 (vw), 452 (w) cm−1
.
Synthesis of Ag[FDNTz]
A solution of AgNO3 (937 mg, 2.50 mmol) in water (5 mL) was
added to a solution of HFDNTz (384 mg, 2.00 mmol). The
resulting white precipitate was filtered off and washed with
water. The white solid was dried in a vacuum in darkness
(yield: 687 mg, 92.0%).
DTA: 185 °C (exotherm); IR (ATR): 1644 (s), 1604 (vs), 1467
(vw), 1375 (vw), 1305 (w), 1255 (w), 1201 (w), 1114 (vw), 1042
(vw), 1004 (vw), 973 (w), 833 (w), 796 (w) cm−1
.
Synthesis of Ag[FDNTz]·12NH3
Single crystals of Ag[FDNTz]·12NH3 were obtained by dissolving
Ag[FDNTz] (0.243 g; 0.81 mmol) in 25% aqueous ammonia
(5 mL) and letting the solution evaporate under air in
darkness.
When trinitroacetonitrile was reacted with N2H4·H2O in
water, a vigorous gas evolution was observed. However, no evi-
dence for the formation of the dinitrocyanomethanide anion
could be obtained. Instead, yellow crystals of [N2H5][(NO2)2CH]
were formed when the resulting bright yellow solution was
taken to dryness (Scheme 2). The mechanism for the for-
mation of the dinitromethanide anion is unknown. However,
DTA: 165 °C (endotherm, loss of NH3), 180 °C (exotherm);
IR (ATR): 3363 (m), 3201 (m), 2339 (vw), 2261 (w), 2166 (m),
1665 (s), 1594 (vs), 1498 (vw), 1465 (w), 1356 (s), 1308 (m), 1243
(m), 1195 (w), 1112 (m), 1048 (vw), 979 (m), 834 (ms), 799 (ms),
617 (m), 538 (w) cm−1
.
Synthesis of [PPh4][FDNTz]
A solution of PPh4Cl (425 mg, 2.50 mmol) in water (5 mL) was
added to a solution of HFDNTz (384 mg, 2.00 mmol). The
resulting white precipitate was filtered off and washed with
water. The white solid was dried in a vacuum (yield: 430 mg,
98.9%).
DTA: 175 °C (exotherm); NMR (CDCl3) δ(ppm): 1H
(599.80 MHz) 7.5–7.9 (m, PPh4); 13C (150.84 MHz) 117.9 (d,
1
1J(13C19F), = 290.1 Hz CF(NO2)2), 117.5 (d, J(13C31P = 88.0 Hz,
PPh4), 120.6 (d, 1J(13C19F = 282.0 Hz, CF(NO2)2), 130.8 (d,
2
2J(13C31P = 15.6 Hz, PPh4), 134.4 (d, J(13C31P = 10.5 Hz, PPh4),
135.9 (d, 3J(13C31P = 3.2 Hz, PPh4), 150.8 (d, 1J(13C19F = 88.0 Scheme 1 Synthesis of 5-(fluorodinitromethyl)-2H-tetrazole.
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Scheme 2 Reaction of trinitroacetonitrile with hydrazine hydrate.
it should be noted that a mixture of pure trinitroacetonitrile
and neat N2H4 is hypergolic. The reaction of the two com-
pounds is highly exothermic. On several occasions, flames
and/or explosions were observed when neat hydrazine was
mixed with solid trinitroacetonitrile.
Scheme 4 Synthesis of 5-(fluorodinitromethyl)tetrazolate (FDNTz) salts.
When a clear colourless solution of trinitroacetonitrile in aqueous solution of silver nitrate was added to a solution of
dichloromethane was treated with an aqueous ammonia solu- HFDNTz in water. Colourless crystals of the ammonia adduct
tion at ambient temperature, a yellow effervescing mixture was [Ag][FDNTz]·12NH3 were obtained by recrystallization of the
obtained. Yellow crystals of [NH4][(NO2)2CCN] were isolated in amorphous precipitate from an aqueous ammonia solution.
quantitative yield when the solvent was removed from the reac- While the nitrotetrazoles of this work are energetic and must
tion mixture after 12 hours of stirring at ambient temperature. be treated with great care, both silver salts are especially
The evolved gas was identified by IR spectroscopy as N2O treacherous and can explode upon provocation (heat or mecha-
(Scheme 3).
nical shock). The tetraphenylphosphonium (PPh4) salt of
Fluorodinitroacetonitrile, F(NO2)2CCN, was obtained by FDNTz was precipitated from an aqueous solution of HFDNTz
aqueous fluorination of sodium dinitrocyanomethanide with by the addition of an aqueous PPh4Cl solution. Crystalline
10% F2 in N2 (Scheme 1). The off-gas of the fluorination reac- [PPh4][FDNTz] was obtained by recrystallization from acetone.
tion was passed trough a series of cold traps at −78 °C. Lower
X-ray crystal structures
cold trap temperatures were not used to avoid trapping of flu-
orine nitrate, a possible fluorination side product. While Wies-
boeck and Ruff reported only moderate yields of 29% of
F(NO2)2CCN and the formation of the hydrolysis products aceto-
nitrile and fluorodinitroacetamide when aqueous solutions
with more than 3% Na[(NO2)2CCN] were fluorinated,28 we did
not observe the formation of appreciable amounts on hydro-
lysis products even in the case of reaction mixtures containing
more than 10% of Na[(NO2)2CCN]. However, we did observe a
contamination of the crude F(NO2)2CCN with up to 10% fluoro-
trinitromethane, FC(NO2)3, and also trace amounts of CO2.
Although not necessary for this work, crude F(NO2)2CCN could
be purified by fractional condensation at −31 °C, −78 °C and
−196 °C. The F(NO2)2CCN stopped in the −78 °C trap and
was isolated as a colourless liquid with a vapour pressure of
56 Torr at 23 °C.
The 1,3-dipolar cycloaddition reaction of F(NO2)2CCN with
HN3, followed by extraction with dichloromethane resulted in
the isolation of HFDNTz as a colourless, hygroscopic solid in
approximately 85% yield. Single crystals suitable for an X-ray
crystal structure determination were obtained from a dichloro-
methane solution by slow evaporation of the solvent in vacuo.
HFDNTz is acidic and forms ammonium 5-(fluorodinitro-
methyl)tetrazolate in quantitative yield when treated with
aqueous ammonia (Scheme 4).
Single crystals suitable for X-ray crystal structure determinations
were obtained for Na[(NO2)2CCN]·H2O, NH4[(NO2)2CCN], [PPh4]-
[(NO2)2CCN], [N2H5][(NO2)2CH], HFDNTz, [NH4][FDNTz],
[Ag][FDNTz]·12NH3, and [PPh4][FDNTz]. The relevant data and
parameters for the X-ray measurements and refinements of
the crystal structures are summarized in Tables 1 and 2.
Further crystallographic data and representations of the unit
cells for all crystal structures are given in the ESI.†
From an aqueous solution, sodium dinitrocyanomethanide
crystallizes as a monohydrate in the orthorhombic space group
P212121 with the unit cell parameters a = 7.5138(6) Å, b =
8.1663(6) Å and c = 19.9151(14) Å. The solid-state structure of
Na[(NO2)2CCN]·H2O does not consist of isolated ions but is
dominated by cation–anion interactions that result in a poly-
meric structure. The asymmetric unit of the structure contains
two formula units (Z′ = 2). One CN nitrogen atom as well as
several oxygen atoms of the anion coordinate each sodium
ion, which in turn is bridged to another sodium ion through a
water molecule (Fig. 1).
The ammonium salt of the dinitrocyanomethanide anion
crystallizes with four formula units per unit cell (Z = 4) in the
monoclinic space group P21/n. Not surprisingly, the solid-state
structure of [NH4][(NO2)2CCN] contains hydrogen bonds
between the ammonium ions and the oxygen atoms as well as
the CN nitrogen atom of the anions (Fig. 2). The observed C–N
and CuN bond distances of 1.385(2)/1.390(2) Å and 1.152(2) Å,
respectively, in the anion in [NH4][(NO2)2CCN] are virtually
identical to the ones observed for Na[(NO2)2CCN]·H2O (1.385(2)/
1.390(2) Å and 1.147(2) Å).
Silver 5-(fluorodinitromethyl)tetrazolate was obtained as a
white amorphous precipitate in quantitative yield when an
Single crystals of [PPh4][(NO2)2CCN] suitable for structure
determination were obtained from an acetone solution by slow
evaporation of the solvent. The compound crystallizes in
Scheme 3 Reaction of trinitroacetonitrile with aqueous ammonia.
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Table 1 Crystallographic data of the dinitromethanide salts
Na[(NO2)2CCN]·H2O
[NH4][(NO2)2CCN]
[PPh4][(NO2)2CCN]
[N2H5][(NO2)2CH]
Formula
mol wt [g mol−1
Temp [K]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C2H2N3NaO5
171.06
100(2)
Orthorhombic
P212121
7.5138(6)
8.1663(6)
19.9151(14)
90
C2H4N4O4
148.09
100(2)
Monoclinic
P21/n
8.1144(12)
4.8009(8)
14.218(2)
90
C26H20N3O4P
469.42
104(2)
Monoclinic
P21/n
11.6601(8)
14.2600(9)
13.4402(9)
90
CH6N4O4
138.10
100(2)
monoclinic
P21/n
3.6434(4)
13.7827(13)
10.6457(10)
90
]
β [°]
90
90
96.914(3)
90
549.85(15)
4
90.099 (1)
90
2234.7(3)
4
98.230(2)
90
529.08(9)
4
γ [°]
V [Å3]
1221.99(16)
8
Z
λ [Å]
0.71073
1.860
0.237
0.71073
1.789
0.170
0.71073
1.395
0.163
0.71073
1.734
0.169
ρcalc [g cm−3
]
μ [mm−1
F(000)
]
688
304
976
288
Reflns collected
Ind reflns
Rint
No. of parameters
R1 [I > 2σ(I)]
wR2 [I > 2σ(I)]
GOF
30 172
3734
0.0355
201
0.0253
0.0651
1.060
12 950
1681
0.0265
103
0.0292
0.795
1.053
55 116
6814
0.0385
307
0.0359
0.0922
1.035
12 436
1614
0.2311
100
0.0255
0.0769
1.087
Table 2 Crystallographic data of the 5-(fluorodinitromethyl)tetrazoles
HFDNTz
[NH4][FDNTz]
Ag[FDNTz]·12NH3
[PPh4][FDNTz]
Formula
Mol wt [g mol−1
Temp. [K]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C2HFN6O4
192.09
100(2)
Monoclinic
C2/c
28.8030(7)
5.3703(1)
28.897(1)
90
119.723(2)
90
3881.71(19)
24
C2H4FN7O4
209.12
101(2)
Monoclinic
P21/c
13.9642(7)
8.9672(5)
13.9957(7)
90
115.4716(1)
90
1582.19(14)
8
C24H18Ag12F12N78O48
3689.60
100(2)
C26H20FN6O4P
530.45
101(2)
Monoclinic
P21
11.8077(14)
7.1276(8)
14.7721(18)
90
95.585(2)
90
1237.3(3)
2
]
Triclinic
ˉ
P1
15.4270(10)
15.4526(10)
20.5225(13)
82.7270(10)
88.1560(10)
82.6690(10)
4812.6(5)
2
γ [°]
V [Å3]
Z
λ [Å]
0.71073
1.972
0.200
0.71073
1.756
0.174
0.71073
2.546
2.540
0.71073
1.424
0.165
ρcalc [g cm−3
]
μ [mm−1
F(000)
]
2304
848
3528
548
Reflns collected
Ind reflns
Rint
No. of parameters
R1 [I > 2σ(I)]
wR2 [I > 2σ(I)]
GOF
46 406
5932
0.0774
361
0.0414
0.0830
1.035
37 464
4778
0.0384
277
0.0329
0.0786
1.026
22 050
22 050
0.0939
1576
0.0584
0.0977
0.992
26 729
7495
0.0451
343
0.0435
0.0916
1.023
the monoclinic space group P21/n with four formula units
Single crystals of [N2H5][(NO2)2CH] were obtained from an
in the unit cell (Z = 4). The solid state structure consists of aqueous solution by slow evaporation. The compound crystal-
isolated PPh4 cations and [(NO2)2CCN]− anions (Fig. 3). The lizes without crystal water in the monoclinic space group P21/n
+
closest cation–anion interactions are 3.122(2) Å (O2⋯C19) and (Z = 4) with the unit cell parameters a = 3.6434(4) Å, b =
3.187(2) Å (O1⋯C10). The observed C–N and CuN bond dis- 13.7827(13) Å, and c = 10.6457(10) Å. The solid-state structure
+
tances of 1.3966(15)/1.4150(7) Å and 1.1513(17) Å, respectively, consists of N2H5 cations and [(NO2)2CH]− anions (Fig. 4) that
in the [(NO2)2CCN] anion are in good agreement with the ones are linked through hydrogen bonds between the cation and the
observed for the Na+ and NH4+ salts.
oxygen atoms of the anion. The observed C–N bond distances
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Fig. 3 The solid-state structure of Na[(NO2)2CCN]. Thermal ellipsoids
are shown at the 50% probability level. Hydrogen atoms were omitted
for clarity. Selected bond distances (Å): C1–C2 1.4150(17), C1–N1 1.3966(15),
C1–N2 1.3994(16), C2–N3 1.1513(17), N1–O1 1.2571(14), N1–O2 1.2360(14),
N2–O3 1.2518(15), N2–O4 1.2305(14).
Fig. 1 The solid-state structure of Na[(NO2)2CCN]·H2O. Thermal ellip-
soids 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 bond distances (Å): C1–C2 1.412(2),
C1–N1 1.390(2), C1–N2 1.385(2), C2–N3 1.147(2), N1–O1 1.250(2), N1–
O2 1.245(2), N2–O3 1.249(2), N2–O4 1.246(2), Na1–O1’ 2.418(1), Na1–
O3 2.450(1), Na1–O6 2.475(1), Na1–N6 2.421(1), Na1–O1s 2.362(1), Na1–
O2s 2.292(1), Na2–O2 2.575(1), Na2–O4 2.445(1), Na2–O2’ (1), Na2’–O4
2.508(1), Na2’–O4’ 2.445(1).
Fig. 4 The crystal structure of [N2H5][(NO2)2CH]. 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 bond distances (Å): C1–N1 1.368(1), C1–N2
1.3647(9), N1–O1 1.2648(8), N1–O2 1.2647(8), N2–O3 1.2621(8), N2–O4
1.2648(8).
Fig. 2 Hydrogen bonding in the solid-state structure of [NH4]-
[(NO2)2CCN]. 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): C1–C2 1.412(2), C1–N1 1.385(2), C1–N2 1.402(2), C2–N3 1.152(2),
N1–O1 1.240 (1), N1–O2 1.266(1), N2–O3 1.233(1), N2–O4 1.253(1), N3–
N4 3.068(1) O1–N4 3.032(1), O2–N4 2.999(1)/3.130(1), O3–N4 2.841(1),
O4–N4 2.920(1).
in the [(NO2)2CH]− anion of 1.368(1) Å and 1.365(1) Å are
noticeable shorter than the ones observed for the [(NO2)2CCN]−
anion in the PPh4+ salt (1.3966(15) and 1.4150(7) Å).
Single crystals of 5-(fluorodinitromethyl)-2H-tetrazole
(HFDNTz) were obtained by slow evaporation of a dichloro-
methane solution in vacuo at a temperature of −20 °C. The
compound crystallizes in the monoclinic space group C2/c
with a unit cell volume of 3881.71(19) Å3 (Z = 24). Further crys-
tallographic details for the compound are listed in Table 2.
The structure of HDNTz is depicted in Fig. 5, while the bond
Fig. 5 The molecular structure of 5-(fluorodinitromethyl)-2H-tetra-
zole. Thermal ellipsoids are shown at the 50% probability level. The posi-
tion of the hydrogen atom was determined from the electron density
map. It is depicted as a sphere of arbitrary radius. Selected bond dis-
tances (Å) and bond angles (°): C1–C2 1.490(2), C1–N1 1.325(2), C1–N4
1.350(2), C2–N5 1.540(2), C2–N6 1.539(2), C2–F1 1.318(2), N1–N2 1.324(2),
C1–C2–F1 113.0(1), C1–C2–N5 109.7(1), C1–C2–N6 113.0(1), N1–C1–C2
122.5(2).
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Table 3 Selected bond lengths (Å) and angles (°) for the 5-(fluorodinitromethyl)tetrazoles
HFDNTza
[NH4][FDNTz]a
Ag[FDNTz]·12NH3
[PPh4][FDNTz]
a
C1–C2
C1–N1
C1–N4
N1–N2
N2–N3
N3–N4
C2–F
C2–N5
1.490(2)
1.325(2)
1.350(2)
1.324(2)
1.319(2)
1.325(2)
1.318(2)
1.540(2)
1.4850(14)
1.3298(13)
1.3357(13)
1.3438(12)
1.3224(13)
1.3383(12)
1.3328(11)
1.5466(14)
1.5381(14)
103.48(8)
103.42(8)
109.64(8)
109.91(8)
113.55(9)
124.33(9)
113.60(8)
112.04(8)
103.55(8)
1.463(10)
1.324(9)
1.325(8)
1.343(8)
1.327(8)
1.348(7)
1.313(8)
1.540(9)
1.545(9)
104.0(6)
104.4(5)
109.8(6)
108.6(6)
113.2(6)
125.0(7)
113.1(6)
108.7(6)
103.9(5)
1.476(4)
1.335(4)
1.319(4)
1.347(3)
1.311(4)
1.347(3)
1.339(4)
1.543(4)
1.534(4)
102.9(2)
103.5(2)
110.0(2)
109.7(2)
113.9(2)
119.9(2)
114.7(2)
110.9(2)
102.7(2)
C2–N6
1.539(2)
C1–N1–N2
C1–N4–N3
N1–N2–N3
N2–N3–N4
N1–C1–N4
N1–C1–C2
C1–C2–N5
C1–C2–N6
N5–C2–N6
100.36(14)
105.48(14)
115.32(14)
105.32(13)
113.51(15)
122.49(15)
109.68(13)
113.00(13)
104.60(12)
a Values given for only one of the different molecules in the asymmetric unit.
lengths and angles of the tetrazole ring in this compound are
summarized in Table 3 together with the ones for the related
tetrazolates of this work.
The geometry of the five-membered ring in HFDNTz is
essentially identical to the one of 5-(trinitromethyl)-2H-tetra-
zole (HTNTz).5 Due to the strong electron withdrawing effect
of the fluorodinitromethyl group, the hydrogen atom of the tet-
razole moiety is exclusively located in the 2-position (N2) of
the five-membered ring. Similar to HTNTz and atypical for
alkyl-substituted tetrazoles, the distance between C1 and N1
(1.325(2) Å) is shorter than the one between C1 and N4 (1.350(2)
Å). In addition, the three N–N distances in the five-mem-
bered ring of HFDNTz can be considered identical within their
margins of error. This is in good agreement with the observed
geometry of HTNTz but is unlike the distance pattern of a
regular alkyl-substituted tetrazole.5 The asymmetric unit of the
5-(fluorodinitromethyl)-2H-tetrazole solid-state structure con-
sists of three HFDNTz molecules (Z′ = 3) that are arranged in a
triangular fashion with the fluorine atoms of the –CF(NO2)2
groups facing each other (Fig. 6). The three fluorine atoms
form the corners of a slightly disordered regular triangle with
F–F distances of 2.886(2) and 2.939(2) Å and F–F–F angles of
58.82(4) and 60.59(4)°. In addition, the HFDNTz molecules are
associated through N(2)–H⋯N(4) hydrogen bonds.
The solid-state structure of ammonium 5-(fluorodinitro-
methyl)tetrazolate consists of ammonium cations and FDNTz
anions that are associated through hydrogen bonding (Fig. 7).
Further crystallographic details of the structure are listed in
Table 2, the observed bond lengths and angles for the FDNTz−
anion are summarized in Table 3.
Fig. 6 The asymmetric unit in the solid-state structure of 5-(fluorodini-
tromethyl)-2H-tetrazole. Thermal ellipsoids are shown at the 50% prob-
ability level. Selected distances (Å) and angles (°): F1–F2 2.886(2), F1–F3
2.939(1), F2–F3 2.939(2), F1–F2–F3 60.59(4), F2–F3–F1 58.82(4), F2–
F1–F3 60.59(4).
mination were unsuccessful. The crystallization of an
amorphous sample of AgFDNTz from an aqueous ammonia
solution resulted in crystals of the ammonia adduct
Ag[FDNTz]·12NH3 instead. Selected crystallographic data of the
compound are listed in Table 2. The solid-state structure of the
silver salt contains [Ag(NH3)2]+ cations and polymeric anion
chains. The anion chains are made up from [Ag4(FDNTz)4]
units in which two silver atoms are linked in a 1,2-fashion by
always two bridging FDNTz− anions. Every tetrazolate anion is
coordinated to three different Ag atoms. The units are linked
All attempts to grow single crystals of silver 5-(fluorodinitro-
methyl)tetrazolate (AgFDNTz) suitable for X-ray structure deter-
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Fig. 7 Hydrogen bonding in the solid-state structure of [NH4][FDNTz].
Hydrogen atom positions were determined from the electron density
map and are depicted as spheres of arbitrary radius. Selected distances
(Å): N1–N14 2.915(2), N2–N13 3.007(1), N7–N13’ 2.944(1), N8–N13,
2.982(2), N9–N14 2.965(1), N10–N13’’ 3.018(1).
Fig. 9 Molecular structure of [PPh4][FDNTz]. Hydrogen atoms have
been omitted for clarity. Selected bond distances (Å) and bond angles
(°): C1–C2 1.476(4), C1–N1 1.335(4), C1–N4 1.319(4), C2–N5 1.543(4),
C2–N6 1.534(4), C2–F1 1.339(4), N1–N2 1.347(4), C1–C2–F1 114.1(2),
C1–C2–N5 114.7(2), C1–C2–N6 110.9(2), N1–C1–C2 119.9(3).
anion in [PPh4][FDNTz], the geometry of the five-membered
ring changes. While the C1–N1 distance increases only slightly
(0.01 Å), the second C–N distance (C1–N4) shortens by over
0.03 Å).
It is interesting to note that the N1–N2 and N3–N4 dis-
tances in the anion are longer by about 0.02 Å than the ones in
the parent tetrazole. The third N–N distance (N2–N3) remains
essentially unchanged within the error margins.
Stability of the compounds
The impact and friction sensitivities of most of the com-
pounds of this study were determined using a BAM Fall
Hammer and BAM Friction tester. In addition, decomposition
temperatures were determined through DTA scans with
heating rates of 5 °C min−1. The obtained sensitivity and stabi-
lity data is summarized in Table 4. The impact and friction
sensitivities, and decomposition temperature of F(NO2)2CCN
were not determined due to the volatility of the compound.
Fig. 8 Part of the polymeric anion structure of Ag[FDNTz]·21NH3. Hydro-
gen atoms have been omitted for clarity. Selected bond distances (Å):
Ag1–N2, Ag1–N7, Ag1–N15, Ag2–N2, Ag2–N78, Ag2–N79, Ag3–N14,
Ag3–N8, Ag3–N21.
together by Ag(NH3) and Ag(NH3)2 units, resulting in a
complex polymeric anion chain. The resulting overall structure
can be described as [Ag(NH3)2]3[Ag21(NH3)6(FDNTz)24]. Part of
a polymeric anion chain of the structure is depicted in Fig. 8.
Further crystallographic details of the structure are listed in
Table 2, the observed bond lengths and angles for the FDNTz−
anion are summarized in Table 3.
Table 4 Sensitivity and stability data for the compounds studieda
Compound
Td [°C]b
FS [N]
IS [J]
OB [%]
RDX
(NO2)3CCN
Na[(NO2)2CCN]
[NH4][(NO2)2CCN]
[PPh4][(NO2)2CCN]
[N2H5][(NO2)2CH]
HFDNTz
220
—
150
120
112
>360
>360
>360
230
40
50
<2
<2
>360
7.5
12
80
75
>100
90
3.5
4
−21
17.4
−5.2
c
240
−21.6
−206.2
−11.6
−2.1
240d
134
The tetraphenylphosphonium salt [PPh4][FDNTz] crystal-
lizes in the monoclinic space group P21 with two formula units
per unit cell (Z = 2). The solid-state structure consists of iso-
110e
140e
185
[NH4][FDNTz]
[Ag][FDNTz]
−13.4
−1.3
−5.2
+
lated and well-separated PPh4 cations and FDNTz− anions
2
2
>100
[Ag][FDNTz]·1NH3
[PPh4][FDNT2z]
180f
175
(Fig. 9). The closest cation–anion distance is 2.989(3) Å
(C18⋯O4). Further crystallographic details of the structure are
listed in Table 2, the observed bond lengths and angles for the
FDNTz− anion are summarized in Table 3. In going from the
neutral tetrazole HFDNTz to the weakly coordinated tetrazolate
−181.7
a Td: decomposition temperature, FS: friction sensitivity, IS: impact
sensitivity, OB: oxygen balance. b DTA onset. c Sample evaporates.
d Endotherm at 180 °C (melting). e Explosion. f Endotherm at 165 °C
(loss of NH3).
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With the exception of trinitroacetonitrile, all investigated and characterization of ammonium 5-(fluorodinitromethyl)-
compounds are under-oxidized and have a negative oxygen tetrazolate.30
balance. It is not surprising that based on the impact and fric-
tion sensitivities, the two most stable compounds, [PPh4]-
[(NO2)2CCN] and [PPh4][FDNTz], are the ones with the lowest
oxygen balances. Explosion upon heating were observed only
Acknowledgements
in the case of the free tetrazole HFDNTz as well as the corres- The Office of Naval Research (ONR) and the Defence
ponding ammonium salt [NH4][FDNTz]. All other investigated Threat Reduction Agency (DTRA) financially supported this
compounds showed smooth thermal decompositions. In the work. We acknowledge NSF CRIF grant 1048807 for the
case of (NO2)3CCN, it was not possible to determine a support of an X-ray diffractometer. We thank Professors
decomposition temperature because the sample evaporated G. K. S. Prakash and G. A. Olah for their help and stimulating
completely upon heating with a nitrogen purge before its discussions.
decomposition. The thermally least stable compounds are
HFDNTz, [N2H5][NO2)2CH], [NH4][FDNTz], and Na[(NO2)2CCN]
with decomposition temperatures of 110 °C, 134 °C, 140 °C,
and 150 °C, respectively. It is interesting that [NH4]-
Notes and references
[(NO2)2CCN)] shows a much higher thermal stability of 240 °C
than the closely related Na[(NO2)2CCN)] (150 °C). This might
be related to the different oxygen balances as well as the pres-
ence of stabilizing hydrogen bonding in the case of the
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+
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or less, these compounds must be considered explosion
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5-(Fluorodinitromethyl)-2H-tetrazole was prepared by a four-
step synthesis starting from cyanoacetamide. Nitration of cyano-
acetamide with fuming nitric acid in oleum resulted in the
formation of trinitroacetonitrile, which was converted into
sodium dinitrocyanomethanide by reaction with HBr, followed
by treatment with NaOH. Aqueous fluorination with 10% fluor-
ine in nitrogen resulted in the formation of fluorodinitroaceto-
nitrile and, after reaction with HN3, in the isolation of
5-(fluorodinitromethyl)-2H-tetrazole. The tetrazole was converted
into ammonium, silver and tetraphenylphosphonium 5-(fluoro-
dinitromethyl)-2H-tetrazolate. While the treatment of trini-
troacetonitrile with aqueous NH3 resulted in the isolation of
[NH4][(NO2)2CCN], [N2H5][(NO2)2CH] is formed in the reaction
of trinitroacetonitrile with hydrazine hydrate. Most com-
pounds of this study have been fully characterized by their
X-ray crystal structure, vibrational and multinuclear NMR
spectra, their decomposition temperature, as well as friction
and impact sensitivities.
Note added at Proof
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