Energetic high-nitrogen compounds: 5-(trinitromethyl)-2 H -tetrazole and -tetrazolates, preparation, characterization, and conversion into 5-(dinitromethyl)tetrazoles

Article abstract of DOI:10.1021/ic400919n

A convenient access to 5-(trinitromethyl)-2H-tetrazole (HTNTz) has been developed, based on the exhaustive nitration of 1H-tetrazole-5-acetic acid, which was prepared from ethyl cyanoacetate and HN₃ in a 1,3-dipolar cycloaddition reaction, followed by basic hydrolysis. HTNTz was converted into the ammonium, guanidinium, rubidium, cesium, copper, and silver 5-(trinitromethyl)-2H-tetrazolates. In addition, the ammonia adducts of the copper and silver salts were isolated. The reaction of HTNTz with hydrazine and hydroxylamine resulted in the formation of hydrazinium 5-(dinitromethyl) tetrazolate and hydroxylammonium 5-(dinitromethyl)-1H-tetrazolate, respectively. Acid treatment of both 5-(dinitromethyl)tetrazolates resulted in the isolation of 5-(dinitromethylene)-4,5-dihydro-1H-tetrazole, which was converted into potassium 5-(dinitromethyl)-1H-tetrazolate by reaction with K₂CO ₃. All prepared compounds were fully characterized by ¹H, ¹³C, ¹⁴N, and ¹⁵N NMR spectroscopy and X-ray crystal structure determination. Initial safety testing (impact, friction, and electrostatic sensitivity) and thermal stability measurements (differential thermal analysis, DTA) were also carried out. The 5-(trinitromethyl) and 5-(dinitromethyl)tetrazoles are highly energetic materials that explode upon impact or heating.

Full text of DOI:10.1021/ic400919n

Article
pubs.acs.org/IC
Energetic High-Nitrogen Compounds:
‑(Trinitromethyl)‑2H‑tetrazole and -tetrazolates, Preparation,
5
Characterization, and Conversion into 5‑(Dinitromethyl)tetrazoles
Ralf Haiges* and Karl O. Christe
Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, California
90089-1661, United States
*
S Supporting Information
ABSTRACT: A convenient access to 5-(trinitromethyl)-2H-tetrazole (HTNTz) has
been developed, based on the exhaustive nitration of 1H-tetrazole-5-acetic acid, which
was prepared from ethyl cyanoacetate and HN in a 1,3-dipolar cycloaddition reaction,
3
followed by basic hydrolysis. HTNTz was converted into the ammonium, guanidinium,
rubidium, cesium, copper, and silver 5-(trinitromethyl)-2H-tetrazolates. In addition, the
ammonia adducts of the copper and silver salts were isolated. The reaction of HTNTz
with hydrazine and hydroxylamine resulted in the formation of hydrazinium 5-
(
dinitromethyl)tetrazolate and hydroxylammonium 5-(dinitromethyl)-1H-tetrazolate,
respectively. Acid treatment of both 5-(dinitromethyl)tetrazolates resulted in the
isolation of 5-(dinitromethylene)-4,5-dihydro-1H-tetrazole, which was converted into
1
potassium 5-(dinitromethyl)-1H-tetrazolate by reaction with K CO . All prepared compounds were fully characterized by H,
2
3
1
3
14
15
C, N, and N NMR spectroscopy and X-ray crystal structure determination. Initial safety testing (impact, friction, and
electrostatic sensitivity) and thermal stability measurements (differential thermal analysis, DTA) were also carried out. The 5-
trinitromethyl) and 5-(dinitromethyl)tetrazoles are highly energetic materials that explode upon impact or heating.
(
INTRODUCTION
EXPERIMENTAL SECTION
■
■
In energetic materials research, much effort has been devoted to
the development of environmentally benign, “green” energetic
Caution! Most compounds of this work are energetic materials that can
explode under certain conditions (e.g., elevated temperatures, impact,
friction, or electric discharge). On several occasions, cesium and rubidium
1
materials. Tetrazoles are readily accessible nitrogen-rich
5
-(trinitromethyl)tetrazolate even exploded upon crystallization. A mixture
energetic compounds. The oxygen balance of a molecule and
its potential usefulness as an energetic material can be increased
by the introduction of nitro functionalities. 5-Nitro-2H-
tetrazole (HNT) and salts with the related 5-nitrotetrazolate
of anhydrous hydrazine and neat 5-(trinitromethyl)-2H-tetrazole is
hypergolic: mixing both compounds results in an instantaneous fire.
2
2
Appropriate safety precautions, 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
precautions may lead to serious injuries!
−
anion (NT ) are well-known and have attracted much interest
2
−9
as primary explosives and energetic materials.
thyltetrazole was discovered in 1964, and salts of its anion have
been the subject of studies for many years.
Dinitrome-
1
0−19
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 in (CD ) CO or D O solutions in
The synthesis
of 5-(trinitromethyl)-2H-tetrazole (HTNTz) 4 by reaction of
trinitroacetonitrile 3 and trimethylsilyl azide has been reported,
but the obtained product was described as an orange-yellow oil
that evolved nitrogen oxides on prolonged standing at ambient
temperatures and was successively converted into the
3
2
2
standard 5 mm glass tubes. Chemical shifts are given relative to neat
1
13
14
15
tetramethylsilane ( H, C) or neat CH
NO ( N, N); br = broad;
3
2
sh = shoulder; s = singlet. Raman spectra were recorded at ambient
−1
2
0
temperatures in Pyrex glass tubes in the range 4000−80 cm 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
ammonium salt. In a later report, HTNTz 4 was not isolated
or fully characterized but has been prepared as an intermediate
by the reaction of trinitroacetonitrile 3 with hydrogen azide and
−1
spectra were recorded in the range 4000−400 cm on Midac, M
21
was immediately converted into the tetrabutylammonium salt.
In this Article, we communicate an improved synthesis and
X-ray crystallographic characterization of 5-(trinitromethyl)-
H-tetrazole (HTNTz), which had previously been obtained
only as an impure oil and several energetic salts with the 5-
trinitromethyl)tetrazolate anion. In addition, we report the
Series or Bruker Optics Alpha FT-IR spectrometers by use of KBr
pellets. The pellets were prepared very carefully on an Econo mini-
press (Barnes Engineering Co.). Differential thermal analysis (DTA)
curves were recorded with a purge of dry nitrogen gas on an OZM
Research DTA552-Ex instrument with Meavy 2.2.0 software. The
2
(
preparation of several 5-(dinitromethyl)tetrazolates from
HTNTz, as well as their X-ray crystal structures.
Received: April 14, 2013
©
XXXX American Chemical Society
A
dx.doi.org/10.1021/ic400919n | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
heating rate was 5 °C/min and 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
with RDX.
was stirring vigorously, 100% nitric acid (16 mL) was added through
an addition funnel within a time period of 2 min. The cyanoacetamide
dissolved and a yellow two-layer mixture was obtained. The mixture
was cooled to −20 °C and oleum (20% SO ) (19 mL) was added
3
within a time period of 2 min. The temperature was now raised to 0
°C, and the mixture was stirred for 2 h at this temperature and for an
additional 8 h at ambient temperature. The pale yellow two-phase
mixture was transferred into a separatory funnel and the upper organic
layer was removed. The lower acidic layer was extracted three times
with tetrachloromethane (15 mL each). The combined organic layers
were extracted twice with cold (−5 °C) concentrated sulfuric acid (10
mL each), and the obtained colorless solution was kept over
magnesium sulfate. Because of the reported instability of trinitroace-
2
3,24
Synthesis of Ethyl 2-(1H-Tetrazol-5-yl)acetate (1).
solution of ethyl cyanoacetate (69.0 g, 0.62 mol), ammonium chloride
35.4 g, 0.66 mol), and sodium azide (43.0 g, 0.66 mol) in dimethyl
A
(
formamide (600 mL) was heated under nitrogen to 100 °C for 16 h.
The obtained orange solution with some off-white precipitate was
allowed to cool to ambient temperature and the solvent was removed
under vacuum in a rotary evaporator. The orange residue was
dissolved in water (200 mL) and acidified with 5 M hydrochloric acid
solution. After a short while crystals started to form, and eventually the
mixture took on a gel-like consistency. The off-white solid was filtered
off by use of a Buchner funnel. Recrystallization from an ethanol/water
mixture gave colorless crystals of ethyl 2-(1H-tetrazol-5-yl)acetate
2
5
13
tonitrile, no efforts were made to isolate the neat compound.
C
1
3 14
NMR (CDCl , ppm) δ 103.4 (CN); 112.1 septet, J(1 C N) = 9.5 Hz
3
14
[
C(NO ) ]. N NMR (CDCl , ppm) δ −45.4, τ = 20 Hz (NO );
88.3, τ1/2 = 320 Hz (CN).
Synthesis of 5-(Trinitromethyl)-2H-tetrazole (4). Method 1.
2
3
3
1/2
2
−
2
1
(
49.0 g). Theoretical mass expected for 0.62 mol of C H N O = 96.8
5 8 4 2
Acetic acid (150 mL) was added to a stirred suspension of sodium
azide (6.5 g, 0.10 mol) in tetrachloromethane (140 mL) at 0 °C. After
2−3 min, the temperature was lowered to −25 °C and a solution of
trinitroacetonitrile (0.1 mol) in tetrachloromethane (45 mL)
(prepared as described above) was slowly added at a speed so that
the temperature never rose above −15 °C. When the addition was
complete, the yellow reaction mixture was kept at −25 °C for an
additional 15 min before the temperature was raised to ambient
temperature. The mixture was stirred at ambient temperature for 8 h
and then taken to dryness on a rotary evaporator. The tacky yellow
residue was dissolved in a mixture of dichloromethane (30 mL) and 1
M sulfuric acid (5 mL). The organic phase was separated and the
aqueous layer was extracted three times with dichloromethane (5 mL
each). The combined organic phases were dried over magnesium
sulfate and taken to dryness on a rotary evaporator. The colorless, oily
residue solidified to a crystalline solid after 8 h of pumping in a
vacuum at ambient temperature. 5-(Trinitromethyl)-2H-tetrazole (4)
was obtained as colorless crystals (14.0 g). Theoretical mass expected
for 0.10 mol of C HN O = 21.9 g (yield = 63.7% based on
−1
1
g (yield = 50.6%). DTA (5 °C·min ) 124.4 °C melting. H NMR
3
(
acetone-d , ppm) δ 1.21 t, J(HH) = 7.3 Hz (CH CH ); 3.4 br s
CN H); 4.16 s (CH CN H); 4.17 q, J(HH) = 7.3 Hz (CH CH ).
6
2
3
3
(
4
2
4
2
3
1
3
C NMR (acetone-d , ppm) δ 14.4 (CH CH ), 30.5 (CH CO Et),
6
3
2
2
2
14
6
2.3 (CH CH ), 168.5 (CN H). N NMR (acetone-d , ppm) δ −12,
3
2
4
6
−1
τ1/2 = 870 Hz. Raman (1064 nm, 80 mW) ν (cm ) = 2978 (7.5),
942 (10.0), 2915 (2.3), 2876 (1.8), 2779 (0.2), 2732 (0.2), 1751
1.5), 1686 (0.1), 1567 (0.6), 1551 (0.2 sh), 1483 (0.3), 1456 (1.3),
397 (0.9), 1384 (0.7), 1372 (0.5 sh), 1339 (1.1), 1259 (1.1), 1219
2
(
1
(
(
0.3), 1201 (0.5), 1164 (0.1), 1113 (0.9), 1091 (1.5), 1052 (1.0), 1008
0.1), 949 (0.5), 885 (1.5), 789 (0.2), 727 (0.1), 713 (0.6), 687 (0.4),
6
30 (0.1), 568 (0.6), 422 (0.1), 358 (0.2), 339 (2.0), 310 (0.7), 300
−1
(
(
0.4 sh), 211 (0.3), 169 (4.5). IR (KBr): ν (cm ) = 3473 (m), 3132
m), 3022 (m sh), 2997 (s sh), 2987 (s), 2974 (s sh), 2941 (m sh),
2
2
1
911 (s sh), 2871 (m sh), 2798 (m sh), 2733 (m sh), 2688 (m sh),
611 (w sh), 2462 (vw sh), 1745 (vs), 1703 (w), 1567 (m), 1480 (m),
454 (m), 1438 (mw), 1395 (s), 1382 (s), 1333 (s), 1249 (m), 1220
(
s), 1199 (vs), 1161 (w sh), 1105 (m), 1051 (s), 1034 (s), 942 (s),
2
7
6
8
4
82 (m br), 807 (vw), 787 (m), 723 (w), 711 (w), 684 (m), 565 (m),
53 (vw), 422 (w).
cyanoacetamide).
Method 2. 1H-Tetrazole-5-acetic acid (10.0 g, 78.1 mmol) was
slowly added to a cooled and well-stirred mixture of 98% sulfuric acid
2
4
Synthesis of 1H-Tetrazole-5-acetic Acid (2). Ethyl 2-(1H-
tetrazol-5-yl)acetate (45.2 g, 0.29 mol) and sodium hydroxide (45 g,
.13 mol) were dissolved in water (1000 mL) and the solution was
(64 mL) and 100% nitric acid (52 mL) at 0 °C during the course of 1
1
h. The temperature was slowly raised to ambient temperature over a
period of 2 h, and the mixture was stirred for an additional 8 h at this
temperature. The light yellow solution was carefully poured onto
crushed ice (250 g) and the obtained solution was extracted four times
with dichloromethane (100 mL each). The combined organic phases
were dried over magnesium sulfate and filtered, and the solvent was
evaporated at ambient temperature in a vacuum. Initially, a yellow oil
was obtained that eventually solidified in a vacuum. 5-(Trinitrometh-
yl)-2H-tetrazole (4) was obtained as a pale yellow solid (10.2 g).
Theoretical mass expected for 78.1 mmol of C HN O = 17.1 g (yield
heated under reflux for 4 h. After the solution was allowed to cool to
ambient temperature, it was acidified to pH 2 with 5 M hydrochloric
acid solution and taken to dryness on a rotary evaporator. The off-
white residue was extracted four times with hot acetonitrile (75 mL
each). The combined acetonitrile phases were taken to dryness on the
rotary evaporator. The white residue was recrystallized from
acetonitrile. Colorless crystals of 1H-tetrazole-5-acetic acid (2) (35.1
g) were obtained. Theoretical mass expected for 0.29 mol of
−1
C H N O = 37.1 g (yield = 94.5%). DTA (5 °C·min ) 167.1 °C
3
4
4
2
1
2
7
6
melting. H NMR (acetone-d , ppm) δ 4.15 s (CH CN H); 6.2 br s
6
2
4
−1
1
13
= 59.7%). DTA (5 °C·min ) 100.9 °C explosion. H NMR (5% C D
6 6
13
(
(
(
CO H) and (CN H). C NMR (acetone-d , ppm) δ 30.2 s
2
4
6
1
4
in acetone, ppm) δ 14.1 s, τ1/2 = 150 Hz (CN H). C NMR (5%
4
CH CO H); 151.7 s (CN H); 169.5 s (CO H). N NMR
2
2
4
2
1
13 14
C D in acetone, ppm) δ 122.5 septet, J( C N) = 7.6 Hz
acetone-d , ppm) δ −12, τ = 800 Hz (CN H). Raman (1064
6
6
6
1/2
4
14
−1
[C(NO ) ]; 152.8 s (CN H). N NMR (5% C D6 in acetone,
nm, 80 mW) ν (cm ) = 2978 (4.7), 2940 (10.0), 1744 (0.4), 1728
2.2), 1565 (1.7), 1549 (0.5 sh), 1451 90.6), 1441 (0.4 sh), 1420 (0.6),
2 3 4 6
ppm) δ −35.6, τ = 6 Hz (NO ); δ −47.0, τ = 700 Hz (CN H).
(
1/2
2
1/2
4
15
N NMR (5% C D in acetone, ppm) δ −35.7 s (NO ); δ −53.8 s,
1
1
7
389 (0.7), 1354 (1.7), 1318 (1.3), 1260 (0.6), 1219 (0.8), 1192 (0.4),
123 (0.6), 1105 (2.0), 1063 (1.4), 1019 (0.1), 949 (0.1), 918 (2.1),
86 (0.6), 724 (0.1), 698 (0.9), 664 (1.3), 575 (0.1), 545 (0.6), 413
6
6
2
−1
τ1/2 = 15 Hz (CN H). Raman (1064 nm, 45 mW) ν (cm ) = 3200−
4
2800 (0.4), 1628 (1.0), 1620 (1.9) 1610 (1.9), 1492 (3.0), 1456 (3.1),
1366 (0.6), 1351 (1.0), 1334 (0.8), 1282 (2.0), 1256 (1.4), 1236 (1.2),
1134 (3.5), 1108 (0.6). 1035 (0.4), 986 (0.8), 967 (2.0), 949 (2.2),
846 (3.0), 800 (0.4), 745 (0.4), 681 (0.6), 639 (0.7), 623 (0.7), 427
(2.0), 400 (3.5), 376 (3.8), 357 (8.0), 340 (3.2), 228 (0.4), 208 (0.6),
(
2.2), 361 (0.1), 344 (0.4), 290 (2.9), 196 (0.7), 169 (5.8), 133 (2.3).
−1
IR (KBr) ν (cm ) = 1737 (vs), 1695 (w sh), 1563 (s), 1549 (w sh),
1
1
1
7
451 (m), 1441 (m), 1423 (w sh), 1382 (s), 1351 (w), 1315 (m),
263 (m), 1220 (m sh), 1200 (vs), 1121 (vw), 1099 (w), 1066 (m br),
014 (w), 947 (m), 899 (m nr), 865 (m br), 813 (vw sh), 785 (w),
21 (w), 705 (vw), 698 (w), 662 (vs), 599 (vw sh), 574 (vw), 545
−1
179 (1.1), 140 (5.7 sh), 128 (10.0). IR (KBr) ν (cm ) = 3441 (m,
br), 3060 (m, br), 2894 (m, br), 2777 (m, br), 1610 (vs), 1489 (v),
1455 (v), 1436 (v), 1394 (vw), 1332 (m), 1311 (m), 1280 (s), 1255
(vw, sh), 1238 (w), 1189 (m), 1132 (m), 1102 (w), 1038 (m), 985
(m), 947 (vw), 863 (w), 844 (m), 803 (s), 742 (m), 697 (vw), 680
(w), 637 (w), 622 (w).
(
vw), 453 (w br), 411 (s).
2
1,25
Synthesis of Trinitroacetonitrile (3).
Under an atmosphere
of nitrogen, a mixture of cyanoacetamide (8.401 g, 0.1 mol) and
tetrachloromethane (25 mL) was cooled to 0 °C. While the mixture
B
dx.doi.org/10.1021/ic400919n | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
−1
Synthesis of Ammonium 5-(Trinitromethyl)tetrazolate (5). 5-
(CN ). Raman (1064 nm, 35 mW): ν (cm ) = 1636 (2.0), 1610
4
(
Trinitromethyl)-2H-tetrazole (0.438 g, 2.00 mmol) was dissolved in
(0.8), 1442 (10.0), 1412 (0.5), 1370 (1.2), 1299 (1.5), 1289 (1.0 sh),
1150 (1.8), 1145 (0.5 sh), 1082 (4.2), 1000 (3.2), 951 (4.7), 882
(7.2), 812 (1.9), 652 (0.8), 453 (2.8), 370 (4.6), 352 (7.6), 324 (5.6),
water (5 mL), and 30% aqueous ammonium hydroxide solution (5
mL) was added. The resulting pale yellow solution was taken to
dryness at ambient temperature on a rotary evaporator. Ammonium 5-
−1
232 (2.7), 172 (3.7 sh), 163 (5.9), 125 (4.5). IR (KBr): ν (cm ) =
2961 (w sh), 2921 (m sh), 2897 (m br), 2853 (w sh), 2457 (w), 2423
(vw), 2242 (vw), 2209 (vw), 2175 (w), 2165 (vw), 2062 (vw), 2048
(vw), 1619 (vs), 1604 (vs), 1588 (vs), 1429 (m), 1393 (m), 1364 (vw
sh), 1314 (s), 1297 (s), 1284 (s), 1235 (vw sh), 1186 (w), 1143 (w),
1099 (m), 1038 (w), 987 (m), 982 (m sh), 946 (w), 845 (s), 802 (vs),
737 (w), 731 (w), 704 (w), 675 (m), 644 (m), 619 (m), 599 (vw sh),
452 (w).
(
trinitromethyl)tetrazolate (5) was isolated as colorless crystals (0.465
g). Theoretical mass expected for 2.00 mmol of C H N O = 0.472 g
2
4
8
6
−1
1
(
(
yield = 98.5%). DTA (5 °C·min ) 115.7 °C explosion. H NMR
1 1 14 13
D O, ppm) δ 7.56 q, J( H N) = 59.4 Hz (NH ). C NMR (D O,
2
4
2
14
ppm) δ 126.2 s [C(NO ) ]; 152.0 s (CN ). N NMR (D O ppm) δ
2
3
4
2
−
32.1, τ = 8 Hz (NO ); δ −61, τ = 650 Hz (CN ); −361.8 quint,
1/2
2
1/2
4
1
1
4
1
−
1
J( N H) = 60.1 Hz (NH ). Raman (1064 nm, 45 mW) ν (cm ) =
4
3
200−2800 (2.5), 1712 (0.4), 1621 (3.0), 1612 (1.5), 1598 (1.5),
Synthesis of Silver 5-(Trinitromethyl)tetrazolate (9). A
solution of silver nitrate (0.425 g, 2.50 mmol) in water (5 mL) was
added to a solution of 5-(trinitromethyl)-2H-tetrazole (0.438 g, 2.00
mmol) in water (5 mL). The pale yellow precipitate was filtered off,
washed with water, and dried in the air. Silver 5-(trinitromethyl)-
tetrazolate (9) was obtained as a pale yellow solid (0.626 g).
Theoretical mass expected for 2.00 mmol of C AgN O = 0.604 g
1
470 (0.6), 1435 (10.0), 1391 (0.7), 1358 (1.7), 1292 (1.4), 1207
(
(
(
1.7), 1165 (0.6), 1110 (2.9), 1073 (3.5), 1022 (0.3), 992 (3.2 m), 966
1.5 sh), 953 (3.4), 845 (8.1), 822 (0.5), 801 (0.6), 691 (0.9), 641
0.7), 618 (1.0), 436 (2.5), 386 (5.8), 372 (5.0), 361 (9.0), 347 (3.5
sh), 341 (3.7), 229 (1.5), 212 (3.0), 198 (2.9), 160 (5.1 sh), 141 (9.0
sh), 131 (9.8), 113 (7.5). IR (KBr) ν (cm ) = 3424 (s br), 3203 (s),
−1
2
7
6
−
1
3
2
181 (s), 3136 (m), 3060 (s br), 3000 (s br), 2925 (m), 2883 (s),
182 (w), 2128 (w), 1945 (w), 1699 (m), 1625 (vs), 1606 (vs), 1589
(quantitative yield). DTA (5 °C·min ) 123.4 °C explosion.
Recrystallization from 30% ammonium hydroxide solution resulted
in isolation of the ammonia adduct (9a) [Ag(NH ) ] [C Ag N O ]
(
vs), 1460 (s), 1443 (s), 1392 (m), 1357 (w), 1333 (w), 1315 (w),
3
2
2
12
4
42 36
−1
1
1
6
286 (m), 1228 (vw), 1205 (vw), 1163 (w), 1107 (m), 1070 (vw),
052 (vw), 989 (m), 960 (w br), 844 (s), 805 (s), 800 (s), 736 (w),
88 (w), 640 (m), 615 (m), 596 (m), 451 (m).
as pale yellow crystals. DTA (5 °C·min ) 122.8 °C explosion. Raman
−1
(1064 nm, 30 mW) ν (cm ) = 3200−2850 (2.0), 1615 (1.0), 1452
(7.5 sh), 1444 (10.0), 1283 (1.0), 1218 (2.5), 1177 (1.0), 1115 (4.0),
1090 (1.5), 1062 (0.8), 1043 (1.0), 993 (3.7), 970 (1.1), 960 (2.0),
946 (0.7), 846 (8.1), 428 (2.2), 404 (1.1), 363 (9.0), 321 (0.6), 309
(1.2), 214 (1.5), 151 (4.5 sh), 135 (6.0).
Synthesis of Guanidinium, Rubidium, and Cesium 5-
(
Trinitromethyl)tetrazolates (6−8). A solution of (5-trinitrometh-
yl)-2H-tetrazole (0.438 g, 2.00 mmol) in acetone (5 mL) was added to
a stirred suspension of guanidinium, rubidium, or cesium carbonate
Synthesis of Copper 5-(Trinitromethyl)tetrazolate (10). A
solution of copper sulfate pentahydrate (0.375 g, 1.50 mmol) in water
(5 mL) was added to a solution of 5-(trinitromethyl)-2H-tetrazole
(0.438 g, 2.00 mmol) in water (5 mL). The blue precipitate was
filtered off, washed with water, and dried in air. Copper 5-
(trinitromethyl)tetrazolate (10) was obtained as a blue solid (0.541
g). Theoretical mass expected for 1.00 mmol of C CuN O = 0.500
(
5.0 mmol) in acetone (5 mL). Immediately, carbon dioxide gas was
evolved and the solution turned yellow. After 30 min, the solution was
filtered through a Buchner funnel and the solid was washed with some
acetone. The solvent was evaporated from the filtrate in a stream of
nitrogen.
Guanidinium 5-(Trinitromethyl)tetrazolate (6). Pale yellow
4
14 12
−1
crystals (0.525 g), theoretical mass expected for 2.00 mmol of
C H N O = 0.556 g (yield = 94.5%). DTA (5 °C·min ) 115.5 °C
explosion. H NMR (DMSO-d , ppm) δ 6.9 (CN H ). C NMR
g. DTA (5 °C·min ): 122.8 °C explosion. Recrystallization from 30%
ammonium hydroxide solution resulted in isolation of the ammonia
adduct (10a) as dark blue crystals (0.519 g). Theoretical mass
expected for 1.00 mmol of C H CuN O ·3NH = 0.551 g (94.2%).
DTA (5 °C·min ) 117.3 °C explosion. Raman (1064 nm, 35 mW) ν
(cm ) = 3300−2900 (0.5), 1610 (1.7), 1456 (10.0), 1369 (1.1), 1275
(2.5), 1155 (1.3), 1078 (1.5), 993 (6.0), 966 (2.8), 847 (7.0), 611
−1
3
6
10
6
1
13
6
3
6
(
D O, ppm) δ 125.4 s [C(NO ) ]; 150.9 s (CN ); 155.3 s (CN H ).
2 2 3 4 3 6
4
9
17 12
3
1
4
−1
N NMR (D O ppm) δ −31.2 s, τ = 20 Hz (NO ); δ −65, τ
=
2
1/2
2
1/2
−1
8
00 Hz (CN ); −308, τ = 900 Hz (CN H ). Raman (1064 nm, 100
4
1/2
3
6
−
1
mW) ν (cm ) = 1619 (1.1), 1444 (7.3), 1368 (1.5), 1368 (1.5 br),
−1
1
9
210 (1.1), 1179 (0.7), 1114 (1.5), 1068 (2.0), 1017 (9.5), 969 (2.0),
60 (1.7), 851 (5.4), 836 (1.6 sh), 623 (0.7), 534 (2.2), 523 (1.3), 450
(0.8), 482 (1.0), 432 (1.9), 364 (8.2). IR (KBr) ν (cm ) = 2964 (w
br), 2927 (w br), 2901 (w br), 1600 (vs), 1387 (w), 1340 (vw sh),
1281 (s), 1238 (w), 1141 (w sh), 1104 (m), 1082 (w), 991 (m), 844
(s), 800 (s), 741 (w), 675 (vw), 645 (w), 623 (w), 593 (w), 458 (m).
Synthesis of Hydroxylammonium 5-(Dinitromethyl)-1H-
tetrazolate (11). An aqueous solution of 50% hydroxylamine (2.0
g, 61 mmol) was slowly added to a solution of 5-(trinitromethyl)-2H-
tetrazole (0.438 g, 2.00 mmol) in water (5 mL). After gas evolution
ceased, the yellow solution was taken to dryness by a stream of
nitrogen and the yellow residue was recrystallized from water.
Hydroxylammonium 5-(dinitromethyl)-1H-tetrazolate (11) was ob-
tained as yellow crystals (0.379 g). Theoretical mass expected for 2.00
(
(
0.8), 423 (0.8), 408 (1.1), 362 (10.0), 349 (3.1 sh), 324 (1.1), 286
0.7), 221 (1.6).
Rubidium 5-(Trinitromethyl)tetrazolate (7). Pale yellow crystals
(
0.608 g), theoretical mass expected for 2.00 mmol of C N O Rb =
.607 g (quantitative yield). DTA (5 °C·min ) 119.6 °C explosion.
2
7
6
−1
0
1
3
14
C NMR (D O, ppm) δ 125.9 s [C(NO ) ], 152.0, s (CN ).
N
2
2
3
4
NMR (D O ppm) δ −32.4, τ = 10 Hz (NO ); δ −62, τ = 650 Hz
2
1/2
2
1/2
−1
(
CN ). Raman (1064 nm, 35 mW) ν (cm ) = 1622 (3.0), 1605 (1.5),
4
1
593 (0.8), 1434 (10.0), 1399 (1.5), 1368 (1.4), 1334 (0.2), 1316
(
(
0.7), 1301 (1.0), 1289 (1.0), 1191 (1.0), 1147 (0.5), 1104 (2.4), 1044
1.6 sh), 1037 (1.5 sh), 1018 (0.1), 992 (2.5), 951 (4.7), 849 (5.9),
−
1
mmol of C
H N O = 0.414 g (yield = 91.6%). DTA (5 °C·min )
5 7 5
1
2
8
04 (1.2), 739 (0.4), 680 (0.6), 648 (0.5), 622 (0.6), 431 (2.2), 391
149.9 °C explosion. H NMR (D
2
O, ppm) δ 3.98 br (NH
O, ppm) δ 129.0 br s [C(NO ]; 156.3 s
O ppm) δ −24.6, τ1/2 = 110 Hz (NO ); δ −68,
); −291, τ1/2 = 500 Hz (NH OH). Raman (1064
3
OH and
13
(
4.6), 375 (2.9), 360 (7.6), 348 (4.0), 226 (1.5 sh), 216 (2.1), 164 (6.1
CN
(CN
1/2 = 850 Hz (CN
4
H). C NMR (D
2
)
2 2
−1
14
sh), 158 (6.6), 132 (5.6). IR (KBr) ν (cm ) = 2959 (vw), 2926 (w
br), 2903 (vw sh), 2859 (w), 2470 (vw), 2428 (vw), 2176 (vw sh),
4
). N NMR (D
2
2
τ
4
3
−1
2
1
169 (vw), 2152 (vw), 2069 (vw), 2057 (vw), 1616 (vs sh), 1595 (vs),
433 (m), 1395 (w), 1384 (m), 1365 (vw sh), 1313 (s sh), 1296 (s
nm, 40 mW) ν (cm ) = 3230−3065 (1.4), 3010−2800 (1.5), 2889
(1.2), 1593 (0.7), 1515 (1.8), 1486 (4.3), 1425 (6.8), 1376 (7.5), 1338
(1.5), 1243 (1.7), 1222 (4.1), 1200 (1.2), 1164 (6.7), 1126 (10.0),
1087 (0.9), 1022 (6.7), 993 (3.4), 838 (6.4), 820 (1.7), 778 (1.5), 759
(1.1), 471 (4.4), 445 (2.9), 415 (1.3), 326 (2.0), 291 (3.3), 248 (3.3),
203 (1.6). IR (KBr) ν (cm ) = 3448 (m br), 3170 (m br), 3094 (w
br), 2924 (m br), 2857 (w sh), 2694 (w br), 1596 (m), 1558 (w sh),
1529 (vs), 1466 (m), 1418 (m), 1369 (s), 1326 (m), 1258 (s), 1215
(vs), 1200 (s sh), 1143 (s), 1116 (m), 1052 (s), 1015 (m), 995 (m),
871 (w), 835 (m), 783 (w), 751 (s), 736 (w), 712 (vw), 701 (vw), 696
(vw), 668 (vw), 638 (w), 591 (m), 453 (w).
sh), 1285 (s), 1233 (vw), 1188 (w), 1143 (w), 1126 (vw), 1102 (m),
1
7
4
040 (w), 1035 (w), 1017 (vw), 990 (m), 948 (w), 846 (s), 803 (vs),
38 (w), 731 (w), 599 (w sh), 677 (w), 644 (m), 617 (m), 489 (vw),
53 (m br).
−1
Cesium 5-(Trinitromethyl)tetrazolate (8). Pale yellow crystals
(
0.691 g), theoretical mass expected for 2.00 mmol of C CsN O =
2 7 6
−1
13
0
.702 g (yield = 98.4%). DTA (5 °C·min ) 129.9 °C explosion. C
14
NMR (D O, ppm) δ 125.7 s [C(NO ) ]; 152.4 s (CN ). N NMR
2
2
3
4
(
D O ppm) δ −31.7, τ = 10 Hz (NO ); δ −62, τ = 600 Hz
2
1/2
2
1/2
C
dx.doi.org/10.1021/ic400919n | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 1. Synthesis of 5-(Trinitromethyl)-2H-tetrazole 4
Synthesis of Hydrazinium 5-(Dinitromethyl)tetrazolate (12).
A solution of hydrazine (2.00 g, 62.5 mmol) in water (5 mL) was
slowly added to a solution of 5-(trinitromethyl)-2H-tetrazole (0.438 g,
(m), 1072 (w sh), 1054 (s), 1020 (m), 998 (m), 837 (m), 800 (w),
753 (s), 744 (w sh), 712 (w sh), 429 (m).
Synthesis of Potassium 5-(Dinitromethyl)-1H-tetrazolate
(14). A solution of 5-(dinitromethylene)-4,5-dihydro-1H-tetrazole
(0.174 g, 1.00 mmol) in acetone (5 mL) was added to a stirred
suspension of potassium carbonate (0.138 g, 1.00 mmol) and acetone
(5 mL). After 30 min, the reaction mixture was filtered through a
Buchner funnel and the filtrate was taken to dryness by a stream of
nitrogen. Potassium 5-(dinitromethyl)-1H-tetrazolate (14) was
obtained as pale yellow crystals (0.195 g). Theoretical mass expected
for 1.00 mmol of C HKN O = 0.212 g (yield = 91.9%). DTA (5
2
.00 mmol) in water (5 mL). After gas evolution ceased, the obtained
yellow solution was taken to dryness by a stream of nitrogen.
Hydrazinium 5-(dinitromethyl)tetrazolate (12) was obtained as dark
yellow crystals (0.437 g). Theoretical mass expected for 2.00 mmol of
−
1
C H N O = 0.476 g (yield = 91.7%). DTA (5 °C·min ) 152.2 °C
2
10 10
4
explosion. Recrystallization from water resulted in isolation of
hydrazinium 5-(dinitromethyl)tetrazolate monohydrate (12·H O,
2
−
1
C H N O ·H O) as yellow crystals. DTA (5 °C·min ) 151.0 °C
explosion. H NMR (D O, ppm) δ 1.2 and 1.9 br (N H ). C NMR
2
10 10
4
2
2
6
4
1
13
−1
13
2
2
5
°C·min ) 155.2 °C explosion. C NMR (DMSO-d , ppm) δ 121.5 s
6
1
4
14
(
D O, ppm) δ 129.0 br s [C(NO ) ]; 156.4 s (CN ). N NMR (D O
[C(NO ) ]; 149.4 s (CN ). N NMR (DMSO-d ppm) δ −24.5, τ
2
2
2
4
2
2
2
4
6
1/2
ppm) δ −24.6, τ = 90 Hz (NO ); δ −70, τ = 680 Hz (CN );
1/2
2
1/2
4
= 60 Hz (NO ); δ −275, τ = 200 Hz (NH). Raman (1064 nm, 15
2
1/2
−1
−
332 ppm, τ = 390 Hz (N H ). Raman (1064 nm, 40 mW) ν
cm ) = 3352 (0.3), 3342 (0.2), 3293 (0.7), 3265 (0.3), 3255 (0.3),
1/2 2 5
mW) ν (cm ) = 3240 (0.3 br), 1541 (2.0 sh), 1523 (10.0), 1487
−1
(
(
(
1.7), 1419 (1.0), 1397 (0.5), 1365 (9.1), 1336 (2.0), 1320 (5.0), 1246
3.3), 1184 (7.3), 1147 (3.0), 1133 (2.1 sh), 1117 (2.0), 1052 (1.5),
3
1
220 (0.5), 3150 (0.6), 1648 (0.4), 1625 (0.3), 1588 (0.4), 1523 (2.3),
501 (1.2 sh), 1487 (0.9), 1467 (0.4), 1431 (1.8), 1406 (1.1), 1363
1
016 (1.1), 1001 (8.8), 840 (6.4), 780 (1.4), 473 (2.0), 453 (0.9), 440
(
1
(
6
7.2), 1268 (0.4), 1214 (3.0), 1202 (2.0 sh), 1148 (1.6), 1132 (2.7),
103 (1.1), 1079 (1.8), 1072 (1.2 sh), 1023 (8.7), 945 (1.2), 823
10.0), 789 (0.5), 756 (0.6), 735 (0.7), 482 (2.3), 448 (1.6), 422 (2.0),
04 (0.3), 369 (0.4), 315 (0.5), 267 (1.1), 168 (3.5), 145 (5.1). IR
(
(
(
(
1.0 sh), 432 (1.4), 388 (0.7), 352 (1.2), 316 (0.5), 236 (0.7), 206
0.3), 155 (3.1). IR (KBr) ν (cm ) = 3217 (m br), 1616 (w br), 1539
m sh), 1525 (m), 1478 (m), 1468 (w sh), 1419 (m), 1362 (m), 1334
w), 1317 (m), 1244 (s), 1190 (w sh), 1182 (vs), 1142 (m), 1136 (w
−1
−1
(
2
KBr) ν (cm ) = 3500−3380 (s), 3350−3250 (s), 3230−2900 (s),
sh), 1113 (s), 1052 (vs), 1013 (w), 998 (m), 837 (m), 801 (m), 776
694 (vw br), 2618 (w br), 1615 (m br), 1528 (s), 1505 (vw), 1446
(w), 753 (m), 697 (m), 604 (w).
(
(
(
m sh), 1430 (s), 1383 (m), 1356 (m), 1270 (m sh), 1230 (vs), 1219
vs), 1130 (vs), 1083 (m br), 1013 (s), 957 (m br), 826 (m), 789
vw), 750 (m), 736 (nw), 637 (w), 593 (w), 490 (nw), 449 (w).
Synthesis of 5-(Dinitromethylene)-4,5-dihydro-1H-tetrazole
X-ray Crystal Structure Determination. Single-crystal X-ray
diffraction data were collected on a Bruker Smart Apex Duo 3-circle
platform diffractometer, equipped with an Apex II charge-coupled
device (CCD) detector with the χ-axis fixed at 54.74° and using Mo
Kα radiation (Triumph curved-crystal monochromator) from a fine-
focus tube. The diffractometer was equipped with an Oxford
Cryostream 700 apparatus for low-temperature data collection. A
complete hemisphere of data was scanned on ω (0.5°) with a run time
of 1, 2, or 10 s/frame at a detector resolution of 512 × 512 pixels by
(13). Hydrazinium 5-(dinitromethyl)tetrazolate (0.238 g, 1.00 mmol)
or hydroxylammonium 5-(dinitromethyl)tetrazolate (0.207 g, 1.00
mmol) was dissolved in 2 M sulfuric acid (10 mL) and the solution
was extracted three times with ethyl acetate (5 mL each). The
combined organic phases were dried over magnesium sulfate, and the
solvent was evaporated on a rotary evaporator. 5-(Dinitromethylene)-
1
8
use of the BIS software package. The frames were then integrated
4
,5-dihydro-1H-tetrazole (13) was obtained as white solid (0.150 g).
2
6
with the SAINT algorithm to give the hkl files corrected for Lp/
Theoretical mass expected for 1.00 mmol of C H N O = 0.174 g
2
2
6
4
−1
decay. Absorption correction was performed with the SADABS
(
yield = 85.9%). DTA (5 °C·min ) 92.2 °C explosion. Recrystalliza-
tion from acetone/water resulted in isolation of 5-(dinitromethylene)-
,5-dihydro-1H-tetrazole dihydrate (C H N O ·2H O, 13·2H O) as
2
7
program. The structures were solved by the direct method and
2
28−31
refined on F by use of the Bruker SHELXTL software package.
4
2
2
6
4
2
2
−1
1
All non-hydrogen atoms were refined anisotropically. ORTEP
colorless crystals. DTA (5 °C·min ) 103.1 °C explosion. H NMR
(
13
drawings were prepared with the ORTEP-III for Windows V2.02
DMSO-d , ppm) δ 11.0 br (NH). C NMR (DMSO-d , ppm) δ
6
6
3
2
14
program. Further crystallographic details for compounds 1 and 2 can
be obtained from the Cambridge Crystallographic Data Centre
[CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K.; fax (+44)
1223-336-033; e-mail deposit@ccdc.cam.ac.uk] on quoting the
deposition numbers CCDC 895075 and 895076) and for compounds
4−14 from the Fachinformationszentrum Karlsruhe, 76344 Eggen-
stein-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
425032−425043.
1
22.0 [C(NO ) ]; 150.4 (CN ). N NMR (DMSO-d , ppm) δ −24.1,
2
2
4
6
τ1/2 = 80 Hz (NO ); δ −42/-64, τ = 550/600 Hz (CN ). Raman
2
1/2
4
−
1
(
488 nm, 100 mW) ν (cm ) = 3058 (0.4), 2958 (0.5), 1581 (6.4),
523 (0.4), 1509 (0.4), 1493 (0.4), 1460 (0.2), 1419 (6.3), 1396 (1.0),
314 (10.0), 1290 (2.5), 1278 (0.6 sh), 1242 (2.8), 1194 (1.0), 995
−1
30 (1.0). IR (KBr) ν (cm ) = 3400−3000 (m br), 1585 (s), 1524
sh), 1248 (s), 1226 (w sh), 1201 (vs), 1183 (w sh), 1144 (m), 1114
D
dx.doi.org/10.1021/ic400919n | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 2. Synthesis of 5-(Trinitromethyl)tetrazolate Salts 5−10a
Scheme 3. Synthesis of Dinitromethyltetrazoles 11−14
RESULTS AND DISCUSSION
ester 1, resulted in isolation of 1H-tetrazole-5-acetic acid
■
2
3,24,33
2
.
Nitration of 2 with fuming nitric acid in concentrated
Syntheses. The employed synthetic routes for the
preparation of HTNTz 4 are shown in Scheme 1. Initially, 4
was prepared from cyanoacetamide according to a slightly
sulfuric acid, followed by extraction with dichloromethane,
resulted in isolation of HTNTz 4 in 60% yield. In contrast to
the fact that 4 was previously described as an orange-yellow
21
modified literature method. Nitration of cyanoacetamide with
fuming nitric acid in 20% oleum under anhydrous conditions
resulted in formation of trinitroacetonitrile 3. Because of its
20
oil, it was obtained as colorless crystals that tend to explode
upon impact, shock, and friction. The compound explodes
upon heating at about 95 °C and is soluble in water,
acetonitrile, dichloromethane, and acetone. HTNTz 4 is
strongly acidic and reacts with bases yielding the formation of
25
reported sensitivity and instability, 3 was not isolated as a neat
compound and was handled only in the form of solutions in
tetrachloromethane. The 1,3-dipolar cycloaddition reaction of 3
−
salts containing the 5-(trinitromethyl)tetrazolate (TNTz )
with HN , followed by extraction with dichloromethane,
3
anion (Scheme 2).
resulted in isolation of HTNTz 4 in approximately 60% yield.
Due to the high moisture sensitivity of the nitration step, as
well as the sensitivity and instability of trinitroacetonitrile 3,
the following more convenient synthesis of HTNTz 4 was
Ammonium 5-(trinitromethyl)tetrazolate 5 was obtained in
quantitative yield by a convenient acid−base reaction between
aqueous solutions of 4 and ammonia. The guanidinium,
rubidium, and cesium salts 6−8 were obtained in quantitative
yields by reaction of a solution of 4 in acetone with an excess of
the corresponding carbonate. Silver and copper(II) 5-
25
developed. The 1,3-dipolar cycloaddition of ethyl cyanoacetate
with HN , followed by basic hydrolysis of the obtained ethyl
3
E
dx.doi.org/10.1021/ic400919n | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 1. Crystallographic Data and Structure Determination
Details for Tetrazoles 1, 2, and 4
nium 5-(dinitromethyl)-1H-tetrazolate 11 was obtained in over
90% isolated yield when neat HTNTz 4 or an aqueous solution
of 4 was reacted with 50% aqueous hydroxylamine (Scheme 3).
Exposure of neat HTNTz 4 to 100% hydrazine resulted in a
violent reaction with ignition of the material followed by an
explosion. However, when an aqueous solution of 4 was reacted
with 50% aqueous hydrazine, yellow to orange hydrazinium 5-
1
2
4
formula
C H N O
C H N O
C HN O
6
5
8
4
2
3
4
4
2
2
7
weight (g/mol)
temp (K)
crystal system
space group
a (Å)
156.12
100(2)
128.10
100(2)
219.10
100(2)
orthorhombic
Pca21
monoclinic
monoclinic
(
(
dinitromethyl)tetrazolate 12 was obtained in high yield
scheme 3). Recrystallization of 12 from water resulted in
P2 /c
1
P2 /n
1
9.7840(3)
11.0429(4)
6.5982(2)
90
7.2196(11)
7.3128(10)
10.0239(14)
90
5.9141(3)
21.5244(11)
6.0357(3)
90
crystals of the monohydrate 12·H O as pale orange crystals.
2
b (Å)
Treatment of 11 and 12 with 2 M sulfuric acid resulted in
formation of colorless 5-(dinitromethylene)-4,5-dihydro-1H-
tetrazole 13 in good yields of 85%. The compound was
recrystallized from acetone/water and isolated as the crystalline
dihydrate 13·2H O. Treatment of 13 or 13·2H O with
c (Å)
α (deg)
β (deg)
90
102.734(3)
90
99.0760(10)
90
γ (deg)
V (Å3)
90
2
2
712.89(4)
4
516.20(13)
4
758.71(7)
4
potassium carbonate in acetone solution resulted in formation
of potassium 5-(dinitromethyl)-1H-tetrazolate 14, which was
isolated as pale yellow crystals in over 90% yield.
X-ray Crystal Structures. Single crystals suitable for X-ray
crystal structure determination were obtained for compounds 1,
Z
ρcalc (g/cm3)
μ (mm−1)
F(000)
1.455
1.648
1.918
0.116
0.140
0.188
328
264
440
reflns collected
ind reflns
Rint
16 196
2149
12 286
1578
18 128
2313
2
, 4−8, 9a, 10a, and 11−14. The relevant data and parameters
for the X-ray measurements and refinements of the tetrazoles 1,
, and 4 are summarized in Table 1. For all three compounds,
0.0260
105
0.0364
85
0.0399
136
2
no. of params
R1 [I > 2σ(I)]
the hydrogen atom of the tetrazole ring has been located via the
difference electron density map.
The molecular structure of the ethyl ester 1 is shown in
0.0255
0.0669
1.073
0.0339
0.0841
1.043
0.0318
0.0725
1.012
wR [I > 2σ(I)]
2
GoF
Figure 1, and the geometric parameters of the CN ring are
4
summarized in Table 2. The observed bond length pattern
within the five-membered ring [N2−N3 1.296(1) Å, C1−N4
(
trinitromethyl)tetrazolate 9 and 10 were obtained as colorless
1
.328(1) Å, C1−N1 1.338(1) Å, N1−N2 1.352(1) Å, and N3−
or blue amorphous precipitates when aqueous solutions of
silver nitrate or copper(II) sulfate, respectively, were added to
aqueous solutions of 4 (Scheme 2). Colorless or intense blue
crystals of the ammonia adducts 9a and 10a, respectively, were
obtained by recrystallization of the amorphous precipitates 9
and 10 from aqueous ammonia solutions. While all 5-
N4 1.368(1) Å] indicates significant double-bond character for
bonds N2−N3 and C1−N4. This conclusion is further
supported by the fact that the hydrogen atom of the tetrazole
ring is located solely at N1 and is in good agreement with the
24
common description of such compounds in the literature.
The corresponding free acid 2 crystallizes in the monoclinic
space group P2 /c. Table 2 summarizes selected bond lengths
(
trinitromethyl)tetrazolates of this work are energetic and can
explode upon provocation (heat or mechanical shock),
compounds 7−10 are especially sensitive and treacherous.
For example, in several instances, crystals of 7 and 8 exploded
during crystallization without any further provocation. These
salts should be handled with great care, proper safety
precautions and only on a small scale.
1
and angles of 2, and Figure 2 depicts the molecular structure of
the compound. The observed bond lengths pattern of the five-
membered ring is very similar to that of compound 1.
The molecular structure of 5-(trinitromethyl)-2H-tetrazole is
depicted in Figure 3, while Table 2 summarizes the bond
lengths and angles of the tetrazole ring in this compound. The
crystal packing of the compound is dominated by hydrogen
bonding (Supporting Information).
While the conversion of trinitromethyl-substituted imida-
zoles and triazoles into the corresponding dinitromethylide
salts by use of hydroxylamine has previously been
1
4,17,34
reported,
the mechanism of these reactions is unknown.
In comparison to compounds 1 and 2, the geometry of the
In an analogous conversion, yellow to orange hydroxylammo-
five-membered ring in 4 is different. While the hydrogen atom
Figure 1. X-ray crystal structure of 1. Hydrogen atoms are shown as spheres of arbitrary radius. Thermal displacement ellipsoids are set at 50%
probability.
F
dx.doi.org/10.1021/ic400919n | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
a
Table 2. Selected Bond Lengths and Angles for Compounds 1, 2, and 4−14
a
Bond lengths are given in angstroms; bond angles are given in degrees.
Figure 2. Molecular unit of 2 in the crystal. Hydrogen atoms are
shown as spheres of arbitrary radius. Thermal displacement ellipsoids
are set at 50% probability.
Figure 3. Molecular structure of 5-(trinitromethyl)-2H-tetrazole 4 in
the crystal. The hydrogen atom is shown as a sphere of arbitrary
radius. Thermal displacement ellipsoids are set at 30% probability.
of the tetrazole moiety in compounds 1 and 2 is located at the
-position of the ring (N1), in HTNTz the hydrogen atom is
1
solely located at the 2-position (N2) of the five-membered ring.
The different location of the hydrogen atom can be attributed
to the much stronger electron-withdrawing effect of the
−
(trinitromethyl)-2H-tetrazolate (TNTz ) anions that are
associated through hydrogen bonds (Supporting Information).
Figure 4 shows the structure of the 5-(trinitromethyl)-
tetrazolate anion in this salt, and further crystallographic details
of the structure are listed in Table 3. The observed bond
trinitromethyl group in comparison to the CH COOR group.
2
The different location of the tetrazole hydrogen atom affects
the bond lengths pattern within the five-membered ring. While
the distance C1−N1 is longer than the one for C1−N4 in
compounds 1 and 2, it is the opposite for compound 4. In
HTNTz, the distance between C1 and N1 [1.324(1) Å] is 0.02
Å shorter than that between C1 and N4. While the N−N
distances in the five-membered rings of 1 and 2 differ by about
−
lengths and angles for the TNTz anion are summarized in
Table 2.
Guanidinium 5-(trinitromethyl)-2H-tetrazolate 6 crystallizes
in the monoclinic space group P2 /c (Z = 8). The observed
bond lengths and angles for the 5-(trinitromethyl)tetrazolate
anion in the guanidinium salt 6 are very similar to those
previously discussed for compound 5 and are summarized in
Table 2, while further details of the structure determination and
crystallographic parameters are listed in Table 3. As has already
1
0.06 Å, in 4 these distances can be considered identical within
their margins of error.
The solid-state structure of ammonium 5-(trinitromethyl)-
H-tetrazolate 5 consists of ammonium cations and 5-
2
G
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Inorganic Chemistry
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Figure 5. Asymmetric unit in the crystal structure of guanidinium salt
6
with hydrogen bonding. For clarity, only some of the observed
hydrogen bonds are included. Hydrogen atoms are shown as spheres
of arbitrary radius.
Figure 4. Structure of the 5-(trinitromethyl)-2H-tetrazolate anion in
compound 5. Thermal displacement ellipsoids are drawn at 30%
probability.
state structures of the Rb and Cs salts do not consist of isolated
ions but are dominated by strong interactions between the
metal cation and the nitrogen atoms of the tetrazolate ring and
also six oxygen atoms from the nitro groups of the anion
(Figure 6). The closest Rb−N and Cs−N distances are
2.951(1) and 3.119(1) Å (M−N4), respectively, and the closest
Rb−O and Cs−O distances are 3.0312(9) and 3.159(1) Å (M−
O6), respectively.
been observed for the ammonium salt 5, the solid state packing
in 6 is defined by strong hydrogen bonding between the
guanidinium cations and the anions (Figure 5).
The observed crystal structures of the rubidium salt 7 and
cesium salt 8 of the 5-(trinitromethyl)-2H-tetrazolate anion are
isostructural. Both compounds crystallize in the triclinic space
group P-1 with two formula units in the unit cell. As can be
seen from Table 3, even the unit cell parameters are very
similar, with the cesium salt having a slightly larger unit cell
All attempts to grow single crystals of AgTNTz 9 suitable for
X-ray structure determination were unsuccessful. Recrystalliza-
tion of an amorphous sample of 9 from an aqueous ammonia
solution resulted in crystals of the ammonia adduct ([Ag-
(NH ) ] [Ag (TNTz) ]) 9a instead. Selected crystallographic
3
2 2
2
3
2
3
3
volume of 453.85(2) Å compared to 423.78(2) Å for the Rb
salt. The basic geometry of the anion in both compounds is
identical to that observed for the NH4+ salt 5, which is depicted−
in Figure 4. Selected bond lengths and angles for the TNTz
anion in compounds 7 and 8 are listed in Table 2. The solid-
data of compound 9a are listed in Table 3. The crystal structure
+
of 9a contains isolated [Ag(NH ) ] cations and polymeric
3
2
anion chains. The anion chains are made up from
−
[Ag (TNTz) ] units in which two silver atoms are linked in
2
3
−
a 1,2-fashion by three bridging TNTz anions. The resulting
Table 3. Crystallographic Data and Structure Determination Details for Trinitromethyl-2H-tetrazolates 5−10a
5
6
7
8
9a
10a
formula
C H N O
C H N O
C N O Rb
C CsN O
C H Ag N O
C H CuN O
17 12
2
4
8
6
3
6
10
6
2
7
6
2
7
6
12 12
6
46 36
4
9
weight (g/mol)
temp (K)
crystal system
space group
a (Å)
236.13
100(2)
278.18
100(2)
303.56
100(2)
351.00
2023.90
550.82
100(2)
100(2)
100(2)
triclinic
P-1
monoclinic
triclinic
P-1
triclinic
monoclinic
orthorhombic
P2 /c
1
P-1
P2 /c
1
P2 2 2
1 1 1
7.0369(3)
7.3590(3)
9.1760(4)
9.8509(5)
8.8922(4)
24.3416(12)
90
5.8577(1)
7.5152(2)
9.8610(2)
85.1310(10)
78.4680(1)
88.4250(10)
423.78(2)
2
5.9537(2)
7.7298(2)
10.0994(3)
84.2842(5)
79.0115(5)
88.5204(5)
453.85(2)
2
11.7121(9)
22.171(4)
21.479(3)
90
7.6843(2)
12.1514(3)
19.8358(4)
90
b (Å)
c (Å)
α (deg)
104.8260(10)
91.8040(10)
109.1510(10)
430.45(3)
2
β (deg)
100.636(1)
90
91.600(2)
90
90
γ (deg)
V (Å3)
90
2095.60(18)
8
5575.3(15)
4
1852.17(8)
4
Z
ρcalc (g/cm3)
μ (mm−1)
F(000)
1.822
1.763
2.379
2.568
2.411
1.975
0.175
0.164
5.878
4.114
2.208
1.286
240
1136
292
328
3904
1108
reflns collected
ind reflns
Rint
10 695
2585
50 468
6349
24 037
3719
11 222
2721
130 059
16 785
0.0701
908
31 958
4222
0.0262
159
0.0440
353
0.0316
145
0.0200
146
0.0444
311
no. of params
R1 [I > 2σ(I)]
0.0318
0.0777
1.074
0.0375
0.0887
1.024
0.0203
0.0406
1.028
0.018
0.0494
0.1223
1.039
0.0310
0.0526
1.022
wR [I > 2σ(I)]
2
0.0279
1.097
GoF
H
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Inorganic Chemistry
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Figure 6. Interactions between cesium cation and 5-(trinitromethyl)-
2H-tetrazolate anion in its cesium salt 8.
Figure 9. Molecular structure of hydroxylammonium 5-(dinitrometh-
yl)-1H-tetrazolate 11. Ellipsoids are drawn at the 30% probability level.
Hydrogen atoms are shown as spheres of arbitrary radius.
basic geometry is similar to the one of bicyclo[2.2.2]octane
with the silver atoms acting as bridgeheads. The Ag−N
distances within such units range from 2.267(4) to 2.478(5) Å.
In addition, each of the Ag atoms is bonded to a nitrogen atom
−
of a neighboring [Ag (TNTz) ] unit, resulting in the
2
3
−
formation of an anion chain in which the [Ag (TNTz) ]
2
3
units are interconnected through near-planar six-membered
−
rings. Figure 7 shows two such interconnected [Ag (TNTz) ]
2
3
units.
In analogy to the problems encountered in growing single
crystals of 9, all attempts to grow single crystals of the copper
compound 10 suitable for X-ray diffraction were unsuccessful.
Recrystallization of 10 from an aqueous ammonia solution
resulted in intense blue crystals of Cu(NH ) (TNTz) 10a.
3
3
2
The structure of the Cu(NH ) (TNTz) 10a complex is
3
3
2
−
Figure 7. Two [Ag (TNTz) ] units of an anion chain in the crystal
depicted in Figure 8, and further crystallographic details for the
crystal structure of 10a are listed in Table 3. It can be seen from
Figure 8 that the Cu atom is exclusively bound through the 2-
2
3
structure of 9a. The individual Ag (TNTz) units are emphasized by
red contacts, while contacts connecting the units are drawn in green.
The trinitromethyl groups have been omitted for clarity.
2
3
9
position of the tetrazole ring. In accord with the d electron
configuration of the central Cu atom, the ligand arrangement in
the complex can be derived from a Jahn−Teller distorted
octahedron in which one axial position remains unoccupied and
the second axial position is occupied by one 5-(trinitromethyl)-
2
H-tetrazolate anion. The equatorial positions are occupied by
three NH groups and one 5-(trinitromethyl)-2H-tetrazolate.
3
The second axial position remains unoccupied. The equatorial
Cu−N distances range from 2.006(2) to 2.029(2) Å. The
longer axial Cu−N distance of 2.247(2) Å is in accordance with
9
the Jahn−Teller distortion typically observed for d electron
configuration.
The molecular structure of hydroxylammonium 5-(dinitro-
methyl)-1H-tetrazolate 11 is shown in Figure 9, and further
crystallographic data are summarized in Table 4. Structural
parameters of the 5-(dinitromethyl)-1H-tetrazolate anion in 11
are summarized in Table 2 and are in good agreement with the
Figure 8. Structure of Cu(NH ) (TNTz) 10a. Hydrogen atoms have
been omitted. Thermal displacement ellipsoids are drawn at the 30%
probability level.
3
3
2
13,16
ones described previously for this compound.
I
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Inorganic Chemistry
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Table 4. Crystallographic Data and Structure Determination Details for Dinitromethyltetrazoles 11−14
1
1
12
12·H O
13·2H O
14
2
2
formula
C H N O
C H N O
C H N O
C H N O
C HKN O
2
5
7
5
2
10 10
4
2
12 10
5
2
6
6
6
2
6
4
weight (g/mol)
temp (K)
crystal system
space group
a (Å)
207.13
100(2)
238.20
256.22
210.13
100(2)
212.17
100(2)
100(2)
100(2)
monoclinic
monoclinic
monoclinic
orthorhombic
Pnma
10.605(3)
15.718(4)
4.8189(12)
90
monoclinic
P21
P2 /c
1
P2 /c
1
P2 /c
1
9.1235(5)
9.3899(5)
8.1626(4)
90
9.9843(4)
6.9914(3)
13.8195(5)
90
11.3187(4)
9.0679(3)
10.1352(4)
90
4.7849(2)
9.1100(3)
7.5085(3)
90
b (Å)
c (Å)
α (deg)
β (deg)
91.9210(10)
90
105.8260(10)
90
90.9770(10)
90
90
90.9830(10)
90
γ (deg)
V [Å3]
90
698.89(6)
4
928.09(6)
4
1040.09(6)
4
803.3(3)
4
327.25(2)
2
Z
ρcalc (g/cm3)
μ (mm−1)
F(000)
1.969
1.705
0.153
496
1.636
0.150
536
1.738
2.153
0.186
0.169
0.807
424
432
212
reflns collected
ind reflns
Rint
7529
21 591
2813
24 959
3169
17 653
1212
6491
2089
1954
0.0212
131
0.0317
185
0.0262
202
0.0408
73
0.0186
122
no. of params
R1 [I > 2σ(I)]
0.0300
0.0806
1.043
0.0322
0.0834
1.040
0.0289
0.0796
1.060
0.0297
0.0821
1.098
0.0201
0.0527
1.058
wR [I > 2σ(I)]
2
GoF
Stability of the Compounds. The impact and friction
sensitivities of the tetrazoles of this study were determined by
use of a BAM fall hammer and BAM friction tester, respectively.
The obtained sensitivities are summarized in Table 5, together
with the oxygen balances (OB) of the compounds. 5-
(
Trinitromethyl)-2H-tetrazole 4 and the corresponding salts
7
−9 as well as hydroxylammonium 5-(dinitromethyl)-1H-
tetrazolate 11 are overoxidized and possess a positive oxygen
balance; compounds 1, 2, 6, 10a, and 12−14 are underoxidized
with a negative oxygen balance; and ammonium 5-
(
trinitromethyl)tetrazolate 5 is oxygen-balanced. It is often
Figure 10. Molecular structure of potassium 5-(dinitromethyl)-1H-
tetrazolate 14. Ellipsoids are drawn at the 30% probability level. The
hydrogen atom is shown as a sphere of arbitrary radius. Selected
distances and angles: K1−O2, 2.8318(10) Å; K1−O4, 2.7882(11) Å;
O2−K1−O4, 52.87(3)°.
assumed that a compound with an oxygen balance closer to
zero will be more brisant, powerful, or sensitive. This
relationship is not universally correct and there are many
exceptions to this simple rule. For example, RbTNTz 7 and
CsTNTz 8 have higher impact and friction sensitivities than
NH TNTz 5, despite their more positive oxygen balances.
4
However, the oxygen balance can be very useful in the
processing of energetic materials formulations (e.g., rocket
propellants or mixtures of explosives). In general, formulations
with an oxygen balance close to zero yield higher performances
than formulations that are over- or underoxidized.
With the exception of ethyl 2-(1H-tetrazol-5-yl)acetate 1 and
The dihydrazinium salt of 5-(dinitromethyl)tetrazole 12
crystallizes in the monoclinic space group P2 /c with four
1
formula units in the unit cell. Recrystallization of 12 from water
afforded crystals of the hydrate 12·H O, whose crystal structure
2
35
13
has previously been described. The obtained structures of the
5
-(dinitromethyl)tetrazolate anion in 12 and 12·H O (see
2
1
H-tetrazole-5-ethanoic acid 2, all tetrazole compounds of this
Supporting Information) are in good agreement with the one
described previously for the sodium, ammonium, hydroxylam-
study proved to be highly energetic and sensitive to mechanical
stress. While compounds 1 and 2 could not be exploded with
impacts of up to 100 J, all studied nitro-2H-tetrazoles showed
impact sensitivities of 30 J or less. The neutral 5-(nitromethyl)-
2H-tetrazoles 4 and 13, as well as the 5-(trinitromethyl)-2H-
tetrazolates 5−8, are highly sensitive and explode violently at
impacts of under 5 J. By comparison of the sensitivity data of 9/
16
monium, and aminoguanidinium salts and are summarized in
Table 2.
Details of the obtained crystal structure of dinitromethylene-
4
,5-dihydro-1H-tetrazole dihydrate 13·2H O can be found in
2
Table 4. The obtained structural parameters (Table 2) of the
dinitromethylene-4,5-dihydro-1H-tetrazole molecule in
1
3·2H O are in good agreement with the ones described
9a, 12/12·H O, and 13/13·2H O, it can be seen that
2
2
2
16
previously for this compound.
incorporation of water or ammonia into the crystal lattice
results in lowered impact sensitivity of the compound. The
friction sensitivity of the compounds follows similar trends.
Also, all compounds were screened for sensitivity toward
The asymmetric unit in the crystal structure of potassium 5-
dinitromethyl)-1H-tetrazolate 14 is depicted in Figure 10.
Crystallographic details of the structure are listed in Table 4.
(
J
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Inorganic Chemistry
Article
Table 5. Properties of Compounds 1, 2, and 4−14
a
b
c
compd
OB (%)
Texplosion (°C)
impact sensitivity (J)
friction sensitivity (N)
1
−123.0
−75.0
+11.0
0.0
>100
>100
9.0
>360
>360
9.0
20
2
HTNTz, 4
100.9
115.7
115.5
119.6
129.9
123.4
122.8
122.8
117.3
149.9
152.2
151.0
92.2
NH TNTz, 5
6.0
4
d
GuaTNTz,
RbTNTz, 7
CsTNTz, 8
AgTNTz, 9
6
−17.3
+7.9
4.0
40
0.5
<1
+6.8
0.5
<1
+7.4
5.0
5.0
5.0
80
([Ag(NH ) ] [Ag (TNTz) ]) , 9a
+12.3
9.5
3
2
2
2
3
2
Cu(TNTz) ·xH O, 10
Cu(NH ) (TNTz) , 10a
2.0
2
2
−4.4
+3.4
2.5
95
3
3
2
e
NH OHHDNTz, 11
5.5
144
160
>360
64
3
(
(
N H ) DNTz, 12
−17.8
−16.7
−9.9
−8.1
−8.0
10.0
30.0
5.0
2
5 2
N H ) DNTz·H O, 12·H O
2
5
2
2
2
H DNTz, 13
2
H DNTz·2H O, 13·2H O
KHDNTz, 14
103.1
155.2
15.0
168
10
2
2
2
3.5
a
b
c
OB = oxygen balance. The impact sensitivity of RDX was found as 7.0 J on the instrument used. The friction sensitivity of RDX was found as 160
N on the instrument used. Gua = guanidinium. HDNTz = 5-dinitromethylene-4,5-dihydro-1H-tetrazole.
d
e
electrostatic discharge by exposing small amounts (∼5 mg) to
sparks from a Tesla coil (∼20 kV). All compounds, except 4,
failed to explode under these conditions.
resolve individual signals for the chemically nonequivalent
nitrogen atoms of the tetrazole ring. The 13C NMR resonance
for the carbon atom of the tetrazole ring was observed in the
range 145−160 ppm. The carbon resonance of the C(NO2)3
and C(NO ) groups at around 120−125 ppm was less intense,
The thermal stabilities of all compounds of this study were
determined by differential thermal analysis (DTA) scans with a
2
2
−1
heating rate of 5 °C·min . The results of these scans are
summarized in Table 5. As expected, compounds 1 and 2 did
not explode but melted at onset temperatures of 124.4 °C (lit.
broader, and more difficult to observe than that of the CN
4
ring. In the case of the C(NO ) group in 5-(trinitromethyl)-
2
3
1
13 14
2
(
H-tetrazole, it was possible to resolve the J( C N) coupling
7.6 Hz), which resulted in a septet in the C spectrum.
2
4
24
1
28−130 °C) and 167.1 °C (lit. 170 °C), respectively. All
13
thermogravimetric scans of compounds 4−14 resulted in
violent explosive decompositions at temperatures less than
CONCLUSION
160 °C. While the parent compound 5-(trinitromethyl)-2H-
■
tetrazole 4 explodes at a temperature of about 100 °C, the
corresponding salts with the 5-(trinitromethyl)-2H-tetrazolate
anion explode at higher temperatures ranging from 115 to 130
A new and convenient synthesis of 5-(trinitromethyl)-2H-
tetrazole based on the nitration of 1H-tetrazole-5-acetic acid
was developed. This synthesis circumvents the handling of
dangerously sensitive trinitroacetonitrile. For the first time, 5-
°
C. It is interesting to note that the nature of the cation has
only a limited effect on the decomposition temperature of the
salt. A comparison of the decomposition temperatures of
compounds 9/9a, 10/10a, 12/12·H O, and 13/13·2H O
(
trinitromethyl)-2H-tetrazole was fully characterized, including
an X-ray structure determination. The compound was
converted into ammonium, guanidinium, rubidium, cesium,
copper(II), and silver 5-(trinitromethyl)-2H-tetrazolates. The
reactions of 5-(trinitromethyl)-2H-tetrazole with hydroxyl-
amine or hydrazine give easy access to 5-(dinitromethyl)-
tetrazoles. All compounds in this study have been fully
characterized by their X-ray crystal structures, decomposition
temperatures, and vibrational and multinuclear NMR spectra.
2
2
indicates that the incorporation of water or ammonia in the
crystal does not have a significant influence on the thermal
stability of these materials. As already observed for HTNTz and
its related compounds, the salts 11, 12, and 14 with the
(dinitromethyl)tetrazolate anion have higher decomposition
temperatures (150−155 °C) than the related free acid 13 and
its dihydrate 13·2H O, which decompose at 92.2 and 103.1 °C,
2
16
respectively (lit. 88 °C).
Spectroscopy. With the exception of compound 3, all
compounds of this study have been characterized by their IR
and Raman spectra. The observed frequencies and intensities
are listed in the Experimental Section. In addition, compounds
ASSOCIATED CONTENT
■
*
S
Supporting Information
Sixty-four figures and 102 tables with characterization of
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
1
13
14
1
, 2, 4−8, and 11−14 were also characterized by H, C, N,
15
and in some cases N NMR spectroscopy. The recorded
chemical shifts are also listed in the Experimental Section. The
1
4
N NMR spectra of the nitromethyltetrazoles are dominated
AUTHOR INFORMATION
■
*
by the NO groups, which result in relatively sharp signals (τ1/2
2
Corresponding Author
E-mail: haiges@usc.edu.
<
100 Hz) at around −25 to −35 ppm. The resonances of the
nitrogen atoms of the tetrazole ring result in one broad feature
1
4
Notes
(
−
τ1/2 ∼700 − 1000 Hz) in the N spectrum at about −45 to
1
5
65 ppm. Even in the N NMR spectra, it was not possible to
The authors declare no competing financial interest.
K
dx.doi.org/10.1021/ic400919n | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(
(
(
(
(
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31) Sheldrick, G. M. Acta Crystallogr. A 2008, 64, 112−122.
32) Farrugia, L. J. Appl. Crystallogr. 1997, 30, 565.
ACKNOWLEDGMENTS
■
Financial support was provided by the Office of Naval
Research, Air Force Office of Scientific Research, Defense
Threat Reduction Agency, and National Science Foundation.
We appreciate NSF CRIF Grant 1048807 for an X-ray
diffractometer.
(33) Hartdegen, V.; Klapo
48, 9549−9556.
34) Thottempudi, V.; Gao, H. X.; Shreeve, J. M. J. Am. Chem. Soc.
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dx.doi.org/10.1021/ic400919n | Inorg. Chem. XXXX, XXX, XXX−XXX