Nitrogen-rich 5,5′-bistetrazolates and their potential use in propellant systems: A comprehensive study

Article abstract of DOI:10.1002/chem.201103737

A large variety of twice-deprotonated nitrogen-rich 5,5′- bistetrazolates, that is, the ammonium (1), hydrazinium (2), hydroxylammonium (3), guanidinium (4), aminoguanidinium (5), diaminoguanidinium (6), triaminoguanidinium (7), and diaminouronium (8) salts, have been synthesized. Energetic compounds 1-8 were fully characterized by single-crystal X-ray diffraction (except 8), NMR spectroscopy, IR and Raman spectroscopy, and differential scanning calorimetry (DSC) measurements. With respect to their potential use in propellant applications, the sensitivity towards impact, friction, and electrical discharge were determined. Several propulsion and detonation parameters (e.g., heat of explosion, detonation velocity) were computed by using the EXPLO5 computer code based on calculated (CBS-4M) heats of formation and X-ray densities. Additionally, the performance of 1-8 in various formulations was investigated by calculating the specific energy and specific impulse of the compounds under isochoric conditions. The thrust generation: The synthesis and complete characterization of a series of nitrogen-rich salts of 5,5′-bistetrazole gave promising materials with potential applications in novel propellant systems (see figure). In addition to their good thermal and chemical stability, the high nitrogen content leads to good N₂/CO ratios when combusted, which is desirable to avoid environmental and corrosion problems. Copyright

Full text of DOI:10.1002/chem.201103737

FULL PAPER
DOI: 10.1002/chem.201103737
Nitrogen-Rich 5,5’-Bistetrazolates and their Potential Use in Propellant
Systems: A Comprehensive Study
Niko Fischer, Dꢀniel Izsꢀk, Thomas M. Klapçtke,* Sebastian Rappenglꢁck, and
Jçrg Stierstorfer[a]
Abstract: A large variety of twice-de-
protonated nitrogen-rich 5,5’-bistetra-
zolates, that is, the ammonium (1), hy-
drazinium (2), hydroxylammonium (3),
guanidinium (4), aminoguanidinium
(5), diaminoguanidinium (6), triamino-
guanidinium (7), and diaminouronium
(8) salts, have been synthesized. Ener-
getic compounds 1–8 were fully charac-
terized by single-crystal X-ray diffrac-
tion (except 8), NMR spectroscopy, IR
and Raman spectroscopy, and differen-
tial scanning calorimetry (DSC) meas-
urements. With respect to their poten-
tial use in propellant applications, the
sensitivity towards impact, friction, and
electrical discharge were determined.
Several propulsion and detonation pa-
rameters (e.g., heat of explosion, deto-
nation velocity) were computed by
using the EXPLO5 computer code
based on calculated (CBS-4M) heats of
formation and X-ray densities. Addi-
tionally, the performance of 1–8 in vari-
ous formulations was investigated by
calculating the specific energy and spe-
cific impulse of the compounds under
isochoric conditions.
Keywords: energetic materials · ni-
trogen heterocycles · propellants ·
sensitivities · X-ray diffraction
Introduction
decomposition temperature, ammonium 5,5’-bistetrazolate
was investigated as a gas-generating component in fire-re-
sistant resins and fire-proof adhesives in airbags.[6] However,
Hiskey et al. have reported on the suitability of several ni-
trogen-rich 5,5’-bistetrazolates for use as low-smoke pyro-
technic fuels.[7] The above-mentioned properties of thermal
stability and high nitrogen content make these molecules
appropriate materials for investigation as ingredients in gun
or rocket propellant systems, particularly considering barrel
erosion problems. Barrel corrosion arises from the forma-
tion of iron carbide due to the high carbon contents of cur-
rently used propellant mixtures, such as M1 (85% nitrocel-
lulose, 10% 2,4-dinitrotoluene, 5% dibutyl phthalate). An
increased N2/CO ratio in the combustion gases when using
nitrogen-rich materials results in the formation of iron ni-
tride in the gun barrel, which has a higher melting point
than iron carbide and forms a protective layer on the inside
of the gun barrel and helps to increase the lifespan of the
equipment by a factor of up to four.[8] Additionally, the sen-
sitivity of the material used plays an important role for its
safe handling; ideally the materials should be less sensitive
than RDX (hexogen). Two very interesting additives cur-
rently being developed for use in composite modified
double base (CMDB) propellant formulations[9] are hydrazi-
nium 5,5’-azotetrazolate[10,11] and triaminoguanidinium 5,5’-
azotetrazolate.[12,13] The latter compound is included in the
NILE (Navy insensitive low-erosion) propellant mixture,
which was developed at NSWC, Indian Head division. The
NILE mixture was successfully fielded as a propellant in, for
example, the 105 mm Howitzer.[14]
Nitrogen-rich materials play an important role in the design
of new energetic compounds and their use as propellants,
explosives, and pyrotechnics.[1] The most promising hetero-
cyclic backbone for the preparation of high-performance en-
ergetics is considered to be the tetrazole ring.
Tetrazole ring systems demonstrate high heats of forma-
tion that result from inherently energetic nitrogen–nitrogen
and nitrogen–carbon bonds, high ring strain, and high densi-
ty, and have allowed the preparation of a variety of high-
performance primary[2] and secondary[3] explosives, which il-
lustrate their dynamic nature. Depending on the ring sub-
stituents and anion/cation pairing, tetrazole-based energetic
compounds can span the entire spectrum of sensitivity from
insensitive to highly sensitive (primary explosives). Since its
discovery in the early 20th century,[4] 5,5’-bistetrazole, which
has one of the highest nitrogen contents, and in particular
its nitrogen-rich salts have been the focus of research for
many decades, which has resulted in a wide variety of appli-
cations. However, only very few structurally investigated ex-
amples of nitrogen-rich salts of 5,5’-bistetrazole are known
to literature.[5] Owing to its high nitrogen content and high
[a] N. Fischer, D. Izsꢀk, Prof. Dr. T. M. Klapçtke, S. Rappenglꢁck,
Dr. J. Stierstorfer
Department of Chemistry
Energetic Materials Research
Ludwig Maximilian University
Butenandtstr. 5–13 (D)
81377 Mꢁnchen (Germany)
Fax : (+49)89-2180-77492
Unfortunately, 5,5’-azotetrazolates are not stable under
mineral-acidic conditions because neutral 5,5’-azotetrazole
decomposes into 5-hydrazinotetrazole, dinitrogen, and
E-mail: tmk@cup.uni-muenchen.de
Chem. Eur. J. 2012, 18, 4051 – 4062
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4051

formic acid (see Scheme 1).[15]
The corresponding salts of 5,5’-
bistetrazole reported herein are
stable in acidic media and show
performance similar to 5,5’-azo-
tetrazolates. The parent com-
Scheme 1. Hydrazinium (a) and 1,3,5-triaminoguanidinium 5,5’-azotetrazolate (b) and their decomposition re-
action in mineralic acids.
pound,
5,5’-bistetrazole,
is
easily accessible in high quanti-
ties and unlike 5,5’-azotetrazole
is stable in acidic media.
Results and Discussion
Synthesis: The synthesis of 5,5’-bistetrazole (H2-5,5’-BT) has
already been described in the literature;[4,7] the basic princi-
ple is a ring-closure reaction in a [2+3] dipolar cycloaddition
reaction starting from cyanogen. Depending on the litera-
ture source, cyanogen can either be prepared and isolated in
an additional step and treated with either sodium azide or
hydrazoic acid or it can be generated in situ from sodium cy-
anide and manganese dioxide as the oxidizing agent under
acidic conditions and be further treated with sodium azide.
Herein, we chose the latter synthetic route because it is the
Scheme 2. Synthesis of 5,5’-bistetrazole according to Hiskey et al.[7] Con-
ditions: i) MnO2, 908C, 3 h, H2SO4, CH3COOH, CuSO4·5H2O;
ii) Na2CO3; iii) concd HCl.
more
convenient
strategy
(Scheme 2).
The workup involves two fur-
ther steps because the manga-
nese(II) salt of 5,5’-bistetrazole
is formed in the first synthetic
step. It is treated with sodium
carbonate to form the less solu-
ble MnCO3 and the sodium salt
of 5,5’-BT, which stays in solu-
tion. The free acid H2-5,5’-BT
can be precipitated by adding
excess concentrated HCl to the
mixture. After further recrystal-
lization, the product can be
treated with the respective
bases to give compounds 1–8
through Brønsted acid–base
chemistry or metathesis reac-
tions (Scheme 3).
For compounds 1–3, 7, and 8,
the free bases were reacted
with an aqueous solution of
5,5’-bistetrazole, whereas for 4
and 5 an aqueous acidic solu-
tion of 5,5’-BT was heated to
reflux with a suspension of the
corresponding carbonates. Dia-
minoguanidinium salt 6 had to
be prepared by a metathesis re-
action, in which 5,5’-BT was
first converted into the sodium
Scheme 3. Synthesis of the nitrogen-rich salts 1–8. Conditions: i) NH3, H2O, reflux, 5 min; ii) N2H4·H2O, H2O,
reflux, 5 min; iii) NH2OH, H2O, reflux, 5 min; iv) G2CO3, H2O, reflux, 10 min; v) AG+HCO3ꢀ, H2O, reflux,
10 min; vi) NaOH, H2O, RT, then BaCl2, H2O, RT, then DAG2SO4, reflux, 5 min; vii) TAG, RT; viii) DAU, RT.
G=guanidinium, AG=aminoguanidinium, DAG=diaminoguanidinium, TAG=triaminoguanidinium, DAU=
salt. After addition of barium diaminouronium.
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Chem. Eur. J. 2012, 18, 4051 – 4062

Nitrogen-Rich 5,5’-Bistetrazolates
FULL PAPER
chloride, the barium salt precipitates and can be isolated
and further treated with diaminoguanidinium sulfate to
obtain 6. The solubility of nitrogen-rich 5,5’-bistetrazolates
1–7 is only moderate in water, so crystals of 1–7 suitable for
X-ray single-crystal analysis were obtained after filtration
and slow evaporation of the aqueous mother liquors.
fined. The absorptions were corrected by using a SCALE3
ABSPACK multi-scan method.[21] Important data and pa-
rameters are listed in Table 1.
Compound 1 crystallizes in the monoclinic space group
C2m with two formula units in the unit cell and a calculated
density of 1.590 gcmꢀ3. The asymmetric unit contains only
one quarter of the molecular unit (Figure 1). Therefore, the
anion consists of two identical tetrazolate rings. The struc-
ture of the bistetrazolate dianion is in agreement with corre-
Crystal structures: Suitable single crystals of the described
compounds (1–7) were selected from the crystallization mix-
ture and mounted in Kel-F oil, transferred to the N2 stream
of an Oxford Xcalibur3 diffractometer equipped with a
Spellman generator (voltage 50 kV, current 40 mA) and a
KappaCCD detector (MoKa radiation, l=0.71073 ꢃ). All
structures were measured at ꢀ1008C. The data collection
and data reduction was carried out by using the CrysAlisPro
software.[16] The structures were solved by using Sir-92[17] or
Sir-97,[17] refined with Shelxl-97,[18] and finally checked using
the Platon software[19] integrated in the WinGX software
suite.[20] The non-hydrogen atoms were refined anisotropi-
cally and the hydrogen atoms were located and freely re-
sponding structures of, for example, the erbiumACHTNUTRGNE(NUG III) salt de-
scribed in the literature.[22] The N N bond lengths lie be-
ꢀ
ꢀ
tween N N single bonds (1.48 ꢃ) and N=N double bonds
ꢀ
ꢀ
(1.20 ꢃ), and the C N bonds lie between C N single
(1.47 ꢃ) and C=N double bonds (1.22 ꢃ).[23] Both are com-
parable to other tetrazolates, for example, alkali 5-aminote-
trazolates.[24] The torsion angles N1-N2-N2i-N1i (0.0(1)8) and
N1-C1-N1i-N2i (0.2(1)8) indicate a completely planar ring,
which together with the bond lengths leads to the assump-
ii
ꢀ
tion of a 6p aromatic system. The C1 C1 bond (1.46 ꢃ) is
slightly longer than in the neutral 5,5’-bistetrazole.[25] How-
Table 1. X-ray data and parameters.[a]
1
2
3
4
5
6
7
formula
C2H8N10
172.18
C2H10N12
202.18
C2H8N10O2
204.18
C4H12N14
256.28
C4H18N16O2
322.34
C4H20N18O2
352.38
C4H18N20
346.38
Mr [gmolꢀ1
]
crystal system
space group
color, habit
monoclinic
C2/m (No. 12)
colorless,
block
monoclinic
P1 (No. 2)
colorless,
needle
monoclinic
P1 (No. 2)
colorless,
block
monoclinic
P21/c (No. 14)
colorless,
rod
monoclinic
P21/n (No. 14)
colorless,
rod
triclinic
P1 (No. 2)
colorless,
needle
monoclinic
P21/n (No. 14)
colorless,
rod
¯
¯
¯
size [mm]
a [ꢃ]
b [ꢃ]
c [ꢃ]
a [8]
0.30ꢄ0.20ꢄ0.08 0.30ꢄ0.05ꢄ 0.05 0.15ꢄ0.23ꢄ0.31 0.11ꢄ0.14ꢄ0.20 0.18ꢄ0.22ꢄ0.23 0.13ꢄ0.14ꢄ0.30 0.10ꢄ0.11ꢄ0.28
8.8511(8)
11.1956(9)
3.6809(4)
90
99.608(9)
90
3.6096(5)
7.9134(12)
8.2992(16)
72.058(15)
79.051(14)
79.132(13)
219.27(6)
1
3.6736(3)
7.3455(7)
7.4908(8)
102.666(9)
95.283(8)
96.302(8)
194.61(3)
1
3.588(4)
15.014(5)
10.048(6)
90
97.362(5)
90
11.8344(11)
3.8684(4)
14.9914(14)
90
95.741(9)
90
7.3878(6)
7.5263(8)
8.1937(8)
83.689(8)
70.034(8)
64.158(9)
384.98(7)
1
10.417(5)
3.929(5)
18.660(5)
90
101.092(5)
90
b [8]
g [8]
V [ꢃ3]
Z
359.64(6)
2
536.8(7)
2
682.87(11)
2
749.5(10)
2
1calcd [gcmꢀ3
]
1.590
1.531
1.742
1.586
1.568
1.520
1.535
m [mmꢀ1
(000)
(MoKa) [ꢃ]
]
0.125
0.121
0.148
0.122
0.128
0.124
0.120
F
A
180
106
106
268
340
186
364
l
A
0.71073
173
0.71073
173
0.71073
173
0.71073
173
0.71073
173
0.71073
173
0.71073
173
T [K]
q range [8]
dataset (h, k, l)
4.7–27.0
ꢀ6ꢁhꢁ11
ꢀ14ꢁkꢁ12
ꢀ4ꢁlꢁ3
1026
4.3–26.0
ꢀ4ꢁhꢁ4
ꢀ6ꢁkꢁ9
ꢀ9ꢁlꢁ10
1152
4.5–26.5
ꢀ4ꢁhꢁ4
ꢀ9ꢁkꢁ9
ꢀ9ꢁlꢁ9
2302
4.3–26.0
ꢀ4ꢁhꢁ4
ꢀ18ꢁkꢁ18
ꢀ12ꢁlꢁ12
5201
4.3–26.2
ꢀ14ꢁhꢁ14
ꢀ4ꢁkꢁ4
ꢀ18ꢁlꢁ11
3275
4.8–26.0
ꢀ9ꢁhꢁ9
ꢀ9ꢁkꢁ9
ꢀ10ꢁlꢁ10
3896
4.2–26.5
ꢀ10ꢁhꢁ13
ꢀ4ꢁkꢁ4
ꢀ23ꢁlꢁ23
3786
reflns. collected
independent reflns.
Rint
416
0.027
868
0.020
806
0.029
1061
0.048
1372
0.034
1507
0.029
1536
0.032
observed reflns
parameters
R1 (obsd)
343
38
580
84
0.0362
0.0883
595
80
0.0333
0.0782
740
106
1012
136
0.0350
0.0900
1143
149
0.0329
0.0815
1027
145
0.0320
0.0803
1.05
ꢀ0.29, 0.17
SIR-97
SHELXL-97
multi-scan
0.0356
0.0885
0.91
ꢀ0.17, 0.20
SIR-92
SHELXL-97
multi-scan
0.0325
0.0752
0.87
ꢀ0.15, 0.20
SIR-92
SHELXL-97
multi-scan
wR2 (all data)
S
0.88
0.94
0.97
0.95
residual density [eꢃꢀ3
solution
]
ꢀ0.17, 0.21
SIR-97
SHELXL-97
multi-scan
ꢀ0.20, 0.21
SIR-92
SHELXL-97
multi-scan
ꢀ0.17, 0.20
SIR-92
SHELXL-97
multi-scan
ꢀ0.21, 0.17
SIR-92
SHELXL-97
multi-scan
refinement
absorption
correction
[a] CCDC-854127 (1), -854128 (2), -854126 (3), -854129 (4), -854132 (5), -854131 (6), and -854130 (7) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Chem. Eur. J. 2012, 18, 4051 – 4062
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4053

J. Stierstorfer et al.
ent hydrogen bonds. The resulting hydrogen-bonding net-
work consists of multiple ring patterns, of which R44(14) and
R44(10) are the most characteristic.
Suitable single crystals of 2 were directly obtained from
the mother liquor in the form of fine needles. The com-
¯
pound crystallizes in the triclinic space group P1 with one
formula unit in the unit cell and a calculated density of
1.531 gcmꢀ3. Due to the lower symmetry of the space group,
the asymmetric unit contains one half of the molecular unit
shown in Figure 3. The bond lengths and angles are never-
Figure 1. Molecular unit of diammonium 5,5’-bistetrazolate (1). Ellipsoids
of non-hydrogen atoms are drawn at the 50% probability level. Bond
i
ii
ꢀ
ꢀ
ꢀ
ꢀ
lengths [ꢃ]: N1 C1 1.334(1), N1 N2 1.342(1), N2 N2 1.314(1), C1 C1
1.461(2); bond angles [8]: N1-C1-N1i 112.1(1), N2-N1-C1 104.4(1), N1-
N2-N2i 109.6(1), N1-C1-C1ii 123.9(1); torsion angles [8]: N1-N2-N2i-N1i
0.0(1), N1-C1-N1i-N2i 0.2(1), N1-C1-C1ii-N1ii ꢀ180.0(1), N1-C1-C1ii-N1iii
ꢀ0.9(2); symmetry codes: i: x, ꢀy, z; ii: ꢀx, y, 2ꢀz; iii: ꢀx, ꢀy, 2ꢀz;
iv: 0.5ꢀx, 0.5ꢀy, 1ꢀz.
Figure 3. Molecular unit of dihydrazinium 5,5’-bistetrazolate (2). Ellip-
soids of non-hydrogen atoms are drawn at the 50% probability level.
ꢀ
ꢀ
ꢀ
Bond lengths [ꢃ]: N1 C1 1.332(2), N1 N2 1.346(2), N2 N3 1.314(2),
i
ꢀ
ꢀ
ꢀ
ꢀ
N3 N4 1.347(2), N4 C1 1.338(2), C1 C1 1.460(2), N5 N6 1.454(2);
bond angles [8]: N1-C1-N4 112.1(1), N2-N1-C1 104.4(1), N1-N2-N3
109.7(1), N2-N3-N4 109.5(1), N3-N4-C1 104.4(1), N1-C1-C1i 124.2(1),
N4-C1-C1i 123.7(1); torsion angles [8]: N1-N2-N3-N4 ꢀ0.0(2), N1-C1-N4-
N3 0.1(2), N2-N1-C1-N4 ꢀ0.1(2), N1-C1-C1-N1 180.0(2), N1-C1-C1-N4
ꢀ0.7(3); symmetry codes: i: 1ꢀx, 1ꢀy, ꢀ1ꢀz; ii: x, y, ꢀ1+z; iii: 1ꢀx,
1ꢀy, ꢀz.
ꢀ
ever, the C C bonds of all structures observed in this work
are significantly shorter (mean value 1.46 ꢃ) than typical
[23]
ꢀ
C C single bonds of approximately 1.54 ꢃ. The N1-C1-
C1ii-N1ii torsion angle is ꢀ180.0(1)8, which shows the com-
plete planarity of the whole anion. In the crystal structure,
layers comprised of infinite parallel chains of longitudinal
bistetrazolate anions are stacked with ammonium cations
between the layers (Figure 2). One ammonium is coordinat-
ed by four bistetrazolates, two from each layer above and
below the cation, through two crystallographically independ-
theless almost identical to those in 1, and so are also the tor-
ꢀ
sion angles. The N5 N6 bond of the hydrazinium is in the
ꢀ
range of a N N single bond and is comparable to the bond
in other hydrazinium compounds, such as hydrazinium 5-
aminotetrazolate[3] or hydrazinium tetrafluoroborate.[26] The
geometry of the hydrogen atoms is staggered. The hydrazini-
um cation is coordinated by one other cation and three
anions, which leads to all hydrogen atoms being involved in
ꢀ
the formation of hydrogen bonds (Figure 4). The longest N
H bond and shortest H···A contact is observed in the hydro-
gen bond involving the two hydrazinium cations, which re-
sults in C11(3) chains.
Figure 2. A) Layer structure of 1 (view along [010]); B) hydrogen-bond-
ing network with the three most characteristic graph-set descriptors
(view along [001]).
Figure 4. Coordination sphere of the hydrazinium cation in 2. Ellipsoids
of non-hydrogen atoms are drawn at the 50% probability level. Symme-
try codes: i: ꢀ1+x, y, z; ii: 2ꢀx, ꢀy, ꢀz; iii: x, y, 1+z; iv: 1ꢀx, 1ꢀy, ꢀz.
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Chem. Eur. J. 2012, 18, 4051 – 4062

Nitrogen-Rich 5,5’-Bistetrazolates
FULL PAPER
Figure 5. Molecular unit of di(hydroxylammonium) 5,5’-bistetrazolate (3).
Ellipsoids of non-hydrogen atoms are drawn at the 50% probability
Figure 7. Molecular unit of bis(aminoguanidinium) 5,5’-bistetrazolate (5).
Ellipsoids of non-hydrogen atoms are drawn at the 50% probability
level. Symmetry code: i: 1ꢀx, 1ꢀy, 1ꢀz.
ꢀ
ꢀ
level. Selected bond lengths [ꢃ]: N3 N2 1.3128(19), N3 N4 1.3452(18),
i
ꢀ
ꢀ
ꢀ
ꢀ
N4 C1 1.333(2), C1 N1 1.336(2), C1 C1 1.461(3), N1 N2 1.3443(17),
ꢀ
O1 N5 1.4181(16); selected bond angles [8]: N2-N3-N4 109.84(12), C1-
N4-N3 104.45(13), N4-C1-N1 111.77(13), N4-C1-C1i 124.02(18), N1-C1-
C1i 124.20(18), C1-N1-N2 104.84(13), N3-N2-N1 109.10(12); symmetry
codes: i: 2ꢀx, 1ꢀy, 1ꢀz, ii: 1ꢀx, 1ꢀy, 1ꢀz.
Single crystals of di(hydroxylammonium) 5,5’-bistetrazo-
¯
late (3) crystallized in the triclinic (P1) space group with
one molecular moiety (Figure 5) in the unit cell. Its density
of 1.742 gcmꢀ3 is the highest of the salts investigated herein
and
is
comparable
to
the
neutral
compound
(1.738 gcmꢀ3).[25] The structure of the dianion is in agree-
ment with those of 1 and 2.
Compounds 4 and 5 (Figures 6 and 7) crystallize in the
monoclinic space groups P21/c (4) and P21/n (5) with two
Figure 8. Molecular unit of bis(diaminoguanidinium) 5,5’-bistetrazolate
(6). Ellipsoids of non-hydrogen atoms are drawn at the 50% probability
level. Symmetry codes: i: 1ꢀx, 1ꢀy, ꢀz; ii: 1ꢀx, 1ꢀy, ꢀz; iii: ꢀx, 1ꢀy,
ꢀz.
Figure 6. Molecular unit of bis(guanidinium) 5,5’-bistetrazolate (4). Ellip-
soids of non-hydrogen atoms are drawn at the 50% probability level.
Symmetry codes: i: 2ꢀx, ꢀy, 2ꢀz; ii: 1ꢀx, ꢀy, 2ꢀz.
formula units per unit cell and densities of 1.586 gcmꢀ3 (4)
and 1.568 gcmꢀ3 (5). Diaminoguanidinium salt dihydrate 6
¯
(Figure 8) crystallizes in the triclinic space group P1 with a
density of 1.520 gcmꢀ3, which is the lowest density observed
herein. Triaminoguanidinium salt 7 (Figure 9) crystallizes in
the monoclinic space group P21/n and has a density of
1.535 gcmꢀ3. Crystals of compound 8 were also obtained by
recrystallization from water and measured by XRD. Howev-
er, the refinement could not be finished due to a twinning
problem along the c axis. The cell volume of 606.68 ꢃ3 was
used to calculate a density of 1.742 gcmꢀ3, which is equal to
that observed for 3. Of guanidines 4–7, compounds 5 and 6
Figure 9. Molecular unit of bis(triaminoguanidinium) 5,5’-bistetrazolate
(7). Ellipsoids of non-hydrogen atoms are drawn at the 50% probability
level. Symmetry codes: i: 2ꢀx, ꢀy, 1ꢀz; ii: 1.5ꢀx, ꢀ0.5+y, 0.5ꢀz;
iii: 2.5ꢀx, 0.5+y, 0.5ꢀz.
Chem. Eur. J. 2012, 18, 4051 – 4062
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4055

J. Stierstorfer et al.
crystallized as dihydrates, whereas 4 and 7 were obtained as
solvent-free crystals. The structures of the guanidines are in
agreement with those observed for other guanidinium tetra-
zolates in the literature,[27] which participate strongly in
many classical hydrogen bonds. Regarding the structure of
the dianions, all compounds show planar geometries compa-
rable to that discussed in detail for compound 1.
bond at 1650 to 1890 cmꢀ1. The latter is in the same range as
the C=N stretching vibration of the guanidine derivatives.
ꢀ
Due to the presence of amino groups, N H and NH2 wag-
ging absorptions can be observed between 603 and 781 cmꢀ1
and the corresponding bending vibrations appear in the
ꢀ1
ꢀ
range of 1536 to 1614 cm . In compound 8, N H and NH2
bending vibrations are in the same range as the C=O
ꢀ
stretching vibration of 1,3-diaminourea. N H stretching vi-
Spectroscopy: All compounds described were investigated
by using 1H and 13C NMR spectroscopy. Additionally a
14N NMR spectrum was recorded for ammonium salt 1. For
better comparison all spectra (except for 1 and 7) were mea-
sured in [D6]DMSO as the solvent and all chemical shifts
are given with respect to TMS (1H, 13C).
brations are partly shifted to lower frequencies by H-bond-
ing effects, and can be found between 3092 and 3470 cmꢀ1.
In the spectra of 4, 5, and 8, two well-defined sharp charac-
teristic absorptions due to the asymmetric and symmetric
ꢀ
N H stretching vibrations of the primary amino groups
appear at 3350 to 3449 cmꢀ1 (4), 3345 to 3409 cmꢀ1 (5), and
Proton signals for the C-NH2 protons of the guanidinium
derivatives can be found at d=7.73 (4, 5) and 7.76 ppm (6).
Due to the presence of both NH and NH2 groups in 5, 6,
and 7, additional resonances at d=4.63–4.77 (NHNH2) and
9.61–9.65 ppm (NH) are observed. Due to the poor solubili-
ty of 1 and 7 in DMSO, D2O was used instead and thus only
one singlet is observed in both proton spectra due to fast
proton exchange. Because of fast proton exchange in the
protonated 1,3-diaminourunium cation of 8, only a broad
signal at d=7.22 ppm is observed for all protons. The mea-
sured 13C NMR spectra of all guanidine derivatives reveal a
single resonance at d=154.6–155.1 ppm, which can be as-
signed to the bistetrazolate ring carbon atom. The guanidine
carbon atom signal is found at d=158.9–160.6 ppm for 4, 5,
and 6, but not for 7, the NMR spectrum of which was mea-
sured in D2O. The 13C NMR spectrum of 8 reveals two
single resonances at d=150.1 ppm for the bistetrazolate ring
carbon and at d=161.1 ppm for the urea carbonyl group of
the cation. Unfortunately no 1H or 13C NMR spectrum
could be recorded for ammonium salt 1 in DMSO due to its
low solubility in this solvent, however the spectra recorded
in D2O show the expected signals. The 14N NMR spectrum
reveals a sharp singlet for the ammonium cation at d=
ꢀ356 ppm and two singlets at d=ꢀ66 and 3 ppm assigned
to the two nonequivalent nitrogen atoms in the 5,5’-bistetra-
zolate anion. In the proton spectrum of the hydrazinium (2)
and hydroxylammonium (3) salt, a singlet at d=7.20 (2) and
10.50 ppm (3) is observed, which nicely demonstrates the
lower pKa value of protonated hydroxylamine compared to
the hydrazinium monocation, which is shown by the down-
field shift in the spectrum of 3 compared to 2. The bistetra-
zole carbon atom signals are found at d=152.6 (3) and
154.5 ppm (2), respectively, which is the same region as ob-
served for the guanidinium derivatives.
3185 to 3296 cmꢀ1 (8). All Raman spectra show the charac-
ꢀ
teristic and very intense signal of the 5,5’-bistetrazole C C
bond at 1582 to 1591 cmꢀ1, which has a partial double-bond
character, as can be seen from the bond lengths discussed
above in the X-ray crystallography section, and very weak
N H vibrations at 3166 to 3429 cm . However, bistetrazole
framework vibrations are visible in all Raman spectra in the
range of 1013 to 1207 cmꢀ1. The measured IR and Raman
spectra correspond very well and verify the structural ele-
ments in all investigated compounds.
ꢀ1
ꢀ
Sensitivities and thermal behavior: The impact sensitivity
tests were carried out according to STANAG 4489[31] modi-
fied instructions[32] by using a BAM (Bundesanstalt fꢁr Ma-
terialforschung) drop hammer.[33] The friction sensitivity
tests were carried out according to STANAG 4487[34] modi-
fied instructions[35] by using the BAM friction tester. The
classification of the tested compounds results from the “UN
Recommendations on the Transport of Dangerous
Goods”.[36] All compounds were tested for sensitivity to-
wards electrical discharge by using the Electric Spark Tester
ESD 2010 EN.[37] Generally, all investigated materials
showed surprisingly low sensitivities towards both impact
and friction despite their high nitrogen contents. Com-
pounds 1, 2, 4, 5, and 8 are classified as less sensitive to-
wards impact (2, 4, 5: 40 J; 1, 8: 35 J), whereas 3, 6, and 7
are classified as sensitive (3: 10 J; 6: 30 J; 7: 15 J). As ex-
pected, the hydroxylammonium and the triaminoguanidini-
um salt are the most sensitive towards impact, which is
partly due to the low carbon content of the cation and,
therefore, the highest nitrogen content for the ionic com-
pounds, and partly due to the fact that both species crystal-
lize without the inclusion of crystal water. This trend is also
observed for the friction sensitivity. The hydroxylammonium
(3: 240 N), the aminoguanidinium (5: 324 N), and the tria-
minoguanidinium (7: 285 N) salts are classified as sensitive
towards friction, whereas 2, 6, and 8 are less sensitive (2, 6,
8: 360 N). The ammonium and the guanidinium salts did not
show any response and are, therefore, classified as insensi-
tive (1,4: >360 N). The inclusion of water, as in the case of
5 and 6, usually also plays a role, but because the materials
are comparatively insensitive no obvious trend for the de-
sensitization of 5 and 6 was observed. The sensitivity to-
IR and Raman spectroscopy were used for the identifica-
tion of structural elements and functional groups in all com-
pounds. Absorptions were assigned according to values re-
ported in the literature.[28,29] The characteristic vibrations of
the bistetrazole system were observed in all IR spectra, in-
cluding the bistetrazole framework vibrations at 1011 to
1184 cmꢀ1, the asymmetric and symmetric stretching vibra-
tions of the N1-C1-N4 fragment[30] in the range of 1299 to
1335 cmꢀ1 and the stretching vibration of the cyclic C=N
4056
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Chem. Eur. J. 2012, 18, 4051 – 4062

Nitrogen-Rich 5,5’-Bistetrazolates
FULL PAPER
wards electrostatic discharge for most of the substances is
low, with values between 0.50 for 8 and 1.0 J for 4 and 5.
However, the hydrazinium (2: 0.23 J) and the hydroxylam-
monium (3: 0.10 J) salts do not follow this trend. The ob-
served results of the impact sensitivity testing are compara-
ble to the results observed by Hiskey et al. They also deter-
mined the impact sensitivities of the diammonium, the dihy-
drazinium, and the dihydroxylammonium salt by using a dif-
ferent method, and stated that those fuels are fairly
insensitive when not mixed with an oxidizer, such as ammo-
nium perchlorate.[7]
hydrazine at temperatures starting from 1308C in a ther-
mogravimetric analysis experiment. The lower temperature
compared to 1658C as observed in our case can be ex-
plained by the lower heating rate used by Hiskey et al.
(0.18Cminꢀ1). The same could be true for the diaminouroni-
um salt because the cation in 8 is also a hydrazine deriva-
tive, however, a thermogravimetrical analysis would be nec-
essary to support this assumption.
Theoretical calculations
Differential scanning calorimetry (DSC) measurements to
determine the melting and decomposition temperatures of
1–8 (about 1.5 mg of each energetic material) were per-
formed in covered Al-containers with a hole (0.1 mm) in the
lid for gas release and a nitrogen flow of 20 mLminꢀ1 on a
Linseis PT 10 DSC[38] calibrated by standard pure indium
and zinc at a heating rate of 58C minꢀ1. The decomposition
temperatures are given as absolute onset temperatures. It is
very remarkable that despite their very high nitrogen con-
tent, except for 2 and 8, none of the compounds show any
decomposition at temperatures below 2008C. Even the hy-
droxylammonium (3) and triaminoguanidinium salts (7) de-
compose at temperatures of 205 (3) and 2078C (7), which is
in the same range as observed for RDX (hexogen), whereas
the ammonium (1) and guanidinium salts (4) reach decom-
position temperatures as high as 312 (1) and 3168C (4),
which is comparable to the melting- and decomposition
point of HNS (hexanitrostilbene, a highly thermally stable
explosive). The remaining compounds fill the range between
these extreme values, with the lowest temperature being re-
corded for 6 (2088C) up to 234 and 2378C for 2 and 8 and
2518C for 5. The ammonium (1), hydroxylammonium (3),
and triaminoguanidinium salts (7) do not show any endo-
thermic steps in their DSC curve before decomposition,
whereas the guanidinium (4), aminoguanidinium (5), and di-
aminoguanidinium salts (6) melt directly before they decom-
pose, as indicated by endothermic steps observed prior to
their exothemic decomposition peaks. Two salts, namely, the
hydrazinium (2) and the diaminouronium salts (8), show
one or more endothermic peaks in their respective DSC
curves at 165, 185, and 2178C (2), and at 1758C (8). These
observations are in accordance with results published by
Hiskey et al.,[7] who found that the dihydrazinium salt loses
Heats of formation: Usually energetic materials tend to ex-
plode in bomb calorimetric measurements and consequently
doubtful combustion energies are obtained. Therefore, the
heats of formation of energetic materials are mostly calcu-
lated theoretically. In our group, we combine the atomiza-
tion energy method [Eq. (1)] with CBS-4M electronic ener-
Table 2. CBS-4M results and gas-phase enthalpies.
Formula
ꢀH298 [a.u.]
513.511502
DfH(g) [kJmolꢀ1
]
2ꢀ
BT2ꢀ
C2N8
NH4
596.7
635.8
774.1
687.2
571.9
671.6
772.7
874.3
651.3
+
+
NH4
N2H5
Hx+
G+
56.796608
+
+
N2H5
112.030523
131.863229
205.453192
260.701802
315.949896
371.197775
335.795706
H4NO+
+
CH6N3
CH7N4
CH8N5
CH9N6
+
AG+
+
DAG +
TAG +
DAU +
+
CH7N4O+
gies (Table 2), which has been shown to be suitable in many
recently published studies.[39] CBS-4M energies of the atoms,
cations, and anions were calculated by using the Gaussian 09
(revision A1) software package[42] and checked for imagina-
ry frequencies. Values for DfH8 (atoms) were taken from the
NIST database.[43]
X
X
DfHꢂðg, M, 298Þ¼HðM, 298Þ
ꢀ
HꢂðAtoms, 298Þ þ
DfHꢂðAtoms, 298Þ ð1Þ
For calculation of the solid-state energy of formation
(Table 3) of 4–8, the lattice energy (UL) and lattice enthalpy
(DHL) were calculated from the corresponding molecular
volumes (obtained from X-ray elucidations) according to
Table 3. Solid-state energies of formation (DfU8).
Formula
DfH8(g)
VM
UL
DHL
DfH8(s)
Dn DfU8(s)
M
DfU8(s)
[kJmolꢀ1
]
[nm3]
[kJmolꢀ1
]
[kJmolꢀ1
]
[kJmolꢀ1
]
[kJmolꢀ1
]
[gmolꢀ1
]
[kJkgꢀ1
]
1
2
3
4
5
6
7
8
C2H8N10
C2H10N12
C2H8N10O2 1971.1
1868.3
2144.9
0.180
0.219
0.195
0.268
0.291
0.335
0.374
0.300
1578.4
1465.9
1532.7
1358.8
1317.2
1249.2
1196.9
1302.8
1589.3
1476.9
1543.6
1369.7
1328.1
1260.2
1207.8
1313.7
279.0
668.1
427.5
370.8
131.1
401.2
1137.4
585.6
9
301.4
172.18
202.18
204.18
256.28
322.34
352.38
346.38
318.34
1750.0
3438.2
2215.0
1572.5
545.1
1279.1
3419.2
1964.2
11 695.3
10 452.3
13 403.0
18 175.7
20 450.8
19 1184.5
16 625.3
C4H12N14
1740.5
C4H18N16O2 1459.2[a]
C4H20N18O2 1661.3[a]
C4H18N20
C4H14N16O2 1899.3
2345.2
[a] Value has been corrected (ꢀ483.4 kJmolꢀ1) due to dihydrate formation.
Chem. Eur. J. 2012, 18, 4051 – 4062
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4057

J. Stierstorfer et al.
Table 4. Composition of the calculated gun propellant charges.
Formulation Components Ratio
Table 5. Calculated performance of the gun propellant charges.
Tc [K]
pmax [bar]
fE [kJgꢀ1
]
bE [cm3 gꢀ1
]
N2/CO [w/w]
[wt%]
M1
EX-99
HN-1
2834
3406
2922
2735
2798
2610
2975
2783
3130
2928
2737
2556
2942
2756
2960
2770
2591
3249
3042
2848
2890
2691
3109
2910
3157
2964
2830
2635
3091
2896
3037
2845
1.005
1.257
1.161
1.088
1.103
1.030
1.186
1.111
1.211
1.138
1.080
1.008
1.178
1.105
1.161
1.089
1.125
1.129
1.185
1.181
1.181
1.174
1.187
1.183
1.164
1.163
1.183
1.175
1.190
1.185
1.176
1.172
0.23
0.71
0.95
1.05
0.95
1.06
0.96
1.06
0.87
0.96
0.90
1.01
0.93
1.03
0.87
0.96
M1
EX-99
HN-1
NC (13.25)/2,4-DNT[a]/DBP[b]/DPA[c]
86/10/3/1
76/12/8/4
56/20/12/8/4
RDX/CAB[d]/BDNPA/F[e]/NC (13.25)
RDX/TAGzT/CAB[d]/BDNPA/F[e]/NC
(13.25)
HN-2
1 HN-1
1 HN-2
2 HN-1
2 HN-2
3 HN-1
3 HN-2
4 HN-1
4 HN-2
7 HN-1
7 HN-2
8 HN-1
8 HN-2
HN-2
RDX/TAGzT/FOX-12[f]/CAB[d]/BDNPA/F[e]
NC (13.25)
/
40/20/16/12/
8/4
56/20/12/8/4
HN-1·1–4;
7; 8
HN-2·1–4;
7; 8
RDX/1–4; 7; 8/CAB[d]/BDNPA/F[e]/NC
(13.25)
RDX/1–4; 7; 8/FOX-12[f]/CAB[d]/BDNPA/
F[e]/NC (13.25)
40/20/16/12/
8/4
[a] 2,4-Dinitrotoluene. [b] Dibutyl phthalate. [c] Diphenyl amine. [d] Cel-
lulose acetate butyrate. [e] 1:1 mixture of bis(2,2-dinitroprop-1-yl)acetal
and -formal. [f] 1,1-Dinitro-2,2-diaminoethylene.
the equations provided by Jenkins et al.[42] With the calculat-
ed lattice enthalpy (Table 3), the gas-phase enthalpy of for-
mation was converted into the solid-state (standard condi-
tions) enthalpy of formation. These molar standard enthal-
pies of formation (DHm) were used to calculate the molar
solid-state energies of formation (DUm, see Table 4) accord-
ing to Equation (2):
equation of state with a loading density of 0.2 gcmꢀ3; the re-
sults are compiled in Table 5.
As expected from the ingredients, the M1 and EX-99 for-
mulations have the worst N2/CO ratios, but EX-99 also has
the highest performance. The formulations based on HN-1
have generally higher performance than those based on
HN-2, due to the higher content of RDX, but also have
higher combustion temperatures (Tc) and N2/CO ratios that
are lower by about 0.1. The most promising compound is
the hydrazinium salt 2, which outperforms HN-2 itself, with
an fE of 1.111 kJgꢀ1, a pmax of 2910 bar, and, together with 1,
the best N2/CO ratio of 1.06. The Tc value of 2783 K is com-
parable to the triaminoguanidinium-based formulations HN-
2 (Tc =2735 K) and 7 HN-2 (Tc =2756 K). Guanidinium salt
formulation 4 HN-2 has the lowest Tc value of 2556 K, but
also the lowest general performance. Figure 10 illustrates
the calculated performances of M1, EX-99, HN-2, and the
HN-2 analogues of 1, 2, 4, and 7. As expected, the formula-
tions with 3 and 8 show the worst N2/CO ratios due to the
higher oxygen content at the expense of the nitrogen con-
tent. Additionally, compound 3 has the highest specific
energy in both HN-1 and HN-2 formulations, outperforming
the original formulations.
DUm ¼ DHmꢀDnRT
ð2Þ
in which Dn is the change in moles of gaseous components.
Gun propellant evaluations: The most important parameters
for gun propellant formulations are the specific energy fE
([Jgꢀ1], fE =nRTc), the combustion temperature Tc [K], the
co-volume bE [cm3 gꢀ1], and the pressure pmax ([bar], 3000–
4000 bar) while assuming isochoric combustion. These pa-
rameters and furthermore the N2/CO ratio can be calculated
with the program package EXPLO5 (v. 5.04),[43] with an
error of usually less than 5% (loading densities ca.
0.2 gcmꢀ3) when the maximum pressure, the specific energy,
and the co-volume are considered.
Table 4 contains the compositions of the calculated gun
propellant charges. M1 is a typical single-base propellant
based on nitrocellulose (NC), used for large caliber artillery
guns.[44] The drawbacks of this formulation are the relatively
low performance and the toxicity of almost all ingredients.[45]
EX-99 is a typical formulation for large naval guns and con-
tains high amounts of the highly energetic RDX.[46] The for-
mulations herein referred to as High-Nitrogen 1 and 2 (HN-
1 and HN-2, respectively) are two erosion-reduced formula-
tions derived from EX-99, which contain the nitrogen-rich
compound bis(triaminoguanidinium) 5,5’-azobistetrazolate
(TAGzT, 82% nitrogen). Synthesized compounds 1–8
(except for 5 and 6 due to the formation of hydrates) were
calculated in formulations based on HN-1 and HN-2, in
which they replace the TAGzT. The heats of formation were
either taken from the EXPLO5 database, from the literature
(BDNPA/F),[47] or calculated in this study.
Detonation parameters and specific impulse: Although com-
pounds 1–8 show promise as alternative additives in gun
propellants, they nevertheless detonate when stimulated by
using a primary explosive in combination with a booster
charge. All compounds show better detonation behavior
than TNT (trinitrotoluene), compound 3 is even better than
RDX (hexogen). Table 6 shows the detonation values of 1–8
calculated by using the EXPLO5.04 software, the heats of
formation, and X-ray densities. In addition, the specific im-
pulse of the pure compounds when used as monopropellants
was calculated assuming rocket propellant conditions (iso-
baric combustion with a chamber pressure of 60 bar).
The combustion parameters of the formulations were cal-
culated assuming isochoric conditions by using the virial
4058
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Chem. Eur. J. 2012, 18, 4051 – 4062

Nitrogen-Rich 5,5’-Bistetrazolates
FULL PAPER
corresponding bases. The crys-
tal structures of 1–7 were deter-
mined
by
low-temperature
single-crystal X-ray diffraction.
The compounds crystallize in
¯
the space groups P1 (2, 3, 6),
C2/m (1), P21/c (4), and P21/n
(5, 7) with densities between
1.520 (for the bis(aminoguanidi-
nium) salt dihydrate) and
1.742 gcmꢀ3 (for the di(hydrox-
ylammonium) salt). Additional-
ly, all compounds were fully
characterized by using vibra-
tional spectroscopy (IR and
1
Raman), H and 13C NMR spec-
troscopy, mass spectrometry,
and elemental analysis. The
thermal stabilities of 1–8 were
investigated by DSC. All com-
pounds decompose at tempera-
tures higher than 2008C, with
the guanidinium salt being the
most thermally stable salt
(3168C).
The sensitivity of compounds
1–8 towards friction, impact,
and electrostatic discharge were
investigated by BAM methods.
Figure 10. Comparison of the calculated performances of M1, EX-99, HN-2, 2 HN-2, 3 HN-2 and 7 HN-2. For
each formulation, column 1: Tc [K], column 2: pmax [bar], column 3: fE [Jgꢀ1], column 4: N2/CO/0.001.
Table 6. Calculated specific impulses, nitrogen contents, oxygen balances, and detona-
Compounds 1–8 were found to have impact sensi-
tivities between 10 (3, sensitive) and 40 J (2, 4, 5,
less sensitive), friction sensitivities of between 240
(3, sensitive) and >360 N (1, 4, insensitive), and
ESD sensitivities of between 0.1 (3) and 1.0 J (4, 5).
Therefore, the hydroxylammonium salt 3 is the
most sensitive, whereas the guanidinium salt 4 is
the least sensitive compound. However, all materi-
als are less sensitive than commonly used high ex-
plosives, such as RDX.
tion parameters of 1–8.
Isp
N
W
1
ꢀDEU8
TE
pC-J
VDet.
V0
[a]
[d]
[e]
[h]
[i]
[sꢀ1
]
[%][b] [%][c]
[gcmꢀ3
]
[kJkgꢀ1
]
[K][f] [kbar][g] [msꢀ1
]
[Lkgꢀ1
]
1
2
3
4
5
6
7
8
172.3 81.36 ꢀ74.34 1.590
225.2 83.13 ꢀ71.21 1.531
227.9 68.61 ꢀ47.02 1.742
165.8 76.53 ꢀ87.41 1.586
174.6 69.54 ꢀ74.46 1.568
190.1 71.56 ꢀ72.65 1.520
224.1 80.89 ꢀ78.53 1.535
204.8 70.42 ꢀ65.35 1.742
2415
4126
4829
2239
2656
3284
4129
3893
1976 189
2744 236
3243 317
1869 176
2049 193
2320 205
2698 238
2676 288
7417
8265
8854
7199
7504
7711
8181
8562
826
853
843
790
859
872
846
824
[a] Specific impulse. [b] Nitrogen content. [c] Oxygen balance.[48] [d] Density calculated
By using calculated heats of formation and load-
from X-ray structure. [e] Energy of explosion. [f] Explosion temperature. [g] Detona- ing densities of 0.2 gcmꢀ3, the isochoric combustion
tion pressure. [h] Detonation velocity. [i] Volume of detonation gases.
parameters (specific energy, combustion tempera-
ture, pressure, co-volume, and N2/CO ratios) for
formulations of 1–4, 7, and 8 were calculated with
Conclusion
the EPXLO5 program and compared to common formula-
tions found in the literature. The most promising compound
for gun propellant formulations is 2, which has a specific
energy of 1.111 kJgꢀ1, a pressure of 2910 bar, a combustion
temperature of 2783 K, and an N2/CO ratio of 1.06. Formu-
lations with 1, 3, 4, 7, and 8 are similar in performance to
formulations reported in the literature.
From this combined theoretical and experimental study, sev-
eral conclusions can be drawn. Deprotonation of 5,5’-bis-
ACHTUNGTRENNUNGtetrazole with nitrogen-rich bases leads to a variety of com-
pounds, namely, the diammonium salt (1), the dihydrazinium
salt (2), the di(hydroxylammonium) salt (3), the bis(guanidi-
nium) salt (4), the bis(aminoguanidinium) salt (5), the
bis(diaminoguanidinium) salt (6), the bis(triaminoguanidini-
um) salt (7), and the bis(diaminouronium) salt (8), which
were prepared in high yields and good purity. Only the
double-deprotonated 5,5’-bistetrazolates could be isolated
even when using stoichiometric amounts (1.0 equiv) of the
Experimental Section
Caution! 5,5’-Bistetrazole and its salts are energetic materials with in-
creased sensitivities towards shock and friction. Therefore, proper safety
Chem. Eur. J. 2012, 18, 4051 – 4062
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4059

J. Stierstorfer et al.
precautions (safety glass, face shield, earthed equipment and shoes,
Kevlar gloves, and ear plugs) have to be applied while synthesizing and
handling the described compounds.
1534 (m), 1385 (w), 1339 (m), 1314 (m), 1247 (s), 1184 (m), 1145 (m),
1095 (w), 1056 (m), 1030 (m), 1000 (m), 769 (m), 725 cmꢀ1 (m); Raman
(1064 nm, 350 mW, 258C): ~n=2958 (1), 2752 (1), 1591 (100), 1436 (2),
1251 (1), 1205 (17), 1144 (9), 1224 (34), 1093 (17), 1002 (22), 779 (3), 426
(5), 387 cmꢀ1 (8); MS (FAB+): m/z: 34.0 [NH3OH+]; MS (FABꢀ): m/z:
137.0 [C2HN8ꢀ]; elemental analysis calcd (%) for C2H8N10O2 (204.15): C
11.77, H 3.95, N 68.61; found: C 12.25, H 3.74, N 68.01; BAM dropham-
mer: 10 J; friction tester: 240 N (neg.); ESD: 0.10 J (at grain size 100–
500 mm).
All chemicals and solvents were employed as received (Sigma–Aldrich,
Fluka, Acros). 1H and 13C NMR spectra were recorded by using a JEOL
Eclipse 270, JEOL EX 400 or a JEOL Eclipse 400 instrument. The chem-
ical shifts are quoted in ppm and refer to typical standards, such as tetra-
methylsilane (1H, 13C) and nitromethane (14N). To determine the melting
and decomposition temperatures of the described compounds, a Linseis
PT 10 DSC instrument (heating rate 58Cminꢀ1) was used. Infrared spec-
tra were measured as KBr pellets by using a Perkin–Elmer Spectrum
One FT-IR spectrometer. Raman spectra were recorded by using a
Bruker MultiRAM Raman Sample Compartment D418 equipped with a
Nd-YAG laser (l=1064 nm) and a LN-Ge diode as the detector. Mass
spectra of the described compounds were measured by using a JEOL
MStation JMS 700 spectrometer and the FAB technique. To record ele-
mental analyses, a Netsch STA 429 simultaneous thermal analyzer was
used. 5,5’-Bistetrazole was synthesized according to a literature proce-
dure.[7]
Bis(guanidinium) 5,5’-bistetrazolate (4): A solution of guanidine carbon-
ate (1.80 g, 9.99 mmol, 1.00 equiv) in H2O (10 mL) was added to a solu-
tion of 5,5’-bistetrazole (1.38 g, 9.99 mmol, 1.00 equiv) in H2O (15 mL).
The resulting solution was heated until all solids were dissolved, then fil-
tered. Slow evaporation of the solvent gave colorless crystals of com-
pound 4 that were suitable for X-ray diffraction (yield: 1.88 g, 7.34 mmol,
73%). DSC (58Cminꢀ1): 316 (m.p.), 3198C (decomp.); 1H NMR
([D6]DMSO, 258C): d=7.73 ppm (s, 6H; NH2); 13C NMR ([D6]DMSO,
~
258C): d=158.9 (CACUTHGNTR(NENGU NH2)3), 154.9 ppm (N4C-CN4); IR (KBr): n=3449
(vs), 3350 (s), 3092 (s), 2194 (w), 1707 (m), 1650 (vs), 1584 (m), 1384 (m),
1327 (m), 1308 (m), 1183 (m), 1142 (m), 1088 (w), 1044 (w), 1017 (w),
Diammonium 5,5’-bistetrazolate (1): 5,5’-Bistetrazole (5.52 g, 40.0 mmol)
was dissolved in warm water (20 mL) and aqueous half-concentrated am-
monia (100 mL) was added. Water was added to the reaction mixture,
which was heated to reflux, until a clear solution was obtained (40 mL).
After heating to reflux for 20 min, the reaction mixture was cooled to RT
and then stored for 20 h at 48C. The precipitate was filtered off, washed
with a small amount of water and plentiful ethanol, and dried in medium
vacuum to give the title compound as colorless needles (yield: 5.25 g,
30.5 mmol, 76%). DSC (58Cminꢀ1): 3128C (decomp.); 1H NMR (D2O,
608C): d=4.80 ppm (s, NH4+, H2O); 13C NMR ([D6]DMSO, 258C): d=
155.2 ppm (N4C-CN4); 14N NMR ([D6]DMSO, 258C): d=ꢀ356 (NH4+),
726 (w), 603 (m), 543 cmꢀ1 (m); Raman (1064 nm, 300 mW, 258C): n=
~
3177 (2), 1592 (100), 1563 (3), 1207 (7), 1139 (4), 1123 (20), 1073 (26),
1014 (50), 780 (4), 542 (20), 483 (3), 421 (4), 382 (7), 167 (13), 156 (5),
131 (5), 115 (68), 107 (12), 70 cmꢀ1 (6); MS (FAB+): m/z: 60.1 [CH6N3+];
MS (FABꢀ): m/z: 137.0 [C2HN8ꢀ]; elemental analysis calcd (%) for
C4H12N14 (256.23): C 18.75, H 4.72, N 76.53; found: C 19.06, H 4.46, N
75.24; BAM drophammer: 40 J; friction tester: >360 N; ESD: 1.0 J (at
grain size 100–500 mm).
Bis(aminoguanidinium) 5,5’-bistetrazolate dihydrate (5): A suspension of
aminoguanidine bicarbonate (2.73 g, 20.1 mmol, 2.00 equiv) in H2O
(30 mL) was added to a solution of 5,5’-bistetrazole (1.38 g, 9.99 mmol,
1.00 equiv) in H2O (15 mL). The resulting suspension was diluted with
H2O (45 mL) and heated to reflux until all solids were dissolved. Slow
evaporation of the solvent gave colorless crystals of compound 5 that
were suitable for X-ray diffraction (yield: 1.72 g, 6.01 mmol, 60%). DSC
(58Cminꢀ1): 247 (m.p.), 2518C (decomp.); 1H NMR ([D6]DMSO, 258C):
d=9.65 (brs, 1H; NH), 7.73 (brs, 4H; C-(NH2)2) 4.73 ppm (s, 2H;
~
ꢀ66 (CN4), 3 ppm (CN4); IR (ATR): n=3170 (w), 2984 (w), 2875 (w),
2360 (w), 2341 (w), 2140 (w), 1880 (w), 1722 (w), 1692 (m), 1680 (m),
1432 (s), 1327 (s), 1302 (s), 1184 (s), 1147 (s), 1084 (m), 1051 (m), 1016
(s), 732 cmꢀ1 (w); Raman (1064 nm, 250 mW, 258C): n=3005 (8), 1588
~
(100), 1568 (9), 1208 (22), 1144 (8), 1116 (33), 1109 (8), 1074 (26),
784 cmꢀ1 (5); MS (FAB+): m/z: 18.0 [NH4+]; MS (FABꢀ): m/z: 137.0
[C2HN8ꢀ]; elemental analysis calcd (%) for C2H8N10O (172.15): C 13.95,
H 4.68, N 81.36; found: C 14.36, H 4.46, N 81.36; BAM drophammer:
35 J; friction tester: >360 N; ESD: 0.60 J (at grain size 500–1000 mm).
NHNH2);
13C NMR
([D6]DMSO,
258C):
d=159.7
(C-
~
AHCTNUGTERNNG(UN NHNH2)(NH)NH2), 155.1 ppm (N4C-CN4); IR (KBr): n=3409 (vs),
3345 (vs), 3162 (vs), 2994 (s), 2891 (s), 2175 (w), 1690 (vs), 1668 (vs),
1553 (w), 1463 (m), 1384 (w), 1327 (s), 1299 (m), 1223 (w), 1169 (m),
1145 (m), 1079 (w), 1042 (w), 1015 (m), 983 (m), 957 (m), 758 (w), 728
(w), 687 (m), 607 (m), 511 (w), 463 cmꢀ1 (w); Raman (1064 nm, 300 mW,
Dihydrazinium
5,5’-bistetrazolate
(2):
5,5’-Bistetrazole
(2.76 g,
20.0 mmol) was suspended in warm water (5 mL) and hydrazine hydrate
(5.01 g, 100 mmol, 5.00 equiv) was added. The reaction mixture was
heated to reflux for 20 min, then cooled to RT and stored at 48C for 5 h.
The resulting precipitate was filtered off and washed with a small amount
of water, ethanol, and diethyl ether to give the title compound as color-
less, fine needles (yield: 0.50 g, 2.47 mmol, 12%). DSC (58Cminꢀ1):
2348C (decomp.); 1H NMR ([D6]DMSO, 258C): d=7.20 ppm (brs,
NH2NH3+); 13C NMR ([D6]DMSO, 258C): d=154.5 ppm (N4C-CN4); IR
~
258C): n=3347 (2), 3279 (5), 3166 (1), 1670 (3), 1587 (100), 1564 (10),
1423 (2), 1194 (8), 1142 (5), 1108 (32), 1073 (19), 973 (11), 783 (4), 626
(3), 512 (7), 480 (1), 424 (9), 394 (6), 329 (2), 133 (39), 100 (7), 70 cmꢀ1
(13); MS (FAB+): m/z: 75.0 [CH7N4+]; MS (FABꢀ): m/z: 136.9
[C2HN8ꢀ]; elemental analysis calcd (%) for C4H18N16O2 (322.29): C 14.91,
H 5.63, N 69.54; found: C 15.21, H 5.56, N 69.42; BAM drophammer:
40 J; friction tester: 324 N; ESD: 1.0 J (at grain size 500–1000 mm).
~
(ATR): n=3235 (m), 3142 (m), 2883 (m, br), 2574 (s, br), 2350 (m), 2248
(m, br), 1613 (m, br), 1549 (m), 1529 (m), 1328 (s), 1306 (m), 1185 (m),
1167 (m), 1120 (vs), 1079 (s), 1051 (s), 1019 (s), 968 (vs), 728 cmꢀ1 (m);
Bis(diaminoguanidinium) 5,5’-bistetrazolate dihydrate (6): A solution of
bis(diaminoguanidinium) sulfate (1.26 g, 4.56 mmol, 1.00 equiv) in H2O
(10 mL) was added to a solution of barium 5,5’-bistetrazolate tetrahy-
drate (1.58 g, 4.57 mmol, 1.00 equiv) in H2O (40 mL). Filtration and slow
evaporation of the solvent gave colorless crystals of compound 6 that
were suitable for X-ray diffraction (yield: 1.23 g, 3.49 mmol, 77%). DSC
(58Cminꢀ1): 97 (H2O), 204 (m.p.), 2088C (decomp.); 1H NMR
([D6]DMSO, 258C): d=9.61 (brs 2H; NH), 7.64 (s, 2H; C-NH2),
4.63 ppm (s, 4H; NHNH2); 13C NMR ([D6]DMSO, 258C): d=160.6 (C-
~
Raman (1064 nm, 250 mW, 258C): n=3151 (6), 1586 (100), 1563 (10),
1210 (16), 1141 (8), 1113 (27), 1078 (18), 971 (11), 782 cmꢀ1 (6); MS
(FAB+): m/z: 33.0 [N2H5+]; MS (FABꢀ): m/z: 137.0 [C2HN8ꢀ]; elemental
analysis calcd (%) for C2H10N12 (202.18): C 11.88, H 4.99, N 81.13; found:
C 12.30, H 4.62, N 81.15; BAM drophammer: 40 J; friction tester: 360 N;
ESD: 0.23 J (at grain size 100–500 mm).
Dihydroxylammonium 5,5’-bistetrazolate (3): 5,5’-Bistetrazole (1.38 g,
10 mmol) was dissolved in hot water (20 mL). A solution of hydroxyla-
mine (50% w/w in H2O, 1.32 g, 20 mmol, 2.00 equiv) was added slowly
and the resulting clear solution was evaporated under vacuum. The color-
less solid residue was recrystallized from ethanol/water to give 3 as color-
less, fine needles suitable for X-ray crystallography (yield: 1.79 g,
8.8 mmol, 88%). Alternatively, single crystals could be obtained by slow
evaporation of the mother liquor. DSC (58Cminꢀ1): 2058C (decomp.);
1H NMR ([D6]DMSO, 258C): d=10.50 ppm (s, 8H; NH3OH); 13C NMR
~
AHCTUNGTRENNUNG
(m), 593 (m), 473 cmꢀ1 (w); Raman (1064 nm, 300 mW, 258C): n=3330
~
(3), 3219 (6), 1670 (2), 1585 (100), 1565 (5), 1417 (2), 1206 (17), 1185 (2),
1146 (3), 1129 (4), 1109 (29), 1072 (18), 922 (12), 783 (3), 655 (2), 547 (4),
471 (1), 425 (8), 402 (5), 366 (3), 282 (3), 224 cmꢀ1 (3); MS (FAB+): m/z:
90.1 [CH8N5+]; MS (FABꢀ): m/z: 137.0 [C2HN8ꢀ]; elemental analysis
~
([D6]DMSO, 258C): d=152.6 ppm (N4C-CN4); IR (KBr): n=3425 (m),
3030 (vs), 2815 (s), 2744 (s), 2203 (m), 2056 (m), 1987 (m), 1626 (m),
4060
www.chemeurj.org
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 4051 – 4062

Nitrogen-Rich 5,5’-Bistetrazolates
FULL PAPER
calcd (%) for C4H20N18O2 (352.32): C 13.64, H 5.72, N 71.56; found: C
14.22, H 5.46, N 71.16; BAM drophammer: 30 J; friction tester: 360 N;
ESD: 0.70 J (at grain size 100–500 mm).
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Bis(triaminoguanidinium) 5,5’-bistetrazolate (7): Triaminoguanidine
(1.04 g, 9.99 mmol, 1.00 equiv) was added to a solution of 5,5’-bistetrazole
(1.45 g, 10.5 mmol, 1.05 equiv) in H2O (25 mL). Filtration and slow evap-
oration of the solvent gave slightly purple crystals of 7 that were suitable
for X-ray diffraction (yield: 1.42 g, 4.10 mmol, 82%). DSC (58Cminꢀ1):
2078C (decomp.); 1H NMR (D2O, 25 8C): d=4.77 ppm (s, 6H; NH2);
13
~
C NMR (D2O, 25 8C): d=154.6 ppm (N4C-CN4); IR (KBr): n=3340
[6] S. Hachiya, M. Sato (Jpn. Kokai Tokkyo) JP 2006096860A
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(m), 3320 (s), 3289 (m), 3211 (vs), 3139 (s), 2178 (w), 1685 (vs), 1614 (m),
1451 (w), 1383 (w), 1335 (m), 1322 (m), 1303 (m), 1224 (w), 1177 (w),
1171 (w), 1157 (m), 1128 (s), 1078 (w), 1043 (w), 1017 (m), 1011 (m), 952
(s), 764 (w), 732 (w), 638 (w), 611 (m), 566 cmꢀ1 (w); Raman (1064 nm,
~
[8] T. M. Klapçtke in Chemistry of High-Energy Materials, de Gruyter,
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2001, 40, 3570–3575.
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300 mW, 258C): n=3340 (5), 3292 (2), 3240 (2), 3195 (11), 1686 (4), 1664
(1), 1582 (100), 1564 (7), 1457 (2), 1423 (2), 1339 (3), 1198 (26), 1158 (4),
1137 (5), 1111 (38), 1073 (27), 1026 (2), 885 (12), 783 (4), 650 (1), 608 (2),
478 (2), 431 (8), 393 (4), 295 (3), 265 cmꢀ1 (2); MS (FAB+): m/z: 105.1
[CH9N6+]; MS (FABꢀ): m/z: 137.0 [C2HN8ꢀ]; elemental analysis calcd
(%) for C4H18N20 (346.32): C 13.87, H 5.24, N 80.89; found: C 14.02, H
4.87, N 79.21; BAM drophammer: 15 J; friction tester: 285 N; ESD:
0.70 J (at grain size 100–500 mm).
Bis(diaminouronium) 5,5’-bistetrazolate dihydrate (8): Diaminourea
(1.81 g, 20.1 mmol, 2.00 equiv) in H2O (25 mL) was added to a solution
of 5,5’-bistetrazole (1.39 g, 10.1 mmol, 1.00 equiv) in H2O (30 mL). The
solvent was removed under reduced pressure and the residue was recrys-
tallized from EtOH/H2O (1:4) to give colorless crystals of compound 8
(yield: 2.84 g, 8.92 mmol, 88%). DSC (58Cminꢀ1): 174 (m.p.), 2378C
(decomp.); 1H NMR ([D6]DMSO, 258C): d=7.22 ppm (brs, 7H);
13C NMR ([D6]DMSO, 258C): d=161.1 (C=O), 150.1 ppm (N4C-CN4);
~
IR (KBr): n=3296 (vs), 3185 (vs), 2996 (vs), 2718 (vs), 2490 (vs), 2225
(s), 2083 (s), 1739 (w), 1681 (s), 1646 (vs), 1621 (vs), 1590 (vs), 1560 (vs),
1536 (vs), 1384 (m), 1335 (vs), 1306 (vs), 1251 (m), 1225 (s), 1183 (s),
1144 (s), 1122 (vs), 1092 (s), 1056 (m), 1015 (s), 977 (m), 817 (m), 727 (s),
702 (s), 534 (w), 504 cmꢀ1 (w); Raman (1064 nm, 300 mW, 258C): n=
~
3297 (1), 3184 (4), 1679 (2), 1588 (100), 1560 (6), 1432 (2), 1340 (2), 1325
(5), 1226 (2), 1204 (22), 1143 (9), 1119 (28), 1092 (19), 1017 (5), 975 (9),
780 (4), 512 (7), 426 (12), 385 (9), 365 (3), 192 (7), 161 (3), 144 (34), 126
(9), 107 (42), 90 (27), 67 cmꢀ1 (3); MS (FAB+): m/z: 91.0 [CH7N4O+];
MS (FABꢀ): m/z: 137.0 [C2HN8ꢀ]; elemental analysis calcd (%) for
C4H18N16O4 (318.26): C 15.10, H 4.43, N 70.42; found: C 15.46, H 4.10, N
69.48; BAM drophammer: 35 J; friction tester: 360 N; ESD: 0.50 J (at
grain size 100–500 mm).
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Acknowledgements
Financial support of this work by the Ludwig Maximilian University of
Munich (LMU), the U.S. Army Research Laboratory (ARL), the Arma-
ment Research, Development and Engineering Center (ARDEC), the
Strategic Environmental Research and Development Program (SERDP),
and the Office of Naval Research (ONR Global, title: “Synthesis and
Characterization of New High Energy Dense Oxidizers (HEDO)
-
NICOP Effort”) under contract nos. W911NF-09-2-0018 (ARL),
W911NF-09-1-0120 (ARDEC), W011NF-09-1-0056 (ARDEC), and 10
WPSEED01-002/WP-1765 (SERDP) is gratefully acknowledged. The au-
thors acknowledge collaborations with Dr. Mila Krupka (OZM Research,
Czech Republic) for the development of new testing and evaluation
methods for energetic materials and Dr. Muhamed Sucesca (Brodarski
Institute, Croatia) for the development of new computational codes to
predict the detonation and propulsion parameters of novel explosives.
We are indebted to and thank Drs. Betsy M. Rice and Brad Forch (ARL,
Aberdeen, Proving Ground, MD) and Mr. Gary Chen (ARDEC, Picatin-
ny Arsenal, NJ) for many helpful and inspired discussions and support of
our work. Mr. Stefan Huber is thanked for performing the sensitivity
tests.
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Inorg. Chem. 2008, 47, 6014–6027.
[31] NATO standardization agreement (STANAG) on explosives, Impact
Sensitivity Tests, no. 4489, 1st ed., Sept. 17, 1999.
Chem. Eur. J. 2012, 18, 4051 – 4062
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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J. Stierstorfer et al.
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[48] Calculation
of
oxygen
balance:
W [%]=(wOꢀ2xCꢀ1/
2yHꢀ2zS)1600/M. (w: number of oxygen atoms, x: number of
carbon atoms, y: number of hydrogen atoms, z: number of sulfur
atoms, M: molecular weight).
Received: November 28, 2011
Published online: February 24, 2012
4062
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ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 4051 – 4062