Synthesis and stability of 2-tetrazenium salts

Article abstract of DOI:10.1039/c1nj20278b

The geometry and electronic structure of (E)-N₄Me₄ (1) and the (E)-N₄Me₄H⁺ and the (E)-N ₄Me₅⁺ cations was examined by a DFT approach. By using the B3LYP/6-31+G(d,p) model we showed that the terminal nitrogen atoms in 1 are strongly basic, as evidenced by their highly negative NBO charges in comparison to the azo nitrogen atoms. Interestingly, protonation of 1 to form the (E)-N₄Me₄H⁺ cation does not result in significant changes in the NBO charges of the protonated nitrogen atom, which is in contrast with classical views that describe tetracoordinated nitrogen atoms as being positively charged. Insight into the thermal stability of salts of the (E)-N₄Me₄H⁺ and the (E)-N₄Me ₅⁺ cations was gained experimentally by DSC measurements of two salts of the (E)-N₄Me₄H⁺ cation, namely with chloride (2) and picrate (3) anions and the iodide salt of the (E)-N ₄Me₅⁺ cation (4), which were synthesized by protonation of 1 with hydrochloric (2) and picric (3) acids and by methylation of 1 with methyl iodide (4), respectively. Compounds 2-4 were characterized by analytical (elemental analysis and mass spectrometry) and spectroscopic ( ¹H/¹³C NMR, IR/Raman and UV spectroscopies) methods. Protonation and methylation of 1 to form the (E)-N₄Me ₄H⁺ (compounds 2 and 3) and (E)-N₄Me ₅⁺ (compound 4) cations, respectively, appears to occur at the terminal nitrogen atoms, in keeping with the results of the NBO analysis and the higher stabilization energy of the conformations with a protonated/methylated terminal nitrogen atom. The geometry optimization by the B3LYP/6-31+G(d,p) method points at very weak N3-N4 bonds (N4 = protonated/methylated nitrogen atom), which explains the formation of dimethylammonium picrate in the thermal decomposition of picrate salt 3 and suggests that dialkylaminium radicals (R₂N⁺) are involved in the decomposition pathway.

Full text of DOI:10.1039/c1nj20278b

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
NJC
Cite this: New J. Chem., 2011, 35, 1640–1648
www.rsc.org/njc
PAPER
Synthesis and stability of 2-tetrazenium saltsw
´ ´
Carles Miro Sabate* and Henri Delalu
Received (in Montpellier, France) 25th March 2011, Accepted 10th May 2011
DOI: 10.1039/c1nj20278b
The geometry and electronic structure of (E)-N4Me4 (1) and the (E)-N4Me4H+ and the
+
(E)-N4Me5 cations was examined by a DFT approach. By using the B3LYP/6-31+G(d,p) model
we showed that the terminal nitrogen atoms in 1 are strongly basic, as evidenced by their highly
negative NBO charges in comparison to the azo nitrogen atoms. Interestingly, protonation of 1 to
form the (E)-N4Me4H+ cation does not result in significant changes in the NBO charges of the
protonated nitrogen atom, which is in contrast with classical views that describe tetracoordinated
nitrogen atoms as being positively charged. Insight into the thermal stability of salts of the
(E)-N4Me4H+ and the (E)-N4Me5 cations was gained experimentally by DSC measurements of
+
two salts of the (E)-N4Me4H+ cation, namely with chloride (2) and picrate (3) anions and the
+
iodide salt of the (E)-N4Me5 cation (4), which were synthesized by protonation of 1 with
hydrochloric (2) and picric (3) acids and by methylation of 1 with methyl iodide (4), respectively.
Compounds 2–4 were characterized by analytical (elemental analysis and mass spectrometry) and
spectroscopic (1H/13C NMR, IR/Raman and UV spectroscopies) methods. Protonation and
+
methylation of 1 to form the (E)-N4Me4H+ (compounds 2 and 3) and (E)-N4Me5 (compound 4)
cations, respectively, appears to occur at the terminal nitrogen atoms, in keeping with the results of
the NBO analysis and the higher stabilization energy of the conformations with a protonated/
methylated terminal nitrogen atom. The geometry optimization by the B3LYP/6-31+G(d,p) method
points at very weak N3–N4 bonds (N4 = protonated/methylated nitrogen atom), which explains
the formation of dimethylammonium picrate in the thermal decomposition of picrate salt
3 and suggests that dialkylaminium radicals (R2N+ꢀ) are involved in the decomposition pathway.
bipropellant component. Unfortunately, hydrazine and its
Introduction
derivatives have high vapour pressures and are known to be
toxic and carcinogenic. Additionally, high purity hydrazines
might form explosive mixtures with air.12 In this context, salt
formation is known to stabilize a material13 and, additionally,
ionic materials tend to display lower vapour pressures and
higher densities (related to the performance of the compound)
than their atomically similar non-ionic derivatives.14
Interest in the synthesis and analysis of the energetic properties of
HEDMs = high-energy density materials continues.1–7 Classical
energetic materials such as TNT = trinitrotoluene or RDX =
cyclotrimethylenetrinitramine derive their energy from the
oxidation of their carbon backbones,8,9 in contrast to N–N
compounds, which owe their high energies to their positive heats
of formation.10,11 Unfortunately, many of these materials are
highly sensitive and accidents have occurred in the past. Other
compounds such as hydrazine and its derivatives, e.g., MMH =
monomethylhydrazine or UDMH = unsymmetrical dimethyl-
hydrazine form hypergolic mixtures with oxidizers such as
NTO = nitrogen tetroxide or LOX = liquid oxygen and
are, therefore, widely used in hypergolic rocket fuels as a
Recently, 2-tetrazenes (Fig. 1) have emerged as a class of
energetic materials with good chemical and thermal stability
and lower toxicity than commonly used compounds.15 2-Tetra-
zenes are isoelectronic with the butadiene dianion, i.e., they are
electron-rich compounds with several lone pairs. For this
reason they are involved in both intra- and extra-molecular
hydrogen-bonding.16 The electron-rich character give them also
a high intrinsic basicity (e.g., pKb (N4Et4) = 5.12),17 which
increases with the larger the size of the substituent. The simplest
`
Laboratoire Hydrazines et Composes Energetiques Polyazotes,
´
Universite Claude Bernard Lyon 1, Batiment Berthollet, 3e etage,
´
´
´
22, avenue Gaston Berger, 69622 Villeurbanne, France.
ˆ
` ´
E-mail: carlos.miro-sabate@univ-lyon1.fr; Fax: +33-472-431-291
w Electronic supplementary information (ESI) available: Calculated
IR/Raman frequencies and Mulliken charges for (E)-N4Me4 (1) and
the N4Me4H+ and the N4Me5 cations and hydrogen-bonding and
+
graph-set tables for dimethylammonium picrate. See DOI: 10.1039/
c1nj20278b
Fig. 1 Formula structures of cis- and trans-2-tetrazenes.
c
1640 New J. Chem., 2011, 35, 1640–1648
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011

View Article Online
2-tetrazene possible, i.e., N4H4, (R = H) was synthesized as the
trans- form by Wiberg and coworkers in 1975 over a four steps
procedure starting from hydrazine.18 Unfortunately, this highly
energetic compound is thermally labile and crystals of pure
N4H4 might decompose explosively forming nitrogen gas,
hydrazine and ammonium azide, even when stored at 0 1C.
Additionally, salts based on the 2-tetrazenium cation, i.e.,
N4H5+, decompose at temperatures above ca. ꢁ20 1C forming
ammonium salts and hydrazoic acid.19 The simplest 2-tetrazene
known, which is stable at room conditions is the methyl
derivative (E)-N4Me4 (R = Me) and much work has been
carried out concerning the synthesis of the latter compound by
the oxidation reaction of UDMH.15c,17,20–27
iodide salt 4 decomposes within a few days and the picrate salt
3 is stable for several weeks, slowly decomposing to form
picric acid and 1. In the refrigerator, compounds 3 and 4 can
be stored for (at least) several weeks or even months, while 2
decomposes after a few days. In the freezer at ca. ꢁ20 1C, none
of the three salts 2–4 showed appreciable decomposition after
several months. When the solids are left standing in air, 4
decomposes within minutes into a reddish powder, i.e., iodine
formation, while 2 turns yellow and finally into a brown sticky
mass with UV (H2O) maxima at 242 nm, characteristic of
(E)-N4Me4 (1). When the (E)-N4Me4H+ salts (2 and 3) are
overlayered with ether and left to stand for several hours (2) or
days (3) in a closed vial and then the ether phase is analyzed by
GC–MS, a signal at 2.01 min28 with m/z = 116.1 is observed,
which can be attributed to (E)-N4Me4 (1).
Due to the interesting electronic properties of 2-tetrazenes
and their potential for energetic applications, we became
interested in studying the reaction of (E)-N4Me4 with hydro-
chloric and picric acids as well as with methyl iodide and the
thermal stability of the resulting products.
The thermal lability of compounds 2–4 is in keeping with
the differential scanning calorimetry (DSC) results. Whereas
(E)-N4Me4 (1) is stable up to its boiling point (ca. 130 1C), the
chloride salt 2 decomposes already at ca. 57 1C and compound
3, with the generally more thermally robust picrate anion,29,30
is stable up to ca. 72 1C. The above mentioned observations
are also in agreement with the lower decomposition point
of iodide 4, which shows a sharp exotherm in the DSC
measurements at ca. 52 1C (explosive decomposition!). All
these results are in keeping with previous studies indicating
that tetraaryl 2-tetrazenes start to decompose at ca. 40 1C.31
The low decomposition points of these compounds would
limit their application in the field of energetic materials,
however, the chloride salt 2 and the iodide salt 4 are expected
to be useful intermediates for the synthesis of compounds
with higher thermal stabilities that might be of energetic
interest.
Results and discussion
Synthesis and stability
Oxidation of 1,1-dimethylhydrazine using mercury oxide in
ether according to the method of Madgzinski and coworkers23
afforded (E)-N4Me4 (1) as a pale yellow liquid. 1 was subsequently
reacted with an equivalent amount of hydrochloric and picric
acids to form the (E)-N4Me4H+ cation as its chloride (2) and
picrate (3) salts, which separated in high purity and yield from the
ether reaction mixture. Additionally, 1 was reacted with an
equivalent amount of methyl iodide in the cold and in the absence
+
of solvent to form the iodide salt of the (E)-N4Me5 cation (4),
The UV spectra of the salts of the (E)-N4Me4H+ cation
(2 and 3) were measured in distilled water. We omitted the
measurement for the salt of the (E)-N4Me5+ cation (4) due to
the strong gas evolution observed in this solvent, which lead to
unreliable results. Salts 2 and 3 show one single maxima at 239
(e = 7904 L molꢁ1 cmꢁ1) and 245 (e = 20520 L molꢁ1 cmꢁ1) nm,
respectively. By comparison, we measured (E)-N4Me4 (1) to
give a single maxima at 242 (e = 7640 L molꢁ1 cmꢁ1),
although depending on the solvent and/or concentration one
peak at 277 nm with a shoulder at 250 nm might be observed.
This effect has been attributed to the tendency of 2-tetrazenes
to form protonated species in acidic solvents.17
which separated out of the reaction mixture (Scheme 1).
Compounds 2 and 4 were obtained as white powders, whereas
the picrate salt 3 is a bright yellow solid. Both salts of the
(E)-N4Me4H+ cation (2 and 3) and that of the (E)-N4Me5
+
cation (4) are readily soluble in polar solvents such as water,
DMSO or ethanol and insoluble in apolar solvent such as
cyclohexane. In solvents like wet ether or toluene, suspensions
of compound 3 turn yellow, possibly because of the formation of
picric acid, which is soluble in these solvents. A similar behaviour
is observed for 2 with the formation of hydrochloric acid. When
dissolved in DMSO, compounds 3 and 4 give strong gas
evolution. In water, 3 seems to have relatively good stability,
however, when aqueous solutions of the compound are warmed,
crystals of dimethylammonium picrate can be obtained (see
discussion below).
Spectroscopic discussion
In the solid state and in the absence of moisture, compound
2 decomposes within hours at room temperature, whereas the
In order to facilitate the assignment of the signals observed in
the infrared (IR) and Raman (Ra) spectra of (E)-N4Me4 (1) and
+
the salts of the (E)-N4Me4H+ (2 and 3) and (E)-N4Me5 (4)
cations, we used DFT calculations (B3LYP/6-311+G(d,p))
to calculate the expected (gas phase) vibrational frequencies
of (E)-N4Me4 (1) and the (E)-N4Me4H+ and (E)-N4Me5
+
cations (see Experimental section for Computational details).
Tables 1–3 of the ESIw show a summary of the computed
frequencies (scaled and unscaled) with infrared intensities and
Raman activities, comparison with the experimental results
and tentative assignment of the vibrational bands for all three
species.
Scheme 1 Protonation and alkylation of N4Me4 (1) to form the
N4Me4H+ and N4Me5 cations.
+
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
New J. Chem., 2011, 35, 1640–1648 1641

View Article Online
The computed frequencies for compounds 1–4 are in relatively
good agreement with the experimental values. The most important
band observed in the vibrational spectra of compounds 1–4
is the N2–N3 azo bridge stretch, which is observed at IR/Ra
frequencies of 1469/1473 cmꢁ1 (1), 1490/Raman inactive cmꢁ1
(averaged value for 2 and 3) and 1480/1475 cmꢁ1 (4). The
stretching vibrations of the methyl groups C–H are observed
in the range between 2960 and 3090 cmꢁ1 (asymmetric C–H
stretch) and between 2820 and 2885 cmꢁ1 (symmetric C–H
stretch) for compound 1, between 2955 and 3020 cmꢁ1
(asymmetric C–H stretch) and ca. 2920 cmꢁ1 (symmetric
C–H stretch) for salts 2 and 3 and between 3010 and 3070 cmꢁ1
(asymmetric C–H stretch) and between 2840 and 2945 cmꢁ1
(symmetric C–H stretch) for the iodide derivative 4. Below
these wave numbers in-plane bending vibrations of the methyl
groups C–H are found, which go from 1440 to 1475 cmꢁ1 (1),
at ca. 1430 cmꢁ1 (2 and 3) and from 1405 to 1480 cmꢁ1 (4). At
lower frequencies, the dominant vibrations are the stretching
modes of the different C–N and N–N bonds present in the
‘‘N4Me4’’ moiety (‘‘N4Me5’’ moiety for salt 4) of compounds
1–4. These vibrations extend up to ca. 600 cmꢁ1 and are
dominant in the IR spectra, obscuring the signals of the
bending modes of the methyl groups C–H.30a,32
Geometry and NBO analysis of (E)-N4Me4 (1) and the
(E)-N4Me4H+ and (E)-N4Me5 cations
+
The optimized geometry of (E)-N4Me4 (1) and the (E)-N4Me4H+
and (E)-N4Me5+ cations was obtained as described above (see
Computational Details section) and used for the natural bond
orbital (NBO) calculations. Table 1 contains a summary of the
bond distances and angles calculated for the optimized (gas
phase) structures of (E)-N4Me4 (1) and the (E)-N4Me4H+ and
+
(E)-N4Me5 cations (see Fig. 2–4 for the labelling scheme of
all three species). The optimized geometry of (E)-N4Me4 (1)
shows N–N distances for the terminal nitrogen atoms of
N1–N2 = N3–N4 = 1.377 A between N–N single (1.454 A)
and NQN double bonds (1.245 A).33 The azo bridge distance
(N2–N3 = 1.257 A) is slightly longer than the average NQN
double bond and comparable to the analogous X-ray distances
found in salts of the 5,50-azotetrazolate anion.34 As expected,
the C–N distances (1.457 A) are typical for C–N single
bonds (1.47 A).19 Protonation/methylation of 1 to form the
+
(E)-N4Me4H+ and (E)-N4Me5 cations, respectively, results,
in a significant weakening (lengthening) of the bond distances
1
In the H NMR spectra of salts of the (E)-N4Me4H+ cation
(2 and 3) in DMSO-[D6], two resonances are observed at
ca. 3.05 ppm for the protons of the methyl groups and at
13.19 (2) and 11.51 ppm (3) for the proton of the nitrogen
atom. Note the low field shift of the resonance of the N–H
proton in compound 2 in comparison to 3, in agreement with
the higher acidity of hydrochloric acid in comparison to picric
acid. In the 13C NMR spectra, both 2 and 3 show only one
signal for the carbon atoms of the methyl groups at ca. 34 ppm.
By comparison, (E)-N4Me4 (1) has resonances at 2.72
(1H NMR) and ca. 39.9 (13C NMR) ppm. The extra methyl
group in the (E)-N4Me5+ cation of compound 4 in comparison
to the (E)-N4Me4H+ cation of salts 2 and 3, results in loss of
symmetry and the carbon and hydrogen atoms of the –NMe2 and
Fig. 2 Optimized geometry and charge distribution in (E)-N4Me4 (1)
as found with NBO analysis (B3LYP/6-31+G(d,p)).
1
–NMe3 fragments show different resonances. In the H NMR
spectrum two resonances are observed at 3.12 (–NMe3) and 3.49
(–NMe2) ppm. In analogy, the 13C NMR spectrum of 4 also
shows two resonances for the carbon atoms, which can be found
at 38.1 (–NMe2) and 42.4 (–NMe3) ppm. Lastly, all compounds
2, 3 and 4 were too insoluble or unstable in any solvent tried to
record a 15N NMR spectrum (natural abundance).
Fig.
3 Optimized geometry and charge distribution for the
(E)-N4Me4H+ cation as found with NBO analysis (B3LYP/6-31+G(d,p)).
Table 1 Selected optimized geometry parameters for (E)-N4Me4 (1) and the (E)-N4Me4H+ and (E)-N4Me5 cations in the gas phase (B3LYP/
+
6-31+G(d,p)a
(E)-N4Me4H+
(E)-N4Me5
(E)-N4Me4 (1)
(E)-N4Me4H+
(E)-N4Me5
+
+
(E)-N4Me4 (1)
R(N1–N2)
R(N1–C2)
R(N1–C1)
R(N4–N3)
A(N2–N1–C2)
A(N2–N1–C1)
A(C2–N1–C1)
A(N3–N4–C3)
A(N3–N4–C4)
A(C3–N4–C4)
1.377
1.457
1.457
1.377
118.4
110.9
116.0
118.4
110.9
116.0
1.294
1.465
1.465
1.477
109.2
109.2
112.9
121.6
117.2
121.1
1.296
1.465
1.465
1.507
121.7
117.4
121.0
110.9
110.9
110.9
R(N4–C3)
R(N4–C4)
R(N2–N3)
R(N4–C5)
A(N1–N2–N3)
A(N4–N3–N2)
A(N3–N4–C5)
A(C3–N4–C5)
A(C4–N4–C5)
1.457
1.457
1.257
1.500
1.500
1.277
1.505
1.505
1.272
1.502
115.9
107.8
103.4
110.2
110.2
114.1
114.1
106.0
116.3
a
R = bond distance (in A), A = bond angle (in 1).
c
1642 New J. Chem., 2011, 35, 1640–1648
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011

View Article Online
both the (E)-N4Me4H+ and (E)-N4Me5 cations with the
proton/methyl group at N1 or N4 positions, have approximately
the same electronic and zero point energies. However, the
conformations with the proton/methyl group at N2 or N3
positions, have different energies between them and are
predicted to be less stable by 51.4 and 55.6 kcal molꢁ1
((E)-N4Me4H+ cation protonated at N3 and N2, respectively)
and by 71.6 and 80.2 kcal molꢁ1 ((E)-N4Me5+ cation methylated
at N3 and N2, respectively). Note that the electronic energy
calculated by Porath et al.16 for 1 (ꢁ378.59825990 a.u.) points
at the protonation/methylation of 1 playing a stabilizing role.
Fig. 2–4 show the calculated NBO charges for (E)-N4Me4
+
(1) and the (E)-N4Me4H+ and (E)-N4Me5 cations. For
+
Fig. 4 Optimized geometry and charge distribution for the (E)-
+
N4Me5 cation as found with NBO analysis (B3LYP/6-31+G(d,p)).
(E)-N4Me4 (1), the azo bridge nitrogen atoms (N2 and N3) bear
small negative charges (ꢁ0.094e) in contrast to the terminal
nitrogen atoms (N1 and N4) that hold a more negative charge
of ꢁ0.334e. The more negative charge of the terminal nitrogen
atoms supports the conclusion that protonation/methylation
will be easier on these atoms, in keeping with the results of the
around the protonated/methylated nitrogen atom (N4), which
+
is more accentuated in the case of the (E)-N4Me5 cation
(N3–N4 = 1.507 A and C3–N4 = C4–N4 = 1.505 A) than for
the (E)-N4Me4H+ cation (N3–N4 = 1.477 A and C3–N4 =
C4–N4 = 1.500 A). In contrast, the N–N bond distance of the
non-protonated/non-methylated terminal nitrogen atom (N1)
+
calculated energies of the (E)-N4Me4H+ and (E)-N4Me5
cations (see discussion above). This finding is also supported
by previous studies that report high proton affinities for
tetrasubstituted 2-tetrazenes and an appreciable electron density
concentration at the terminal nitrogen atoms.35 Unfortunately,
we were not able to grow high quality single crystals of
compounds 2–4, however, low quality single crystals of the
iodide salt 4 showed a ‘‘N4Me2’’ fragment and an iodide
anion. We assume that the high electron density of iodine
+
is significantly shorter for the (E)-N4Me4H+ and the (E)-N4Me5
cations (N1–N2 = 1.294 A and 1.296 A, respectively) than
for 1. Lastly, the azo N2–N3 distances and the remainder of
the C–N distances are comparable in all three species.
Tables 2 and 3 contain a summary of the electronic and zero
point energies as well as the dipole moment of the (E)-N4Me4H+
and (E)-N4Me5+ cations. According to our B3LYP calculations,
Table 2 Computational results for the (E)-N4Me4H+ cation using DFT calculations (B3LYP/6-31+G(d,p))a
Species
Formula
p.g
ꢁE
D
zpe
NI
m
[Me2N–NQN–NHMe2]+
C1
378.98013950
0
118.92
0
2.5088
[Me2N–NQNH–NMe2]+
C1
378.95897678
55.6
117.82
0
3.9485
[Me2N–NHQN–NMe2]+
C1
378.96054150
378.98013950
51.4
118.13
118.92
0
0
2.6372
2.5086
[Me2NH–NQN–NMe2]+
C1
0
a
p.g = point group; E = electronic energy in atomic units; D = destabilization energy relative to the most favourable isomer in kcal molꢁ1
;
zpe = zero point energy in kcal molꢁ1; NI = number of imaginary frequencies; m = dipole moment in Debye.
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
New J. Chem., 2011, 35, 1640–1648 1643

View Article Online
+
Table 3 Computational results for the (E)-N4Me5 cation using DFT calculations (RB3LYP/6-31+G(d,p))a
Species
Formula
p.g
ꢁE
D
zpe
NI
m
[Me2N–NQN–NMe3]+
C1
418.29313426
0
136.23
0
1.7643
[Me2N–NQNMe–NMe2]+
C1
418.26256972
80.2
135.72
0
3.5831
[Me2N–NMeQN–NMe2]+
C1
418.26587491
418.29313424
71.6
135.77
136.23
0
0
2.9582
1.7646
[Me3N–NQN–NMe2]+
C1
5.2 ꢂ 10ꢁ5
a
p.g = point group; E = electronic energy in atomic units; D = destabilization energy relative to the most favourable isomer in kcal molꢁ1
;
zpe = zero point energy in kcal molꢁ1; NI = number of imaginary frequencies; m = dipole moment in Debye.
did not allow to locate the three missing methyl groups but
they are probably placed on N4, confirming the results of our
calculations. On the other hand, protonation/methylation
results in loss of symmetry in comparison to 1 and while one
of the azo nitrogen atoms (N2) carries an almost neutral
suggest tetraalkyl-2-tetrazenes might decompose to form two
entities of the dialkylaminium radical (R2N+ꢀ) and molecular
nitrogen23,36 and suggest the following mechanism for the
decomposition of 3 (see Scheme 2):16
charge in both the (E)-N4Me4H+ and (E)-N4Me5 cations,
+
the other azo nitrogen atom (N3) carries a significant negative
charge in both species (ca. ꢁ0.180e). In a similar way, the
protonated/methylated nitrogen atom (N4) bears a more
significant negative charge than the other terminal nitrogen
atom (N1). Note that the charge of the protonated nitrogen
atom (N4) in the (E)-N4Me4H+ cation (ꢁ0.339e) does not
differ significantly from that of 1 (ꢁ0.334e), which is in
contrast with classical chemistry, which describes a tetra-
coordinated nitrogen atom as being positively charged. This
interpretation to explain the quadricovalency of the nitrogen
atoms is misleading in conjugate acids because the positive
charge is uniformly distributed in this type of compounds.39
Lastly, similar trends are observed for the Mulliken charges
(Fig. 1–3 of the ESIw).
Fig. 5 Asymmetric unit of dimethylammonium picrate with the
labeling scheme (diamond ellipsoids at 50% probability).
Decomposition of 3 in hot water
As mentioned above, when dissolving 3 in water at room
temperature, no appreciable decomposition was observed,
however, when the compound was dissolved in hot water
and the solvent was left to evaporate, single crystals of
dimethylammonium picrate were obtained (see Fig. 5). This
decomposition is in agreement with previous studies, which
Scheme 2 Proposed mechanism for the decomposition reaction of
picrate salt 3 in hot water. Picꢁ = picrate anion.
c
1644 New J. Chem., 2011, 35, 1640–1648
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011

View Article Online
The crystal structure of dimethylammonium picrate has
already been reported in the literature,37 therefore, only
attention to the hydrogen-bonding networks is paid here.
X-Ray quality crystals of the compound were obtained as
described above. Table SI 5 (ESIw) shows a summary of the
hydrogen-bonding graph-sets found in the structure of the
compound. The formation of dimeric networks is dominant.
These take the descriptors D1,1(2), D1,2(3) and D2,2(X)
(X = 5, 7, 9). Additionally, ring graph-sets of the type R2,1(6)
are also formed (Fig. 6), which are reminiscent to those found in
the crystal structure of azolium salts of the same anion.29b
(E)-N4Me4H+ and (E)-N4Me5+ cations with larger and nitrogen-
rich anions, which might have the possibility of stabilizing the
materials via electrostatic dipole–dipole interactions, are
expected to have improved thermal stabilities. We are currently
studying the effect of several anions in the thermal stability of
the resulting 2-tetrazenium salts. The results of this work will
be presented in a future report.
Experimental section
Safety note
2-Tetrazenes and their derivatives are potentially explosive
compounds. Preliminary testing showed decreased sensitivities
towards impact and friction, however, we recommend care to
be taken at all times, particularly, when working on a large
scale. We further recommend the synthesis of the compounds
reported here to be carried out only by experienced personnel
using non-conductive equipment (e.g., plastic spatulas and
plastic wear) and wearing safety gear such as Kevlar gloves
and jacket, conductive shoes and face shield.
X-Ray measurements
Fig. 6 Ring hydrogen-bonding networks in the crystal structure of
dimethylammonium picrate.
The crystallographic data of dimethylammonium picrate were
collected using an Oxford Diffraction Xcalibur 3 diffracto-
meter, which was equipped with a CCD detector using the
CrysAlis CCD software.38 For the data reduction, the CrysAlis
RED software39 was used and the structure was solved using
the WinGX software.40,41 The non-hydrogen atoms were
refined anisotropically and we applied a multi-scan absorption
correction.42 Ref. 43 contains a summary of the results of the
crystal structure and refinement. Lastly, the geometry of the
hydrogen bonds and the results of the graph-set analysis44,45
have been collected in Tables 4 and 5 of the ESIw.
Conclusions
From this combined experimental and theoretical study, the
following conclusions can be drawn:
We synthesized two salts of the (E)-N4Me4H+ cation with
chloride (2) and picrate (3) anions and the iodide salt of the
+
(E)-N4Me5 cation (4) and characterized the compounds
extensively by analytical (elemental analysis and mass spectro-
metry) and spectroscopic methods (IR, Raman, NMR and
UV). The low thermal stability of compounds 2–4 as the pure
solids and in several solvents is in agreement with the low
decomposition temperatures obtained from the DSC measure-
ments. NBO analysis on (E)-N4Me4 (1) anticipate a high
concentration of electron density on the terminal nitrogen
atoms, which suggest these atoms as the most likely to undergo
protonation/methylation to form the (E)-N4Me4H+ and
Computational details
The (gas phase) geometry of (E)-N4Me4 (1) and the
(E)-N4Me4H+ and (E)-N4Me5 cations (i.e., (E)-N4Me4 (1)
+
protonated/methylated at the N4 position) was optimized
using DFT calculations with the B3LYP method46,47 at the
6-311+G(d,p) level of theory. For all three geometries no
imaginary frequencies were found and the potential energy
surface showed a true minimum. The optimized geometries of
(E)-N4Me4 (1) and the (E)-N4Me4H+ and (E)-N4Me5+ cations
were subsequently used to calculate the harmonic vibrational
frequencies with infrared (IR) intensities and Raman activities
using the computer program Gaussian 03W.48 A scaling factor
of 0.9613, as suggested by Scott and Radom for calculations
using B3LYP/6-311+G(d,p),49 was used for the computed
frequencies. In addition, we performed a natural bond
(NBO) analysis on the optimized structures of (E)-N4Me4 (1)
+
the (E)-N4Me5 cations. These results are in agreement with
the DFT energy calculations for the (E)-N4Me4H+ and the
+
(E)-N4Me5 cations, that predict the conformations with
the proton/methyl group on the terminal nitrogen atom to
be the most stable, and fit the experimental observations.
Additionally, the long N3–N4 distances calculated for the
optimized geometries of the (E)-N4Me4H+ and the (E)-N4Me5
+
cations in comparison to the analogous distances in
(E)-N4Me4 (1), suggest this bond to be the initiating point for
the decomposition of 2-tetrazenium salts to form molecular
nitrogen and ammonium salts, as supported by the formation
of dimethylammonium picrate upon decomposition of 3 in hot
water. These results suggest the formation of dialkylaminium
radicals (R2N+ꢀ) during the decomposition pathway of 3.
Lastly, the low thermal stability of compounds 2–4 limits their
application in the field of energetic materials, however, salts 2
and 4 should be regarded as valuable intermediates for the
synthesis of salts of the energetically interesting (E)-N4Me4H+
+
and the (E)-N4Me4H+ and (E)-N4Me5 cations using the
option implemented in Gaussian 03W.
General method
All chemical reagents and solvents of analytical grade were
obtained from Sigma-Aldrich Inc. or Acros Organics and used
as supplied. 1H and 13C NMR spectra were recorded on a
JEOL Eclipse 400 instrument. The chemical shifts are given
+
and (E)-N4Me5 cations. In particular, combination of the
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
New J. Chem., 2011, 35, 1640–1648 1645

View Article Online
relative to tetramethylsilane as an external standard. Infrared
(IR) spectra were recorded at room temperature on a
Perkin-Elmer Spectrum instrument equipped with a Universal
ATR sampling accessory. Raman spectra were recorded on a
Perkin-Elmer Spectrum 2000R NIR FT-Raman instrument
equipped with a Nd:YAG laser (1064 nm). IR intensities
are given in parentheses as vw = very weak, w = weak,
m = medium, s = strong and vs = very strong. Raman
activities are reported in percentages relative to the most
intense peak and are given in parentheses. Elemental analyses
were performed with a Netsch Simultaneous Thermal Analyzer
STA 429. The thermal behaviour was analysed by differential
scanning calorimetry (SETARAM DSC131 instrument,
calibrated with standard pure indium and zinc) at a heating
rate of b = 5 1C minꢁ1 in closed aluminium containers and
with a nitrogen flow of 20 mL minꢁ1. The reference sample
was a closed aluminium container.
1062(w) 1045(w) 1001(m) 947(m) 895(w) 814(w) 677(w)
617(vs) 575(vw) 566(vw); UV (water, 7.86 10ꢁ5 M, nm): 239
(e = 7904 L molꢁ1 cmꢁ1).
(E)-1,1,4,4-Tetramethyl-2-tetrazenium picrate (3). Com-
pound 1 (780 mL, 0.701 g, 6.04 mmol) was added dropwise
to a suspension of picric acid (1.374 g, 6.00 mmol) in ether
(50 mL) causing the immediate precipitation of a bright yellow
powder and the formation of a bright yellow solution. The
insoluble compound was filtered after stirring for ca. 1 h,
washed with little ether and dried under high vacuum. No
further purification was necessary (1.960 g, 95%).
r (picnometer, 17.4 1C): 1.440 g cmꢁ3; C10H15N7O7 (MW =
345.27 g molꢁ1, calc./found): C 34.78/34.79, H 4.38/4.31,
N 28.40/28.23; DSC (5 1C minꢁ1): two exothermic peaks
(peak 1: sharp, onset: 72.50 1C, peak maximum: 76.64 1C,
DH = ꢁ442.66 J gꢁ1; peak 2: broad, onset: 231.76 1C, peak
maximum: 253.76 1C, DH = ꢁ560.36 J gꢁ1); m/z (–c ESI):
228.1 (76, Aꢁ), 478.9 (17, [A2Na]ꢁ), 708.0 (19), 724.0 (25),
729.8 (78, [A3Na2]ꢁ), 974.7 (100), 1225.5 (15), 1476.1 (4);
m/z (+c ESI): 74.0 (15, [Cat ꢁ N(CH3)2]+), 102.1 (100,
Syntheses
(E)-1,1,4,4-Tetramethyl-2-tetrazene (1). 1 was synthesized
according to a literature procedure.23 C4H12N4 (MW =
116.16 g molꢁ1, calc./found): C 41.35/41.28, H 10.42/10.40,
N 48.23/48.06%; 1H NMR (CDCl3, 400.18 MHz, TMS)
d/ppm: 2.72 (12 H, s, –CH3); Raman v˜/cmꢁ1 (rel. int.):
202(11), 328(10), 372(10), 458(6), 584(5), 897(21), 1036(1),
1090(1), 1142(25), 1240(1), 1290(1), 1395(9), 1415(27),
1443(15), 1473(100), 2777(31), 2822(31), 2853(33), 2883(29),
2962(72), 2999(22), 3088(13); IR v˜/cmꢁ1 (golden gate, rel. int.):
2999(vw) 2961(w) 2857(w) 2822(w) 2788(vw) 1633(vw)
1593(vw) 1469(m) 1441(w) 1399(vw) 1277(m) 1244(w)
1141(m) 1091(vw) 1037(w) 997(vs) 891(w) 822(m) 591(s).
1
[Cat ꢁ CH3]+), 126.9 (18), 201.9 (12), 273.9 (14); H NMR
(DMSO-d6, 400.18 MHz, 25 1C, TMS) d/ppm: 11.51 (s(br),
1 H, –NH), 8.58 (2 H, s, H-aromat.), 3.04 (12 H, s, CH3);
13C{1H} NMR (DMSO-d6, 100.63 MHz, 25 1C, TMS)
d/ppm: 160.9 (1 C, C1), 141.7 (2 C, C2), 125.3 (2 C, C3), 124.5
(1 C, C4), 34.4 (4 C, CH3); Raman v˜/cmꢁ1 (rel. int.): 78(11),
175(6), 193(4), 327(5), 536(1), 823(4), 917(2), 944(2), 1085(2),
1168(7), 1240(1), 1295(33), 1315(100), 1360(2), 1405(1), 1514(2),
1549(7), 1611(2), 2956(2), 2968(1); IR v˜/cmꢁ1 (golden gate, rel.
int.): 3082(w) 3023(w) 2960(w) 2441(w) 1633(w) 1606(m) 1562(m)
1538(m) 1494(m) 1434(m) 1405(w) 1384(m) 1361(m) 1314(s)
1271(vs) 1238(m) 1182(m) 1162(m) 1112(m) 1079(m) 1053(m)
1004(w) 942(w) 913(m) 837(w) 818(w) 791(m) 770(w) 743(m)
721(m) 709(vs) 670(m) 620(m); UV (water, 7.33 10ꢁ5 M, nm):
235 (e = 20 520 L molꢁ1 cmꢁ1).
(E)-1,1,4,4-Tetramethyl-2-tetrazenium chloride (2). Com-
pound 1 (0.238 g, 2.0 mmol) was dissolved in diethyl ether
(4 mL) under exclusion of air to give a slightly yellow solution.
A 2 N ethereal hydrochloric acid solution (1.0 mL, 2.0 mmol)
was added dropwise resulting in a slightly exothermic reaction
and the immediate precipitation of a colorless solid. After the
addition was finished, the reaction mixture was stirred at room
temperature for 10 min and the insoluble material was filtered
under vacuum, washed with diethyl ether (2 ꢂ 2 mL) and dried
under vacuum. The title compound was obtained as a colorless
powder (0.295 g, 97%) and no further purification was necessary.
C4H13N4Cl (MW = 152.63 g molꢁ1, calc./found): C 31.48/31.09,
H 8.58/8.37, N 36.71/36.44; DSC (5 1C minꢁ1): one exothermic
peak (sharp, peak onset: 56.61 1C, peak maximum: 59.67 1C,
DH = ꢁ296.97 J gꢁ1); m/z (FAB+, Xenon, 6 keV, m-NBA
matrix): 117.0 (N4Me4H+); 1H NMR (DMSO-[D6], 400.18 MHz,
TMS) d/ppm: 3.05 (s, 12 H, –CH3), 13.19 (s(br), 1 H, –NH);
13C{1H} NMR (DMSO-d6, 100.63 MHz, 25 1C, TMS)
d/ppm: 33.6 (4 C, CH3); Raman v˜/cmꢁ1 (rel. int.): 78(25),
96(21), 178(11), 245(5), 327(26), 364(7), 426(4), 502(12), 541(5),
620(2), 711(1), 820(3), 898(33), 952(3), 1005(6), 1064(1), 1106(24),
1375(35), 1385(100), 1452(18), 1702(3), 1762(2), 1786(1),
2292(3), 2790(2), 2840(3), 2963(25), 3006(21), 3021(14);
IR v˜/cmꢁ1 (golden gate, rel. int.): 3016(w) 3001(w) 2954(w)
2917(w) 2780(vw) 2526(w) 2492(w) 2356(m) 2274(m) 2121(m)
1487(m) 1456(m) 1446(m) 1433(w) 1414(w) 1397(m) 1380(m)
1357(s) 1297(w) 1229(w) 1188(w) 1177(m) 1129(vw) 1102(w)
(E)-1,1,1,4,4-Pentamethyl-2-tetrazenium iodide (4)50. Com-
pound 1 (1.290 mL, 1.16 g, 9.99 mmol) was loaded in a 10 mL
round-bottom flask and cooled to 0 1C by means of a water/ice
bath. At this point, previously cooled methyl iodide (0.615 mL,
1.42 g, 10.00 mmol) was added dropwise with strong stirring
(careful, very exothermic reaction!). Immediate cloudiness was
observed and a white precipitate formed after a few minutes.
The reaction mixture was stirred for ca. 15 min at 0 1C and the
white precipitate was filtered at this temperature, washed with
ether and vacuum-dried (1.158 g, 45%). Low quality single
crystals were grown by dissolving 4 in dry ethanol and storing
in an ether chamber in the fridge over two weeks. C5H15N4I
(MW = 258.10 g molꢁ1, calc./found): C 23.27/22.94, H 5.86/
5.53, N 21.71/21.09; DSC (5 1C minꢁ1): one exothermic peak
(sharp, peak onset: 52.15 1C, EX. dec.); m/z (ESI+): 46.0
(5, [Me2NH2]+), 60.1 (26, [Me3NH]+), 74.1 (2, [Me2N ꢁ N =
NH2]+), 87.1 (3, [Cat+ ꢁ Me2N]+), 116.1 (10, [Cat+
ꢁ
Me]+), 128.1 (14, Cat+), 219.0 (77, [2 Cat+ ꢁ HN3]+),
233.1 (100, [2 Cat+ ꢁ HN2]+), 247.1 (75, [2 Cat+ ꢁ HN]+),
261.2 (52, [2 Cat+ ꢁ H+]+); m/z (ESIꢁ): 126.9 (37, Iꢁ), 254.8
(12, [2 Iꢁ + H+]ꢁ), 276.8 (19, [2 Iꢁ + Na+]ꢁ), 285.9 (20),
1
299.9 (100), 380.7 (31); H NMR (DMSO-[D6], 400.18 MHz,
c
1646 New J. Chem., 2011, 35, 1640–1648
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011

View Article Online
TMS) d/ppm: 3.12 (s, 9 H, –CH3), 3.49 (s, 6 H, –CH3);
13C{1H} NMR (DMSO-d6, 100.63 MHz, 25 1C, TMS)
d/ppm: 42.4 (3 C, CH3), 38.1 (2 C, CH3); Raman v˜/cmꢁ1 (rel.
int.): 291(13), 343(8), 384(4), 420(4), 495(3), 562(7), 777(9),
825(9), 916(3), 949(1), 966(4), 1106(5), 1145(3), 1251(5),
1304(3), 1364(6), 1396(21), 1427(11), 1444(9), 1475(37), 2730(2),
2762(1), 2791(5), 2840(11), 2945(92), 3008(100), 3018(86);
IR v˜/cmꢁ1 (golden gate, rel. int.): 3071(w) 3010(w) 2945(w)
2356(w) 2182(w) 2168(w) 2042(w) 1963(w) 1946(w) 1704(w)
1629(w) 1598(w) 1555(w) 1482(m) 1461(m) 1439(w) 1407(m)
1385(s) 1361(m) 1299(w) 1261(m) 1229(m) 1139(w) 1113(w)
1101(m) 1049(w) 968(m) 948(m) 908(m) 820(w) 775(m) 746(w)
707(w) 638(w) 589(s) 558(w) 497(w) 473(w) 463(w).
2007, 2025–2030; R. W. Wang, H. Gao, C. Ye, B. Twamley and
J. M. Shreeve, Inorg. Chem., 2007, 46, 932–938.
6 G. Kaplan, G. Drake, K. Tollison, L. Hall and T. Hawkins,
J. Heterocycl. Chem., 2005, 42, 19–27; H. Oestmark, Proceedings
of the 9th Seminar on New Trends in the Research of Energetic
Materials, Institute of Energetic Materials, University of
Pardubice, Czech Republic, April 19–21, 2006.
7 J. Uddin, V. Barone and G. E. Scuseria, Mol. Phys., 2006, 104,
745–749; H. Oestmark, S. Walin and P. Goede, Cent. Eur. J. Energ.
Mater., 2007, 4, 83–108.
8 H. Feuer and A. T. Nielsen, Nitro Compounds, Wiley-VCH,
Weinheim, Germany, 1990.
9 A. T. Nielsen, Nitrocarbons, Wiley-VCH, Weinheim, Germany, 1995.
10 D. E. Chavez, M. A. Hiskey and R. D. Gilardi, Angew. Chem., Int.
Ed., 2000, 39, 1861–1863.
11 A. Hammerl, T. M. Klapotke, H. Noth, M. Warchhold, G. Holl
¨
and M. Kaiser, Inorg. Chem., 2001, 40, 3570–3575.
¨
12 International Conference on Green Propellant for Space Propul-
sion, Noordwijk, The Netherlands, June 20–22, 2001; http://
esamultimedia.esa.int/conferences/01a05/index.html.
Acknowledgements
13 A. K. Sikder and N. Sikder, J. Hazard. Mater., 2004, A112, 1–15.
14 H. Gao, Y. Huang, C. Ye, B. Twamley and J. M. Shreeve,
Chem.–Eur. J., 2008, 14, 5596–5603.
Financial support by the Centre Nationale de la Recherche
´
Scientifique (CNRS), the Centre Nationale d’Etudes Spatiales
15 (a) T. M. Klapoetke, P. Mayer, A. Schulz and J. J. Weigand,
Propellants, Explos., Pyrotech., 2004, 29, 325; (b) J. Heppekausen,
(CNES), the Societe Nationale des Poudres et des Explosifs
´
(SNPE) and the University Claude Bernard of Lyon are
gratefully acknowledged.
T. M. Klapotke and S. M. Sproll, J. Org. Chem., 2009, 74,
¨
D. Blaser, Z. Naturforsch., B: Chem. Sci., 2002, 57, 365–376;
¨
2460–2466; (c) B. Porath, P. Rademacher, R. Bose and
¨
(d) B. Rose, D. Schollmeyer and H. Meier, Liebigs Ann./Recl.,
1997, 409–412.
16 B. Porath, R. Munzenberg, P. Heymans, P. Rademacher, R. Bose,
¨
references therein.
17 W. E. Bull, H. A. Seaton and L. F. Audrieth, J. Am. Chem. Soc.,
1958, 80, 2516–2518.
Notes and references
¨
D. Blaser and R. Latz, Eur. J. Org. Chem., 1998, 1431–1440 and
1 T. M. Klapotke, P. Mayer, C. Miro
´
Sabate
N. Wiegand, Inorg. Chem., 2008, 47(13), 6014–6027;
T. M. Klapotke, C. Miro Sabate and J. Stierstorfer, Z. Anorg.
Allg. Chem., 2008, 11, 1867–1874; M. von Denffer, T. M. Klapotke
´
, J. M. Welch and
¨
´
´
¨
¨
18 N. Wiberg, H. Bayer and H. Bachhuber, Angew. Chem., 1975,
87(6), 202–203; N. Wiberg, H. W. Haering and S. K. Vasisht,
Z. Naturforsch. B: Anorg. Chem. Org. Chem., 1979, 34(2), 356–357.
19 A. F. Holleman, E. Wiberg and N. Wiberg, Lehrbuch der
Anorganischen Chemie, Walter de Gruyter, Berlin, Germany,
101st edn, 1995.
20 F. O. Rice and C. J. Grelecki, J. Am. Chem. Soc., 1957, 79(11),
2679–2680.
21 R. A. Rowe and L. F. Audrieth, J. Am. Chem. Soc., 1956, 78(3),
563–564.
22 H. H. Sisler, M. A. Mathur, S. R. Jain and R. Greengard, Ind. Eng.
Chem. Prod. Res. Dev., 1981, 20, 181–185.
23 L. J. Madgzinski, K. S. Pillay, H. Richard and Y. L. Chow, Can. J.
Chem., 1978, 56, 1657–1667 and references therein.
24 W. McBride and H. W. Kruse, J. Am. Chem. Soc., 1957, 79(3),
572–577.
and C. Miro
T. M. Klapo
2009, 1825–1834; T. M. Klapotke and C. Miro
´
Sabate
´
, Z. Anorg. Allg. Chem., 2008, 634, 2575–2582;
Sabate and M. Rasp, Dalton Trans.,
Sabate, Dalton
Trans., 2009, 1835–1841; M. Ebespacher, T. M. Klapotke and
´
´
¨
tke, C. Miro
´
´
¨
¨
¨
C. Miro
´
Sabate
´
,
Helv. Chim. Acta, 2009, 92, 977–996;
Sabate and J. M. Welch, Eur. J. Inorg.
Chem., 2009, 769–776; M. Ebespacher, T. M. Klapotke and
T. M. Klapotke, C. Miro
´
´
¨
¨
¨
C. Miro Sabate, New J. Chem., 2009, 33, 517–527; H. Delalu,
´ ´
, Cent. Eur.
K. Karaghiosoff, T. M. Klapotke and C. Miro
´
Sabate
´
¨
J. Energ. Mater, 2010, 7(3), 115–129.
2 T. M. Klapotke, P. Mayer, A. Schulz and J. J. Weigand,
¨
Propellants, Explos., Pyrotech., 2004, 29, 325–332; D. L. Strout,
J. Phys. Chem. A, 2004, 108, 10911–10916; M. H. V. Huynh,
M. A. Hiskey, E. L. Hartline, D. P. Montoya and R. Gilardi,
Angew. Chem., 2004, 116, 5032–5036 (Angew. Chem., Int. Ed.,
2004, 43, 4924–4928); R. Haiges, S. Schneider, T. Schroer and
K. O. Christe, Angew. Chem., 2004, 116, 5027–5032 (Angew.
Chem., Int. Ed., 2004, 43, 4919–4924).
25 W. H. Urry, P. Szecsi and D. W. Moore, J. Am. Chem. Soc., 1964,
86(11), 2224–2229.
26 S. N. Singh and R. K. Prasad, J. Indian Chem. Soc., 1992, 69(10),
648–650.
3 R. P. Singh, R. D. Verma, D. T. Meshri and J. M. Shreeve, Angew.
Chem., 2006, 118, 3664–3682 (Angew. Chem., Int. Ed., 2006, 45,
27 W. R. McBride and H. W. Kruse, US Pat., 3 135 800, 1952.
28 Method A: hold temperature at 90 1C for 1 min, then heat at
2 1C minꢁ1 to 130 1C.
3584–3601); T. M. Klapotke, Structure and Bonding, Springer,
¨
Berlin/Heidelberg, Germany, 2007; G. Drake, US Pat., 6 509
473, 2003; V. A. Dulles and G. Drake, AFOSR Ionic Liquids
Workshop, Aberdeen, MD, 2003.
29 (a) T. M. Klapotke and C. Miro
´
Sabate
´
, Z. Anorg. Allg. Chem.,
¨
2008, 634, 1017–1024; (b) T. M. Klapotke and C. Miro
´
Sabate,
´
¨
4 T. Abe, Y.-H. Joo, G.-H. Tao and J. M. Shreeve, Chem.–Eur. J.,
2009, 15, 4102–4110; Y.-H. Joo and J. M. Shreeve, Eur. J. Org.
Chem., 2009, 3573–3578; G.-H. Tao, Y.-H. Joo, B. Twamley and
J. M. Shreeve, J. Mater. Chem., 2009, 19, 5850–5854; Y. Guo,
G.-H. Tao, Z. Zeng, H. Gao and J. M. Shreeve, Chem.–Eur. J.,
2010, 16, 3753–3762; G.-H. Tao, Y. Guo, D. A. Parrish and
J. M. Shreeve, J. Mater. Chem., 2010, 20, 2999–3005; Y.-H. Joo
and J. M. Shreeve, Angew. Chem., Int. Ed., 2010, 49, 7320–7323;
Y.-H. Joo and J. M. Shreeve, J. Am. Chem. Soc., 2010, 132,
15081–15090.
Eur. J. Inorg. Chem., 2008, 5350–5366.
30 (a) K. Karaghiosoff, T. M. Klapotke, P. Mayer, C. Miro
´
Sabate
A. Penger and J. M. Welch, Inorg. Chem., 2008, 47, 1007–1019;
(b) C. Darwich, T. M. Klapotke and C. Miro Sabate, Chem.–Eur. J.,
2008, 14, 5756–5771; (c) T. M. Klapotke, C. Miro Sabate, A. Penger,
´
,
¨
´
´
¨
´
´
¨
M. Rusan and J. M. Welch, Eur. J. Inorg. Chem., 2009,
880–896.
31 F. R. Benson, The High Nitrogen Compounds, Wiley, New York,
1984.
32 N. B. Colthup, L. H. Daly and S. E. Wiberley, Introduction to
Infrared and Raman Spectroscopy, Academic Press, Boston, USA,
1990.
33 N–N and NQN bond lengths from: International Tables for X-ray
Crystallography, Kluwer Academic Publishers, Dordrecht, 1992,
vol. C.
5 H. Gao, C. Ye, R. W. Winter, G. L. Gard, M. E. Sitzmann and
J. M. Shreeve, Eur. J. Inorg. Chem., 2006, 3221–3226; Y. Gao,
C. F. Ye, B. Twamley and J. M. Shreeve, Chem.–Eur. J., 2006, 12,
9010–9018; G. Gao, R. Wang, B. Twamley, M. A. Hiskey and
J. M. Shreeve, Chem. Commun., 2006, 4007–4009; Y. Huang,
H. Gao, B. Twamley and J. M. Shreeve, Eur. J. Inorg. Chem.,
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
New J. Chem., 2011, 35, 1640–1648 1647

View Article Online
34 T. M. Klapotke and C. Miro
´
Sabate
´
, Chem. Mater., 2008, 20(5),
Sabate, Chem. Mater.,
2008, 20(11), 3629–3637; T. M. Klapotke and C. Miro Sabate, New
43 Crystal structure solution and refinement: formula = C8H10N4O7,
MW=274.18 g molꢁ1, T = 100(2) K, cryst. syst. = orthorhombic,
space gr. = Pb2a, a = 9.989(1) A, b = 11.085(1) A, c = 21.314(1) A,
¨
1750–1763; T. M. Klapotke and C. Miro
´
´
¨
´
´
¨
V = 2360.1(4) A3, Z = 8, r = 1.544 g cmꢁ3, m = 0.352 cmꢁ1
,
J. Chem., 2009, 33, 1605–1617.
35 B. Kovacevic, Z. B. Maksic and P. Rademacher, Chem. Phys.
Lett., 1998, 293, 245–250.
36 G. S. Hammond, B. Seidel and R. E. Pincock, J. Org. Chem., 1963,
28, 3275–3279.
F(000) = 780 e, y range = 3.82–29.601, hkl range = ꢁ10 r h r 10,
ꢁ9 r k r 9 and ꢁ11 r l r 11, refl. meas. = 7345, refl. unique =
1378, Rint
= = 0.0502/0.0937,
0.033, R(F)/wR(F2) (all refl.)
GoF (F2) = 0.9963.
37 M. D. Walkinshaw, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun., 1986, 42, 246–249.
44 M. C. Etter and J. C. MacDonald, Acta Crystallogr., Sect. B:
Struct. Sci., 1990, 46, 256–262; J. Bernstein, R. E. Davis,
L. Shimoni and N. L. Chang, Angew. Chem., 1995, 107,
1689–1708 (Angew. Chem., Int. Ed. Engl., 1995, 34, 1555).
45 http://www.ccdc.cam.ac.uk/suport/documentation/rpluto/TOC.html.
46 A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
47 C. Lee, W. Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785.
48 E. D. Glendening, A. E. Reed, J. E. Carpenter and F. Weinhold,
Gaussian 03, Revision, D.01, Gaussian, Inc., Wallingford, CT,
2004.
38 CrysAlis CCD, Version 1.171.27p5 beta; Oxford Diffraction Ltd.
39 CrysAlis RED, Version 1.171.27p5 beta; Oxford Diffraction Ltd.
40 SIR-92, A program for crystal structure solution: A. Altomare,
G. Cascarano, C. Giacovazzo and A. Guagliardi, J. Appl. Crystallogr.,
1993, 26, 343; G. M. Sheldrick, SHELXS-97, Program for Crystal
Structure Solution, University of Gottingen, Germany, 1994;
¨
G. M. Sheldrick, SHELXS-97, Program for Crystal Structure Solution,
University of Gottingen, Germany, 1997.
¨
41 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837.
42 SCALE3 ABSPACK—An Oxford Diffraction program, Oxford
Diffraction Ltd., 2005.
49 A. P. Scott and L. Radom, J. Phys. Chem., 1996, 100, 16502.
50 W. H. Bruning, C. J. Michejda and D. Romains, Chem. Commun.,
1967, 11–12.
c
1648 New J. Chem., 2011, 35, 1640–1648
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011