Synthesis and comparison of copper(ii) complexes with various: N -aminotetrazole ligands involving trinitrophenol anions

Article abstract of DOI:10.1039/c9nj03937f

Due to the ongoing research on lead-free energetic materials, two different ligand systems (1-amino-5H-tetrazole (1-AT), 2-amino-5H-tetrazole (2-AT), 1-amino-5-methyltetrazole (1-AMT), and 2-amino-5-methyltetrazole (2-AMT)) were applied for the synthesis of 12 new energetic coordination compounds (ECC) with copper(ii) as the central metal. Different anions based on trinitrophenols (picric acid (HPA), styphnic acid (H₂TNR), and trinitrophloroglucinol (H₃TNPG)) were used for the specifical tuning of the energetic and physico-chemical properties of the complexes. Through the choice of ligand, the characteristics of the resulting products can be easily adjusted either towards sensitive primary explosives usable for classical initiation setups or towards laser-ignitable explosives with decreased sensitivities. The ECC were extensively characterized by e.g., X-ray diffraction (XRD), elemental analysis (EA), IR, differential thermal analysis (DTA), and UV/vis. In addition, the most promising compounds were analyzed by TGA and in classical initiation tests using nitropenta (PETN). Furthermore, the sensitivities towards external stimuli (impact, friction, and electrostatic discharge) were determined by standard methods and the influence of the anions towards them was investigated. Compounds [Cu(TNR)(1-AMT)₂] and [Cu(HTNPG)(1-AMT)₂] both possess appropriate sensitivities as well as thermal stabilities above 200 °C and show promising results to be used as potential lead azide replacements. In addition, all ECC were irradiated with a near infrared light (NIR) laser diode leading to different responses.

Full text of DOI:10.1039/c9nj03937f

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Synthesis and comparison of copper(II) complexes
with various N-aminotetrazole ligands involving
trinitrophenol anions†‡
Cite this: New J. Chem., 2019,
43, 18193
Maximilian H. H. Wurzenberger,
Benjamin R. G. Bissinger,
Marcus Lommel,
Michael S. Gruhne, Norbert Szimhardt
and Jorg Stierstorfer
*
¨
Due to the ongoing research on lead-free energetic materials, two different ligand systems (1-amino-
5H-tetrazole (1-AT), 2-amino-5H-tetrazole (2-AT), 1-amino-5-methyltetrazole (1-AMT), and 2-amino-5-
methyltetrazole (2-AMT)) were applied for the synthesis of 12 new energetic coordination compounds
(ECC) with copper(II) as the central metal. Different anions based on trinitrophenols (picric acid (HPA),
styphnic acid (H2TNR), and trinitrophloroglucinol (H3TNPG)) were used for the specifical tuning of the
energetic and physico-chemical properties of the complexes. Through the choice of ligand, the
characteristics of the resulting products can be easily adjusted either towards sensitive primary
explosives usable for classical initiation setups or towards laser-ignitable explosives with decreased
sensitivities. The ECC were extensively characterized by e.g., X-ray diffraction (XRD), elemental analysis
(EA), IR, differential thermal analysis (DTA), and UV/vis. In addition, the most promising compounds were
analyzed by TGA and in classical initiation tests using nitropenta (PETN). Furthermore, the sensitivities
towards external stimuli (impact, friction, and electrostatic discharge) were determined by standard
methods and the influence of the anions towards them was investigated. Compounds [Cu(TNR)(1-AMT)2]
and [Cu(HTNPG)(1-AMT)2] both possess appropriate sensitivities as well as thermal stabilities above
200 1C and show promising results to be used as potential lead azide replacements. In addition, all ECC
were irradiated with a near infrared light (NIR) laser diode leading to different responses.
Received 30th July 2019,
Accepted 28th October 2019
DOI: 10.1039/c9nj03937f
rsc.li/njc
Introduction
The energetic character of many nitroaromatic compounds
derives from the oxidation of the carbon-backbone and the
circumstance that these substances combine both the fuel (C–H
backbone) and the oxidizer (nitro groups) within one molecule.
As a result of this, selected polynitroaromatics can be used as
explosives, most notably trinitrotoluene (TNT).1 A close structural
relative of TNT is picric acid (HPA, 1) (Chart 1), which was
discovered in the form of its potassium salt by Johann Glauber
in 1742.2
Chart 1 Trinitrophenols picric acid (1), styphnic acid (2) and trinitrophloro-
glucinol (3).
The compound was obtained via treatment of wool or horn
with HNO3 and has since been applied as a dye for silk, and,
due to its intensely bitter taste and tinctorial power, as a
replacement for hops in beer. However, it wasn’t until more
than 100 years later that German chemist Hermann Sprengel
demonstrated that picric acid could be brought to detonation,
and therefore filed the related patents. Following this, HPA
replaced black powder in nearly all military applications.2–4
Styphnic acid (H2TNR, 2) and 2,4,6-trinitrophloroglucinol
(H3TNPG, 3) derive structurally from picric acid and have a
wide history of military applications together with their metal
salts. The most prominent is lead styphnate (LS), a rather
sensitive and highly toxic primary explosive. Together with lead
Department of Chemistry, Ludwig Maximilian University of Munich, Butenandtstr.
5-13, D-81377 Munich, Germany. E-mail: jstch@cup.uni-muenchen.de;
Web: http://www.cup.lmu.de/ac/stierstorfer/, http://www.hedm.cup.uni-muenchen.de;
Fax: +49-89-2180-77492
† Parts of this work were presented at the 22nd Seminar on New Trends in Research
of Energetic Materials 2019 at the University of Pardubice (Czech Republic).
‡ Electronic supplementary information (ESI) available: Compound overview; IR
spectroscopy; X-ray diffraction; TGA plots of 6, 8, 11–13, and 16; DTA plots of 4b,
5b, and 6–17; column diagrams of the complexes; hot plate and hot needle tests;
laser ignition tests; UV-vis spectra of 6–14a and 15–17; experimental part and
general methods. CCDC 1934798–1934813. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c9nj03937f
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Fig. 1 Schematic overview of the formation of either complex monomers (left) or polymeric structures (right) caused by the deprotonation level of the
nitroaromatic anions.
azide (LA), LS has been employed since the beginning of the
The linking of the anions allows the formation of polymeric
20th century and was originally developed as a replacement for structures with varying properties such as increased thermal
mercury fulminate.2,5 One major drawback of the highly acidic stabilities.
compounds 1–3 is their potential to corrode metal shells, along
Recently, our research group published several of the most
with the formation of the corresponding highly sensitive metal powerful ECC available, based on 1-amino-5H-tetrazole (1-AT)
salts. This process significantly lowers the manageability of and 2-amino-5H-tetrazole (2-AT), in combination with highly
such explosives and is known to have caused fatal accidents.6
oxidizing anions such as perchlorate and nitrate.25 Some of the
With LA and LS still being the most predominantly used most auspicious of these candidates combine excellent energetic
primary explosives e.g., in small arms ammunition, people in properties with good thermal stabilities and low environmental
frequent contact with firearms and commercial applications toxicities, however, the highly endothermic aminotetrazole
(mining, deconstruction works, etc.) are at high risk of chronic ligands and oxidizing anions induce extreme sensitivities to
damage due to heavy metal poisoning. A recent study revealed various mechanical stimuli. This diminishes their applicability
elevated blood lead levels in regular visitors of shooting ranges, as primary explosives in classical, as well as optical initiation
accredited to the discharge of lead upon firing a gun. The systems. To manage the excessive energetic capacities and
adverse health effects associated with shooting are especially sensitivities of 1-AT and 2-AT based ECC, we replaced the
critical to women and children, relating to the impact on future common anions nitrate and perchlorate with nitroaromatic
generations.7 In order to reduce or even prevent the use of toxic mono- and dianions of 1–3. Furthermore, an additional methyl
explosives, scientists all around the world are focusing on the group was introduced at the 5-position of the ligands (1-amino-
development of new substances with superior properties.8–15 5-methyltetrazole (1-AMT) and 2-amino-5-methyltetrazole (2-AMT))
One very promising concept for replacing toxic primary explosives to further stabilize the system by lowering the enthalpies of
which has gained increasing attention in recent years is focused formation (Fig. 2).
on the laser ignition of energetic materials. By combining the right
This extensive study describes the effect of various N-amino-
building blocks, this approach could ensure lifelong economic tetrazole ligands on nitroaromatic copper(II) complexes and
efficiency with environmentally friendly disposal management. At
the same time, it can increase safety by allowing the application of
less sensitive explosives.16 3D Metal coordination compounds with
trinitrophenolates of 1–3 as counteranions are known in the litera-
ture for only a few tetrazole derivatives, especially TNPG-based
anions are rather uncommon. Copper(II) complexes have a unique
position among these described compounds since in every single
example the anions coordinate to the central metal and thus in
almost all cases anhydrous compounds are obtained. Especially, the
nitroaromatic complexes based on Mn(II), Co(II), Ni(II) and Zn(II) have
a high tendency to incorporate aqua ligands, crystal water molecules
or even both of them.17–23 Another characteristic of styphnic acid
and trinitrophloroglucinol is their ability to work either as singly or
multiply deprotonated anions and it has also been shown that
Fig. 2 Comparison of the calculated enthalpies of formation for several
N-substituted monotetrazoles showing decreased values for AMT ligands
within one ligand system both cases can be obtained. A great
advantage of the twofold deprotonation of trinitrophenols is their
potential to bridge different metal centres. In contrast, abstraction of
a single proton usually leads to complex monomers (Fig. 1).24
compared to AT. Gas phase enthalpies of formation were calculated using the
P
P
atomization method (DfH0(g,M) = H(M)
computed CBS-4M electronic enthalpies.
–
H0(A)
+
DfH0(A)) using Gaussian09
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their selective potential to be used as either laser ignitable
explosives or as classical lead-free primary explosives for the
initiation of PETN (nitropenta). Furthermore, the influence of the
level of deprotonation as well as the number of hydroxy groups in
the anions towards the properties of the ECC is compared.
Results and discussion
Synthesis
Fig. 4 Proton coupled 15N NMR spectra of 5b.
1-AMT (4b) and 2-AMT (5b) were prepared in accordance with
the synthesis25 of 4a and 5a via nucleophilic amination of
commercially available 5-methyl-1H-tetrazole with hydroxylamine-
O-sulfonic acid under basic conditions, giving the isomers 4b and
5b in 33% and 25% yield, respectively (Scheme 1). Due to the
positive inductive effect of the additional methyl group, which
increases the nucleophilicity of the electron-poor heterocycle, the
overall yield of the reaction could be increased compared to the
amination of unsubstituted tetrazole (58% vs. 46%).
In analogy to 4a, 1-AMT can be obtained directly and isomerically
pure via a simple and scalable three-step reaction.25 The synthesis is
initiated by the condensation of benzaldehyde and hydrazine
hydrate, followed by [3+1+1] cyclization with sodium azide and
triethyl orthoacetate, which generates the 5-methyltetrazole-moiety
(4b_pro). Cleavage under acidic conditions followed by water steam
distillation furnishes the ligand 4b in a relatively low yield of 18%
(Scheme 2).
achieved by reaction of copper(II) carbonate with the respective
acid 1–3 in aqueous medium at elevated temperatures. In the
case of amino-5H-tetrazole derivates, each of the performed
syntheses was carried out by slow addition of an aqueous
solution of the ligand to the respective solution of metal(II) salt
at 80 1C (Schemes 3 and 4). After continuous stirring of the
particular reaction mixture, the solutions were left for crystal-
lization at room temperature. After a few days, the compounds
were filtered off, washed with ethanol and dried in air. This
synthetic strategy can easily be performed on a large scale and
the products can be isolated almost quantitatively if the solvent
of the reaction mixture is removed by rotary evaporation.
Synthesis of the analogous AMT-based complexes 12–17
proceeded identically (Schemes 5 and 6), the only noteworthy
divergence being the immediate precipitation of green and
brown solids during the synthesis of compounds 13 and 14a,
respectively. Both compounds form polymeric structures that
arise from the twofold deprotonation of the corresponding
anions (13: styphnate, 14a: 5-hydroxy-2,4,6-trinitroresorcinate)
leading to bridging between different central metals, which
significantly reduces their water solubility. All other isolated
AMT-complexes were obtained after crystallisation from the
mother liquor within a few days. After formation, the products
were filtered off, washed with ethanol and dried in air. Even
though final products 13 and 14a are formed of only one
The isomers 4b and 5b can easily be differentiated by IR (Fig. S1,
ESI‡) or by 1H and 13C NMR spectroscopy. Furthermore, proton
coupled 15N NMR measurements were performed for both
compounds (Fig. 3 and 4).
The synthesis of ECC 6–17 starts with the in situ generation
of the copper(II) salt of the required trinitrophenol, which is
Scheme 1 Synthesis of aminotetrazole ligands 4 and 5 by amination of
1H-tetrazole with hydroxylamine-O-sulfonic acid (HOSA).
Scheme 3 Synthesis of copper(II) picrate, 3-hydroxy-2,4,6-trinitrophenolate
and 3,5-dihydroxy-2,4,6-trinitrophenolate complexes 6–8 of 1-AT (4a).
Scheme 2 Selective synthesis of 1-amino-5-methyltetrazole (1-AMT, 4b).
Scheme 4 Synthesis of the ECC 9–11 based on 2-amino-5H-tetrazole
(2-AT, 5a).
Fig. 3 Proton coupled 15N NMR spectra of 4b.
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The crystal datasets were uploaded to the CSD database26 and
can be obtained free of charge with the CCDC 1934808 (4_pro),
1934810 (4b), 1934799 (6), 1934801 (7), 1934798 (8), 1934809 (9),
1934811 (10), 1934812 (11), 1934806 (12), 1934805 (13), 1934803 (14a),
1934807 (14b), 1934813 (14c), 1934800 (15), 1934802 (16), and
1934804 (17). All complexes, except side species 14b, show
octahedral coordination spheres around the copper(II) central
cations with typical Jahn–Teller distortions along the axial
Scheme 5 Synthesis of copper(II) picrate (PA), styphnate (TNR) and 2,4,6-
trinitrophloroglucol-based (HTNPG/H2TNPG) complexes of 1-amino-5- O–Cu–O axes. In every structure, the ligands are solely coordi-
methyltetrazole (1-AMT, 4b).
nated through the N4 nitrogen atom of the tetrazole rings. In
almost all compounds electrostatic intermolecular interactions
can be observed, leading to specific orientations of the nitro
groups of the phenolate anions. Normally the nitro groups of
the trinitrophenols are aligned with the aromatic system, while
nitro–nitro interactions between different anions twist one or
two of the functional groups in the complexes. This perpendi-
cular arrangement of nitro groups enables the electrostatic
interaction of the vertical p-orbital with the oxygen atom of a
second nitro group. The distances ONitro–p(N)Nitro in the crystal
Scheme 6 Synthesis of ECC 15–17 based on 2-amino-5-methyltetrazole
(2-AMT, 5b).
structures lie in the typical range of nitro–nitro interactions
described in the literature.27
Similar to 4a,25 tetrazole 4b crystallises in the orthorhombic
equivalent of the corresponding anions, for complete reaction
of copper(II) carbonate twice the amount of free acid is
required. Interestingly, the formation of a second (14b) and a
third (14c) species during the reaction of copper(II) carbonate,
trinitrophloroglucinol and 1-AMT was observed.
space group P212121 with four formula units per unit cell and a
slightly lower calculated density of 1.420 g cmÀ3 at 143 K. This
relatively significant difference in density arises from the
presence of the methyl group in 4b, preventing closer packing
due to the increased steric hindrance (Fig. 5). It crystallises
in the form of colourless blocks and all non-hydrogen atoms
lie within a plane with torsion angles close to 01 (C1–N1–
N2–N3 1.25(15)1, N5–N1–C1–C2 À2.2(2)1, and N2–N1–C1–N4
À1.13(16)1). The bond angles and lengths lie within the range
of typical values for tetrazole compounds and differ only
slightly from 1-AT.
Picrate compounds 6 (green platelets) and 12 (green blocks)
crystallise in similar monoclinic space groups P21/c and P21/n with
calculated densities of 1.952 g cmÀ3 and 1.786 g cmÀ3 at 143 K,
respectively. The slightly distorted octahedral coordination
spheres – 12 shows a stronger deviation than 6 – around the
Single crystal experiments reveal the composition of two
different aqua complexes [Cu(1-AMT)4(H2O)](H2TNPG)2 (14b)
and [Cu(H2TNPG)(1-AMT)2(H2O)2](H2TNPG) (14c) with only singly
deprotonated anions (3,5-dihydroxy-2,4,6-trinitrophenolate). The
dark green needles of 14a crystallised quickly from the filtrate
and accumulated on the inner walls of the crystallisation vessel.
Contrary to 14a, however, 14b turned out to be extremely water-
soluble, which prevented the execution of further analytical
investigation, because sufficient amounts could not be isolated.
Similar to 14b, 14c is highly water soluble and some single
crystals could only be obtained after complete desiccation of the
filtrate of 14a. To the best of our knowledge, 14b and 14c are the
first copper(II) complexes with non-coordinating counteranions
based on trinitrophenols of 1–3.
Compared to the anhydrous compounds 6–11 it becomes
clear that the AMT ligands slightly increase the hydrophilicity
of the formed products and thus the formation of complexes
with aqua ligands (14b and 14c), crystal water molecules (12) or
even both of them (16) can partly be observed.
Crystal structures
Nitrogen-rich ligand 4b and its precursor 4b_pro, as well as all
ECC, were investigated by low-temperature single crystal X-ray
diffraction. In contrast to their 1-amino isomers, 2-AT (5a) and
2-AMT (5b) were not able to be crystallised, even when subjected to
liquid nitrogen. The crystal structure of ligand 4a has already been
published;25 the results of the crystallographic analysis of 4b_pro
(Fig. S4, ESI‡) are given in the ESI,‡ together with the measurement
Fig. 5 Molecular unit (left) and unit cell (right) of 1-AMT (4b). Thermal
ellipsoids of nonhydrogen atoms in all structures are set to the 50% probability
level. Selected bond lengths (Å): N1–N2 1.3482(16), N1–N5 1.3908(17),
N1–C1 1.3341(18), N2–N3 1.2959(19), N3–N4 1.3648(19), N4–C1 1.3206(19);
selected bond angles (1): N2–N1–N5 123.54(11), N2–N1–C1 109.92(12),
and refinement data of all experiments (Tables S1–S4, ESI‡). N5–N1–C1 126.53(12), N3–N4–C1 106.14(12), N4–C1–C2 127.78(13).
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Fig. 7 Molecular unit of [Cu(HTNR)2(1-AT)2] (7) (left) and the copper(II)
coordination environment of [Cu(TNR)(1-AMT)2] (13) (right). Selected bond
lengths (Å) of 7: Cu1–O1 2.316(3), Cu1–O3 1.962(2), Cu1–N1 1.998(3);
selected bond angles (1) of 7: O1–Cu1–O3 81.17(10), O1–Cu1–N1 87.63(12),
O3–Cu1–N1 90.00(11). Symmetry code of 7: (i) 2 À x, 1 À y, 1 À z. Selected
bond lengths (Å) of 13: Cu1–O1 1.958(5), Cu1–O8 2.515(6), Cu1–N5 1.994(6),
Cu1–N10 2.010(6); selected bond angles (1) of 13: O1–Cu1–O8 72.54(16),
O1–Cu1–N5 86.0(2), O1–Cu1–N10 167.1(2), N5–Cu1–N10 94.7(2). Sym-
metry code of 13: (i) 1 À x, 2 À y, 0.5 + z.
Fig. 6 Molecular unit of [Cu(PA)2(1-AT)2] (6) (left) and segment of the unit
cell of [Cu2(PA)4(1-AMT)4]ÁH2O (12) (right). Selected bond lengths (Å) of 6:
Cu1–O1 1.918(3), Cu1–O7 2.338(3), Cu1–N4 2.010(3); selected bond
angles (1) of 6: O1–Cu1–O7 78.92(10), O1–Cu1–N4 90.18(12), O7–Cu1–
N4 86.01(11). Symmetry code of 6: (i) 2 À x, Ày, 2 À z. Selected bond
lengths (Å) of 12: Cu1–O2 2.467(3), Cu1–O8 1.946(3), Cu1–N4 1.972(3),
Cu1–N9 1.995(3); selected bond angles (1) of 12: O1–Cu1–O2 74.07(11),
O1–Cu1–N4 90.31(13), O1–Cu1–N9 171.19(13), N4–Cu1–N9 89.82(14).
copper(II) central cations in both crystal structures show similar
compositions. The central metals are surrounded by two mono-
dentate tetrazole ligands and two chelating picrate anions.
[Cu(PA)2(1-AT)2] (6) represents a centrosymmetric unit in itself with
trans coordinating 1-AT ligands, while in [Cu2(PA)4(1-AMT)4]ÁH2O
(12) the pairs of ligand molecules and picrate anions each
occupy adjacent coordination sites (Fig. 6). The molecular unit
of picrate 12 is a dimer consisting of two of the previously
described asymmetric units and an additional crystal water
molecule, where the coordinating picrate anions are facing
each other in the centre of the unit and are twisted against
each other at angles of approximately 901.
Complexes 7 and 13, based on 2,4,6-trinitroresorcinol, crystallise
in the monoclinic and orthorhombic space groups P21/c and Pna21
as green platelets and needles, respectively. Their calculated den-
sities of 1.905 g cmÀ3 and 1.887 g cmÀ3 at 143 K vary only slightly.
Except for the crystal water molecule, the compounds’ chemical
building blocks and the arrangement of those are comparable
to those of the analogue picrate complexes 6 and 12. ECC 7
forms complex monomers with a highly symmetrical structure,
in which 1-AT and anionic 3-hydroxy-2,4,6-trinitrophenolate
ligands oppose each other.
1.891 g cmÀ3 (143 K), respectively. The crystal structure of 8 is
composed of four neutral 1-AT ligands and two 3,5-dihydroxy-
2,4,6-trinitrophenolate monoanions around octahedrally coordi-
nated copper(II) centres. The singly deprotonated anions are
monodentate and are building up the Jahn–Teller distorted along
the axial O1–Cu–O1i axis (Fig. 8). All equatorial positions are
occupied by tetrazole derivatives, which form hydrogen bonds
with their amino function to nitro groups of the anions and
tetrazole rings of neighbouring complex monomers. The primary
species obtained from copper(II) carbonate, trinitrophloro-
glucinol and 1-AMT, [Cu(HTNPG)(1-AMT)2] (14a), crystallises
isotypically to 13 with similar cell axes, density, and cell volume.
Again, the double deprotonation leads to higher distortion and
the formation of polymeric 1D chains. The coordination polymer
is otherwise almost identical to 13.
The side species 14b and 14c both crystallise as green rods in
monoclinic space groups (P21/c and P21/n) with calculated densities
of 1.798 g cmÀ3 (143 K) and 1.948 g cmÀ3 (111 K), respectively.
While 14b shows a rare square pyramidal coordination sphere
around the copper(II) centre, the coordination sphere of 14c is a
In fact, both coordinating molecules of 1-AT lie in the same
plane and are aligned perfectly parallel, the singly deprotonated
anions span two parallel planes. In 1-AMT-based compound 13
the pairs of ligand molecules and styphnate anions again occupy
adjacent coordination sites (Fig. 7). The twofold deprotonation of
styphnic acid in 13 leads to the formation of 1D-polymeric
chains, in which each dianion bridges between two copper(II)
centres. The monoanions existent in 7 are not suitable for linking
between metal centres as they only possess a single coordination
site, and thus two of them are required per formula unit.
Comparing the styphnate complexes 7 and 13 with the
Fig. 8 Molecular unit of [Cu(H2TNPG)2(1-AT)4] (8) (left) and the copper(II)
coordination environment of [Cu(HTNPG)(1-AMT)2] (14a) (right). Selected
analogous trinitrophloroglucinol-based compounds, it becomes bond lengths (Å) of 8: Cu1–O1 2.348(4), Cu1–N4 2.015(5), Cu1–N9 1.986(5);
selected bond angles (1) of 8: O1–Cu1–N4 87.64(17), O1–Cu1–N9 96.28(17),
clear that the complexation of the central metal is different
in the case of 8 and almost identical for 14a. They crystallise
in the monoclinic space group P21/n (8) as green-yellow
N4–Cu1–N9 91.1(2). Symmetry code of 8: (i) 1 À x, 1 À y, 1 À z. Selected
bond lengths (Å) of 14a: Cu1–O1 1.933(4), Cu1–O2 2.252(5), Cu1–N4 1.985(6),
Cu1–N9 2.007(6); selected bond angles (1) of 14a: O1–Cu1–O2 81.56(18),
rods and orthorhombic space group Pna21 (14a) as brown
O1–Cu1–N4 171.7(2), O1–Cu1–N9 90.8(2), N4–Cu1–N9 95.5(2). Symmetry
needles with calculated densities of 1.928 g cmÀ3 (173 K) and code of 14a: (i) 1 À x, 1 À y, À0.5 + z.
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Fig. 10 Molecular unit of [Cu(PA)2(2-AT)2] (9) (left) and [Cu(PA)2(2-AMT)2]
(15) (right). Selected bond lengths (Å) of 9: Cu1–O1 2.321(2), Cu1–O3
1.941(2), Cu1–N4 1.982(3); selected bond angles (1) of 9: O1–Cu1–O3
80.03(9), O1–Cu1–N4 87.69(10), O3–Cu1–N4 92.42(10). Symmetry code
of 9: (i) Àx, 1 À y, 1 À z. Selected bond lengths (Å) of 15: Cu1–O1 1.933(2),
Cu1–O2 2.335(2), Cu1–N4 2.003(2); selected bond angles (1) of 15:
O1–Cu1–O2 80.73(8), O1–Cu1–N4 89.67(9), O2–Cu1–N4 88.15(9).
Fig. 9 Molecular units of side species [Cu(1-AMT)4(H2O)](H2TNPG)2 (14b)
(left) and [Cu(H2TNPG)(1-AMT)2(H2O)2](H2TNPG) (14c) (right). Selected
bond lengths (Å) of 14b: Cu1–O1 2.230(3), Cu1–N4 2.000(3), Cu1–N9
2.005(3), Cu1–N14 1.997(3), Cu1–N19 1.997(3); selected bond angles (1)
of 14b: O1–Cu1–N4 103.93(12), O1–Cu1–N9 87.27(12), N4–Cu1–N9
92.78(12), N4–Cu1–N14 149.23(11), N4–Cu1–N19 92.08(12), N9–Cu1–
N19 174.14(12). Selected bond lengths (Å) of 14c: Cu1–O1 1.9934(15),
Cu1–O11 2.0671(17), Cu1–N4 1.9784(16), Cu1–N9 1.9856(16); selected
bond angles (1) of 14c: O1–Cu1–O2 74.84(6), O1–Cu1–O10 107.90(6),
O1–Cu1–O11 163.97(6), O1–Cu1–N4 88.60(7), O1–Cu1–N9 91.36(7),
N4–Cu1–N9 179.38(7).
AMT-based compound with methyl groups pointing in the same
direction, leading to higher steric hindrance (N4–Cu1–N9 172.08(10)1)
and thus lower symmetry.
Styphnate compound 10 shows an almost identical compo-
sition to its 1-AT isomer 7 and crystallises in the Àtr3iclinic space
highly distorted octahedron. In contrast to 14a, 14b possesses
non-coordinating anions and, similar to 8, 11 and 17, the TNPG-
based monoanions are present as 3,5-dihydroxy-2,4,6-trinitro-
phenolates stacked on top of each other. They form hydrogen
bonds to amino groups of neighbouring tetrazole ligands
and typical nitro–nitro interactions between each other. The
coordination sphere around the copper(II) central metal in 14b
is composed of one aqua and four ligand molecules of 1-AMT
(Fig. 9). The water molecule represents the tip of the pyramid
with a slightly longer Cu–O bond (2.230 Å) compared to the Cu–
N bonds (1.997–2.005 Å). To minimise steric hindrance, pairs of
opposing tetrazole ligands are arranged with the methyl groups
facing in alternating directions and the two heterocycles are
slightly angled, leading to a distorted plane of coordinating
nitrogen atoms (N14–N4–N9–N19 23.7(1)1). The molecular unit
of 14c consists of one non-coordinating and one chelating
monoanion, as well as two aqua and two tetrazole ligands.
Interestingly, the Jahn–Teller distortion along the O2–Cu1–O10
axis shows one very long Cu–O bond (Cu1–O2 2.4665(14)), while
the second is only slightly elongated (Cu1–O10 2.1604(16)).
Even though the coordination environments of the copper(II)
centres of picrate complexes 9 and 15 are almost identical
and show similar densities (9: 1.905 g cmÀ3 @ 173 K; 15:
1.860 g cmÀ3 @ 143 K), they crystallise in fundamentally
different space groups. [Cu(PA)2(2-AT)2] (9) crystallises as green
needles in the monoclinic P21/c and [Cu(PA)2(2-AMT)2] (15) as
%
group P1 with a calculated density of 1.864 g cm at 173 K in
the form of green blocks. Its 5-methyltetrazole analogue 16
crystallises as green rods in the monoclinic space group P21/c
with a calculated density of 1.949 g cmÀ3 at 143 K. The only
similarity with its 1-AMT analogue 13 is the formation of
polymer strands due to the twofold deprotonation of the anion.
However, complex 16 only contains one neutral heterocycle and
an additional aqua ligand, which are located cis to each other
(Fig. 11). Also, a molecule of crystal water is present in 16,
which is fixed inside the structure by four hydrogen bonds.
3,5-Dihydroxy-2,4,6-trinitrophenolate complexes 11 and 17
%
both crystallise as green blocks in the triclinic space group P1
with similar calculated densities of 1.909 g cmÀ3 (173 K) and
1.939 g cmÀ3 (143 K), respectively. Again, 11 shows an identically
constructed coordination sphere to 1-AT isomer 8 with four 2-AT
ligands in the equatorial plane and monodentate H2TNPG mono-
anions in axial positions. Compared to 11, the octahedron in
complex 17 consists only of two tetrazole ligands, and once again
%
green blocks in the triclinic space group P1. The equatorial
positions are occupied by deprotonated hydroxyl groups and
two trans coordinating aminotetrazole ligands. In the case of
2-AT based complex 9, the two heterocycles are aligned anti-
parallel, whereas, in complex 15, the 2-AMT molecules are
roughly mirrored in the equatorial plane. The axial positions
are occupied by two nitro functions of the picrate anion
(Fig. 10). Whereas 9, similar to picrate complex 6, shows highly
symmetric coordination of the ligands, compound 15 possesses
a greater deviation from the perfect octahedron. It is the only
Fig. 11 Molecular unit of [Cu(HTNR)2(2-AT)2] (10) (left) and extended
molecular unit of [Cu(TNR)(2-AMT)(H2O)]ÁH2O (16) (right). Selected bond
lengths (Å) of 10: Cu1–O1 1.9410(12), Cu1–O2 2.3932(13), Cu1–N4
1.9858(14); selected bond angles (1) of 10: O1–Cu1–O2 78.44(5),
O1–Cu1–N4 88.72(6), O2–Cu1–N4 88.65(5). Symmetry code of 10:
(i) Àx, 2 À y, Àz. Selected bond lengths (Å) of 16: Cu1–O1 1.941(2), Cu1–
O2 2.284(2), Cu1–O9 1.968(2), Cu1–N4 2.005(2); selected bond angles (1)
of 16: O1–Cu1–O2 82.20(8), O1–Cu1–O9 176.78(9), O1–Cu1–N4
90.48(8), O2–Cu1–N4 92.83(9), O9–Cu1–N4 92.70(10). Symmetry code
of 16: (i) 1 À x, À0.5 + y, 0.5 À z.
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temperature of 200 1C. Styphnate 13, the compound with the
highest decomposition temperature of all investigated com-
plexes (Texo = 212 1C) derives its high thermal stability from its
polymeric structure. A similar case can be observed in ECC 14a
(Texo = 202 1C) with bridging trinitrophenolate anions. However,
the relatively low decomposition temperature of the only other
2-AMT-based coordination polymer 16 (Texo = 172 1C) can be
explained by the presence of aqua ligands and crystal water
molecules. The loss of both (Tendo = 122 1C and 160 1C)
destabilises the crystal structure, leading to a lower exothermic
decomposition temperature. Comparison of the 1-AMT complexes
to those featuring 5H-tetrazole ligands reveals higher exothermic
stabilities for the methyltetrazole based compounds. In the case of
the 2-amino isomers, it is the other way round. The ECC based
on 2-AT are thermally more stable than the analogous 2-AMT
complexes. Apart from 16, an endothermic peak is only observed
in the DTA plot of 11 and is caused by the evaporation of
coordinating 2-AT ligands. More detailed investigations using
thermal gravimetric analysis (TGA) reveals the loss of two tetra-
zole derivatives (818.4%) starting at 135 1C (Fig. 13).
Fig. 12 Molecular unit of [Cu(H2TNPG)2(2-AT)4] (11) (left) and [Cu(H2TNPG)2-
(2-AMT)2] (17) (right). Selected bond lengths (Å) of 11: Cu1–O1 2.3614(18),
Cu1–N4 2.007(2), Cu1–N9 2.0101(19); selected bond angles (1) of 11:
O1–Cu1–N4 88.38(7), O1–Cu1–N9 95.38(7), N4–Cu1–N9 89.16(9). Sym-
metry code of 11: (i) 1 À x, 1 À y, Àz. Selected bond lengths (Å) of 17:
Cu1–O1 1.9180(19), Cu1–O2 2.354(2), Cu1–N4 2.022(3); selected bond
angles (1) of 17: O1–Cu1–O2 81.50(9), O1–Cu1–N4 91.12(10), O2–Cu1–N4
92.03(10). Symmetry code of 17: (i) Àx, 1 À y, Àz.
two H2TNPG monoanions, which are in this case chelating
(Fig. 12). The presence of the anions as 3,5-dihydroxy-2,4,6-
trinitrophenolate (like in 8, 11, 14b, and 14c) is preventing the
bridging between different copper(II) centres.
TGA measurements of ECC 6, 8, 11–13 and 16 clearly show
the loss of water molecules in 12 and 16 and no significant
Sensitivities and thermal stability
Ligands 4b and 5b, as well as energetic complexes 6–17, with mass loss in the other measured compounds, which proves
the exception of side-products 14b and 14c, were subjected to their thermal stability up to the corresponding exothermic
differential thermal analysis (DTA) by heating at a constant rate decomposition points (Fig. S17, ESI‡).
of b = 5 1C minÀ1 in the temperature range of 25–400 1C.
Due to the fact that the crystal morphology has a high effect
Critical points, such as dehydration, loss of a coordinating on sensitivities as well as performance parameters (e.g., a
ligand or decomposition, are listed in Table 1 and are given as higher sensitivity against ESD with decreasing crystal size30),
onset temperatures. The DTA plots can be found in the ESI‡ the compounds’ grain size and habit were determined by light
(Fig. S18–S30). All investigated compounds exhibit exothermic microscopy (Fig. S5 and S16, ESI‡). The sensitivities towards
decomposition temperatures above 170 1C. Five of the examined impact (IS) and friction (FS) of the compounds were deter-
ECC (9, 10, 13, 14a, and 17) even surpass a decomposition mined according to BAM standard techniques (1 of 6) and they
Table 1 Data of thermal stability measurements by DTA,a as well as sensitivities towards various external stimuli and results of hot plate (HP) and hot
needle (HN) experiments of 4a-5b and 6–17
ISd (J)
FSe (N)
ESD f (mJ)
BDISg (mJ)
HPh
HNh
b
c
Tendo (1C)
Texo (1C)
1-AT (4a)
2-AT (5a)
1-AMT (5b)
2-AMT (5b)
—
—
—
—
—
—
—
—
—
135
—
—
—
—
122, 160
—
18223
19723
190
176
178
186
193
203
206
176
190
212
202
176
172
202
320–360
163–170
o128
6428
3628
360
4360
120
48
20
128
48
24
168
16
7
108
38
n.d.
n.d.
n.d.
n.d.
50
16
90
60
20
100
88
6.3
4.9
37
n.d.
n.d.
n.d.
n.d.
207
14
14
4207
55
n.d.
n.d.
n.d.
n.d.
def.
def.
def.
def.
def.
def.
def.
def.
def.
def.
def.
def.
det.
def.
n.d.
n.d.
n.d.
n.d.
def.
def.
def.
def.
def.
def.
def.
def.
det.
def.
def.
def.
det.
def.
o128
440
35
4
1.5
3.5
3
3
2
2
2
1
2.5
2.5
2
2.5–4.0
3.0–4.2
[Cu(PA)2(1-AT)2] (6)
[Cu(HTNR)2(1-AT)2] (7)
[Cu(H2TNPG)2(1-AT)4] (8)
[Cu(PA)2(2-AT)2] (9)
[Cu(HTNR)2(2-AT)2] (10)
[Cu(H2TNPG)2(2-AT)4] (11)
[Cu2(PA)4(1-AMT)4]ÁH2O (12)
[Cu(TNR)(1-AMT)2] (13)
[Cu(HTNPG)(1-AMT)2] (14a)
[Cu(PA)2(2-AMT)2] (15)
[Cu(TNR)(2-AMT)(H2O)]ÁH2O (16)
[Cu(H2TNPG)2(2-AMT)2] (17)
14
4207
10
8
4207
69
41
n.d.
n.d.
840
8.2
7.0
60
20
0.1–1.0
73
29
Pb(N3)2
PETN29
141–143
a
b
Onset temperatures at a heating rate of 5 1C minÀ1
.
Endothermic peak, which indicates melting, dehydration or loss of coordinating molecules.
c
d
e
Exothermic peak, which indicates decomposition. Impact sensitivity according to the BAM drophammer (method 1 of 6). Friction sensitivity
f
g
according to the BAM friction tester (method 1 of 6). Electrostatic discharge sensitivity (OZM Electric XSpark10) (method 1 of 6). Ball drop
impact sensitivity determined with method 1 of 6 in accordance with MIL-STD 1751A (method 1016). def.: deflagration, det.: detonation, dec.:
h
decomposition.
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ball drop impact shows a higher correlation with FS than with
IS. Interestingly, ECC 13 and 14a, based on a less sensitive
ligand, both show the most sensitive values against external
stimuli. The multiple deprotonations of nitroaromatic anions
lead not only to higher thermal stability but also to increased
sensitivities. This concept can be used for the synthesis and
design of sensitive but thermally stable primary explosives for
classical initiation devices.
Primary explosive suitability evaluation
In order to get an insight into the compounds’ behaviour
against fast heating with and without confinement, hot plate
(HP) and hot needle (HN) tests were performed with all ECC
(Fig. 15 and Fig. S34–S47, ESI‡), except for side species 14b and
Fig. 13 TGA plot of 11 showing the loss of two aminotetrazole ligands 14c. The results are displayed in Table 1 and furthermore allow
starting at 127 1C followed by the decomposition of the compound.
a preliminary evaluation of their applicability to be used for the
initiation of energetic materials. The most promising compounds
in these tests have been found to be the 1-AMT-based copper(II)
have been classified in accordance with the ‘‘UN Recommendations
styphnate (13) and 5-hydroxy-2,4,6-trinitroresorcinate (14a)
on the Transport of Dangerous Goods’’.31 Furthermore, the electro-
complexes, which showed either sharp deflagrations or even
static discharge sensitivity (ESD) of all isolated ECC was analysed
detonations in this setup.
and all measurement data are summarised in Table 1. Comparing
For their potential use as lead-free primary explosives, both
the free ligands, it becomes clear that the additional methyl group
compounds were tested towards their capability of initiating
in 1-AMT and 2-AMT is drastically increasing the stability of the
pentaerythritol tetranitrate (PETN). Therefore, 200 mg of the
aminotetrazole derivatives against external stimuli. Concerning the
booster explosive was loaded into a copper shell and the test
impact sensitivity, all ECC show similar values against impact and
substance was filled on top (Fig. 16).
except 6 and 8 (‘‘sensitive’’) have to be classified as ‘‘very sensitive’’.
More details on the test setup can be found in the General
In the case of FS, a clear trend is observable, revealing an increase of
methods of the ESI.‡ Positive transfer of the detonation wave
the sensitivity with the number of hydroxy groups of the anion
from the primary explosive towards PETN is indicated by a hole
(Fig. 14 and Fig. S31–S33, ESI‡), leading to the general trend: PA
in the copper witness plate and fragmentation of the shell. Both
(all friction ‘‘sensitive’’) o TNR (‘‘very sensitive’’) r TNPG
compounds were able to initiate nitropenta; whereas 13 worked
(‘‘very sensitive’’ or even ‘‘extremely sensitive’’ (14a)). Due to
in our standard setup with pressed PETN, 14a was only successful
the more realistic conditions during ball drop impact sensitivity
in combination with uncompressed PETN (Fig. 16). Due to the
(BDIS) measurements, ECC 6–17 were all tested and show
known fact that unconfined PETN requires much lower energies
a similar trend in comparison to the determined FS. This
than the compressed one,30 13 is the more powerful primary
confirms our previous findings22 that the sensitivity against
explosive compared to 14a. Additionally, 13 shows a 10 1C
higher thermal stability and is slightly less sensitive towards
Fig. 15 Moments of deflagration of 13 (left) during hot needle and 14a
(right) during hot plate tests.
Fig. 14 Comparing the sensitivities against external stimuli of the ECC
12–14a.
Fig. 16 Schematic setup of the PETN initiation capability test (left) as well
as positive results of ECC 13 (middle) and 14a (right).
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Table 2 Results of the laser initiation experimentsa
Table 3 Summary of the discovered optical properties of the examined
ECC 6–17
Emax [mJ]
0.17
0.20
0.24
3.00
25.5
30.0
36.0
a
b
Compound
M
Colour
ld–d
l915/ld–d
6
7
8
9
10
11
12
13
14a
15
16
17
dec.
def.
def.
dec.
def.
def.
—
—
neg.
—
dec.
—
—
dec.
def.
—
—
—
—
dec.
—
—
—
—
—
—
—
—
—
dec.
—
—
—
—
—
def.
—
—
—
—
—
—
—
det.
—
—
def.
—
—
dec.
—
—
—
—
—
—
—
dec.
—
—
dec.
—
det.
dec.
dec.
—
6
7
8
9
10
11
12
13
14a
15
16
17
Cu(II)
Cu(II)
Cu(II)
Cu(II)
Cu(II)
Cu(II)
Cu(II)
Cu(II)
Cu(II)
Cu(II)
Cu(II)
Cu(II)
Green
Green
Green-yellow
Green
Green
Green
Green
Green
Brown
Green
405
410
356
424
412
437
431
459
409
426
610
388
0.45
0.65
0.35
0.43
0.52
0.56
0.64
0.57
0.53
0.68
0.97
0.40
—
def.
dec.
—
dec.
—
dec.
—
—
dec.
—
dec.
—
—
—
dec.
dec.
—
Green
Green
a
Not tested; neg.: no reaction; dec.: decomposition; def.: deflagration;
det.: detonation. Operating parameters: voltage U = 4 V; wavelength
l = 915 nm; current I = 7–9 A; pulse length t = 0.1–15 ms; theoretical
maximal output power Pmax = 45 W; theoretical energy Emax = 0.17–36.0 mJ.
a
Absorption intensity maximum wavelength in the observed range of
350–1000 nm, which can be assigned to electron d–d transitions.
Quotient of the absorption intensity at the laser wavelength and the
b
intensity at the d–d absorption wavelength.
all tested external stimuli (IS, FS, ESD, and BDIS) making its
manageability safer.
in Table 3. All ECC show characteristic transitions in the near
infrared, visible and UV regions, as well as moderate to very
strong absorption at a laser wavelength of 915 nm. The observed
absorptions can mainly be assigned to the d–d transitions of the
copper(II) centres. In accordance with previous investigations, the
positive reaction towards laser irradiation could be explained
by the imaginable formation of several hot spots within the
compounds caused by photothermal excitation after irradiation.16
Interestingly, there is no trend between the absorption intensity at
the laser wavelength and the resulting outcome of the irradiation.
Laser initiation experiments
The most tremendous benefits of laser initiation over classical
ignition methods (thermal or mechanical) are the applicability
of less sensitive compounds and the resulting lower risk of
unintended ignition.16 Therefore, this research area has gained
increasing interest within the energetic material community
and a lot of investigations were performed.17,20,32–34 All com-
plexes, except 14b and 14c, were irradiated with an InGaAs laser
diode working in single-pulse mode. Details of the applied test
setup can be found in the ESI.‡ All examined ECC showed a
reaction towards the laser irradiation, differing in the intensity
of the outcome (Table 2 and Fig. S48–S59, ESI‡). The most
interesting compounds in this investigation are the ones
showing both decreased impact and friction sensitivities (Z3 J,
Z48 N), which are close to the values of PETN.29
These values pose slightly increased sensitivities towards
mechanical stimuli but still allow safe handling of the material.
Interestingly, all complexes based on AMT ligands solely exhibit
decomposition or no reaction at all, regardless of the energy they
are irradiated with. In the case of the aminotetrazole compounds,
the picrates display the same outcome, whereas the HTNR- and
H2TNPG-based ECC deflagrate at lower energies or can even be
detonated (7 and 11) when irradiated with higher values.
Comparing the more sensitive compounds (7, 8, 11, 13, 14a,
and 17), it becomes clear that the most sensitive ones (13, 14a
and 17) and also the most energetic ones in classical initiation
tests (13 and 14a) show lower performance in this setup, which
is not in accordance with our previous findings.17,20,22
Conclusions
In this extensive study, the nitrogen-rich ligands 1-amino- (4a,
1-AT) and 2-amino-5H-tetrazole (5a, 2-AT) as well as 1-amino-
(4b, 1-AMT) and 2-amino-5-methyltetrazole (5b, 2-AMT) were
successfully applied for the synthesis of new copper(II) complexes.
It could be demonstrated that ligands 4b and 5b tend to form
complexes with higher thermal stability and lower sensitivity. The
crystal structures of 16 (12 main products, 2 side species, one
ligand, and one precursor) compounds were elucidated by low-
temperature single crystal X-ray diffraction and compared in
detail. Especially the use of anions based on trinitrophloroglucinol
offers a wide range of different complexes with various as well as
interesting coordination modes. Furthermore, like styphnic acid, it
allows the formation of polymeric structures through the multiple
deprotonation of its hydroxy groups, which is accompanied by an
increase in thermal stability. Interestingly, the ECC based on the
more energetic and more sensitive AT-ligands show better stabilities
against external stimuli, such as impact and friction, than the
analogous compounds containing AMT derivatives. Whereas
complexes 13 and 14a were able to successfully initiate nitro-
penta, 7, 8, 10, and 11 show promising results during the laser
UV-vis spectroscopy
UV-vis spectra in the solid state were recorded for the examined ignition experiments. Due to their deflagrations at already
ECC 6–17, except 14b and 14c, in the range of 350–1000 nm 0.17 mJ they are interesting candidates for future laser ignition
(Fig. S60–S63, ESI‡), to reveal any possible correlation between devices, while 13 and 14a could be potential replacements for
the absorption intensity and wavelength of the laser diode. The lead azide in classic initiation devices. The low performances of
discovered optical properties of the complexes are summarised the AMT complexes when irradiated with NIR wavelengths
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16 S. R. Ahmad and M. Cartwright, Laser Ignition of Energetic
Materials, John Wiley & Sons, Ltd., Hoboken, 1st edn, 2015.
17 N. Szimhardt, M. H. H. Wurzenberger, A. Beringer, L. J.
Daumann and J. Stierstorfer, J. Mater. Chem. A, 2017,
5, 23753.
indicate that systems based on copper(II) and nitroaromatic
anions with these are not very suitable for laser initiation or
need substantially higher energies.
Conflicts of interest
18 Y. Cui, T. L. Zhang, J. G. Zhang, L. Yang, J. Zhang and X. Hu,
Propellants, Explos., Pyrotech., 2008, 33, 437.
There are no conflicts to declare.
19 Y. Cui, J. G. Zhang, T. L. Zhang, L. Yang, Y. Zhang and
Y. J. Shu, Chin. J. Chem., 2008, 26, 2029.
Acknowledgements
¨
20 N. Szimhardt, M. H. H. Wurzenberger, T. M. Klapotke,
J. T. Lechner, H. Reichherzer, C. C. Unger and J. Stierstorfer,
J. Mater. Chem. A, 2018, 6, 6565.
Financial support of this work from the Ludwig-Maximilian
University of Munich (LMU). The authors would like to thank
21 Y. G. Bi, Y. A. Feng, Y. Li, B. D. Wu and T. L. Zhang, J. Coord.
Chem., 2015, 68, 181.
22 M. H. H. Wurzenberger, M. S. Gruhne, M. Lommel,
¨
Prof. Dr Thomas M. Klapotke for his scientific support as well
as for providing his research facilities and, furthermore, Prof.
Dr Konstantin Karaghiosoff for measuring the 15N NMR spectra.
Andreas Bartonek and Jasmin Lechner are given thanks for their
great contribution to this work.
¨
N. Szimhardt, T. M. Klapotke and J. Stierstorfer, Chem. –
Asian J., 2019, 14, 2018.
23 Y. Cui, J. G. Zhang, T. L. Zhang, L. Yang, J. Zhang and X. Hu,
J. Hazard. Mater., 2008, 160, 45.
24 N. Szimhardt, M. H. H. Wurzenberger, L. Zeisel, M. S.
Notes and references
¨
Gruhne, M. Lommel, T. M. Klapotke and J. Stierstorfer,
¨
1 T. M. Klapotke, Chemistry of High-Energy Materials, De
Chem. – Eur. J., 2019, 25, 1963.
Gruyter, Berlin/Boston, 4th edn, 2017.
25 N. Szimhardt, M. H. H. Wurzenberger, L. Zeisel, M. S. Gruhne,
M. Lommel and J. Stierstorfer, J. Mater. Chem. A, 2018, 6, 16257.
26 Crystallographic data for the structures has been deposited
with the Cambridge Crystallographic Data Centre. Copies of
the data can be obtained free of charge on application to
The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (Fax: int.code_(1223)336-033; e-mail for inquiry: fileserv@
ccdc.cam.ac.uk; e-mail for deposition: (deposit@ccdc.cam.ac.uk)).
27 M. Daszkiewicz, CrystEngComm, 2013, 15, 10427.
2 J. Akhavan, The Chemistry of Explosives, Royal Society of
Chemistry, Cambridge, 2nd edn, 2004.
3 H. Sprengel, The Discovery of Picric Acid (Melinite, Lyddite) ‘‘As a
Powerful Explosive’’ and of Cumulative Detonation with its Bearing
on wet Gun Cotton, Eyre & Spottiswoode, London, 2nd edn, 1903.
4 H. Sprengel, Br. Pat., #901, 1871.
5 J. S. Wallace, Chemical Analysis of Firearms, Ammunition, and
Gunshot Residue, CRC Press, Boca Raton, 1st edn, 2008.
6 J. P. Agrawal and R. D. Hodgson, Organic Chemistry of
Explosives, John Wiley & Sons, Hoboken, 1st edn, 2007.
7 M. A. S. Laidlaw, G. Filippelli, H. Mielke, B. Gulson and
A. S. Ball, Environ. Health, 2017, 16, 34.
¨
28 T. M. Klapotke, D. G. Piercey and J. Stierstorfer, Dalton
Trans., 2012, 41, 9451.
¨
29 T. M. Klapotke, Energetic Materials Encyclopedia, 1st edn, De
Gryter, Berlin/Boston, 2018.
8 R. V. Kent, T. P. Vaid, J. A. Boissonnault and A. J. Matzger,
Dalton Trans., 2019, 48, 7509.
´ˇ
30 R. Matyas and J. Pachman, Primary Explosives, Springer,
Berlin, 1st edn, 2013.
9 Y. Liu, G. Zhao, Y. Tang, J. Zhang, L. Hu, G. H. Imler, D. A.
Parrish and J. M. Shreeve, J. Mater. Chem. A, 2019, 7, 7875.
10 E. C. Johnson, E. J. Bukowski, J. J. Sabatini, R. C. Sausa,
E. F. C. Byrd, M. A. Garner and D. E. Chavez, ChemPlusChem,
2019, 84, 319.
11 Q. Sun, X. Li, Q. Lin and M. Lu, J. Mater. Chem. A, 2019, 7, 4611.
12 A. A. Larin, N. V. Muravyev, A. N. Pivkina, K. Y. Suponitsky,
I. V. Ananyev, D. V. Khakimov, L. L. Fershtat and N. N.
Makhova, Chem. – Eur. J., 2019, 25, 4225.
31 Impact: insensitive 4 40 J, less sensitive Z 35 J, sensitive Z
4 J, very sensitive r 3 J; friction: insensitive 4 360 N, less
sensitive = 360 N, sensitive o 360 N and 4 80 N, very
sensitive r 80 N, extremely sensitive r 10 N. According to
the UN Recommendations on the Transport of Dangerous
Goods.
32 D. E. Chavez, S. K. Hanson, R. J. Scharff, J. M. Veauthier and
T. W. Myers, US Pat., 20160031767A1, Triad National Security
LLC, 2015.
13 R. Haiges and K. O. Christe, Dalton Trans., 2015, 44, 10166.
14 J.-G. Xu, X.-Z. Li, H.-F. Wu, F.-K. Zheng, J. Chen and
G.-C. Guo, Cryst. Growth Des., 2019, 19, 3934.
33 S. I. Gerasimov, M. A. Ilyushin, I. V. Shugalei, A. V. Smirnov
and Z. V. Kapitonenko, Russ. J. Gen. Chem., 2017, 87, 3156.
15 J.-G. Xu, C. Sun, M.-J. Zhang, B.-W. Liu, X.-Z. Li, J. Lu, S.-H. 34 W. Guo, L. Wu, N. He, S. Chen, W. Zhang, R. Shen and Y. Ye,
Wang, F.-K. Zheng and G.-C. Guo, Chem. Mater., 2017, 29, 9725. Laser Part. Beams, 2018, 36, 29.
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