Energetic silver salts with 5-aminotetrazole ligands

Article abstract of DOI:10.1002/chem.200801666

Methylation of 5-amino-1H-tetrazole (1) gives 1-methyl-5-amino-1H-tetrazole (2) and 2-methyl-5-amino-1H-tetrazole (3). A new family of energetic silver complexes based on ligands 1, 2 and 3 with Perchlorate and nitrate anions (10-15) were synthesized and characterized by using IR, Raman, and NMR ( ¹H, ¹³C, ¹⁴N, and ³⁵Cl NMR) spectroscopy, elemental analysis, and mass spectrometry. The crystal structures of the compounds were determined where possible and reveal interesting structural details that are discussed herein. Additionally, differential scanning calorimetry was used to assess the thermal stability of the new salts, which showed excellent thermal stabilities at temperatures up to and above 225 °C. Standard tests were also used to assess the sensitivity of the materials towards impact and friction. All the silver complexes showed increased sensitivity values in comparison with analogous protonated 5-amino-1H- tetrazolium Perchlorate and nitrate salts. Some of these materials have sensitivity values that are comparable to commonly used primary explosives and allof them either deflagrate (12-14) or detonate loudly (10 and 11) on contact with an open flame. Lastly, nitrate salt 11 is easily initiated by thermal shock. It shows reasonably low sensitivity in comparison with other silver salts (e.g., silver azide or silver fulminate), which makes handling it much less hazardous. Compound 11 also has good thermal stability, decomposing at ≈300 °C, and shows interesting properties as a more environmentally benign alternative to lead(II) diazide in initiation devices for civil and military applications.

Full text of DOI:10.1002/chem.200801666

DOI: 10.1002/chem.200801666
Energetic Silver Salts with 5-Aminotetrazole Ligands
Konstantin Karaghiosoff, Thomas M. Klapçtke,* and Carles Mirꢀ Sabatꢁ[a]
Abstract: Methylation of 5-amino-1H-
which showed excellent thermal stabili-
ties at temperatures up to and above
2258C. Standard tests were also used to
assess the sensitivity of the materials
towards impact and friction. All the
silver complexes showed increased sen-
sitivity values in comparison with anal-
ogous protonated 5-amino-1H-tetrazo-
lium perchlorate and nitrate salts.
Some of these materials have sensitivi-
ty values that are comparable to com-
monly used primary explosives and all
of them either deflagrate (12–14) or
tetrazole (1) gives 1-methyl-5-amino-
1H-tetrazole (2) and 2-methyl-5-amino-
1H-tetrazole (3). A new family of ener-
getic silver complexes based on ligands
1, 2 and 3 with perchlorate and nitrate
anions (10–15) were synthesized and
characterized by using IR, Raman, and
NMR (1H, 13C, 14N, and 35Cl NMR)
spectroscopy, elemental analysis, and
mass spectrometry. The crystal struc-
tures of the compounds were deter-
mined where possible and reveal inter-
esting structural details that are dis-
cussed herein. Additionally, differential
scanning calorimetry was used to assess
the thermal stability of the new salts,
detonate loudly (10 and 11) on contact
with an open flame. Lastly, nitrate salt
11 is easily initiated by thermal shock.
It shows reasonably low sensitivity in
comparison with other silver salts (e.g.,
silver azide or silver fulminate), which
makes handling it much less hazardous.
Compound 11 also has good thermal
stability, decomposing at ꢀ3008C, and
shows interesting properties as a more
environmentally benign alternative to
lead(II) diazide in initiation devices for
civil and military applications.
Keywords: energetic materials
·
heterocycles · silver · spectroscopic
methods · X-ray diffraction
Introduction
We recently reported the synthesis and characterization of
salts of 5-AT with nitrate and perchlorate anions.[7,8] Methyl-
ation of 5-AT is known to give a mixture of 1-methyl- (1-
MAT, 2) and 2-methyl-5-amino-1H-tetrazole (2-MAT, 3),[9]
which can be separated by their different solubilities in
water. We have also studied salts of these tetrazoles with
nitric and perchloric acid as prospective insensitive energetic
materials with reasonably high performances.[1g,2a] Because
highly endothermic compounds often turn out to be very
sensitive towards classical stimuli (i.e., friction and
impact),[10] the introduction of small alkyl chains (i.e.,
methyl groups) helps to reduce the sensitivity of the materi-
al and at the same time increase its thermal stability at the
cost of performance. Additionally, the introduction of
methyl groups also makes interesting compounds accessible.
For example, HN3 is not able to protonate 5-AT to form the
interesting azide salt; however, quaternization of the tetra-
zole allows the formation of different tetrazolium azide
salts.[1g,2a]
Nitrogen-rich materials, and in particular tetrazoles, have
great potential for energetic applications.[1–3] Tetrazole-based
energetic materials[4] tend to have higher (more positive)
heats of formation than analogous imidazoles or triazoles[4,5]
and tend to have high thermal stabilities, regardless of their
large positive enthalpies of formation.[6] Therefore, nitrogen-
rich compounds based on, for example, nitrogen-rich 5-
amino-1H-tetrazole (5-AT, 1) are interesting in relation to
the formation of endothermic (or less exothermic) com-
pounds and environmentally friendly decomposition prod-
ucts.
[a] Prof. Dr. K. Karaghiosoff, Prof. Dr. T. M. Klapçtke, Dr. C. Mirꢀ
Sabatꢁ
Department of Chemistry and Biochemistry
Energetic Materials Research
Ludwig-Maximilian University
Butenandstr. 5-13
81377, Munich (Germany)
Fax : (+49)89-2180-77492
The structure of some commonly used tetrazole-based li-
gands can be seen here. Most of the literature dealing with
tetrazole-based materials concentrates on nitrogen-rich salts
with cations such as ammonium,[11] hydrazinium,[11,12] guana-
E-mail: tmk@cup.uni-muenchen.de
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200801666.
1164
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Chem. Eur. J. 2009, 15, 1164 – 1176

FULL PAPER
AHCTUNGTRENNUNG
dinium,[11] aminoguanadinium,[11] diaminoguanidinium,[11]
and triaminoguanidinium,[11,13] etc.,[14] or salts with energetic
anions such as nitrate, perchlorate, picrate, azide, dinitra-
mide,[15] 5,5’-azotetrazolate,[11a,12a,15] or 5-nitrotetrazolate,[3f,16]
among others.[3f,17] On the other hand, descriptions of metal
compounds that contain a tetrazole moiety are much more
elusive in the literature and many of them are less interest-
ing for use in energetic applications. Compounds of this
type that have been reported before include 5-nitrotetrazole
(5-NT) alkali salts of alkaline earth metals,[18] Fe2+,[19] Co2+/
3+ [20]
,
Ni2+,[16] Cu2+,[21] and Hg+[22]; salts of 1,5-di
ACTHNGUTERNNUaG mino-1H-
tetrazole (1,5-DAT) with Co3+,[23] Ni2+,[24a] Cu2+,[24] Zn2+, and
Cd2+;[24a] complexes of Mg2+ and Ca2+,[25a] Cr3+,[25b] Fe2+/3+ [25b]
Co2+/3+ [25c,d] Ni2+,[25e] Cu2+,[25e,f] Zn2+,[25g] and Cd2+[25h,i] with 5-
,
,
amples reported so far are those of [Ni
G
ACHTUNGTRENNUNG(5-
AT; and 1R-substituted-5-AT transition-metal complexes of
divalent and trivalent metals (Co3+, Ni2+, Cu2+, Zn2+, Ag+,
and Pd2+) with R=Me (1-MAT),[26a] CH2C(=O)NH-
AT)2],[25i] [CuCl (DAT)],[24b] and [Co
N
R
In explosive devices, it is common to construct a so-called
“explosive train”,[30] which is typically made up of an initia-
tor device and primary and secondary explosives. One of
the problems of primary explosives is their low thermal sta-
bility. Silver salts tend to have high decomposition tempera-
tures and are interesting for use as initiators (e.g., silver
azide[31] or silver 5,5’-azotetrazolate[32]) due to the relatively
benign character of silver (which is used in cutlery, for ex-
ample) in comparison with commonly used initiators such as
lead diazide (Pb(N3)2). In addition to heavy metal salts, (or-
ganic) perchlorate salts are also known to be rather sensitive
compounds. In this context, disilver 5-amino-1H-tetrazolium
perchlorate was patented as a new primary explosive with
excellent thermal stability.[30] Therefore, we report herein
the synthesis and full analytical, spectroscopic, and energetic
characterization of silver salts with different 5-amino-1H-tet-
razole ligands and perchlorate and (more environmentally
benign) nitrate anions. These new compounds are analogous
to our previously reported protonated tetrazolium salts and
we compare the energetic properties of both sets of com-
pounds. In addition, we report the crystal structures of four
new silver salts with tetrazole-based ligands, which add to
the few structural reports of azole-based metal salts and rep-
resent the first examples of silver salts with an azole ligand
to have been structurally characterized.
Abstract in Spanish: La metilaciꢀn de 5-amino-1H-tetrazol
(1) da lugar a la formaciꢀn de 1-metil-5-amino-1H-tetrazol
(2) y 2-metil-5-amino-1H-tetrazol (3). Una nueva familia de
sales energꢁticas de plata con los ligandos 1, 2 y 3 y con
aniones perclorato y nitrato (10–15) fueron syntetizadas y ca-
racterizadas mediante espectroscopꢂas de IR, Raman y RMN
(1H, 13C, 14N y 35Cl), analysis elemental y espectrometrꢂa de
masas. La estructura cristalina de los compuestos fue medida
cuando fue posible, mostrando detalles estructurales de inte-
rꢁs que son discutidos. Adicionalmente, la estabilidad tꢁrmica
de las nuevas sales fue medida utilizando calorimetrꢂa explo-
ratoria diferencial, mostrando excelentes estabilidades tꢁrmi-
cas por encima de los 2258C. La sensibilidad de los materials
al impacto y a la fricciꢀn fue tambiꢁn asesorada haciendo
uso de tests estandarizados. Todos los complejos de plata son
mꢃs sensibles a dichos estimulos que sales anꢃlogas conte-
niendo el anion perclorato o nitrato y cationes derivados de
5-amino-1H-tetrazol. Algunos de los materiales tienen sensi-
bilidades que asemejan a compuestos explosivos primarios y
todos ellos deflagran (12–14) o detonan fuertemente (10 y
11) cuando puestos en contacto con una llama. Finalmente,
el nitrato 11 es fꢃcil de iniciar a travꢁs de un choque tꢁrmico,
tiene una sensibilidad razonablemente baja en comparaciꢀn
con otras sales de plata (p.ej., azida de plata o fulminato de
plata) lo cual hace su uso menos peligroso, descompone a
temperaturas elevadas (ꢀ3008C) y no contiene plomo(II) el
cual es muy tꢀxico. Estas caracterꢂsticas lo hacen una alterna-
tiva mꢃs benigna para el medio ambiente para reemplazar la
azida de plomo(II) en detonadores que se encuentran en apli-
caciones tanto militares como civiles.
Results and Discussion
Synthesis: To synthesize the silver–tetrazole complexes, dis-
ilver 5-amino-1H-tetrazolium perchlorate (10) was prepared
by treating 5-AT with silver perchlorate in perchloric acid
(Scheme 1) similarly to a previously reported procedure.[30]
After the addition of water, the compound precipitated as a
highly insoluble white powder that showed great sensitivity
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1165

T. M. Klapçtke et al.
Vibrational and NMR spectros-
copies: All silver salts were
characterized by IR, Raman,
and NMR spectroscopies where
possible. The highly sensitive
perchlorate and nitrate salts 10
and 11 are extremely insoluble
in every common solvent, and
only dissolve in concentrated
acid solutions (e.g., hydrochlo-
ric, nitric, or perchloric acid) to
form the corresponding 5-
amino-1H-tetrazolium
salt
(chloride, nitrate, or perchlo-
rate) in which the silver cations
are no longer coordinating to
Scheme 1. Synthesis of the 5-aminotetrazolium nitrate and perchlorate salts.
the tetrazole ring; therefore, we
omitted any NMR study on
these two compounds.
towards shock and friction (primary explosive!). Primary
explosives differ from secondary explosives in that they un-
dergo a very rapid transition from burning to detonation
and have the ability to transmit the detonation to a less sen-
sitive explosive. Primary explosives will detonate when they
are subjected to heat or shock. The interesting explosive
properties of this compound prompted us to study other
silver salts and we synthesized the nitrate derivative (11). To
tune the high sensitivity of these compounds, 5-AT (1) was
methylated by using dimethyl sulfate to give 1-MAT (2) and
2-MAT (3), which were treated either with silver nitrate or
silver perchlorate in the corresponding acid (i.e., nitric or
perchloric acid) to give a new family of silver salts with
The vibrational spectra show the characteristic bands of
the respective energetic anions (nitrate and perchlorate) for
each one of the compounds studied. In the nitrate salts, the
anion shows a strong, broad IR absorption band centered at
ꢀ1385 cmꢁ1 (see the Supporting Information, Figure S1)
and a sharp strong band at ꢀ1040 cmꢁ1 (1047 cmꢁ1 for 11)
in the Raman (see the Supporting Information, Fig-
ure S2).[33] For the silver salts, the perchlorate anion shows a
strong stretching band with
a maximum at 1085 to
1090 cmꢁ1 in the infrared spectra and strong, sharp bands at
925 to 930 and 460 to 465 cmꢁ1 in the Raman spectra.[34]
These signals are in close agreement with those observed for
our previously reported perchlorate and nitrate salts 4[8] and
5.[7]
methACHTUNGTRENNUNGylated tetrazole ligands (12–15).
Treatment of silver picrate (AgPic) with 1,4-dimethyl-5-
amino-1H-tetrazolium iodide (1,4-DMAT+Iꢁ) to give the
corresponding picrate salt[47c] also gave crystals of a byprod-
uct that could be identified as bis-(1,4-dimethyl-5-imino-1H-
tetrazole)silver picrate (16). Its formation can be explained
by the method of preparation of AgPic from picric acid and
KOH and subsequent metathesis with silver nitrate. Possibly
unreacted KOH deprotonated the 1,4-DMAT+ cation to
form neutral 1,4-dimethyl-5-iminotetrazole (DMIT), which
in turn reacted and coordinated with the silver picrate
formed according to Scheme 2.
Apart from the intense bands corresponding to the anion
(see above), the IR and Raman spectra of the compounds
also contain a set of bands that are characteristic for the
cation. Two sharp, strong bands, with two smaller shoulders,
ꢁ1
ꢁ
at ꢀ3415 and ꢀ3325 cm , which correspond to N H
stretching, were observed in the IR spectra of 10 and 11.
The rest of the compounds show a much more complicated
set of bands in this region, with maxima at ꢀ3325 cmꢁ1 (12
and 13) and ꢀ3390 cmꢁ1 (14 and 15) in addition to C H
ꢁ
stretches between 2950 and 2860 cmꢁ1 in the case of the me-
thylated compounds. After the anion stretch bands, the
strongest absorption is the combined C=NH2 stretching and
NH2 deformation modes found at ꢀ1620 cmꢁ1 in the IR
spectra for 14 and 15 and which is shifted to ꢀ1635 cmꢁ1 for
2-MAT derivatives and as high as ꢀ1670 cmꢁ1 for 1-MAT
derivatives in the methylated derivatives. This is in agree-
ment with signals at higher en-
Lastly, an attempt at recrystallization to obtain crystals of
13 resulted in the formation of tris-(1-methyl-5-amino-1H-
tetrazole)silver nitrate (17) and silver nitrate. The structure
of this compound is discussed below.
ergies (ꢀ1685 cmꢁ1) for proton-
ated compounds
6
and 7.[2a]
Lastly, the rest of the bands are
of lower intensity and can be
assigned as follows: n˜ =1550–
1350 (n(tetrazole ring), das-
Scheme 2. Reaction leading to the formation of 16.
G
ACHTUNGTRENUN(GN CH3)), 1350–
1166
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Chem. Eur. J. 2009, 15, 1164 – 1176

Energetic Silver Salts
FULL PAPER
ꢁ ꢁ
ꢁ
700 (n
(N C N), n
R
sible and is in consequence omitted from this work. Crystals
were obtained for the rest of the compounds as described in
the Experimental Section. The X-ray crystallographic data
for all compounds were collected by using an Oxford Dif-
fraction Xcalibur 3 diffractometer equipped with a CCD de-
tector with graphite-monochromated MoKa radiation (l=
0.71073 ꢃ). All structures were solved by using direct meth-
ods (SHELXS-97 and SIR97) and refined by means of full-
matrix least-squares procedures using SHELXL-97.[39,40] All
hydrogen atoms were located by using difference Fourier
electron-density maps, except for 17 in which the hydrogen
atoms were placed at idealized positions. For all structures,
all hydrogen atoms were refined isotropically. Crystallo-
graphic data are summarized in Table 1, selected bond
lengths and angles are reported in Table 2, and the geometry
around the Ag+ cations can be found in Table 3. Additional-
ly, hydrogen-bonding geometries and the results of the
graph set analysis are available in the Supporting Informa-
tion Tables S1–5. CCDC-693944 (12), -693945 (14), -693946
(16), and -693947 (17) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif
<700 cmꢁ1 (dout-of-plane bend (N H), w
(NH2)).[35]
ꢁ
IR spectroscopy also provides detailed insight into cation
structure and interionic interactions, including hydrogen
bonding.[36] A comparison of the IR spectra of the silver
salts with those of 5-amino-1H-tetrazolium nitrate (5) and
perchlorate (4) shows substantial changes, shifts, and sharp-
ꢁ
ening of the n˜ACHTUNGTRENNUNG(N H) bands observed in 4 and 5 if the ring
protons are substituted by silver atoms. For example, per-
chlorate 4 shows two bands at 3437 and 3348 cmꢁ1,[8] which
are shifted slightly lower to ꢀ3415 and 3326 cmꢁ1 (only one
band at ꢀ3400 cmꢁ1 for the methylated derivatives) in the
silver salts, which indicates a weakening (elongation) of the
ꢁ
N H bonds in the exocyclic amino group. In addition to
providing information about hydrogen bonding and N H
ꢁ
bond strengths, the IR spectra also indicate other structural
differences between silver salts (10–15) and their protonated
analogues (4–9). For example, the IR spectra of 10 and 11
show strong bands at 1617 and 1620 cmꢁ1, respectively, that
correspond to amino group deformation and also at 1557
and 1541 cmꢁ1, respectively, that correspond to C=N ring
stretch.[37,38] In the spectra of 4 and 5, a higher-energy band
attributed to coupled amino group deformation and exocy-
clic C=N stretch is observed at ꢀ1700 cmꢁ1. This observa-
tion can be explained nicely by the structural changes ex-
pected on substitution of the ring protons by silver atoms,
that is, the exocyclic C=NH2 bond length should increase
(decrease in stretching energy) as observed experimentally
(see the X-ray discussion below).
Compound 12 crystallizes with half a molecule of water of
crystallization in a monoclinic unit cell (space group C2/c)
with Z=8. The coordination around the Ag+ cation is de-
picted in Figure 1a and is composed of short interactions of
between ꢀ2.2 and 2.4 ꢃ to each one of the nonsubstituted
ring nitrogen atoms (N3, N4, and N5) and a longer contact
to the water molecule at 2.577(4) ꢃ (3+1). The distances
and angles around the cation agree with those of the rest of
the silver salts in this and other studies.[41]
As mentioned above, 10 and 11 were too insoluble to
record an NMR spectrum in any solvent we tried. For the
rest of the compounds, in the H NMR spectra measured in
1
[D6]DMSO the protons of the amino group displayed reso-
nances at dꢀ6.0 ppm for the 2-MAT derivatives and at d
ꢀ7.0 ppm for the 1-MAT derivatives. Both are strongly
shifted to highfield in comparison with 4[8] or 5,[7] which is
indicative of a decrease in the acidity of these protons in the
silver complexes. The resonances of the methyl protons are
found at dꢀ3.7 and ꢀ4.0 ppm for the 1-MAT derivatives
and the 2-MAT derivatives, respectively. In the 13C NMR
spectrum the signals of the 1-MAT derivatives are shifted to
highfield with respect to those of the 2-MAT derivatives (as
The role of the water molecules in the structure is crucial
in determining the packing. Figure 2 shows the heteronor-
bornane skeleton, which is the main building block of the
structure. This is made from two Ag+ cations, two times two
nitrogen atoms that correspond to two crystallographically
related 1-MAT ligands, and the long contact to O5 of a
water molecule (described above), which coordinate two
contiguous cations. In addition, the third (nonsubstituted)
nitrogen atom in the tetrazole ring (N5) connects the
heteroACHTNUTRGNEnNUG orbornane units with the shortest contact found in
1
also observed in the H NMR spectrum). The shifts of the
the structure (Ag···N5=2.201(5) ꢃ) and forms infinite
chains through the crystal along a direction that is approxi-
mately parallel to the c axis. The chains, which are positively
charged due to the Ag+ cations, are separated from the per-
chlorate anions.
See Figure 3 for a representative view of a super cell of
the crystal structure of 12 that shows the loose (noncoordi-
nating) perchlorate anions and a front view of the structure
skeleton along the c axis with the norbornane moieties
crossing each other and sharing a common point placed
ꢀ3.7 ꢃ for the water molecules. The computer program
RPLUTO[42,43] identifies the four hydrogen bonds summar-
ized in Table S1 (Supporting Information) as forming a pri-
mary graph set of the type N1 =DDDD, in which one of the
dimeric units (D=D11(2)) is involved in the formation of a
methyl group and the ring carbon atom are observed at d
ꢀ32.0 and ꢀ39.0 ppm and at dꢀ156.0 and ꢀ167.0 ppm (d
ꢀ152.0 ppm for 4),[8] respectively. The 14N NMR spectra
clearly show only the resonance of the anion in the nitrate
salts at dꢀꢁ4 ppm (see the Supporting Information, Fig-
ure S3). In comparison with the protonated species, silver
salts 12–15 tend to show 1H and 13C resonances that are
shifted to higher field.[2a]
Crystal structures: Compounds 10, 11, and 15 always formed
as powders upon recrystallization from several solvents, and
13 formed as a microcrystalline powder and rearranged to
form 17 after recrystallization from water. Therefore, any
structural characterization of these compounds was not pos-
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1167

T. M. Klapçtke et al.
Table 1. Crystal structure solution and refinement for silver–tetrazole complexes.
larger finite pattern with the
label D22(5) (see the Supporting
Information, Table S2). At the
secondary level, many other di-
meric D22(5) graph sets are
found together with ring motifs.
Graph sets of the type R21(4)
are formed between one of the
hydrogen atoms of the amino
group and two oxygen atoms of
the anion (Figure 1b), whereas
the larger R24(8) and R44(12)
motifs are formed by the inter-
action of two anions and two
cations without including and
including the chlorine atoms la-
beled as Cl and Clvi, respective-
ly (symmetry code: vi: ꢁx, y,
ꢁ0.5ꢁz).
12
14
16
17
empirical formula
Mr
C2H6N5O4.5ClAg
315.44
C2H5N5O4ClAg
306.43
C12H16N13O7Ag
562.25
C6H15N16O3Ag
467.21
200(2)
T [K]
100(2)
200(2)
200(2)
crystal size [mm]
crystal system
space group
a [ꢃ]
b [ꢃ]
c [ꢃ]
0.25ꢄ0.20ꢄ0.12
monoclinic
C2/c
13.303(2)
11.616(2)
12.019(2)
90
111.93(1)
90
1723.0(4)
8
2.432
2.651
1224
4.70–26.00
ꢁ15ꢂhꢂ16
ꢁ14ꢂkꢂ13
ꢁ14ꢂlꢂ8
4342
0.26ꢄ0.10ꢄ0.03
monoclinic
P21/c
6.519(5)
7.089(5)
18.378(5)
90
96.901(5)
90
843.2(9)
4
2.414
2.700
592
3.63–27.00
ꢁ8ꢂhꢂ8
ꢁ9ꢂkꢂ9
ꢁ23ꢂlꢂ23
6157
0.35ꢄ0.10ꢄ0.08
triclinic
P1
0.25ꢄ0.10ꢄ0.05
triclinic
¯
¯
P1
7.233(5)
14.260(5)
20.874(5)
72.467(6)
83.214(5)
81.500(5)
2024.2(2)
4
1.845
1.065
1128
3.80–27.00
ꢁ9ꢂhꢂ9
ꢁ18ꢂkꢂ18
ꢁ26ꢂlꢂ26
22441
7.179(1)
11.380(1)
11.440(1)
64.68(1)
79.00(1)
79.87(1)
824.6(1)
2
1.882
1.273
468
3.73–30.00
ꢁ10ꢂhꢂ10
ꢁ16ꢂkꢂ16
ꢁ16ꢂlꢂ16
11037
a [8]
b [8]
g [8]
VUC [ꢃ3]
Z
1calc [gcmꢁ3
]
m [mmꢁ1
(000)
q range [8]
]
F
A
index ranges
Figure 4a shows a view of the
asymmetric unit of perchlorate
14. This, in contrast to 12, crys-
tallizes in the monoclinic space
group P21/c with Z=4 but with
a very similar crystal density
(ꢀ2.4 gcmꢁ3). The lack of water
of crystallization influences the
packing strongly. To start with,
all atoms in the ligand are crys-
reflns collected
indep. reflns
1688
1829
8806
4754
(Rint=0.0729)
1688/0/147
1.016
0.0390
0.0543
(Rint=0.0280)
1829/0/138
1.157
0.0292
0.0325
(Rint=0.0688)
8806/0/611
1.005
0.0533
0.0997
(Rint=0.0414)
4754/0/256
0.822
0.0313
0.0540
data/restraints/params
GOF on F2
R1 [F>4s(F)][a]
R1 (all data)
wR2 [F>4s(F)][b]
wR2 (all data)
0.0877
0.0966
0.0725
0.0745
0.1057
0.1213
0.0609
0.0756
[a] R1 =ꢀjjFo jꢁjFc jj/ꢀjFo j. [b] Rw =[ꢀ(F2oꢁFc2)/ꢀw(Fo)2]1/2; w=[sc2(Fo2)+(xP)2+yP]ꢁ1, P=(Fo2ꢁ2F2c)/3.
tallographically
independent,
Table 2. Selected bond [ꢃ] and angle [8] geometries for silver–tetrazole complexes.[a]
whereas there are two types of
crystallographically related ni-
trogen atoms in the 1-MAT
ligand in 12. More notable is
the type of coordination ob-
served around the Ag+ cations
in 14 (Figure 4b), which in this
case can be described as 2+3
with aN2-Ag-N5ii =159.6(1)8
(symmetry code: ii: 1+x, y, z)
formed by two short contacts to
12
14
16(A)[b]
16(B)[b]
17(A)[c]
17(B)[c]
17(C)[c]
1
ꢁ
R
C
1.338(6)
1.344(7)
1.360(5)
1.295(7)
1.356(6)
1.332(7)
1.452(9)
1.329(4)
1.338(4)
1.335(4)
1.293(4)
1.334(4)
1.352(4)
1.286(1)
1.374(1)
1.371(1)
1.263(1)
1.362(1)
1.354(1)
1.447(1)
1.273(1)
1.358(1)
1.351(1)
1.282(1)
1.360(1)
1.360(1)
1.452(1)
1.457(1)
1.335(3)
1.333(3)
1.361(3)
1.285(3)
1.374(3)
1.335(3)
1.455(3)
1.333(3)
1.338(3)
1.357(3)
1.280(3)
1.363(3)
1.329(3)
1.449(3)
1.338(3)
1.335(3)
1.356(3)
1.278(3)
1.376(3)
1.324(3)
1.447(3)
ꢁ
C N1
ꢁ
N1 N2
ꢁ
N2 N3
N3 N4
N4 C
N1 R
N2 R
N4 R
ꢁ
ꢁ
2
ꢁ
tetrazole
(Ag···Nꢀ2.2 ꢃ)
nitrogen
and
atoms
three
3
ꢁ
1.465(5)
4
ꢁ
1.462(1)
longer ones to perchlorate
anions in the range of ꢀ2.6 to
ꢀ2.8 ꢃ (see Table 3), whereas
in 12 the Ag+ cations and per-
chlorate anions were isolated
from each other.
R1-C-N1
C-N1-N2
N1-N2-N3
N2-N3-N4
N4-C-R1
N4-C-N1
R2-N1-C
R2-N1-N2
R3-N2-N1
R3-N2-N3
R4-N4-N3
R4-N4-C
124.1(4)
107.8(4)
106.9(4)
110.7(4)
106.1(4)
108.4(4)
130.2(5)
121.9(5)
126.2(3)
102.7(2)
114.1(3)
106.0(3)
107.1(3)
110.2(2)
126.6(1)
109.4(1)
109.0(1)
107.9(1)
111.2(1)
102.6(1)
128.4(2)
122.2(2)
127.4(1)
111.5(1)
107.7(2)
108.0(1)
110.7(1)
102.1(1)
130.5(2)
120.1(2)
125.7(2)
108.7(2)
107.1(2)
110.2(2)
126.3(2)
108.0(2)
130.5(2)
120.6(2)
126.0(2)
108.3(2)
107.0(2)
110.6(2)
126.1(2)
107.9(2)
130.9(2)
120.8(2)
125.9(2)
108.6(2)
107.1(2)
110.2(2)
126.1(2)
108.0(2)
130.1(2)
121.2(2)
A view of the unit cell in the
structure of the compound is
depicted in Figure 5, in which
the 2-MAT ligands interact
with Ag+ cations to form infin-
ite chains along the a axis and
the perchlorate anions inter-
vene in the formation of inter-
123.2(3)
122.7(3)
127.2(1)
121.6(1)
129.1(2)
120.2(1)
[a] 12: R1 =NH2, R2 =CH3; 14: R1 =NH2, R3 =CH3; 16: R1 =NH, R2 =R4 =CH3; 17: R1 =NH2, R2 =CH3.
[b] A and B refer to the two asymmetric units of 16 in the crystal structure. [c] A, B, and C refer to the three
asymmetric units of 17 in the crystal structure.
1168
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Chem. Eur. J. 2009, 15, 1164 – 1176

Energetic Silver Salts
FULL PAPER
Table 3. Selected bond [ꢃ] and angle [8] coordination geometries around the Ag+ cations in 12, 14, 16, and
17.
forward. The three finite chains
found at the primary level
(Table S3), combine to form a
12
14[a]
16
17
Ag N5
2.201(4) Ag N2
2.171(3) Ag1 N1
2.088(4) Ag N5
2.186(2) R21(4) graph set, similar to that
ꢁ
ꢁ
ꢁ
ꢁ
i
found in 12, and two C22(6)
chain motifs.
16 was obtained as yellow
needlelike crystals and forms a
ꢁ
ꢁ
ꢁ
ꢁ
Ag N3
2.311(4) Ag O4
2.596(3) Ag1 N16
2.092(5) Ag N10
2.184(2)
ii
ꢁ
ꢁ
ꢁ
ꢁ
Ag N4
2.383(4) Ag O4
2.816(3) Ag2 N6
2.097(5) Ag N15
2.201(2)
ii
ꢁ
ꢁ
ꢁ
Ag O5
2.577(4) Ag N5
2.210(3) Ag2 N11
2.109(4)
iii
ꢁ
Ag O1
2.798(3)
N5-Ag-N3 134.3(1)
N5-Ag-N4 121.1(1)
N2-Ag-N5ii
N2-Ag-O4i
N2-Ag-O4ii
N2-Ag-O1iii
N5ii-Ag-O4i
N5ii-Ag-O4ii
N5ii-Ag-O1iii
O4ii-Ag-O4i
159.63(1)
106.14(1)
105.0(1)
83.1(1)
92.55(1)
81.3(1)
N1-Ag1-N16 176.4(2)
N6-Ag2-N11 169.3(2)
N10-Ag-N5
N10-Ag-N15 118.8(1)
N5-Ag-N15 118.7(1)
122.1(1)
triclinic unit cell (space group
P1), with a significantly low cal-
¯
N3-Ag-N4
94.1(1)
culated density in comparison
to the perchlorate salts report-
N5-Ag-O5 122.8(1)
N3-Ag-O5
N4-Ag-O5
87.3(1)
82.5(1)
ed
above
(1.845 gcmꢁ3).
90.7(1)
Figure 6 shows a view of the
asymmetric unit of the com-
pound. There exists two types
of crystallographically inde-
pendent and noninteracting 16
93.8(1)
O4ii-Ag-O1iii 171.8(1)
O1iii-Ag-O4i
85.2(1)
[a] Symmetry codes for 14: i: 1ꢁx, 0.5+y, 1.5ꢁz; ii: 1+x, y, z; iii: 1+x, 1+y, z.
Figure 2. Heteronorbornane skeleton formed by the coordination of
water molecules to the Ag+ cations (dotted lines) in the crystal structure
of 12, with labeling system (symmetry codes: i: x, 1ꢁy, 0.5+z; ii: ꢁx, y,
0.5ꢁz; iii: x, 1ꢁy, 0.5+z).
Figure 1. a) Full coordination around the Ag+ cations and b) ring graph
sets of interest in the crystal structure of 12 (view along the b axis) (sym-
metry codes: iv: ꢁ0.5+x, 1.5ꢁy, ꢁ0.5+z; v: 0.5ꢁx, 1.5ꢁy, ꢁz; vi: ꢁx, y,
ꢁ0.5ꢁz).
chain interactions to the cations. Lastly, the graph set analy-
sis of 14, which only forms three hydrogen bonds, is straight-
Figure 3. View of a supercell along the c axis in the crystal structure of
12.
Chem. Eur. J. 2009, 15, 1164 – 1176
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1169

T. M. Klapçtke et al.
Figure 5. View of the unit cell along the c axis showing the formation of
chains along the a axis in the crystal structure of 14.
to six different hydrogen bonds in the structure of the com-
pound yields only finite chains at the unitary level (Support-
ing Information, Table S4), as noted for the rest of the com-
pounds. At the secondary level, only some of them combine
to form a small D12(3) and two larger D22(X) (X=7, 9) graph
sets. Lastly, the formation of several R21(6) graph sets by the
interaction of the phenolate oxygen atom and one of the
oxygen atoms of a nitro group at the ortho position with the
imino moiety (NH) is common for azolium picrates.[47]
In contrast with perchlorate salt 12, recrystallization of 13
from water results in rearrangement of the coordination
sphere around the Ag+ cations and more ligands than ex-
pected (i.e., three) are found to coordinate the metal. This
Figure 4. a) Asymmetric unit of 14 showing the labeling system. b) Coor-
dination around the Ag+ cations in the crystal structure of 14 (symmetry
codes: i: 1ꢁx, 0.5+y, 1.5ꢁz; ii: 1+x, y, z; iii: 1+x, 1+y, z).
moieties, both of which show the simple linear coordination
expected for the Ag+ cations, similar to salts with the [Ag-
ACHTUNGTRENNUNG
(NH3)2]+ cation,[45a] with aN-Ag-N=169.2(1) and 176.4(1)8
presenting a distorted linear geometry.
The hydrogen atoms of the imino group interact with the
picrate anions to form a total of
three hydrogen bonds (see the
Supporting
Information,
Table S1) with distances be-
tween donor (N) and acceptor
(O) varying between ꢀ3.0 and
3.2 ꢃ. In addition to classical
hydrogen bonds, strong non-
classical interactions exist be-
tween C3 and O7 and O8 with
distances of 3.263(2) and
3.282(2) ꢃ, respectively, which
is similar to the sum of the van
der Waals radii (rC+rO =
3.26 ꢃ),[46] and is common for
picrate salts. Figure 7 shows a
view of the unit cell of the com-
pound along the a axis. The
[AgACHTUNGTRENNUNG
(DMIT)2]+ moieties form
interrupted chains approximate-
ly parallel to the b axis by inter-
acting(through the hydrogen
bonds described above) with
anions, which are placed at the
vertices of the unit cell and in
Figure 6. View of the asymmetric unit of 16 showing the coordination to the Ag+ cations and the hydrogen
bonding to the picrate anion, with the labeling system. Only half of the asymmetric unit has been labeled for
the center giving rise to
p
stacking. The formation of up clarity reasons.
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Chem. Eur. J. 2009, 15, 1164 – 1176

Energetic Silver Salts
FULL PAPER
mation of almost perfect layers along a direction that cuts
all (a, b, and c) axes at an angle of ꢀ458. Figure 9 shows the
hydrogen bonding in one of these layers, in which the [Ag-
AHCTUNGTRENNUNG
(1-MAT)3]+ units described above are connected to each
other through weak hydrogen bonds in the range of 3.05 to
3.25 ꢃ to nitrate anions. These hydrogen bonds describe sev-
eral graph sets of interest, which are identical for all three li-
gands and are summarized for one of them in Table S5 in
the Supporting Information. As well as the usual dimeric in-
teractions (D11(2), D21(3), and D22(5)), it is worth noting the
formation of R21(4) hydrogen-bonding networks between the
nitrogen atoms of the amino groups (donors) and the
oxygen atoms in the anions (acceptors). We found this motif
to be common for other ionic compounds that contain an
Figure 7. View of the unit cell of 16 along the b axis showing the stacks
of anions in this direction.
-NO2 moiety, such as dinitramide (-NACHTNUGRTNEUNG(NO2)2) and other ni-
results in a lower density compared with the perchlorate
salts in this report (1.882 gcmꢁ3). As represented in
Figure 8, the Ag+ cations are surrounded by three 1-MAT li-
gands to form a slightly distorted T-shape geometry, so the
coordination number in 17 is three. The coordination distan-
ces and angles are summarized in Table 3. All three distan-
trate salts,[2a,44] and also for the perchlorate salts (i.e., -ClO2)
discussed above.
Energetic properties: To assess the energetic properties of
all materials, we experimentally determined the thermal sta-
bility (differential scanning calorimetry (DSC) measurement
onsets) and sensitivity to impact, friction,[48–50] electrostatic
discharge, and thermal shock for each compound. The re-
sults of these studies are summarized in Table 4.
ꢁ
ces are very similar (ꢀ2.2 ꢃ) and comparable to the Ag N
distances in the other complexes described here. On the
other hand, the angles vary little from the ideal angle of
1208. The nitrate anions do not participate in the coordina-
tion sphere, but sit on a plane above and with a staggered
configuration with respect to the coordination of the Ag+
cations. The nearest oxygen atom in the anion is placed fur-
DSC studies on small samples of the energetic silver salts
show excellent thermal stabilities above 2258C. The 1-MAT
derivatives additionally show distinctive melting points
(1548C for 12 and 1828C for 13) and the loss of the half-
molecule of water of crystallization in 12 is shown as a
broad endothermic peak at 1028C, close to the boiling point
of water. 14 shows a small melting endotherm (2868C)
shortly before decomposing at 2898C, whereas 15 decom-
poses without melting at 2598C. The disilver salts 10 and 11
(see Figure 10) have surprisingly high thermal stabilities ac-
cording to DSC measurements (higher than the rest of the
compounds in this study) and decompose at 319 and 2988C,
respectively, (also without melting) so that the trend in the
decomposition points correlates well with the type of tetra-
zole ligand involved and increases in the order 1-MAT<2-
MAT<5-AT. To summarize, the replacement of the ring hy-
drogen atoms in compounds 4–9 to form the corresponding
silver salts (10–15) increases the melting and decomposition
points considerably. Additionally, perchlorate-anion-based
salts show larger liquid ranges among the compounds that
melt and higher decomposition temperatures than the
parent nitrate salts for all cases. Lastly, the decomposition
(and melting) points are in keeping with known heterocycle-
based salts[2a,51] and are comparable to the commonly used
(but highly toxic) primary explosive lead diazide
(Pb(N3)2).[52]
ther away from the metal center than the sum of the van
[46]
ꢁ
der Waals radii (Ag O1=3.359(2) ꢃ).
It is interesting to note that the coplanarity of all cations,
anions, and ligands (excepting the hydrogen atoms) results
in the coordinating 1-MAT ligands sitting on the same plane
and these are in turn linked to each other by weak hydrogen
bonds in the range of 3.25 to 3.45 ꢃ. This results in the for-
In addition to DSC analysis, the response of each com-
pound to fast thermal shock was tested by placing a small
sample of the material in a flame. Again, trends can be es-
tablished for perchlorate and nitrate salts. In general, the
perchlorate salts were more sensitive to fast heating than
the corresponding nitrates. For example, in this study the
four perchlorates, 4, 6, 8, and 10, exploded in the flame,
Figure 8. View of the asymmetric unit of 17 showing the coordination to
the Ag+ cations and the hydrogen bonding between the 1-MAT ligands,
with the labeling system.
Chem. Eur. J. 2009, 15, 1164 – 1176
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1171

T. M. Klapçtke et al.
Data collected for impact,
friction, and electrostatic dis-
charge sensitivities are also
summarized in Table 4. The
trend in the sensitivity values
reflects that found in the re-
sponse to fast heating, that is,
the more sensitive the com-
pound, the more vigorously it
reacted in the flame test. In
general, the perchlorate salts
are very sensitive towards both
friction and impact. For exam-
ple, 4 is a very impact- and fric-
tion-sensitive compound (1.5 J
and 8 N) and introduction of a
methyl group to form 6 or 8
would be expected to result in
lower sensitivity. However, it
must be taken into consider-
ation that there are many other
factors that play a role in deter-
mining the sensitivity properties
of energetic materials.
One factor that plays a major
role in determining the friction
and shock sensitivity of a com-
pound is its crystallinity and the
shape of the crystals. Com-
pounds 4, 6, and 8 were tested
as crystalline compounds; how-
ever, compounds 6 and 8 pre-
cipitate as large thick crystals
whereas 4 forms as very thin
platelets. This would explain
the unexpectedly high friction
and shock values for the two
methylated perchlorate salts in
comparison with those for 4.
Replacement of the two tetra-
zole ring protons in 4 with two
silver cations in 10 results in a
very insoluble compound (in
many ways similar to silver
Figure 9. Hydrogen bonding and coordination around the Ag+ cations in a layer of the crystal structure of 17
(symmetry codes: i: 2ꢁx, 1ꢁy, 1ꢁz; ii: 1ꢁx, 2ꢁy, 1ꢁz; iii: 1ꢁx, 1ꢁy, 2ꢁz). Graph set for rings marked *:
R21(4).
Table 4. Comparison of initial safety testing results for silver complexes and tetrazolium salts.[a]
[c]
[d]
Impact [J]
Friction [N]
ESD (+/ꢁ)[b]
Tm [8C]
Tdecomp [8C]
Thermal shock
4[e]
5[f]
6[g]
7[g]
8[h]
9[h]
10
11
12
13
14
1.5
>30
3
>30
1
>30
2
15
8
>360
10
>360
6
+
ꢁ
+
ꢁ
+
ꢁ
+
+
ꢁ
ꢁ
+
ꢁ
176
none
125
162
125
123
none
none
180
173
245
178
196
161
319
298
252
226
289
259
explodes
deflagrates
explodes
burns
explodes
burns
explodes
explodes
deflagrates
deflagrates
deflagrates
deflagrates
>360
<5
18
<5
10
2
120–360[i]
100–360[i]
<5
102 (ꢁH2O), 154
182
286
none
azide), which has
a similar
15
20
100–360[i]
impact sensitivity to the proton
analogue, which is more sensi-
tive to friction (regardless of
being a powder) and explodes
at the minimum setting in the
friction test (<5 N). The nitrate
salts with ring protons are all
[a] Compounds 4, 5, 6–9, 12 (hemihydrate), 13, and 14 were tested as the crystalline compounds; compounds
10, 11, and 15 were tested as powders; [b] Rough sensitivity to electrostatic discharge, +: sensitive, ꢁ: insensi-
tive (using a Tesla coil); [c] Melting or temperature of water loss (12) and [d] decomposition points (from
DSC measurements); [e] From ref. [8]; [f] From ref. [7]; [g] From ref. [2a]; [h] From ref. [44]; [i] The com-
pounds decompose nonexplosively in this range.
whereas the analogous nitrate salts (5, 7, 9, and 11) either
burned or deflagrated. In addition, the disilver salts (10 and
11) are more reactive (both exploded) than the monosilver
salts (12–15), which deflagrated in the “flame test”.
insensitive towards shock and friction (>30 J and >360 N),
however, the disilver salt (11) shows a much higher sensitivi-
ty to impact (15 J) that is similar to secondary explosives,
such as TNT (15 J), and to friction (18 N).[52] As for the
monosilver 1-MAT and 2-MAT nitrate and perchlorate salts,
1172
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Chem. Eur. J. 2009, 15, 1164 – 1176

Energetic Silver Salts
FULL PAPER
thermal stabilities and some of them can be initiated easily.
Regardless of the toxicity associated with the perchlorate
anion and to a lesser extend with silver (note that silver is
used for cutlery), they provide a more environmentally
friendly alternative to commonly used primary explosives
based on either mercury (e.g., mercury fulminate) or lead
(e.g., lead diazide or styphnate). This is the case for nitrate-
anion-based salt 11 in particular.
Experimental Section
Caution! Although we experienced no difficulties with the compounds
described here, some of them have sensitivity values that classify them as
primary explosives. Appropriate safety precautions should be taken and
larger scale syntheses are not recommended. Laboratories and personnel
should be properly grounded and safety equipment, such as Kevlar
gloves, leather coats, face shields, and ear plugs, is highly recommended.
Figure 10. DSC thermograms for disilver derivatives 10 and 11.
the nitrate salts are impact-sensitive, with values of 10 J (13)
and 20 J (15), and decompose nonexplosively above 100 N
in the friction test. On the other hand, the perchlorate salts
are either sensitive to impact (12, <5 J) or very sensitive
(14, 2 J). This is keeping in with the logic that hydrated com-
pounds, in this case 12, tend to be less sensitive to stimuli
than anhydrous materials; however, it is surprising that al-
though both 12 and 14 were tested as crystalline materials
and both have relatively high impact sensitivity values, in
the friction test 12 decomposes nonexplosively in the range
120 to 360 N, whereas 14 explodes at the lowest setting (<
5 N), similarly to powdery 10. Furthermore, the friction sen-
sitivity values correlate well with the values for sensitivity
towards electrostatic discharge; the very sensitive perchlo-
rate salts 4, 14, and 10 and nitrate salt 11 explode after ini-
tiation by the spark of a Tesla coil. Lastly, all results present-
ed in this section are in agreement with previous studies in
our group dealing with perchlorate and nitrate salts of tetra-
zoles.[2a,11c,44]
General: All chemical reagents and solvents were obtained from Sigma–
Aldrich Fine Chemicals Inc. or from the chemical store at the LMU,
Munich, and were used as supplied. 1-Methyl- and 2-methyl-5-amino-1H-
tetrazole[9c] and 1,4-dimethyl-5-amino-1H-tetrazolium iodide[2a] were syn-
thesized according to previously reported procedures. 1H, 13C, 14N, and
35Cl NMR spectra were recorded in [D6]DMSO at or near 258C by using
a JEOL Eclipse 400 instrument operating at 400.18 (1H), 100.63 (13C),
40.55 (14N), and 39.21 MHz (35Cl). The chemical shifts are given relative
to tetramethylsilane (1H, 13C), nitromethane (14N), and 1.0m aqueous
NaCl (35Cl) as external standards. Infrared (IR) spectra were recorded as
KBr pellets at 208C by using a Perkin–Elmer Spectrum One FT-IR in-
strument[53]. Transmittance values are qualitatively described as very
strong (vs), strong (s), medium (m), and weak (w). Raman spectra were
recorded by using a Perkin–Elmer Spectrum 2000R NIR FT-Raman in-
strument equipped with a Nd:YAG laser (1064 nm). The intensities are
reported as percentages of the most intense peak and are given in paren-
theses. Elemental analyses were performed by using a Netsch Simultane-
ous Thermal Analyzer STA 429. ICP analyses to determine the silver
content were performed by using an ICP-AES instrument (l=328.068).
Melting points were determined by using DSC (Linseis DSC PT-10 in-
strument[54] calibrated with standard pure indium and zinc). Measure-
ments were performed in closed aluminum sample pans with a 1 mm hole
in the top for gas release under a nitrogen flow of 20 mLminꢁ1 and with
an identical empty aluminum sample pan as a reference. Mass spectra
were recorded on a JEOL MStation JMS700 instrument in an m-NBA
matrix by using the FAB+ method.
Conclusion
A new family of silver-substituted tetrazoles with nitrate or
perchlorate anions have been prepared in good yields and
purities and characterized by analytical and spectroscopic
methods. In addition, the crystal structures of some of the
compounds were studied. They show common hydrogen-
bonding networks (graph sets) and interesting coordination
patterns around the metal center, and represent some of the
first examples of silver salts with an azole ligand to have
been structurally characterized. The thermal and energetic
properties of the new materials are presented herein and
compared with those of the parent proton-substituted salts.
Replacement of protons by silver cations results in an in-
crease in the sensitivity (some of the compounds show typi-
cal primary-explosive behavior) and the decomposition
points are markedly increased (>2258C). The trend in the
thermal stability seems to correlate well with the type of
Synthesis of disilver 5-amino-1H-tetrazolium perchlorate (10): 5-Amino-
1H-tetrazolium monohydrate (0.196 g, 1.8 mmol) was dissolved in concd
perchloric acid (4 mL) and a solution of silver perchlorate (0.377 g,
1.8 mmol) in water (1.5 mL) was added dropwise (cloudiness in the solu-
tion was observed as the addition proceeded). The clear solution was
stirred for 30 min before the addition of water (10 mL). Immediate pre-
cipitation of a white (highly sensitive!) powder was observed and the re-
action mixture was stirred for a further 15 min before the solid was fil-
tered under gravity. This solid was washed five times with water, once
with iso-propanol, and once with diethyl ether, then left to air-dry over-
night to give the title compound which was carefully weighed (0.522 g,
73%). DSC (58Cminꢁ1): 3198C (decomp); IR (KBr): n˜ =3414 (s), 3326
(vs), 3228 (m), 2285 (w), 1617 (s), 1557 (s), 1542 (s), 1458 (m), 1439 (w),
1384 (w), 1268 (w), 1143 (s), 1113 (vs), 1086 (vs), 940 (w), 920 (w), 768
(w), 742 (w), 703 (w), 636 (m), 625 (m), 573 (w), 460 (w), 430 cmꢁ1 (w);
Raman (%): n˜ =3332 (8), 1637 (10), 1562 (36), 1464 (22), 1437 (11), 1403
(8), 1281 (55), 1256 (28), 1235 (24), 1150 (57), 1125 (86), 1102 (59), 1026
(23), 930 (100), 769 (40), 625 (27), 464 (38), 349 (10), 166 cmꢁ1 (28); ele-
mental analysis calcd (%) for CH2N5O4ClAg2 (399.25): C 3.02, H 0.51, N
17.65, Ag 53.89; found: C 2.88, H 0.72, N 17.90, Ag 53.60.
ꢁ
ligand (1-MAT<2-MAT<5-AT), the anion (NO3ꢁ <ClO4 ),
and the number of silver cations (monosilver<disilver
Synthesis of disilver 5-amino-1H-tetrazolium nitrate (11): A solution of
salts). Lastly, the compounds described here have excellent
silver nitrate (0.832 g, 4.9 mmol) in water (3 mL) was added dropwise to
Chem. Eur. J. 2009, 15, 1164 – 1176
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1173

T. M. Klapçtke et al.
a
suspension of 5-amino-1H-tetrazolium monohydrate (0.503 g,
title compound formed upon cooling overnight, and were filtered off,
washed thoroughly with acetone and diethyl ether, and left to air-dry
4.9 mmol) in concd nitric acid (10 mL). The reaction mixture was stirred
for 45 min, then water (10 mL) was added. After a few seconds, cloudi-
ness in the solution was observed and after 15 min a white powder pre-
cipitated, which was filtered off under gravity (very sensitive compound!)
and washed thoroughly with isopropanol and diethyl ether. The product
was left to air-dry on a filter paper (1.423 g, 80%). DSC (58Cminꢁ1):
2988C (decomp); IR (KBr): n˜ =3416 (s), 3326 (s), 3227 (m), 2396 (w),
1762 (w), 1620 (m), 1541 (m), 1454 (m), 1434 (m), 1384 (vs), 1282 (m),
1189 (w), 1173 (w), 1153 (m), 1113 (w), 1038 (w), 1021 (w), 833 (w), 824
(w), 816 (w), 769 (w), 747 (w), 567 (w), 461 (w), 431 cmꢁ1 (w); Raman
(%): n˜ =1623 (9), 1543 (8), 1389 (6), 1295 (28), 1164 (13), 1109 (53), 1040
(100), 779 (16), 710 (7), 459 (10), 184 cmꢁ1 (25); elemental analysis calcd
(%) for CH2N6O3Ag2 (359.83): C 3.33, H 0.56, N 23.35, Ag 59.42; found:
C 3.13, H 0.78, N 23.60, Ag 59.42.
1
(0.357 g, 65%). DSC (58Cminꢁ1): m.p. 2868C, 2898C (decomp); H NMR
([D6]DMSO, 400.18 MHz, 258C, TMS): d=6.1 (s, 2H; NH2), 4.1 ppm (s,
3H; CH3); 13C{1H} NMR ([D6]DMSO, 100.63 MHz, 258C, TMS): d=39.0
(CH3), 166.9 ppm (C NH2); 35Cl NMR ([D6]DMSO, 39.21 MHz, 258C,
ꢁ
NaCl): d=+1000 ppm (ClO4ꢁ); IR (KBr): n˜ =3386 (s), 3309 (s), 3220
(m), 3073 (w), 2960 (w), 2676 (w), 2021 (w), 1688 (m), 1635 (s), 1584 (w),
1554 (s), 1452 (m), 1422 (w), 1409 (m), 1377 (w), 1326 (w), 1292 (w),
1205 (m), 1145 (vs), 1112 (vs), 1089 (vs), 941 (w), 809 (w), 757 (w), 707
(m), 684 (w), 668 (w), 649 (m), 636 (s), 626 (s), 488 cmꢁ1 (w); Raman
(%): n˜ =3246 (20), 3223 (20), 2962 (69), 1647 (24), 1578 (25), 1444 (27),
1378 (31), 1196 (28), 1169 (20), 1119 (38), 1036 (30), 963 (24), 926 (100),
892 (33), 812 (22), 675 (18), 649 (47), 623 (44), 594 (21), 461 (42), 429
(22), 348 (22), 250 (19), 167 (18), 150 cmꢁ1 (20); FAB+ (xenon, 6 keV, m-
NBA matrix): m/z (%): 206.0 (6) [C2H4N5Ag], 208.0 (5) [C2H6N5Ag]2+
305.0 (7) [Ag
(C2H5N5)2]+; elemental analysis calcd (%) for
,
Synthesis of silver 1-methyl-5-amino-1H-tetrazolium perchlorate hemihy-
drate (12): The perchlorate salt was synthesized analogously to the ni-
trate derivative by treating 1-methyl-5-amino-1H-tetrazole (0.179 g,
1.8 mmol) in concd perchloric acid (3 mL) with a solution of silver per-
chlorate (0.398 g, 1.9 mmol) in water (3 mL) to give the pure material as
a white powder, and recrystallization from hot water afforded single crys-
tals of the compound in high yield (0.342 g, 63%). DSC (58Cminꢁ1):
1028C (ꢁH2O); m.p. 1548C, 2528C (decomp); 1H NMR ([D6]DMSO,
400.18 MHz, 258C, TMS): d=7.02 (s, 2H; NH2), 3.74 ppm (s, 3H; CH3);
13C{1H} NMR ([D6]DMSO, 100.63 MHz, 258C, TMS): d=30.1 (CH3),
AHCTUNGTRENNUNG
C2H5N5O4ClAg (306.41): C 7.87, H 1.65, N 22.96, Cl 11.47, Ag 35.06;
found: C 7.79, H 1.91, N 22.75, Cl 11.30, Ag 35.26.
Silver 2-methyl-5-amino-1H-tetrazolium nitrate (15): A solution of silver
nitrate (0.385 g, 3 mmol) in water (3 mL) was added dropwise to a solu-
tion of 2-methyl-5-amino-1H-tetrazole (0.198 g, 0 mmol) in nitric acid
(65%, 2 mL), which resulted in a cloudy solution. This cloudy solution
was stirred for 15 min at RT, which caused precipitation of a white
powder, then the mixture was quickly heated to reflux for 5 min. Lastly,
water (3 mL) was added to the reaction mixture at RT and this was left
to stand. The powder that precipitated overnight was filtered off, washed
thoroughly with acetone and diethyl ether, and left to air-dry (0.333 g,
62%). DSC (58Cminꢁ1): m.p. 2598C (decomp); 1H NMR ([D6]DMSO,
400.18 MHz, 258C, TMS): d=6.0 (s, 2H; NH2), 4.0 ppm (s, 3H; CH3);
13C{1H} NMR ([D6]DMSO, 100.63 MHz, 258C, TMS): d=38.8 (CH3),
155.6 ppm (C NH2); 35Cl NMR ([D6]DMSO, 39.21 MHz, 258C, NaCl):
ꢁ
d=+1000 ppm (ClO4ꢁ); IR (KBr): n˜ =3326 (s), 3155 (vs), 2951 (m), 2742
(w), 1669 (vs), 1596 (s), 1485 (m), 1454 (w), 1428 (w), 1384 (w), 1322 (m),
1280 (w), 1237 (w), 1144 (s), 1120 (s), 1088 (s), 970 (w), 940 (w), 790 (m),
742 (w), 707 (w), 680 (m), 669 (w), 636 (m), 626 (m), 544 cmꢁ1 (m);
Raman (%): n˜ =3014 (8), 2956 (26), 1658 (13), 1595 (9), 1499 (12), 457
(13), 1421 (12), 1369 (15), 1344 (29), 1280 (19), 1152 (27), 1080 (22), 929
(89), 795 (67), 684 (21), 635 (14), 622 (18), 466 (20), 449 (20), 300 (22),
248 cmꢁ1 (13); FAB+ (xenon, 6 keV, m-NBA matrix): m/z (%): 206.0 (8)
166.9 ppm (C NH2); 14N NMR ([D6]DMSO, 40.51 MHz, 258C, CH3NO2):
ꢁ
d=ꢁ4.1 ppm (1N; NO3ꢁ); IR (KBr): n˜ =3395 (s), 3034 (m), 2957 (w),
2426 (w), 1921 (w), 1842 (w), 1762 (w), 1636 (m), 1554 (m), 1484 (vs),
1436 (m), 1423 (m), 1384 (vs), 1324 (vs), 1273 (s), 1210 (s), 1122 (m),
1094 (vs), 1054 (s), 1036 (s), 1011 (s), 881 (s), 839 (w), 808 (w), 776 (s),
760 (s), 748 (m), 701 (s), 674 (m), 649 (w), 468 cmꢁ1 (w); Raman (%): n˜ =
3215 (4), 3045 (6), 2987 (100), 2921 (6), 1590 (11), 1533 (58), 1526 (51),
1509 (22), 1471 (22), 1423 (15), 1391 (18), 1363 (15), 1256 (13), 1225 (18),
1082 (12), 1047 (89), 1011 (19), 941 (8), 875 (7), 824 (8), 760 (19), 718
(11), 455 (14), 439 (9), 399 (9), 359 (13), 275 (8), 241 cmꢁ1 (11); FAB+
(xenon, 6 keV, m-NBA matrix): m/z (%): 206.0 (3) [C2H4N5Ag], 208.0 (3)
ACTHNUTRGNEUNG
[C2H4N5Ag], 208.0 (7) [C2H6N5Ag]2+, 305.0 (10) [Ag(C2H5N5)2]+; elemen-
tal analysis calcd (%) for C2H6N5O4.5ClAg (315.42): C 7.62, H 1.92, N
22.20, Ag 34.20; found: C 7.89, H 1.69, N 22.09, Ag 34.58.
Synthesis of silver 1-methyl-5-amino-1H-tetrazolium nitrate (13): A solu-
tion of silver nitrate (0.368 g, 2 mmol) in water (4 mL) was added to a so-
lution of 1-methyl-5-amino-1H-tetrazole (0.198 g, 0 mmol) in concd nitric
acid (3 mL), which resulted in some cloudiness. The mixture was stirred
for 20 min and the precipitate formed was filtered off under vacuum,
washed with methanol and then with diethyl ether, and dried under high
vacuum to give the pure title compound as an insoluble white powder, as
confirmed by elemental analysis (0.262 g, 48%). Recrystallization from
hot water gave X-ray-quality crystals of 17 and silver nitrate. DSC
(58Cminꢁ1): m.p. 1828C, 2268C (decomp); 1H NMR ([D6]DMSO,
400.18 MHz, 258C, TMS): d=7.01 (s, 2H; NH2), 3.74 ppm (s, 3H; CH3);
13C{1H} NMR ([D6]DMSO, 100.63 MHz, 258C, TMS): d=31.9 (CH3),
ACTHNUTRGNEUNG
[C2H6N5Ag]2+, 305.0 (4) [Ag(C2H5N5)2]+; elemental analysis calcd (%) for
C2H5N6O3Ag (268.97): C 8.96, H 1.88, N 31.36, Ag 39.90; found: C 8.97,
H 1.89, N 31.09, Ag 39.65%.
Bis-(1,4-dimethyl-5-iminotetrazole) silver picrate (16): Picric acid
(0.229 g, 1.00 mmol) was dissolved in methanol (5 mL) and treated with
neat potassium hydroxide (0.056 g, 1.00 mmol), which resulted in the pre-
cipitation of a bright orange solid. The reaction mixture was stirred for
30 min at RT and then reacted with a small excess of anhydrous silver
perchlorate (0.249 g, 1.20 mmol; weighed in a glovebox). The immediate
precipitation of brown silver picrate (highly sensitive!) took place and
the reaction mixture was stirred for further 1 h in the absence of light.
Then the insoluble solid was filtered off carefully and washed with water
(to remove excess AgClO4) and methanol. The methanol-wet silver pic-
rate was carefully transferred into a plastic beaker, suspended in metha-
nol (10 mL), and treated with a solution of 1,4-dimethyl-5-aminotetrazoli-
um iodide (0.193 g, 0.80 mmol) in methanol (5 mL) to give the immediate
precipitation of yellow silver iodide. The reaction mixture was stirred for
30 min in the absence of light, then the silver iodide was filtered off,
washed with methanol, and discarded. The filtrate was left to slowly
evaporate to give two types of yellow single crystals, namely, bright
yellow prismic single crystals, which were identified as 1,4-dimethyl-5-
aminotetrazolium picrate and light yellow needle-like crystals, which
were identified as the title compound. The crystals of 16 (formed as a by-
product) were mechanically separated and analyzed (0.012 g, 5%).
1H NMR ([D6]DMSO, 400.18 MHz, 258C, TMS): d=8.58 (s, 2H; aromat-
ic H), 3.74 (s, 12 ; CH3), 3.29–3.43 ppm (brs, 2H; NH); 13C{1H} NMR
155.7 ppm (C NH2); 14N NMR ([D6]DMSO, 40.51 MHz, 258C, CH3NO2):
ꢁ
d=ꢁ4.3 ppm (1N; NO3ꢁ); IR (KBr): n˜ =3402 (m), 3323 (s), 3265 (m),
2948 (w), 2192 (m), 3157 (s), 2950 (w), 2426 (w), 2345 (w), 1767 (w), 1747
(w), 1667 (s), 1648 (s), 1595 (s), 1494 (m), 1384 (vs), 1338 (s), 1320 (s),
1303 (s), 1238 (m), 1144 (m), 1121 (w), 1089 (m), 1051 (w), 1041 (m), 984
(w), 833 (w), 825 (w), 817 (w), 788 (m), 742 (w), 736 (w), 707 (w), 679
(m), 568 (w), 483 cmꢁ1 (w); Raman (%): n˜ =2986 (22), 2960 (16), 2798
(5), 1652 (57), 1497 (60), 1416 (62), 1339 (66), 1281 (62), 1144 (59), 1082
(57), 1043 (100), 989 (42), 791 (70), 680 (39), 481 (31), 304 cmꢁ1 (30);
FAB+ (xenon, 6 keV, m-NBA matrix): m/z (%): 206.0 (3) [C2H4N5Ag],
ACTHNUTRGNEUNG
208.0 (3) [C2H6N5Ag]2+, 305.0 (5) [Ag(C2H5N5)2]+; elemental analysis
calcd (%) for C2H5N6O3Ag (268.97): C 8.96, H 1.88, N 31.36, Ag 39.90;
found: C 8.90, H 2.09, N 31.19, Ag 39.68.
Silver 2-methyl-5-amino-1H-tetrazolium perchlorate (14): Anhydrous
silver perchlorate (0.400 g, 1.9 mmol; weighed in a glovebox) was dis-
solved in water (3 mL) and added to a solution of 2-methyl-5-amino-1H-
tetrazole (0.179 g, 1.8 mmol) in perchloric acid (70%, 2 mL). After
15 min, a white powder precipitated and the reaction mixture was quickly
heated to reflux for 5 min (not all solid dissolved). Single crystals of the
ꢁ
([D6]DMSO, 100.63 MHz, 258C, TMS): d=160.9 (1C; C O), 149.9 (2C;
1174
www.chemeurj.org
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 1164 – 1176

Energetic Silver Salts
FULL PAPER
ꢁ
ꢁ
ꢁ
ꢁ
C NH2), 141.8 (2C; C NO2), 125.2 (2C; C H), 124.4 (1C; C NO2),
33.0 ppm (CH3); 14N NMR ([D6]DMSO, 40.55 MHz, 258C, MeNO2): d=
ꢁ12 ppm (3N; NO2); IR (KBr): n˜ =3320 (s), 3070 (m), 2922 (m), 1645
(vs), 1630 (s), 1449 (m), 1395 (s), 1364 (m), 1174 (w), 1053 (w), 1061 (m),
1049 (m), 1030 (m), 975 (w), 712 (w), 690 (w), 578 cmꢁ1 (w); Raman (%):
n˜ =3312 (2), 3078 (16), 2999 (3), 2927 (15), 1566 (41), 1515 (17), 1481
(21), 1366 (27), 1343 (100), 1304 (36), 1290 (66), 1161 (18), 1086 (18), 940
(21), 905 (11), 823 (31), 783 (11), 700 (14), 591 (8), 337 (20), 300 (4),
169 cmꢁ1 (14); FAB+ (xenon, 6 keV, m-NBA matrix): m/z (%): 334.0 (12)
b) T. M. Klapçtke, C. Mirꢀ Sabatꢁ, Proceed. 10th Sem. New Trends
Res. Energ. Mater. (Pardubice, Czech Republic) 2007; c) H. Xue, Y.
Gao, B. Twamley, J. M. Shreeve, Inorg. Chem. 2005, 44, 5068–5072;
d) T. M. Klapçtke, K. Karaghiosoff, P. Mayer, A. Penger, J. M.
Welch, Propellants Explos. Pyrotech. 2006, 31, 188–195; e) H. Xue,
H. Gao, B. Twamley, J. M. Shreeve, Chem. Mater. 2007, 19, 1731–
1739; f) A. Hammerl, G. Holl, M. Kaiser, T. M. Klapçtke, P. Mayer,
H. Nçth, H. Piotrowski, M. Warchhold, Eur. J. Inorg. Chem. 2002,
2002, 834–845; g) A. Hammerl, G. Holl, T. M. Klapçtke, P. Mayer,
H. Nçth, H. Piotrowski, M. T. Suter, Z. Naturforsch. B 2001, 56,
857–870; h) A. Hammerl, T. M. Klapçtke, H. Nçth, M. Warchhold,
G. Holl, M. Kaiser, U. Ticmanis, Inorg. Chem. 2001, 40, 3570–3575;
i) K. A. Clark, T. M. Klapçtke, 230th ACS Nat. Meet. (Washington,
DC, United States) 2005.
[AgACHTUNGTRENNUNG
(C3H7N5)2]+; FABꢁ (xenon, 6 keV, m-NBA matrix) m/z (%): 228.0
(51) [C6H2N3O7]ꢁ; elemental analysis calcd (%) for C12H16N13O7Ag
(562.21): C 25.63, H 2.87, N 32.39; found: C 25.77, H 2.94, N 32.50.
[4] V. A. Ostrovskii, M. S. Pevzner, T. P. Kofman, I. V. Tselinskii, Tar-
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Acknowledgements
[5] R. C. West, S. M. Selby, Handbook of Chemistry and Physics, 48th
ed., The Chemical Rubber Co., Cleveland, OH, 1967–1968,
pp. D22–D51.
Financial support of this work by the Ludwig-Maximilian University of
Munich (LMU), the Fonds der Chemischen Industrie (FCI), the Europe-
an Research Office (ERO) of the U.S. Army Research Laboratory
(ARL) and ARDEC (Armament Research, Development and Engineer-
ing Center) under contract nos. N 62558-05-C-0027, R&D 1284-CH-01,
R&D 1285-CH-01, 9939-AN-01 & W911NF-07–1–0569, and the Bundes-
wehr Research Institute for Materials, Explosives, Fuels and Lubricants
(WIWEB) under contract nos. E/E210/4D004/X5143 & E/E210/7D002/
4F088 is gratefully acknowledged. The authors acknowledge collabora-
tions with Dr. M. Krupka (OZM Research, Czech Republic) in the de-
velopment of new testing and evaluation methods for energetic materials
and with Dr. M. Sucesca (Brodarski Institute, Croatia) in the develop-
ment of new computational codes to predict the detonation parameters
of high-nitrogen explosives. We are indebted to and thank Dr. Betsy M.
Rice (ARL, Aberdeen, Proving Ground, MD) for many helpful and in-
spired discussions and support of our work.
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