A new route to metal azides

Article abstract of DOI:10.1002/anie.201404561

Beside several other applications, metal azides can be used for the synthesis of nitridophosphates and binary nitrides. Herein we present a novel synthetic access to azides: Several metals, such as main-group, transition metals, and rare-earth metals, react with silver azide in liquid ammonia as a solvent giving the corresponding metal azides. In this work Mn(N₃)₂, Sn(N₃)₂, and Eu(N₃)₂, as well as their ammonia complexes were synthesized for the first time through low- temperature methods. Also a simpler access to Zn(N₃)₂ was possible. At room temperature and the respective vapor pressure of NH₃, it became possible to grow single crystals of the dinuclear holmium azide [Ho₂(m-NH₂)₃-(NH₃)₁₀](N₃)₃·1.25NH₃. We are confident that this new route could lead to novel metal azides as well as nitrides of the main-group, the transition, and the rare-earth metals upon careful decomposition.

Full text of DOI:10.1002/anie.201404561

Angewandte
Chemie
DOI: 10.1002/anie.201404561
Metal Azides
A New Route to Metal Azides**
Thomas G. Mꢀller, Friedrich Karau, Wolfgang Schnick,* and Florian Kraus*
Dedicated to Professor Hubert Schmidbaur on the occasion of his 80th birthday
Abstract: Beside several other applications, metal azides can
be used for the synthesis of nitridophosphates and binary
nitrides. Herein we present a novel synthetic access to azides:
Several metals, such as main-group, transition metals, and rare-
earth metals, react with silver azide in liquid ammonia as
a solvent giving the corresponding metal azides. In this work
Mn(N ) , Sn(N ) , and Eu(N ) , as well as their ammonia
cyanates, and thiocyanates is an interesting field. Especially as
most of the crystal structures of transition-metal cyanides,
carbodiimides, cyanates, and thiocyanates are hitherto
unknown, whereas substantial progress has been made in
[
2]
the field of transition-metal azides. Thus, Mo(N ) , W(N ) ,
3
6
3 6
[
3]
and Ti(N3)4 were synthesized and structurally characterized
as well as some new high-explosive main-group azides (e.g.
3
2
3
2
3 2
[
4]
[5]
[6]
[7]
complexes were synthesized for the first time through low-
temperature methods. Also a simpler access to Zn(N ) was
As(N ) , Sb(N ) , Bi(N ) , (P N)(N ) , or Te(N ) ).
3 5 3 3 3 3 3 3 3 3 4
Other transition-metal azides, such as, Nb(N ) or Ta(N ) ,
3
2
3
5
3 5
possible. At room temperature and the respective vapor
are difficult to synthesize and a full characterization has been
[
8]
pressure of NH , it became possible to grow single crystals of
hampered by their highly explosive character. Another
modern application of azides employs the high synthetic
3
the
dinuclear
holmium
azide
[Ho (m-NH ) -
2 2 3
[9]
(
NH ) ](N ) ·1.25NH . We are confident that this new route
potential of these compounds in organic syntheses, for
3
10
3
3
3
[10]
could lead to novel metal azides as well as nitrides of the main-
group, the transition, and the rare-earth metals upon careful
decomposition.
example, the Curtius reaction or click cycloadditions.
During the last few years, we have successfully utilized
[
11–13]
metal azides for the synthesis of novel nitridophosphates
and binary nitrides.
[
14]
High N partial pressures, resulting
2
T
he synthetic approach to hydrazoic acid and simple metal
in situ from thermolysis reactions of azides, have been used
frequently in our synthetic approaches to synthesize metal-
containing nitridophosphates starting from the respective
metal azide and P N . Thereby phosphorus nitride P N
5
azides (e.g. NaN ) deriving from HN were discovered during
3
3
the pioneering work of Theodor Curtius at the end of the 19th
century. However, it was only in the mid-1960s that chemists
[
1]
3
5
3
began to look at HN and its derivative compounds in more
(thermal decomposition > 8508C at normal pressure) is
3
detail. Presumably, the severely explosive decomposition of
most metal azides, especially the more covalent ones, and of
prevented from dissociating into the elements [Eq. (1)] at
[1]
4 P N ! 12 PN þ 4 N ! 3 P þ 10 N
ð1Þ
HN itself, may have discouraged any further investigation.
3
5
2
4
2
3
More recently, azides have moved into research targeting
high-energy density materials (HEDM), thus exhibiting an
expanding field of applications and a promising potential for
chemical syntheses. As pseudohalides the structural–chemical
properties comparison of azides, carbodiimides, cyanides,
the high reaction temperatures of above 10008C that are
indispensable for the crystallization of the targeted metal
[
11,12]
nitridophosphates.
To expand this “azide route” to a more generalized synthetic
approach, it was necessary to make pure azides of a wider
choice of metals available. Interestingly, many of these
potential compounds have never been synthesized in quanti-
ties larger than a few milligrams. Especially, many azides with
oxophilic and hydrophilic cations are to date completely
unknown.
[
*] M. Sc. T. G. Mꢀller, Priv.-Doz. Dr. F. Kraus
AG Fluorchemie, Department Chemie, Technische Universitꢁt
Mꢀnchen
Lichtenbergstrasse 4, 85747 Garching (Germany)
E-mail: florian.kraus@tum.de
Homepage: http://www.fluor.ch.tum.de
Herein we describe the synthesis of the ammonia com-
plexes and the pure, solvent-free, binary metal azides
Dr. F. Karau, Prof. Dr. W. Schnick
Department Chemie, Lehrstuhl fꢀr Anorg. Festkçrperchemie
Ludwig-Maximilians-Universitꢁt
[15]
Mn(N ) ,
Sn(N ) , Eu(N ) , and Zn(N ) utilizing a new
3 2 3 2 3 2
3
2
synthetic approach: Electropositive metals (M) undergo
Butenandtstrasse 5-13, 81377 Mꢀnchen (Germany)
[16–18]
a stoichiometric redox reaction with silver azide
being dissolved in liquid and absolutely water-free ammonia
Eq. (2)].
while
[
**] We thank Dipl.-Chem. Florian Pucher, Ludwig-Maximilians-Univer-
sitꢁt Mꢀnchen, and B.Sc. Georg Monsch, Technische Universitꢁt
Mꢀnchen, for their preparative work. Generous financial support by
the Fonds der Chemischen Industrie (FCI) and the Deutsche
Forschungsgemeinschaft (DFG), project SCHN 377/11-1, is grate-
fully acknowledged. F.K. thanks the DFG for a Heisenberg fellow-
ship.
[
M þ 2 AgN
3
! MðN
3
Þ2 ðsolvÞ þ 2 AgðsÞ
ð2Þ
According to our experience this redox reaction cannot be
carried out in aqueous solutions or suspensions, because
under such conditions the azide ions would be reduced to NH3
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201404561.
Angew. Chem. Int. Ed. 2014, 53, 1 – 4
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1
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.
Angewandte
Communications
and stable aqua or oxo complexes of the respective metals
would be formed.
can easily be avoided by limiting the heating rate to below
ꢀ
1
18Cmin . The compounds Mn(N ) , Sn(N ) , and Zn(N )
3 2
3
2
3
2
The redox reactions of silver azide and metals (M = Mn,
Sn, Zn, Eu) require a reaction time between 9 and 10 days at
were obtained as colorless powders, which readily undergo
severe explosions. Eu(N ) was obtained as an explosive and
3
2
ꢀ
408C. The reaction rates at ꢀ408C are slow though the
deep yellow powder. To our knowledge binary Sn(N ) and
3 2
Eu(N ) have never been described in the literature. Mn(N ) ,
3 2 3 2
redox potentials of Ag and the respective metal M differ
significantly. In this case the reaction mixtures were inten-
sively stirred using a magnetic stirrer when all AgN3 is
dissolved (after approximately one day). As long as there is
Sn(N ) , Eu(N ) , and Zn(N ) were unequivocally identified
3
2
3
2
3 2
as solvent-free azides by FTIR-spectroscopy. Thermogravi-
metric analysis of Mn(N ) (NH ) shows decomposition in
3
2
3 2
a residue of AgN the vessel only should be shaken very
three steps (Figure 2). The first two steps marking the
3
gently to prevent silver azide grains to be ground at the glass
wall of the vessel. Crust formation occurring at the fluid level
and consisting of silver azide at the beginning of the reaction
and the respective metal azide at the end of the reaction have
to be carefully scraped off the glass every day with a Teflon
spatula. The scraping has to be performed with extreme care
to prevent the highly hazardous, friction and shock sensitive
azides (especially silver azide and tin azide) detonating. The
elemental silver, which is generated by the redox reaction
[
Eq. (2)], has to be separated from the azide solution by
filtration at ꢀ408C. After evaporation of NH , the raw metal
3
azide products were obtained. Chemical analyses, X-ray
powder diffraction, and FTIR-spectroscopy showed that
Sn(N3)2 and Eu(N3)2 were obtained as amorphous and
undefined complexes (in terms of their NH3 content),
whereas well-crystallized and phase-pure Mn(N ) (NH )
3 2
3
2
[
19–21]
and Zn(N ) (NH )
were obtained as powders in the
first reaction step. The crystal structure of Zn(N ) (NH ) ,
3
2
3 2
Figure 2. Thermogravimetric analysis of Mn(N ) (NH ) . All percen-
3 2 3 2
3
2
3 2
[
19]
tages are in relation to the initial mass of Mn(N ) (NH ) .
already described, was verified for the bulk material by
a Rietveld refinement. Through powder X-ray diffraction
3
2
3 2
(
Figure 1), the crystal structure of Mn(N ) (NH ) was
3 2 3 2
obtained. Mn(N ) (NH ) crystallizes in the tetragonal space
elimination of ammonia molecules, whereas the last step
can be unequivocally identified as exothermic decomposition
of binary Mn(N ) . The chemical formulae of the binary
3
2
3 2
[
22]
group I4/m and is isotypic to Mg(N ) (NH ) .
3
2
3 2
Finally, the powders of the metal azide ammonia com-
3
2
plexes (M = Mn, Sn, Zn, Eu) were treated in high vacuum (2 ꢀ
azides were calculated from the results of elemental analyses.
Considering that no single crystals of the ammonia
complexes, but only microcrystalline or amorphous powders
were obtained after several days of reaction time by the low-
temperature method, the reaction was carried out in a glass
ampule at room temperature and the respective vapor
pressure of 8.5 bar. By choosing these conditions, the
reactions proceeded to completion within several hours. The
above mentioned azides were then isolated as described
above. This method successfully yielded single crystals in the
case of holmium after an additional storage of only four days
at room temperature. The colorless crystals grew on the
precipitated elemental silver. These were identified by single-
crystal X-ray diffraction (details can be found in the
Supporting Information) as dinuclear ammine complexes of
holmium azide: [Ho (m-NH ) (NH ) ](N ) ·1.25NH . The
ꢀ6
1
0
mbar) for several days at temperatures between 40 and
1
108C to liberate NH . During these procedures explosions
3
2
2
3
3
10
3
3
3
asymmetric unit of tris-m-amido decaammine diholmium(III)
triazide ammonia (1/1.25) is shown in Figure 3. Two holmium
atoms are bridged by three amide ligands. Five ammine
ligands at each metal atom complete the coordination sphere.
The Ho–NH2 distances are in the range 2.361(2) and
2
.441(2) ꢁ and are, of course, shorter than the Ho–NH3
Figure 1. Observed (crosses) and calculated (gray line) X-ray powder
distances which are between 2.543(2) and 2.606(2) ꢁ. Three
azide ions are found as counterions with NꢀN bond lengths
diffraction pattern of Mn(N ) (NH ) . Positions of Bragg reflect-
3
2
3 2
ions (vertical lines), difference profile for the Rietveld refinement (black
line).
2
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Chemie
[
[
1] T. Curtius, Ber. Dtsch. Chem. Ges. 1890, 23, 3023.
2] R. Haiges, J. A. Boatz, R. Bau, S. Schneider, T. Schroer, M.
Yousufuddin, K. O. Christe, Angew. Chem. 2005, 117, 1894 –
1899; Angew. Chem. Int. Ed. 2005, 44, 1860 – 1865.
[
3] R. Haiges, J. A. Boatz, S. Schneider, T. Schroer, M. Yousufuddin,
K. O. Christe, Angew. Chem. 2004, 116, 3210 – 3214; Angew.
Chem. Int. Ed. 2004, 43, 3148 – 3152.
[
[
[
[
4] T. M. Klapçtke, A. Schulz, J. McNamara, J. Chem. Soc. Dalton
Trans. 1996, 2985 – 2987.
5] A. Villinger, A. Schulz, Angew. Chem. 2010, 122, 8190 – 8194;
Angew. Chem. Int. Ed. 2010, 49, 8017 – 8020.
6] M. Gçbel, K. Karaghiosoff, T. M. Klapçtke, Angew. Chem. 2006,
118, 6183 – 6186; Angew. Chem. Int. Ed. 2006, 45, 6037 – 6040.
7] T. M. Klapçtke, B. Krumm, P. Mayer, I. Schwab, Angew. Chem.
2003, 115, 6024 – 6026; Angew. Chem. Int. Ed. 2003, 42, 5843 –
5846.
[
8] R. Haiges, J. A. Boatz, T. Schroer, M. Yousufuddin, K. O.
Christe, Angew. Chem. 2006, 118, 4948 – 4953; Angew. Chem. Int.
Ed. 2006, 45, 4830 – 4835.
Figure 3. View of the asymmetric unit of [Ho (m-NH ) -
2
2 3
(
NH ) ](N ) ·1.25NH . Thermal ellipsoids are set at 70% probability
[9] K. Banert, Y.-H. Joo, T. Rꢂffer, B. Walfort, H. Lang, Angew.
Chem. 2007, 119, 1187 – 1190; Angew. Chem. Int. Ed. 2007, 46,
3
10
3
3
3
[
27]
at 123 K, hydrogen atoms isotropic with arbitrary radii.
1168 – 1171.
[
[
[
10] V. D. Bock, H. Hiemstra, J. H. van Maarseveen, Eur. J. Org.
Chem. 2006, 51 – 68.
11] F. W. Karau, W. Schnick, J. Solid State Chem. 2005, 178, 135 –
around 1.17 ꢁ. Two ammonia molecules of crystallization are
present, whereof one of them is partially occupied (25%).
In summary, the above described two methods afford the
preparation of metal azides of the main-group, the transition
metals, and the rare-earth metals. For the first time, Sn(N ) ,
141.
12] F. Karau, W. Schnick, Angew. Chem. 2006, 118, 4617 – 4620;
Angew. Chem. Int. Ed. 2006, 45, 4505 – 4508.
[13] F. W. Karau, L. Seyfarth, O. Oeckler, J. Senker, K. Landskron,
W. Schnick, Chem. Eur. J. 2007, 13, 6841 – 6852.
3
2
[
[
[
14] F. Karau, W. Schnick, Z. Anorg. Allg. Chem. 2007, 633, 223 – 226.
15] L. Wçhler, F. Martin, Ber. Dtsch. Chem. Ges. 1917, 50, 586 – 596.
16] G.-C. Guo, Q.-M. Wang, T. C. W. Mak, J. Chem. Crystallogr.
and Eu(N ) , as well as their ammine complexes and the NH
3
complexes of Mn and Ho azide, were synthesized and made
available for subsequent investigations and syntheses.
3
2
1999, 29, 561 – 564.
Zn(N3) was obtained with our method in higher purity
2
[17] A. D. Joffe, Proc. R. Soc. London Ser. A 1951, A208, 188 – 199.
[18] A. Stettbacher, Explosivstoffe, 1954.
[19] I. Agrell, N. G. Vannerberg, Acta Chem. Scand. 1971, 25, 1630.
[
[
[
[
[
(
free of solvent) and in a simpler way avoiding the use of
[23,24]
HN3.
In addition, a dinuclear ammine complex of
20] C. Brosset, I. Agrell, Nature 1964, 202, 1210.
holmium azide was synthesized and characterized by the
determination of its single-crystal structure. We predict that
this approach can be expanded to a number of further
electropositive metals; currently, this new route is under
investigation with further transition and rare-earth metals as
well as some actinoids. The methods proposed herein expand
on the currently available routes for the synthesis of azides
21] L. M. Dennis, H. Isham, J. Am. Chem. Soc. 1907, 29, 18 – 31.
22] F. Karau, W. Schnick, Z. Anorg. Allg. Chem. 2006, 632, 49 – 53.
23] H. Winkler, H. Krischner, Indian J. Chem. 1975, 13, 611 – 614.
24] S. R. Yoganarasimhan, R. C. Jain, Indian J. Chem. 1969, 7, 808 –
809.
[25] T. M. Klapçtke, B. Krumm, M. Scherr, R. Haiges, K. O. Christe,
Angew. Chem. 2007, 119, 8840 – 8845; Angew. Chem. Int. Ed.
2
[
25,26]
007, 46, 8686 – 8690.
26] R. Haiges, J. A. Boatz, K. O. Christe, Angew. Chem. 2010, 122,
180 – 8184; Angew. Chem. Int. Ed. 2010, 49, 8008 – 8012.
27] Further details of the crystallographic data of [Ho (m-NH ) -
from fluorides and trimethylsilyl azide.
[
[
8
Received: April 22, 2014
Published online: && &&, &&&&
2
2 3
(
NH ) ](N ) ·1.25NH may be obtained from the Fachinforma-
3 10 3 3 3
tionszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Ger-
many (Fax: + 49-7247-808-666; E-Mail: crysdata@fiz-karlsru-
Keywords: ammonia · azides · rare-earth-metal azide ·
redox reactions · transition-metal azides
he.de,
http://www.fiz-karlsruhe.de/request for deposited da-
.
ta.html) on quoting the depository number CSD-427572.
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www.angewandte.org
3
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.
Angewandte
Communications
Communications
Metal Azides
N(ergy) rich: Several metals, such as
main-group, transition, and rare-earth
metals, react with silver azide in liquid
ammonia as the solvent giving the cor-
responding metal azides. For the first
time, Sn(N ) and Eu(N ) as well as their
T. G. Mꢁller, F. Karau, W. Schnick,*
F. Kraus*
&&&& — &&&&
A New Route to Metal Azides
3
2
3 2
ammonia complexes were synthesized. In
addition, ammine complexes of Mn and
Ho azide are reported (see structure of
[
Ho (m-NH ) (NH ) ](N ) ·1.25NH ;
2 2 3 3 10 3 3 3
green Ho, blue N, white H).
4
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Angew. Chem. Int. Ed. 2014, 53, 1 – 4
These are not the final page numbers!