Highly sensitive ammonium tetraazidoaurates(III)

Article abstract of DOI:10.1021/ic051543i

The preparation and characterization of selected ammonium and methylammonium tetraazidoaurates(III) are reported. All ammonium salts were shown to be highly explosive materials. The first crystal structure of such an ammonium salt, that of [Me₄

Full text of DOI:10.1021/ic051543i

Inorg. Chem. 2005, 44, 9625−9627
Highly Sensitive Ammonium Tetraazidoaurates(III)
Thomas M. Klapo1 1
tke,* Burkhard Krumm, Juan-Carlos Galvez-Ruiz,† and Heinrich Noth†
Departments of Chemistry and Biochemistry, Ludwig-Maximilian UniVersity of Munich,
Butenandtstrasse 5-13(D), D-81377 Munich, Germany
Received September 9, 2005
The preparation and characterization of selected ammonium and
methylammonium tetraazidoaurates(III) are reported. All ammonium
salts were shown to be highly explosive materials. The first crystal
structure of such an ammonium salt, that of [Me4N][Au(N3)4],
features polymeric units of the anion, which are linked by weak
Au‚‚‚Au interactions.
in the size of the ammonium cation should likely cause an
increase of the sensitivity of the salts.
The preparation of tetramethylammonium tetraazidoaurate-
(III) (1) is identical with the procedure described for those
with other larger cations4b,5a (eq 1).
(1) excess NaN3/(2) [Me4N]Br
[Me N][Au(N ) ]
(1)
H[AuCl4]
8
4
3 4
H2O/EtOH
1
In the very recent past, there has been considerable interest
in the chemistry of binary main-group and transition-metal
azides.1,2 Gold azide species, in particular, exist in the anionic
form in the oxidation states I+, [Au(N3)2]-, and III+,
[Au(N3)4]-, whereas the neutral azides AuN3 and Au(N3)3
are unknown to our knowledge.3 The tetraazidoaurate(III)
anion can be stabilized using relatively large counterions,
such as [Ph4As]+, [Et4N]+, [n-Bu4N]+, or [Me3(cetyl)N]+.4,5
In contrast, alkali-metal tetraazidoaurates(III) are reported
to be extremely explosive materials.4-6 Our interest in high-
nitrogen-containing element azides prompted us to carry out
a study on ammonium tetraazidoaurates(III), where only
sparse information, with respect to the above-mentioned
examples, exists. According to previous reports, a decrease
The synthesis of the ammonium salts with lower methyl
content is slightly different (eq 2).
excess AgN3
[R NH ][Au(N ) ]
R ) Me (2), H (3)
[R2NH2][AuCl4]
8
(2)
2
2
3 4
MeOH
The hitherto not described dimethylammonium tetrachlo-
roaurate(III) was prepared in a fashion similar to that
described for [NH4][AuCl4].7 Crystals of [Me2NH2][AuCl4]
suitable for X-ray diffraction decomposed repeatedly upon
contact with the X-ray beam depositing gold. A similar
behavior was observed during the crystal structure determi-
nation of [NH4][AuCl4].8
Explicit Safety Hazard! Ammonium tetraazidoaurate(III),
[NH4][Au(N3)4] (3), exploded on various occasions and is
an extremely dangerous material.9 The dimethyl- and tetra-
methylammonium salts 1 and 2 explode violently upon
contact with a flame.
* To whom correspondence should be addressed. E-mail:
tmk@cup.uni-muenchen.de, bkr@cup.uni-muenchen.de
† Crystal structure determination.
(1) Main group azides (with older references cited therein): (a) Haiges,
R.; Boatz, J. A.; Vij, A.; Vij, V.; Gerken, M.; Schneider, S.; Schroer,
T.; Yousufuddin, M.; Christe, K. O. Angew. Chem., Int. Ed. 2004,
43, 6676. (b) Klapo¨tke, T. M.; Krumm, B.; Mayer, P.; Schwab, I.
Angew. Chem., Int. Ed. 2003, 42, 5843. (c) Haiges, R.; Boatz, J. A.;
Gerken, M.; Schneider, S.; Schroer, T.; Christe, K. O. Angew. Chem.,
Int. Ed. 2003, 42, 5847.
(2) Transition metal azides (with older references cited therein): (a)
Haiges, R.; Boatz, J. A.; Bau, R.; Schneider, S.; Schroer, T.;
Yousufuddin, M.; Christe, K. O. Angew. Chem., Int. Ed. 2005, 44,
1860. (b) Haiges, R.; Boatz, J. A.; Schneider, S.; Schroer, T.;
Yousufuddin, M.; Christe, K. O. Angew. Chem., Int. Ed. 2004, 43,
3148.
(3) Beck, W.; Klapo¨tke, T. M.; Klu¨fers, P.; Kramer, G.; Riena¨cker, C.
M. Z. Anorg. Allg. Chem. 2001, 627, 1669 and references cited therein.
(4) (a) Beck, W.; Schuierer, E.; Feldl, K. Angew. Chem., Int. Ed. Engl.
1966, 5, 249. (b) Beck, W.; Fehlhammer, W. P.; Po¨llmann, P.;
Schuierer, E.; Feldl, K. Chem. Ber. 1967, 100, 2335. (c) Beck, W.;
No¨th, H. Chem. Ber. 1984, 117, 419.
The salts 1,10 2,11 and 311 display red-orange crystalline
solids and exhibit, as to be expected, an increased sensitivity
with less carbon content. Initial studies show that the carbon-
free ammonium tetraazidoaurate (3) is a promising candidate
(7) Stra¨hle, J.; Gelinek, J.; Ko¨lmel, M. Z. Anorg. Allg. Chem. 1979, 456,
241.
(8) Bonamico, M.; Dessy, G. Acta Crystallogr. 1973, B29, 1737.
(9) General considerations: All manipulations were carried out under light
exclusion in plastic beakers and on a small scale with extreme care.
Appropriate shielding is essential; for a detailed description of the
equipment, please see ref 1b. (a) A solution of [NH4][Au(N3)4] in
methanol exploded upon attempts of solvent removal with a rotary
evaporator, leaving no residues of the glass flask except powdered
glass! (b) A solution of [NH4][Au(N3)4] in acetone exploded under
light exclusion upon slow evaporation of the solvent in a polypropylene
beaker surrounded by a wire netting located in a safety cabinet,
resulting in a completely destroyed beaker! The originally intended
preparation of the full methylammonium series including the [MeNH3]
and [Me3NH] tetraazidoaurate(III) salts was refrained from because
of the observed hazards.
(5) (a) Schmidtke, H. H.; Garthoff, D. J. Am. Chem. Soc. 1967, 89, 1317.
(b) Vogler, A.; Quett, C.; Kunkely, H. Ber. Bunsen-Ges. Phys. Chem.
1988, 92, 1486.
(6) (a) Curtius, T.; Rissom, J. J. Prakt. Chem. 1898, 58, 261. (b) Wehlan,
M.; Thiel, R.; Fuchs, J.; Beck, W.; Fehlhammer, W. P. J. Organomet.
Chem. 2000, 613, 159.
10.1021/ic051543i CCC: $30.25
Published on Web 11/24/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 26, 2005 9625

COMMUNICATION
Figure 1. Molecular structure of 1 in the crystal (displayed is a “dimeric”
unit). Ellipsoids are shown with 40% probability. Bond lengths (Å) and
angles (deg) of the anions: Au1-N1 2.015(6), Au1-N4 1.996(9), Au1-
N7 2.071(7), Au1-N10 2.04(1), Au2-N13 2.04(1), Au2-N16 1.95(1),
Au2-N19 2.02(1), Au2-N22 2.06(1), N1/4/7/10-N2/5/8/11 1.19(1)-1.21-
(1), N2/5/8/11-N3/6/9/12 1.15(1)-1.16(1), N13/16/19/22-N14/17/20/23
1.19(1)-1.24(1), N14/17/20/23-N15/18/21/24 1.13(1)-1.16(1), Au1‚‚‚Au2
3.507(3); N1-Au1-N4 99.7(3), N1-Au1-N7 173.3(3), N1-Au1-N10
88.6(3), N10-Au1-N4 171.6(4), Au1-N1/4/7/10-N2/5/8/11 116.6(7)-
124.3(7), N1/4/7/10-N2/5/8/11-N3/6/9/12 172(1)-176(1); corresponding
angles of the Au2 anion are similar.
for the deposition of gold on surfaces, which can serve as a
hydrogenation catalyst.12
The product from the decomposition is always colloidal
gold. The formation of dinitrogen is detected after short
periods by 14N NMR spectroscopy as evidence of slow
decomposition in solution (pressure formed) aside from gold
deposition. In addition to the friction and impact sensitivity
of these salts, light sensitivity is observed, similar to that of
the tetrachloroaurates(III).
Various attempts were required to determine the crystal
structure of 1 because of the additional sensitivity to X-ray
exposure [as observed already for tetrachloroaurate(III) salts],
shown in Figure 1.13
Figure 2. Packing diagram of 1 with a view along the a axis, showing
the stacking of the anions. Dashed lines represent alternating Au‚‚‚Au
contacts of 3.507(3) and 3.584(3) Å.
The gold atoms are surrounded by azide groups in the
expected square-planar fashion with bond lengths and angles
in the expected ranges, similar to those observed for [Ph4-
As][Au(N3)4].3 A striking difference in this structure is the
presence of polymeric stacking of the anion, consisting of
weak Au‚‚‚Au interactions of 3.507(3) and 3.584(3) Å.14
These distances are slightly below the sum of the van der
Waals radii (3.6 Å).15 There is clearly no inversion center
between the gold atoms, although it appears as such.
Figure 2 shows a plot of the packing diagram of 1,
featuring a stacking of monomeric anions in parallel layers
with the [Me4N]+ units located in between.
(10) Into a solution of 0.100 g (0.25 mmol) of H[AuCl4]‚3H2O in 10 mL
of water in a beaker is added 0.7 g (10.0 mmol) of NaN3. The color
changes from yellow to red. Into this mixture is added, with stirring,
a solution of 1.5 g (10.0 mmol) of [Me4N]Br in 10 mL of water/
ethanol. Upon cooling with ice, the salt [Me4N][Au(N3)4] (1)
precipitates as red-orange needles (0.065 g, 59%). 1H NMR (acetone-
d6): δ 3.43 (Me, s). 13C NMR (acetone-d6): δ 55.9 (Me, t, 1JC-14N
)
4.0 Hz). 14N NMR (acetone-d6): δ -132.8 (Nâ), -178 (Nγ), -279
(NR), -338.6 (Me4N). IR (KBr): 3034 w (νCH), 2044/2037/2013 vs
(νas,N ), 1482 m, 1447 w, 1414 w, 1380 w, 1264 m (νs,N ), 949 m, 581
To find out whether there exist intrinsic Au‚‚‚Au contacts
between individual [Au(N3)4]- anions, hybrid density func-
3
3
vw, 566 vw, 424 m cm-1. Raman (100 mW): 3036 (10)/2978 (11)/
2-
tional theory calculations on a possible [Au(N3)4]2 dimer
2953 (9)/2920 (10) (νCH), 2062 (33)/2035 (21)/2011 (15) (νas,N ), 1449
were performed starting with an Au‚‚‚Au distance of 2.0 Å.16
3
(18) (δCH), 1284 (14) (νs,N ), 1020 (12), 999 (13), 950 (12), 755 (14),
3
690 (13), 674 (13), 403 (100) (νAuN), 391 (32), 235 (33), 212 (30),
160 (15) cm-1. Anal. Calcd for C4H12N13Au: C, 10.9; H, 2.8; N, 41.5.
Found: C, 11.3; H, 2.9; N, 41.3.
(13) Triclinic, P1; a ) 9.973(2) Å, b ) 10.246(2) Å, c ) 13.625(3) Å; R
) 94.14(3)°, â ) 93.63(3)°, γ ) 110.42(3)°; V ) 1295.7(4) Å3; Z )
2; F ) 2.252 g/cm3; T ) 213 K; Rint ) 0.0253; R1 ) 0.0444, wR2 )
0.1116 (4σ data); R1 ) 0.0700, wR2 ) 0.1240 (all data); GOF )
0.954; largest diff peak/hole 2.582/-2.929 e/Å3.
(11) Into a solution of 0.2 mmol of [Me2NH2][AuCl4] or [NH4][AuCl4] in
5 mL of methanol in a beaker is added 1.7 mmol of AgN3. An
immediate color change from yellow to red is observed. The mixture
is stirred for 24 h and then separated carefully from insoluble silver
salts. Slow evaporation in the case of the dimethylammonium salt
yields pure [Me2NH2][Au(N3)4] (2) in almost quantitative yield. In
the case of [NH4][Au(N3)4] (3), attempts to isolate the pure salt mostly
result in explosions, probably during the crystallization process.
Spectroscopic data of 2. 1H NMR (acetone-d6): δ 3.78 (NH2, s), 3.01
(Me, s). 13C NMR (acetone-d6): δ 35.9 (Me, br). 14N NMR (acetone-
d6): δ -132.8 (Nâ), -178 (Nγ), -280 (NR), -358.0 (Me2NH2).
Spectroscopic data of 3. 1H NMR (CD3OD): δ 4.85 (NH4, s). 14N
NMR (CD3OD): δ -133.6 (Nâ), -179 (Nγ), -280 (NR), -368.8
(NH4). 14N NMR (H2O): δ -133.9 (Nâ), -179 (Nγ), -282 (NR),
-361.5 (NH4).
(14) Estimated standard deviation.
(15) (a) Schmidbaur, H. Gold: Progress in Chemistry, Biochemistry and
Technology; Wiley: New York, 1999. (b) Mingos, D. M. P. J. Chem.
Soc., Dalton Trans. 1996, 561. (c) Fackler, J. P., Jr. Inorg. Chem.
2002, 41, 6959. (d) Pyykko¨, P. Angew. Chem., Int. Ed. 2004, 43, 4412.
(e) Theoretical studies on AuIII-AuIII systems: Mendizabal, F.; Zapata-
Torres, G.; Olea-Azar, C. Chem. Phys. Lett. 2003, 382, 92. Mendizabal,
F.; Pyykko¨, P. Phys. Chem. Chem. Phys. 2004, 6, 900.
(16) The calculations were performed with the Gaussian03 program
package17a at the B3LYP level of theory using a cc-pVDZ basis set
for nitrogen and a small-core ECP-60-MDF relativistic pseudopotential
replacing 60 core electrons at the gold atoms.17b,c The remaining Au
valence electrons were treated with a basis set of the following
contraction: (12s12p9d3f2g)/[6s6p4d3f2g].
(12) Lopez-Sanchez, J. A.; Winfield, J. M.; Krumm, B.; Klapo¨tke, T. M.;
Lennon, D., manuscript in preparation.
9626 Inorganic Chemistry, Vol. 44, No. 26, 2005

COMMUNICATION
Full geometry optimization always resulted in a dissociation
of the dimer, forming two individual [Au(N3)4]- anions.
From this, it can be concluded that, at the level of theory
applied (not taking a point charge model into account),18 the
two [Au(N3)4]- anions are not bound in the gas phase and
that there are (in the gas phase) no bonding Au‚‚‚Au
interactions. Therefore, it is more likely that the interactions
found in the crystal structure are the result of packing effects.
However, to our knowledge, this is one rare, probably the
first, example found in gold(III) chemistry, while for gold-
(I), cluster and hypercoordinated gold compounds frequently
with Au‚‚‚Au interactions are found.15
A comparison to isoelectronic platinum(II) in the two
available crystal structures of tetraazidoplatinate(II) shows
no comparable Pt‚‚‚Pt interactions between the anionic units
(Pt‚‚‚Pt distance of 11.198 Å, likely because of the large
counterion [Ph4As]+ in both cases).19 However, in the crystal
structures of [Et4N]2[PtBr4] (3.59 Å) and K2[PtCl4] (4.13 Å)
with smaller cations, closer Pt‚‚‚Pt contacts are found, leading
to columnar structures of the tetrahalogenoplatinate(II)
anions.20 Those contacts are in a range comparable to the
distances found in our structure.
In summary, this study has shown that salts of tetraazi-
doaurate(III) with ammonium counterions exist but display
very sensitive materials, which should be handled with great
caution. Attempts to prepare hydrazinium tetraazidoaurate-
(III) failed because of the strong reducing power of the
hydrazinium cation. In straightforward reactions, the forma-
tion of nitrogen and gold as decomposition products is
detected. Work on tetraazidoaurates(III) involving other and
further suitable small cations is in progress.
Acknowledgment. This paper is dedicated to Professor
Wolfgang Beck as one of the pioneers on metal azide
chemistry. The University of Munich and the Fonds der
Chemischen Industrie are gratefully acknowledged. Further
we thank UMICORE AG, Hanau, Germany, for a generous
donation of tetrachlorogold(III) acid trihydrate.
(17) (a) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross,
J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.;
Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg,
J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.;
Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman,
J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03; Gaussian
Inc.: Pittsburgh, PA, 2003. (b) Figgen, D.; Rauhut, G.; Dolg, M.;
Stoll, H. Chem. Phys. 2005, 311, 227. (c) http://iris.theochem.uni-
stuttgart.de/cgi-bin/pe.sh?Au.
Supporting Information Available: X-ray crystallographic files
for compound 1 (CIF). This material is available free of charge
via the Internet at http://pubs.acs.org.
IC051543I
(19) Pt‚‚‚Pt distances are not discussed and examined in the crystal
structures of [Pt(N3)4]2- in the following articles: (a) Beck, W.;
Fehlhammer, W. P.; Feldl, K.; Klapo¨tke, T. M.; Kramer, G.; Mayer,
P.; Piotrowski, H.; Po¨llmann, P.; Ponikwar, W.; Schu¨tt, T.; Schuierer,
E.; Vogt, M. Z. Anorg. Allg. Chem. 2001, 627, 1751. (b) Neumu¨ller,
B.; Schmock, F.; Schlecht, S.; Dehnicke, K. Z. Anorg. Allg. Chem.
2000, 626, 1792.
(20) (a) Russell, D. R.; Tucker, P. A.; Whittacker, C. Acta Crystallogr.
1975, B31, 2530. (b) Wyckoff, R. W. G. Crystal Structures, 2nd ed.;
Wiley-Interscience: New York, 1965; Vol. 3.
(18) Chung, S.; Kru¨ger, S.; Schmidbaur, H.; Ro¨sch, N. Inorg. Chem. 1996,
35, 5387.
Inorganic Chemistry, Vol. 44, No. 26, 2005 9627