Synthesis and Characterization of Hydrazinium Azide Hydrazinate

Anton Hammerl, Thomas M. Klapotke*, and Holger Piotrowski

Department of Chemistry, Ludwig-Maximilians University of Munich, Butenandtstr. 5–13 (Building D), 81377 Munich

(Germany)

Gerhard Holl and Manfred Kaiser

Wehrwissenschaftliches Institut fur Werk-, Explosiv- und Betriebsstoffe (WIWEB), Großes Cent, 53913 Swisttal (Germany)

Summary

Hydrazinium azide hydrazinate, [N2H5]þ[N3]7�N2H4 was synthe-sized from equimolar amounts of hydrazinium azide and hydrazineand characterized by single crystal X-ray diffraction: monoclinic,P 21=c, a¼ 6.3704(2), b¼ 12.1111(4), c¼ 6.9940(2) A, b¼91.8666(2) �, V¼ 539.32(3) A3, Z¼ 4, r¼ 1.320 g cm71. The com-pound is less hygroscopic and less volatile than hydrazinium azide.Explosion of [N2H5]þ[N3]7�N2H4 yielded dinitrogen (N2), ammonia(NH3) and dihydrogen (H2). Compared to hydrazinium azide, thehydrazine adduct produces larger amounts of ammonia in the explo-sion.

1. Introduction

Most high energetic materials, such as TNT, RDX, HMX

and CL-20 derive their energy from the oxidation of the

carbon backbone. Modern compounds such as CL-20(1) or

the recently reported hepta- and octanitrocubanes(2) possess

very high densities and utilize the cage strain of the

molecules. High nitrogen materials were investigated in

recent years where the energy is derived from the high

positive heat of formation of the compound. These com-

pounds are often insensitive to electrostatic discharge, fric-

tion and impact like the recent 3,30-azobis(6-amino-1,2,4,5-

tetrazine)(3).

The detonation velocity correlates to (Q=m)0.5 (Q¼ heat of

explosion, m¼ average molecular mass of products). It was

shown that the detonation velocity of hydrazinium azide at

similar densities is greater than the detonation velocity of

RDX, due to the formation of hydrogen during the explo-

sion(4). Unfortunately, hydrazinium azide is hygroscopic and

volatile and, therefore, not in commercial use. The character-

istics of hydrazinium azide were not improved by introduc-

ing organic substituents(5).

Here, the coordination of a hydrazine molecule to hydra-

zinium azide was investigated. The first indication for a

hydrazine adduct of hydrazinium azide was found by

Rieger, who isolated a colorless solid from a solution of

hydrazinium azide in a mixture of ethanol and hydrazine that

had a different melting point than hydrazinium azide(6).

Although hydrazinium azide hydrazinate was mentioned in

the literature(7) prior to this work, the compound had never

been characterized or examined thoroughly.

2. Synthesis

Hydrazinium azide hydrazinate 1 was synthesized in a

straightforward, quantitative synthesis from equimolar

amounts of hydrazinium azide and hydrazine in an evacuated

Schlenk vessel by heating the vessel for two days to 50 �C

(Eq. 1).

H2NNH3

� �þN3

� �ÿþH2NNH2 !

H2NNH3

� �þN3

� �ÿ�H2NNH2 ð1Þ

3. Analytical Data

m.p.: 65 �C;1H NMR ([D6]DMSO): d=ppm¼ 5.07 (s, NH) (Figure 1);14N NMR ([D6]DMSO): d=ppm¼ÿ133 (NNN), ÿ278

(NNN), ÿ321 (NH2NH3, NH2NH2) (Figure 2);15N NMR ([D6]DMSO): d=ppm¼ÿ133.4 (NNN),

ÿ278.2 (NNN), ÿ332.5 (NH3NH2, NH2NH2) (Figure 2);

IR (KBr): n=cmÿ1¼ 3451 w, sh, 3356 m, 3285 m, 3168 m,

3063 m, 2958 m, 2603 m, sh, 2029 s(nasðNÿ3 Þ), 1603 m,

1530 w, sh, 1342 w, 1260 w, 1096 m, 1016 w, sh, 949 w,

798 w, 649 w, 621 w, 552 w (Figure 3);

Raman (100 mW): n=cmÿ1¼ 3272 w, 3187 m, 1643 w,

1337 s(nsðNÿ3 Þ), 1250 w, 1143 w, 961 w, 942 w, 439 w,

325 w, 233 m, 195 m, 154 m, 129 m (Figure 3);

DSC: 16 �C, 65 �C (m.p.), 151.5 �C (Figure 4);

microanalysis, N7H9: (107.12): calcd.: H 8.5 %, N 91.5 %;

found: H 8.9 %, N 90.2 %.*Corresponding author; e-mail: tmk@cup.uni-muenchen.de

# WILEY-VCH Verlag GmbH, D-69469 Weinheim, 2001 0721-3115/01/0410–0161 $17.50þ:50=0

Propellants, Explosives, Pyrotechnics 26, 161–164 (2001) 161

4. Results and Discussion

1 is a colorless solid that is, in contrast to hydrazinium

azide, not volatile and not hygroscopic. The vibrational

spectra show a larger number of absorption bands than for

hydrazinium azide, the bands of the azide group are observed

at 2029 cmÿ1 (IR, asymmetric stretch) and 1337 cmÿ1

(Raman, symmetric stretch), which are the typical values

for ionic azides (Figure 3).

The resonance of all protons in the 1H NMR spectrum was

found as a singlet at d¼ 5.07 ppm (Figure 1), which is

between the range of the proton signals for a hydrazinium

ion (hydrazinium azide, d¼ 6.97 ppm) and free hydrazine

(d¼ 3.23 ppm). The azide atoms display two signals in

the nitrogen NMR spectra, at d¼ÿ133=ÿ133.4 ppm

(14=15N NMR) for the central nitrogen atom and at

d¼ÿ278=ÿ278.2 ppm (14=15N NMR) for the two term-

inal nitrogen atoms. The hydrazine nitrogen atoms give a

signal at d¼ÿ331=ÿ332.5 ppm (14=15N NMR) that has the

same chemical shift as the signal of the hydrazine nitrogen

atoms in hydrazinium azide d¼ÿ331=ÿ332.8 ppm (14=15N

NMR). The spectroscopic data of hydrazinium azide hydra-

zinate (1) compared to hydrazinium azide are summarized in

Table 1.

Single crystals of hydrazinium azide hydrazinate (1) were

obtained by recrystallization from methanol and were sub-

jected to a single crystal X-ray diffraction study(8). The

bonding parameters of the hydrazinium ion and the hydrazine

molecule agree well with known compounds (Figure 5)(9,10).

The azide ion in 1 is connected via six hydrogen bonds to

three hydrazinium and three hydrazine molecules. The N-N

distances of NH2. . .N hydrogen bonds range from 3.070(2) to

3.135(2) A and are longer than the N-N distance of the

NH3. . .N hydrogen bond with 2.9425(2) A due to the positive

charge on the NH3 group.

The hydrazinium and hydrazine molecules are connected

by two short hydrogen bonds (N-N distance 2.747(2) and

2.875(2) A) between the two hydrogen atoms of the NH3

group of the hydrazinium ion and the ione pairs of the

nitrogen atoms of the hydrazine molecule. The bond

lengths of the azide ion show a slight difference (1.180(2)

Figure 1. 1H NMR spectrum of hydrazinium azide hydrazinate.

Figure 2. 14=15N NMR spectra of hydrazinium azide hydrazinate.

Figure 3. Vibrational (IR, top and Raman, bottom) spectra ofhydrazinium azide hydrazinate.

Figure 4. DSC spectrum of hydrazinium azide hydrazinate.

162 A. Hammerl, T. M. Klapotke, H. Piotrowski, G. Holl, and M. Kaiser Propellants, Explosives, Pyrotechnics 26, 161–164 (2001)

and 1.174(2) A) due to different hydrogen bonding on both

ends of the azide ion.

The explosion, initiated by electrical resistance heating

(Pt wire) in an evacuated steel bomb, gave dinitrogen (N2),

ammonia (NH3) and dihydrogen (H2) as decomposition

products. Compared to hydrazinium azide, 1 produces

larger amounts of ammonia in the explosion (Eqs. 2 and 3).

½N2H5�þ½N3�

ÿ:! 2:18 N2 þ 1:52 H2 þ 0:65 NH3 ð2Þ

½N2H5�þ½N3�

ÿ:N2H4 ! 2:68 N2 þ 2:02 H2 þ 1:65 NH3

ð3Þ

Compound 1 showed no sensitivity to an electrical dis-

charge of 20 kV (electrostatic), in a drop hammer test

(5 kg=50 cm) (shock)(11) and to grinding in a mortar (fric-

tion). Like hydrazinium azide, 1 does not explode when

heated slowly (10 K=min), but detonates under rapid heating

or when put on contact with a hot metal surface.

In the DSC spectrum (Mettler DSC apparatus, 10 mg

sample, hermetically sealed sample pans, see Figure 4) two

endothermic phase transitions were observed. Melting

without decomposition occurs at 65 �C, decomposition at

151 �C. The surprising endothermic decomposition may be

caused by an overlapping evaporation effect probably due to

leaking DSC pans.

We are currently studying hydrazine adducts of other

hydrazinium salts with highly nitrogen-rich anions.

5. Summary and Conclusions

Hydrazinium azide hydrazinate, [N2H5]þ[N3]7�N2H4 was

synthesized from equimolar amounts of hydrazinium azide

and hydrazine and was recrystallized from methanol. The

compound was characterized by IR, Raman, multinuclear

NMR (1H,14=15N) spectroscopy and single crystal X-ray

diffraction. Hydrazinium azide hydrazinate, [N2H5]þ[N3]7

�N2H4, is neither shock nor friction sensitive and also not

sensitive towards electrostatic discharge of 20 kV. The com-

pound, however, explodes, when heated up rapidly or when

exposed to a hot metal surface. The explosion of hydrazinium

azide hydrazinate gives more ammonia than the explosion of

hydrazine-free hydrazinium azide.

6. References

(1) R. L. Simpson, P. A. Urtiew, D. L. Ornellas, G. L. Moody, K. J.Scribner and D. M. Hofman, Propellants, Explos. Pyrotech. 22,249 (1997); and references therein.

(2) M.-X. Zhang, P. E. Eaton and R. Gilardi, Angew. Chem. 112, 422(2000); Angew. Chem., Int. Ed. Engl. 39, 409 (2000).

(3) D. E. Chavez, M. A. Hiskey and R. D. Gilardi, Angew. Chem.112, 1861 (2000); Angew. Chem. Int. Ed. Engl. 39, 1791 (2000).

(4) G. S. Yakovleva, R. Kh. Kurbangalina and L. N. Stesik, Fiz.Goreniya Vzryva 10(2), 270–274 (1974).

(5a) T. Habereder, A. Hammerl, G. Holl, T. M. Klapotke, J. Knizekand H. Noth, Eur. J. Inorg. Chem. 849–852 (1999).

(5b) T. Habereder, A. Hammerl, G. Holl, T. M. Klapotke, P. Mayerand H. Noth, 31st Int. Annual Conference of ICT, Karlsruhe,Germany, June 27–30, 2000, pp. 150.1–150.7.

(5c) A. Hammerl, G. Holl, K. Hubler, T. M. Klapotke and P. Mayer,Eur. J. Inorg. Chem. 755–760 (2000).

Table 1. Spectroscopic Data (NMR and IR, Raman) of Hydrazinium Azide Hydrazinate (1) Compared to Hydrazinium Azide

Compound 1H NMR (ppm) 14N NMR (ppm) 15N NMR (ppm) nas(N3ÿ) (IR) (cmÿ1) ns(N3

ÿ) (Ra) (cmÿ1)

[N2H5]þ[N3]ÿ 6.97 ÿ132 ÿ132.5 2033 1347ÿ281 ÿ281.0ÿ331 ÿ332.8

[N2H5]þ[N3]ÿ�N2H4 (1) 5.07 ÿ132 ÿ133.4 2029 1337ÿ281 ÿ278.2ÿ331 ÿ332.5

Figure 5. Top: hydrogen bonds to the azide ion in hydrazinium azidehydrazinate; bottom: hydrogen bonds to the hydrazinium ions andhydrazine molecules in hydrazinium azide hydrazinate.

Propellants, Explosives, Pyrotechnics 26, 161–164 (2001) Synthesis and Characterization of Hydrazinium Azide Hydrazinate 163

(5d) A. Hammerl, G. Holl, M. Kaiser, T. M. Klapotke, P. Mayer,H. Noth and M. Warchhold, Z. Anorg. Allg. Chem. 627, 1477(2001).

(6) H. D. Rieger, Ph.D. Thesis: Hydronitric acid and hydrazine tri-nitrate, Cornell University, Ithaca, New York (1910).

(7a) A. L. Dresser and A. W. Browne, J. Am. Chem. Soc. 58, 261(1933).

(7b) E. P. Kirpichev, A. P. Alekseev, Y. I. Rubtsov and G. B. Manelis,Russian Journal of Physical Chemistry 47, 1654 (1973).

(8) NONIUS KAPPA CCD diffractometer, Mo-Ka radiation,l¼ 0.71073 A, graphite monochromator. N7H9 (107.14),colorless rod, 0.3060.0760.06 mm, monoclinic, P 21=c,a¼ 6.3704(2), b¼ 12.1111(4), c¼ 6.9940(2) A, b¼ 91.8666(2) �,V¼ 539.32(3) A3, Z¼ 4, r¼ 1.320 g cmÿ1, m¼ 0.106, F(000)232, T¼ 200(2) K, ÿ8� h� 8, ÿ15� k� 15, ÿ9� l� 9, 9191reflections collected, 1226 independent reflections(Rint.¼ 0.0637), 895 observed reflections with I> 2s(I); structuresolution SIR97 (Cascarano et al., Acta Cryst. Sect. A 1996, C79);structure refinement SHELXL-97 (G. M. Sheldrick, University of

Gottingen, Germany, 1997), direct methods, free refinement ofall hydrogen atoms; final R values [I> 2s(I)]: R1¼ 0.0457,wR2¼ 0.0980; all data: R1¼ 0.0723, wR2¼ 0.1106.

(9a) P. G. Chiglien, J. Etienne, S. Jaulmes and P. Laruelle, Acta Cryst.Sect. B 30, 2229–2233 (1974).

(9b) H. Holfter, T. M. Klapotke and A. Schulz, Eur. J. Solid StateInorg. Chem. 33, 855 (1996).

(10) R. L. Collin and W. N. Lipscomb, Acta Cryst. 4, 10 (1951).(11) T. M. Klapotke and C. M. Rienacker, Propellants, Explos.,

Pyrotech. 26, 43–47 (2001).

AcknowledgementsFinancial support of this work by the University of Munich (LMU),

the Deutsche Forschungsgemeinschaft (DFG, KL 636=7-1), the Fondsder Chemischen Industrie and the German Federal Office of DefenseTechnology and Procurement (BWB) is gratefully acknowledged.

(Received April 23, 2001; Ms 2001=033)

164 A. Hammerl, T. M. Klapotke, H. Piotrowski, G. Holl, and M. Kaiser Propellants, Explosives, Pyrotechnics 26, 161–164 (2001)