# Silicon tetraazide

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**Silicon tetraazide** is a thermally unstable [binary compound of silicon](/source/Binary_compound_of_silicon) and [nitrogen](/source/Nitrogen) with a nitrogen content of 85.7% (by [molar mass](/source/Molar_mass)). This high-energy compound combusts spontaneously and can only be studied in a solution.[1][2][3] A further coordination to a six-fold coordinated structure such as a hexaazidosilicate ion [Si(N3)6](2−)[4] or as an adduct with [bidentate](/source/Bidentate) ligands Si(N3)4*L2[2] will result in relatively stable, crystalline solids that can be handled at room temperature.

## Preparation

Silicon tetraazide is synthesized by conversion of [silicon tetrachloride](/source/Silicon_tetrachloride) with [sodium azide](/source/Sodium_azide) in [benzene](/source/Benzene).[1][3]

The reaction of silicon tetrachloride with an excess of sodium azide at room temperature in [acetonitrile](/source/Acetonitrile) will result in the formation of sodium hexaazidosilicate (Na2[Si(N3)6]) which by adding ligands such as [2,2′-bipyridine](/source/2,2%E2%80%B2-bipyridine) and [1,10-phenanthroline](/source/1,10-phenanthroline) will result in stable silicon tetraazide adducts.[2] Other bases such as [pyridine](/source/Pyridine) and [tetramethylethylenediamine](/source/Tetramethylethylenediamine) will not react with the hexaazidosilicate ion.[2]

Another preparation of a [bis(triphenylphosphine)iminium](/source/Bis(triphenylphosphine)iminium_chloride#Synthesis_and_structure) hexaazidosilicate salt [(Ph3P)2N]2[Si(N3)6] is possible by conversion of bis(triphenylphosphine)iminium azide [(Ph3P)2N]N3 with silicon tetrachloride in acetonitrile, where Ph is [phenyl](/source/Phenyl).[4]

## Properties

Silicon tetraazide is a white crystalline compound that will detonate at even 0 °C.[1] The pure compound, and also silicon chloride triazide SiCl(N3)3 and silicon dichloride diazide SiCl2(N3)2 contaminated samples, can detonate spontaneously without clear cause.[5] The compound is susceptible to [hydrolysis](/source/Hydrolysis).[3] It is soluble in [diethylether](/source/Diethylether) and [benzene](/source/Benzene).[1]

The addition compound with 2,2′-bipyridine is much more stable. A [melting point](/source/Melting_point) of 212 °C with a [melting enthalpy](/source/Melting_enthalpy) of 110 J/g is recorded. The [DSC measurement](/source/Differential_scanning_calorimetry) shows at 265 °C a sharp exothermic reaction with an enthalpy of −2400 J/g. Similar results are found for the addition compound with 1,10-phenanthroline. As the hemiacetonitrile solvatated isolated compound expels solvent at 100 °C, and shows then in the DSC measurement from 240 °C onwards a strong exothermic reaction with a generated heat of 2300 J/g.[2] The enthalpies are higher than that of sodium azide with −800 J/g,[6] but still lower than the values encountered with classic explosives such as [RDX](/source/RDX) with −4500 J/g.[2] The addition compounds are stable in solution. It can be concluded from [IR-spectroscopy](/source/IR-spectroscopy) and [proton NMR](/source/Proton_NMR) data that no dissociation occurs in silicon tetraazide and 2,2'-bipyridine or for example 1,10-phenanthroline.[2] The bis(triphenylphosphino)iminium hexaazidosilicate salt [(Ph3P)2N]2[Si(N3)6] on the other hand is relatively stable. The compound melts at 214 °C and shows in the DSC measurement at 250 °C a reaction.[4] One [mass spectrometry](/source/Mass_spectrometry) coupled [thermogravimetric analysis](/source/Thermogravimetric_analysis) investigation indicated as reaction products [nitrogen](/source/Nitrogen), silicon tetraazide and [hydrazoic acid](/source/Hydrazoic_acid).[4]

## Applications

A practical application of free silicon tetraazide is unlikely due to the high instability. In solution the compound has potential uses as raw material for nitrogen-rich materials.[2] One application as reagent in the manufacture of polyolefins has been patented.[7] The stabilized adducts can serve as energetic compounds as a replacement for [lead azide](/source/Lead_azide).[2]

## References

1. Wilberg, E.; Michaud, H.: Z. Naturforsch. B 9 (1954) S. 500.

1. Portius, Peter; Filippou, Alexander C.; Schnakenburg, Gregor; Davis, Martin; Wehrstedt, Klaus-Dieter (2010). "Neutrale Lewis-Basen-Addukte des Siliciumtetraazids". *Angewandte Chemie*. **122** (43): 8185–8189. [Bibcode:2010AngCh.122.8185P](https://ui.adsabs.harvard.edu/abs/2010AngCh.122.8185P). [doi:10.1002/ange.201001826](https://doi.org/10.1002/ange.201001826)

1. Gmelins Handbook of Inorganic Chemistry, 8th Edition, *Silicon* Supplement Volume B4, Springer-Verlag 1989, S. 46.

1. Filippou, Alexander C.; Portius, Peter; Schnakenburg, Gregor (2002). "The Hexaazidosilicate(IV) Ion: Synthesis, Properties, and Molecular Structure". *Journal of the American Chemical Society*. **124** (42): 12396–12397. [Bibcode:2002JAChS.12412396F](https://ui.adsabs.harvard.edu/abs/2002JAChS.12412396F). [doi:10.1021/ja0273187](https://doi.org/10.1021/ja0273187). [PMID 12381165](https://pubmed.ncbi.nlm.nih.gov/12381165)

1. [Bretherick's Handbook of Reactive Chemical Hazards](/source/Bretherick's_Handbook_of_Reactive_Chemical_Hazards), 7th revised edition, Academic Press 2006, ISBN 978-0-12-372563-9

1. T. Grewer: *Thermal Hazards of Chemical Reactions*, Industrial Safety Series 4, Elsevier 1994.

1. Nomura, M.; Tomomatsu, R.; Shimazaki, T.: EP 206 034 (1985) [pdf-Download](http://www.freepatentsonline.com/EP0206034.pdf)

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Adapted from the Wikipedia article [Silicon tetraazide](https://en.wikipedia.org/wiki/Silicon_tetraazide) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Silicon_tetraazide?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.