Silicon tetraazide is a thermally unstable

binary compound of silicon Binary compounds of silicon are binary compound, binary chemical compounds containing silicon and one other chemical element. Technically the term silicide is reserved for any compounds containing silicon bonded to a more Electronegativity#Electro ...

and nitrogen with a nitrogen content of 85.7% (by molar mass). This high-energy compound combusts spontaneously and can only be studied in a solution.Wilberg, E.; Michaud, H.: Z. Naturforsch. B 9 (1954) S. 500.Gmelins Handbook of Inorganic Chemistry, 8th Edition, ''Silicon'' Supplement Volume B4, Springer-Verlag 1989, S. 46. A further coordination to a six-fold coordinated structure such as a hexaazidosilicate ion or as an adduct with bicationic ligands will result in relatively stable, crystalline solids that can be handled at room temperature.

Preparation

Silicon tetraazide is synthesized by conversion of silicon tetrachloride with sodium azide in benzene. Silicon tetraazide synthesis 02

The reaction of silicon tetrachloride with an excess of sodium azide at room temperature in

acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not clas ...

will result in the formation of sodium hexaazidosilicate () which by adding ligands such as 2,2′-bipyridine and

1,10-phenanthroline 1,10-Phenanthroline (phen) is a heterocyclic organic compound. It is a white solid that is soluble in organic solvents. The 1,10 refer to the location of the nitrogen atoms that replace CH's in the hydrocarbon called phenanthrene. Abbreviated ...

will result in stable silicon tetraazide adducts. Other bases such as pyridine and tetramethylethylenediamine will not react with the hexaazidosilicate ion. Silicon tetraazide synthesis 01

Another preparation of a

bis(triphenylphosphine)iminium Bis(triphenylphosphine)iminium chloride is the chemical compound with the formula , often abbreviated , where Ph is phenyl , or even abbreviated PNl or NPl or PPNCl or PNPCl, where PPN or PNP stands for . This colorless salt is a source of the c ...

hexaazidosilicate salt is possible by conversion of bis(triphenylphosphine)iminium azide with silicon tetrachloride in acetonitrile, where Ph is phenyl.

Properties

Silicon tetraazide is a white crystalline compound that will detonate at even 0 °C. The pure compound, and also silicon chloride triazide and silicon dichloride diazide contaminated samples, can detonate spontaneously without clear cause. The compound is susceptible to hydrolysis. It is soluble in diethylether and benzene. The addition compound with 2,2′-bipyridine is much more stable. A melting point of 212 °C with a

melting enthalpy Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which increa ...

of 110 J/g is recorded. The DSC measurement 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. The enthalpies are higher than that of sodium azide with −800 J/g, but still lower than the values encountered with classic explosives such as RDX with −4500 J/g. The addition compounds are stable in solution. It can be concluded from

IR-spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functiona ...

and proton NMR data that no dissociation occurs in silicon tetraazide and 2,2'-bipyridine or for example 1,10-phenanthroline. The bis(triphenylphosphino)iminium hexaazidosilicate salt on the other hand is relatively stable. The compound melts at 214 °C and shows in the DSC measurement at 250 °C a reaction. One

mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is use ...

coupled thermogravimetric analysis investigation indicated as reaction products nitrogen, silicon tetraazide and

hydrazoic acid Hydrazoic acid, also known as hydrogen azide or azoimide, This also contains a detailed description of the contemporaneous production process. is a compound with the chemical formula . It is a colorless, volatile, and explosive liquid at room tem ...

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. One application as reagent in the manufacture of polyolefins has been patented.Nomura, M.; Tomomatsu, R.; Shimazaki, T.: EP 206 034 (1985
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/ref> The stabilized adducts can serve as energetic compounds as a replacement for lead azide.

References

{{Azides Explosive chemicals Azido compounds Inorganic silicon compounds