Silicon tetraazide is a thermally unstable binary compound of silicon and

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

with a nitrogen content of 85.7% (by

molar mass In chemistry, the molar mass of a chemical compound is defined as the mass of a sample of that compound divided by the amount of substance which is the number of moles in that sample, measured in moles. The molar mass is a bulk, not molecular, ...

). 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 Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl4. It is a colourless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications. Preparation Silic ...

with sodium azide in

benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...

The reaction of silicon tetrachloride with an excess of sodium azide at room temperature in acetonitrile will result in the formation of sodium hexaazidosilicate () which by adding ligands such as 2,2′-bipyridine and 1,10-phenanthroline will result in stable silicon tetraazide adducts. Other bases such as

pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a ...

and

tetramethylethylenediamine Tetramethylethylenediamine (TMEDA or TEMED) is a chemical compound with the formula (CH3)2NCH2CH2N(CH3)2. This species is derived from ethylenediamine by replacement of the four amine hydrogens with four methyl groups. It is a colorless liquid, ...

will not react with the hexaazidosilicate ion. Silicon tetraazide synthesis 01

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

phenyl In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6 H5, and is often represented by the symbol Ph. Phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen ...

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 Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolys ...

. It is soluble in

diethylether Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable liq ...

and

. The addition compound with 2,2′-bipyridine is much more stable. A

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...

of 212 °C with a melting enthalpy 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 RDX (abbreviation of "Research Department eXplosive") or hexogen, among other names, is an organic compound with the formula (O2N2CH2)3. It is a white solid without smell or taste, widely used as an explosive. Chemically, it is classified as a ...

with −4500 J/g. The addition compounds are stable in solution. It can be concluded from IR-spectroscopy and

proton NMR Proton nuclear magnetic resonance (proton NMR, hydrogen-1 NMR, or 1H NMR) is the application of nuclear magnetic resonance in NMR spectroscopy with respect to hydrogen-1 nuclei within the molecules of a substance, in order to determine the struct ...

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 coupled

thermogravimetric analysis Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a method of thermal analysis in which the mass of a sample is measured over time as the temperature changes. This measurement provides information about physical phenomena, such ...

investigation indicated as reaction products

, silicon tetraazide and hydrazoic acid.

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 Lead(II) azide is an inorganic compound. More so than other azides, is explosive. It is used in detonators to initiate secondary explosives. In a commercially usable form, it is a white to buff powder. Preparation and handling Lead(II) azid ...

References

{{Azides Explosive chemicals Azido compounds Inorganic silicon compounds