Silicon tetraazide
Encyclopedia
Silicon tetraazide is a thermally instable binary compound of silicon and nitrogen
with a nitrogen content of 85.7 %. This high-energy compound will combust spontaneously and can only be studied in a solution 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 like a hexaazido silicide [Si(N3)6]2− or as an adduct with bicationic ligands Si(N3)4L2 will result in relatively stable, crystalline solids that can be handled at room temperature.
with sodium azide
in benzene
The reaction of silicon tetrachloride with an excess of sodium azide at room temperature in acetonitrile
will result in the formation of sodium hexaazidosilicide 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
and tetramethylethylenediamine
will not react with the hexaazido silicide ion.
Another preparation of a bis(triphenylphosphino)iminiumhexaazido silicide salt ((PPN)2Si(N3)6, [Ph3P=NPPh3][Si(N3)6]) is possible by conversion of bis(triphenylphosphino)iminium azide (PPNN3, [Ph3P=NPPh3]+N3-) with silicon tetrachloride in acetonitrile.
.. 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 of 110 J·g−1 is recorded. The DSC measurement
shows at 265 °C a sharp exothermic reaction with an enthalpy of −2400 J·g−1. Similar results are found for the addition compound with 1,10-phenanthroline. The as 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−1. The enthalpies are higher than that of sodium azide with −800 J·g−1, but still lower than the values encountered with classic explosives such as RDX
with −4500 J·g−1. The addition compounds are stable in solution. It can be concluded from IR-spectroscopy and proton NMR
data that no dissociation occurs in silicon tetraazide and 2,2'-bipyridine or for example 1,10-phenanthroline. The bis(triphenylphosphino)iminiumhexaazidosilicate salt ((PPN)2Si(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 One mass spectrometry
coupled thermogravimetric analysis
investigation indicated as reaction products nitrogen
, silicon tetraazide and hydrazoic acid
.
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
with a nitrogen content of 85.7 %. This high-energy compound will combust spontaneously and can only be studied in a solution 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 like a hexaazido silicide [Si(N3)6]2− or as an adduct with bicationic ligands Si(N3)4L2 will result in relatively stable, crystalline solids that can be handled at room temperature.
Preparation
Silicon tetraazide is synthesized by conversion of silicon tetrachlorideSilicon tetrachloride
Silicon tetrachloride 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:...
with sodium azide
Sodium azide
Sodium azide is the inorganic compound with the formula NaN3. This colourless azide salt is the gas-forming component in many car airbag systems. It is used for the preparation of other azide compounds. It is an ionic substance and is highly soluble in water. It is extremely...
in benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
The reaction of silicon tetrachloride with an excess of sodium azide at room temperature in acetonitrile
Acetonitrile
Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...
will result in the formation of sodium hexaazidosilicide which by adding ligands such as 2,2′-bipyridine and 1,10-phenanthroline
Phenanthroline
Phenanthroline is a heterocyclic organic compound. As a bidentate ligand in coordination chemistry, it forms strong complexes with most metal ions...
will result in stable silicon tetraazide adducts Other bases such as pyridine
Pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...
and tetramethylethylenediamine
Tetramethylethylenediamine
Tetramethylethylenediamine is a chemical compound with the formula 2NCH2CH2N2. This species is derived from ethylenediamine by replacement of the four N-H groups with four N-methyl groups. Its odor is remarkably similar to that of fish.-As a reagent in organic and inorganic synthesis:TMEDA is...
will not react with the hexaazido silicide ion.
Another preparation of a bis(triphenylphosphino)iminiumhexaazido silicide salt ((PPN)2Si(N3)6, [Ph3P=NPPh3][Si(N3)6]) is possible by conversion of bis(triphenylphosphino)iminium azide (PPNN3, [Ph3P=NPPh3]+N3-) with silicon tetrachloride in acetonitrile.
Properties
Silicon tetraazide is a white crystalline compound that will detonate at even 0 °C. The pure compound but also silicon chloride triazide and silicon dichloride diazide contaminated samples can without clear cause detonate spontaneously The compound is susceptible to hydrolysisHydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
.. It is soluble in diethylether and benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
.
The addition compound with 2,2′-bipyridine is much more stable. A melting point
Melting point
The melting point of a solid 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 depends on pressure and is usually specified at standard atmospheric pressure...
of 212 °C with a melting enthalpy of 110 J·g−1 is recorded. The DSC measurement
Differential scanning calorimetry
Differential scanning calorimetry or DSC is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. Both the sample and reference are maintained at nearly the same temperature...
shows at 265 °C a sharp exothermic reaction with an enthalpy of −2400 J·g−1. Similar results are found for the addition compound with 1,10-phenanthroline. The as 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−1. The enthalpies are higher than that of sodium azide with −800 J·g−1, but still lower than the values encountered with classic explosives such as RDX
RDX
RDX, an initialism for Research Department Explosive, is an explosive nitroamine widely used in military and industrial applications. It was developed as an explosive which was more powerful than TNT, and it saw wide use in WWII. RDX is also known as cyclonite, hexogen , and T4...
with −4500 J·g−1. The addition compounds are stable in solution. It can be concluded from IR-spectroscopy and proton NMR
Proton NMR
Proton 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 structure of its molecules. In samples where natural hydrogen is used, practically all of the hydrogen consists of the...
data that no dissociation occurs in silicon tetraazide and 2,2'-bipyridine or for example 1,10-phenanthroline. The bis(triphenylphosphino)iminiumhexaazidosilicate salt ((PPN)2Si(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 One mass spectrometry
Mass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...
coupled thermogravimetric analysis
Thermogravimetric analysis
Thermogravimetric analysis or thermal gravimetric analysis is a type of testing performed on samples that determines changes in weight in relation to change in temperature. Such analysis relies on a high degree of precision in three measurements: weight, temperature, and temperature change...
investigation indicated as reaction products nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, silicon tetraazide and hydrazoic acid
Hydrazoic acid
Hydrazoic acid, also known as hydrogen azide or azoimide, is a colorless, volatile, and extremely explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen, having chemical formula HN3. It was first isolated in 1890 by Theodor Curtius...
.