The hexaazidosilicate(IV) ion: synthesis, properties, and molecular structure

Area of Science:

• Inorganic Chemistry
• Materials Science
• Coordination Chemistry

Background:

• Azido complexes of silicon are of interest due to their high nitrogen content and potential energetic properties.
• Previous research has explored various azidometallates, but silicon-based hexaazido complexes are less common.

Purpose of the Study:

• To synthesize and characterize a novel hexaazidosilicate salt.
• To investigate the thermal stability and decomposition pathways of the synthesized compound.
• To determine the structural and electronic properties of the hexaazidosilicate anion.

Main Methods:

• Synthesis of bis(triphenylphosphoranylidene)ammonium hexaazidosilicate from silicon tetrachloride and bis(triphenylphosphoranylidene)ammonium azide.
• Thermal analysis including thermogravimetric analysis (TG-DTA) to assess stability and decomposition temperatures.
• X-ray crystallography to determine the crystal structure of the salt.
• Spectroscopic techniques (IR, Raman, 29Si, 14N NMR) and computational methods for structural and electronic analysis.

Main Results:

• Selective synthesis of the hexaazidosilicate salt (PPN)2[Si(N3)6] was achieved.
• The compound exhibits remarkable thermal stability, melting at 214°C, with decomposition occurring at 256°C and 321°C.
• The crystal structure reveals discrete PPN+ cations and a rare, octahedral [Si(N3)6]2- anion with S6 symmetry and 90% nitrogen content.
• Spectroscopic and computational data confirm the presence of intact [Si(N3)6]2- anions with S6 symmetry in solution.

Conclusions:

• A novel, highly nitrogenous hexaazidosilicate salt has been successfully synthesized and characterized.
• The compound demonstrates significant thermal stability, with defined decomposition stages.
• The [Si(N3)6]2- anion possesses a rare octahedral SiN6 framework, representing a new benchmark in nitrogen content for hexaazidometallates.