Syntheses and Molecular Structures of Liquid Pyrophoric Hydridosilanes

Area of Science:

• Inorganic Chemistry
• Solid-State Chemistry
• Materials Science

Background:

• Silanes are silicon-hydrogen compounds with diverse applications.
• Understanding their solid-state structures and reactivity is crucial for developing new materials and processes.

Purpose of the Study:

• To synthesize and characterize four specific silanes: trisilane, isotetrasilane, neopentasilane, and cyclohexasilane.
• To determine their single-crystal structures and compare them with theoretical and gas-phase data.
• To investigate the photochemical reactivity of these silanes using UV irradiation and Electron Spin Resonance (ESR) spectroscopy.

Main Methods:

• Gram-scale synthesis of four silanes.
• In-situ cryo-crystallization within sealed capillaries on a diffractometer for single-crystal X-ray diffraction.
• Comparison of structural parameters with gas-phase electron diffraction and quantum chemical calculations.
• UV irradiation (365 nm) coupled with ESR (EPR) measurements.
• Nuclear Magnetic Resonance (NMR) spectroscopy.

Main Results:

• Single-crystal structures of trisilane, isotetrasilane, neopentasilane, and cyclohexasilane were obtained.
• Silanes exhibited significantly higher packing indices compared to analogous alkanes.
• Cyclohexasilane demonstrated susceptibility to radical formation upon UV exposure, leading to oligomerization.
• Trisilane, isotetrasilane, and neopentasilane did not form radicals under the tested conditions.
• NMR spectra for all four compounds were successfully recorded.

Conclusions:

• The study provides detailed solid-state structural data for four important silanes.
• Cyclohexasilane exhibits unique photochemical instability, readily forming radicals and oligomers, unlike the other investigated silanes.
• The findings contribute to a deeper understanding of silane structures, packing, and reactivity, particularly under irradiation.