Hexabromo- and hexaiododisilane: small and simple molecules showing completely different crystal structures

Area of Science:

• Inorganic Chemistry
• Solid-State Chemistry
• Crystallography

Background:

• Hexaphenyldisilane serves as a precursor for synthesizing silicon halides.
• Understanding the crystal structures of simple inorganic molecules is fundamental to materials science.

Purpose of the Study:

• To synthesize and characterize hexabromodisilane (Si2Br6) and hexaiododisilane (Si2I6).
• To investigate the crystal structures of Si2Br6 and a new polymorph of Si2I6.
• To compare the structural properties of Si2Br6 and Si2I6.

Main Methods:

• Dephenylation of hexaphenyldisilane using acetyl bromide or acetyl iodide with aluminum halides.
• Purification of synthesized compounds via sublimation.
• Single crystal X-ray diffraction analysis to determine molecular and crystal structures.

Main Results:

• Successful synthesis and isolation of single crystals of Si2Br6 and a new polymorph of Si2I6.
• Detailed structural analysis revealing unique crystallographic sites and molecular arrangements for Si2Br6 and Si2I6.
• Si2Br6 and Si2I6 were found to adopt staggered conformations with typical bond lengths but do not form isomorphous structures.
• The study identified a new polymorph of Si2I6, distinct from a previously known orthorhombic form.

Conclusions:

• Si2Br6 and Si2I6, despite their small size, exhibit significantly different crystal structures.
• The findings contribute to the understanding of structure-property relationships in simple inorganic compounds.
• This research provides new crystallographic data for silicon halides.