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Difluorosilane

Difluorosilane is a gaseous chemical compound with formula SiH<sub>2</sub>F<sub>2</sub>. It can be considered as a derivative of silane with two hydrogen atoms replaced with fluorine.

Production

Difluorosilane can be made by fluorinating dichlorosilane with antimony trifluoride.

3 SiH<sub>2</sub>Cl<sub>2</sub> + 2 SbF<sub>3</sub> → 3 SiH<sub>2</sub>F<sub>2</sub> + 2 SbCl<sub>3</sub>

Some is also made in a reaction of silicon tetrafluoride with hydrogen

SiF<sub>4</sub> + 2 H<sub>2</sub> → SiH<sub>2</sub>F<sub>2</sub> + 2 HF

Traces of difluorosilane are made when coal is burnt.

Properties

Difluorosilane is a gas with boiling point −77.8 °C, and a freezing point of −122 °C. It has no colour. The silicon–fluorine bond length in difluorosilane is 1.358&nbsp;Å which is greater than that in fluorosilane but less than the length in trifluorosilane.

Reactions

In an electric discharge, hydrogen atoms are preferentially removed from the molecule and SiHF<sub>2</sub>SiHF<sub>2</sub> is formed along with hydrogen.

2 SiH<sub>2</sub>F<sub>2</sub> → SiHF<sub>2</sub>SiHF<sub>2</sub> + H<sub>2</sub>

At elevated temperatures, difluorosilane can disproportionate by swapping hydrogen and fluorine atoms between molecules to form fluorosilane and trifluorosilane.

Use

Difluorosilane is used in dental varnish in order to prevent tooth cavities.

Difluorosilane is also used in chemical vapour deposition to deposit silicon nitride films.

References