Difluorosilane
# Difluorosilane

Difluorosilane is a gaseous chemical compound with formula $SiH_2F_2.$ 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 $SiH_2Cl_2$ + 2 $SbF_3$ → 3 $SiH_2F_2$ + 2 $SbCl_3$

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

    $SiF_4$ + 2 $H_2$ → $SiH_2F_2$ + 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 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 $SiHF_2SiHF_2$ is formed along with hydrogen.

    2 $SiH_2F_2$ → $SiHF_2SiHF_2$ + $H_2$

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.

