What is "h2sif6"

Silicofluoric \Sil`i*co*flu*or"ic\, a. (Chem.) Containing, or composed of, silicon and fluorine; especially, denoting the compounds called silicofluorides.

Silicofluoric acid (Chem.), a compound of hydrofluoric acid and silicon fluoride, known only in watery solution. It is produced by the action of silicon fluoride on water, and is regarded as an acid, H2SiF6, and the type and origin of the silicofluorides.