Tetrasilane Explained

Tetrasilane is a silane with the structure formula SiH3–(SiH2)2–SiH3. It is the silane analog of butane.

Preparation

Tetrasilane can be prepared by reacting magnesium silicide (Mg2Si) with acids like 20% phosphoric acid in 50–60 °C.

Mg2Si+ 4H+ \longrightarrow SinH2n+2

The reaction can produce silanes up to n=15. The reaction of magnesium silicide with 25% hydrochloric acid produces 40% monosilane, 30% disilane, 15% trisilane, 10% tetrasilane and 5% higher silanes. The mixture can be separated by fractional distillation.

In addition, higher silanes can also be obtained by discharges monosilane:

SiH4  →  SiH2 + H2
SiH2 + SiH4 →  H3Si{-SiH
3}
SiH2 + H3Si{-SiH
3

H3Si{-}SiH2{-}SiH3}

SiH2 + H3Si{-SiH
2{-}SiH

3H3Si{-}SiH2{-}SiH2{-}SiH3}

Properties

Tetrasilane is a colourless, pyrophoric liquid that has a disgusting odour. Even below 54 °C, it will still spontaneous combust. It is even more unstable than trisilane, slowly decomposing at room temperature, releasing hydrogen and forming shorter chain silanes.

Reactions

Photochemical disproportionation of tetrasilane will produce 3-silylpentasilane and disilane.

2 Si4H10 →  Si2H6 +H3Si{-SiH(Si
2H

6)2}

With the presence of aluminium chloride, heating tetrasilane in xylene will allow isomerization to isotetrasilane.[1]

2 H3Si{-SiH
2{-}SiH

2{-}SiH3\longrightarrowH3Si{-}SiH(SiH3)2}

References

  1. Fehér . Franz . Ocklenburg . Franz . Skrodzki . Dieter . June 2014 . Beiträge zur Chemie des Siliciums und Germaniums, XXXII, Isomerisierung von höheren Silanen mit Aluminiumchlorid . Zeitschrift für Naturforschung B . 35 . 7 . 869-872 . 10.1515/znb-1980-0715 . . free.