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.

Mg _{2Si} + 4H ^{+ \longrightarrow} Si _{nH} _{2n+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:

SiH _{4} → SiH _{2} + H _{2} SiH _{2} + SiH _{4} → H _{3Si{-} SiH _{3 }} SiH _{2} + H _{3Si{-} SiH _{3} → H _{3Si{-}SiH} _{2{-}SiH} _{3}} SiH _{2} + H _{3Si{-} SiH _{2 { - }SiH} _{3} → H _{3Si{-}SiH} _{2{-}SiH} _{2{-}SiH} _{3}}

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 Si _{4H} _{10} → Si _{2H} _{6} +H _{3Si{-} SiH(Si _{2 H} _{6)} _{2} }

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

2 H _{3Si{-} SiH _{2 { - }SiH} _{2{-}SiH} _{3} \longrightarrow H _{3Si{-}SiH(SiH} _{3)} _{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.