Hexachlorodisilane Explained

Hexachlorodisilane is the inorganic compound with the chemical formula Si₂Cl₆.^[1] It is a colourless liquid that fumes in moist air. It has specialty applications in as a reagent and as a volatile precursor to silicon metal.

Structure and synthesis

The molecule adopts a structure like ethane, with a single Si-Si bond length of 233 pm.^[2]

Hexachlorodisilane is produced in the chlorination of silicides such as e.g. calcium silicide. Idealized syntheses are as follows:^[3]

CaSi₂ + 4 Cl₂ → Si₂Cl₆ + CaCl₂

Reactions and uses

Hexachlorodisilane is stable under air or nitrogen at temperatures of at least up to 400°C for several hours, but decomposes to dodecachloroneopentasilane and silicon tetrachloride in presence of Lewis bases even at room temperature.^[4]

4 Si₂Cl₆ → 3 SiCl₄ + Si₅Cl₁₂

This conversion is useful in making silicon-based components of use in semiconducting devices including photovoltaic cells.

The compound is also useful reagent for the deoxygenation reactions, such as this general process involving a phosphine oxide:

2 Si₂Cl₆ + OPR₃ → OSi₂Cl₆ + PR₃

References

1. Simmler, W. "Silicon Compounds, Inorganic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH.
2. T.L. Cottrell, "The Strengths of Chemical Bonds," 2nd ed., Butterworths, London, 1958
3. 10.1016/S0924-0136(03)00287-5 . Silicon tetrachloride production by chlorination method using rice husk as raw material . 2003 . Seo . E.S.M . Andreoli . M . Chiba . R . Journal of Materials Processing Technology . 141 . 3 . 351.
4. Emeleus, H. J., and Muhammad Tufail. "Reaction of Hexachlorodisilane with Bases and Alkyl Halides." Journal of Inorganic and Nuclear Chemistry 29.8 (1967): 2081-084