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Silicon tetraiodide is the chemical compound with the formula SiI4. It is a tetrahedral molecule with Si-I bond lengths of 2.432(5) Å.[1]

SiI4 is a precursor to silicon amides of the formula Si(NR2)4 (R = alkyl).[2] It has also been of interest in the manufacture and etching of silicon in microelectronics.

Synthesis and reactions

This compound is produced by treating silicon-copper mixture with iodine:[3]

Si + I2 → SiI4

It reacts quickly with water and moisture in the air.

It can also be made on a large scale by reaction of silicon or silicon carbide with iodine on heating to about 200 °C. Of more academic interest is the reaction of silane with iodine vapour at 130 - 150 °C, as this produces a series of compounds ranging from iodosilane SiH3I to diiodosilane SiH2I2 and triiodosilane SiHI3 as well. These compounds are colourless liquids at room temperature.[4] The last one can be readily distinguished from the similar carbon compound, iodoform which is a yellow solid at room temperature.

Comparison with other SiX4 compounds

SiH4 SiF4 SiCl4 SiBr4 SiI4
b.p. (˚C)[5] -111.9 -90.3 56.8 155.0 290.0
m.p. (˚C)[5] -185 -95.0 -68.8 5.0 155.0
Si-X bond length (Å) >0.74 [6] 1.55 2.02 2.20 2.43
Si-X bond energy (kJ/mol)[7] 384 582 391 310 234

References

  1. ^ Kolonits, Maria; Hargittai, Magdolna (1998). "Molecular Structure of Silicon Tetraiodide". Structural Chemistry. 9 (5): 349–352. doi:10.1023/A:1022462926682. S2CID 96658381.
  2. ^ Banerjee, Chiranjib; Wade, Casey R.; Soulet, Axel; Jursich, Gregory; McAndrew, James; Belot, John A. (2006). "Direct syntheses and complete characterization of halide-free tetrakis(dialkylamino)silanes". Inorganic Chemistry Communications. 9 (7): 761. doi:10.1016/j.inoche.2006.04.027.
  3. ^ P. W. Schenk (1963). "Silicon and Germanium". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2page=689. NY, NY: Academic Press.
  4. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  5. ^ a b Silicon Compounds, Silicon Halides. Collins, W.: Kirk-Othmer Encyclopedia of Chemical Technology; John Wiley & Sons, Inc, 2001.
  6. ^ "What is the bond length of the H-H bond?". Answers.com.
  7. ^ Ebsworth, E. A. V. In Volatile Silicon Compounds; Taube, H.; Maddock, A. G.; Inorganic Chemistry; Pergamon Press Book: New York, NY, 1963; Vol. 4.

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