The Chemistry of Siloxene

We have seen in the first chapter that silicon is not able to form double bonds with itself. In the second period of the periodic table, an overlap between two p orbitals is impossible because the distance between two atoms is too great. 

A more sophisticated picture of the Si-Si system shows that bond strengthening can occur via d orbitals, and we have discussed these effects (see page 53). 

In the nineteenth century, when the picture was still rather crude, chemists attempted to prepare compounds with a true Si-Si double bond. An oversimplified analogy was relied on at that time carbon-carbon multibonds are formed during the decomposition of carbides like calcium carbide, therefore compounds with Si-Si multiple bonds ought to be formed in the decomposition of calcium silicide. 

Several chemists tried this approach. The most important paper of this era was published by Friedrich Wohler687) in 1863. It is exciting to read this paper even today. 

In his first paper, Wohler does not discuss any structural aspects of this compound. One of the striking properties of the Wohler compound is its yellow color and strong yellow fluorescence on irradiation with UV light. These very properties prompted Kautsky33S) to start new investigations in 1921. He found that the Wohler compound changes its properties with the conditions of preparation and is actually a mixture of several different compounds. 

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Let us return now to the Wohler compound. What light does the chemistry of siloxene shed on the structure of this compound The Wohler compound is formed from CaSi2 with HC1 in high concentration in light and air. Under these conditions, siloxene forms halogen derivatives which react with water to hydroxysiloxenes. 

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