Bonding in Silicon Compounds

Silicon in its compounds is usually four coordinate. Unlike carbon, however, it can increase its coordination number to five or six, if electrons are donated by atoms of another molecule or ion, thus forming a Lewis acid-Lewis base complex for instance, salts of the complex anions Sip5 and SiF6 are known. 

Using VSEPR theory, predict the shapes of the SiFs and SiFg anions. 

In Sip5 and SiFg we can see again the idea that not all compounds obey the stable octet rule. It is common for elements of the third row to increase their coordination number to five or six (and higher in later rows), and we shall meet more examples in the chemistry of phosphorus and sulfur. 

Compounds of silicon in oxidation number +2, of general type SiX2, are called silylenes they are mostly unstable at room temperature, and are important as reaction intermediates. 

A silicon wafer with microchip circuits etched on it. 

Preparation of tetrakis(di-tbutylmethylsilyl)disilene (Method A) 74 Preparation of tetrakis(di-tbutylmethylsilyl)disilene (Method Bl 75 References 77 

2 Silyl Anion—Substituted Silene (f Bu2MeSi)2(THF2Li) Si—Si= Ad(OSiMefBu2) (Ad = Adamantyl) 78 

Synthesis of silyl anion—substituted silene 78 References 79 

Phosphasilene 1 [LSi(SiMe3)=P(SiMe3j] L=PhC(NtBul2 83 Preparation of phosphasilene 1 [LSi(SiMe3)=P(SiMe3l] (L=PhC(NtBu)2) 84 Phosphasilene 2 LSt=PH[L=CH (C=CH2)CMe(NAr)2 Ar=2,6-iPr2C 3 84 Preparation of bis(phosphido)silane LSi(PH2)2 85 Preparation of phosphidosilane chloride LSi(PH2lCI 86 Preparation of phosphasilene 2 (LSi=PH) 86 References 87 

Effident Methods for Preparing Silicon Compounds. ht //dx.doLcH 10.1016/B9 -0-12-803530-6.00007 X 

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Despite the increasing interest in understanding the phenomena of bonding in silicon compounds, there are, until now, no well established and commonly accepted theories. Silicon compounds are mainly discussed in terms of carbon chemistry. Thus, specific properties of silicon compounds are usually compared with those of the corresponding carbon homologues. In this report some important features of silicon compounds are developed by means of ab initio calculations. From this a set of basic rules will be presented by which more complex phenomena can be explained in turn. 

Acceptance of p-dji bonding in silicon compounds has not been universal and is now being challenged frequently by theoretical studies. The question seems to be down to p-d)TT bonding versus polar effects, either of which can explain most of the data. Whereas ab initio calculations have better reproduced experimental bond lengths and dipole moments by inclusion of d functions in the Si basis set, this better reproduction may simply be the result of compensation for an inadequate s p basis set. 

Bonding in Silicon Compounds — Long-Range Si/N Interactions in Organosilicon Molecules and Molecular Cations... 

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