Silicon halides and related complexes

Silicon and silicon carbide both react readily with all the halogens to form colourless 

The reactions of 81X4 are straightforward and call for little comment. -  

Mixed halides can also be made by halogen exchange reaction, e.g. by use of Sbp3 to successively fluorinate SiCU or SiBr4. The mps and bps of these numerous species are compared with those of the parent hydride and halides in Pig. 9.1. While there is a clear trend to higher mps and bps with increase in molecular weight, this is by no means always regular. More notable is the enormous drop in mp (bp) which occurs for the halides of Si when compared with A1 and earlier elements in the same row of the periodic table, e.g.  

SiHjXj S1X4 SiFj SiFjX, SiX4SiCU SiCljXj SiX SiBij SiBrjIi Sil SiH,X SiHXj SiFjX SiFX, SiOjX SiClX, SiBtjl SiBcLj 

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Silicon, as the heavier homolog of carbon, is fourfold coordinated in its compounds in most cases. This is, for example, reflected by the chemistry of silicates [1]. In these naturally occurring compounds, the silicon atoms are almost exclusively found in Si04-coordination. The situation is similar for synthetic solids, such as extended binary phases like pure silica zeolite-type frameworks [2], SiS2, SiC or Si3N4, and related more complex ternary and multinary solids [3], This is also valid for molecular silicon halides, hydrides, and metal organic (e.g., silicon alkoxides) as well as organometaUic silicon compounds [3, 4],... 

The distinction between between mono- and dinuclear metal complexes is only a formal one in terms of bonding (consider one substituent at silicon the second metal atom instead of an organic group, halide, or hydride substituent). The structural and spectroscopic features related to the three-center bond should therefore be more or less the same as previously discussed. 

Nucleophilic carbenes have been reported to react with Eewis acidic group 14 complexes with the isolation of neutral or ionic compounds via simple adduct formation or displacement of a halide ion. > The range of carbene complexes of silicon, germanium, tin, and lead, as well as some related cyclopropenylidene complexes are described below. 

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