Silicon tetrabromide, also known as tetrabromosilane, is the inorganic compound with the formula SiBr4. This colorless liquid has a suffocating odor due to its tendency to hydrolyze with release of hydrogen bromide. The general properties of silicon tetrabromide closely resemble those of the more commonly used silicon tetrachloride. Comparison of SiX4 The properties of the tetrasilanes, all of which are tetrahedral, are significantly affected by nature of the halide. These trends apply also to the mixed halides. Melting points, boiling points, and bond lengths increase with the atomic mass of the halide. The opposite trend is observed for the Si-X bond energies. Lewis acidity Covalently saturated silicon complexes like SiBr4, along with tetrahalides of germanium (Ge) and tin (Sn), are Lewis acids. Although silicon tetrahalides obey the octet rule, they add Lewis basic ligands to give adducts with the formula SiBr4L and SiBr4L2 (where L is a Lewis base). The Lewis acidic properties of the tetrahalides tend to increase as follows: SiI4 < SiBr4 < SiCl4 < SiF4. This trend is attributed to the relative electronegativities of the halogens. The strength of the Si-X bonds decrease in the order: Si-F > Si-Cl > Si-Br > Si-I. Synthesis Silicon tetrabromide is synthesized by the reaction of silicon with hydrogen bromide at 600 °C.<ref name=booth>Schumb, W. B. Silicobromoform" Inorganic Syntheses 1939, volume 1, pp 38-42. .</ref> Si + 4 HBr → SiBr4 + 2 H2 Side products include dibromosilane (SiH2Br2) and tribromosilane (SiHBr3). Si + 2 HBr → SiH2Br2 Si + 3 HBr → SiHBr3 + H2 Reactivity Like other halosilanes, SiBr4 can be converted to hydrides, alkoxides, amides, and alkyls, i.e., products with the following functional groups: Si-H, Si-OR, Si-NR2, Si-R, and Si-X bonds respectively. Silicon tetrabromide can be readily reduced by hydrides or complex hydrides. 4 R2AlH + SiBr4 → SiH4 + 4 R2AlBr Reactions with alcohols and amines proceed as follows: SiBr4 + 4 ROH → Si(OR)4 + 4 HBr SiBr4 + 8 HNR2 → Si(NR2)4 + 4 HNR2HBr Grignard reactions with metal alkyl halides are particularly important reactions due to their production of organosilicon compounds which can be converted to silicones. SiBr4 + n RMgX → RnSiBr4−n + n'' MgXBr Redistribution reactions occur between two different silicon tetrahalides (as well as halogenated polysilanes) when heated to 100 ˚C, resulting in various mixed halosilanes. The melting points and boiling points of these mixed halosilanes generally increase as their molecular