Silicon Tetra-iodide, SiI₄

Silicon Tetra-iodide (Tetra-iodosilicane), SiI₄, is obtained by the direct combination of its elements, by leading a stream of iodine vapour, by means of carbon dioxide, over red-hot silicon, which may be either pure or in the crude form (Gattermann). It has also been prepared by-passing iodine vapour heated to 180° C. over silicon heated in a vacuum to 500° C. The vapour of silicon tetra-iodide condenses to the solid state when cooled to atmospheric temperature, and the compound may be crystallised from carbon disulphide, in 1 part of which 2 parts dissolve at 27° C. Silicon tetra-iodide crystallises in regular octahedra, isomorphous with carbon tetra-iodide; it melts at 120.5° C. and boils at 290° C., and its vapour density has been estimated to be 19.12, whilst theory requires 18.56. It burns in the air with a red flame evolving iodine vapour, and is hydrolysed normally by water, whilst with alcohol its reaction is unusual, since it gives no ethyl silicate, but silicic acid, ethyl iodide, and hydriodic acid.