Aluminium iodide is the inorganic compound with the composition . It also exists a various hydrates formed by exposure of the anhydrous material to water. For example the hexahydrate is obtained from a reaction between metallic aluminum or aluminum hydroxide with hydroiodic acid. Like the related chloride and bromide, is a strong Lewis acid and will absorb water from the atmosphere. It is employed as a reagent for the scission of certain kinds of C-O and N-O bonds. It cleaves aryl ethers and deoxygenates epoxides.
Aluminium iodide is formed by the reaction of aluminium and iodine or the action of on metal.
Solid is dimeric, consisting of , similar to that of . The structure of monomeric and dimeric forms have been characterized in the gas phase. The monomer, , is trigonal planar with a bond length of 2.448(6) ÃÂ , and the bridged dimer, , at 430 K is a similar to and with bond lengths of 2.456(6) ÃÂ (terminal) and 2.670(8) ÃÂ (bridging). The dimer is described as floppy with an equilibrium geometry of D<sub>2h</sub>.
The name "aluminium iodide" is widely assumed to describe the triiodide or its dimer. In fact, a monoiodide also enjoys a role in the AlâÂÂI system, although the compound AlI is unstable at room temperature relative to the triiodide:
An illustrative derivative of aluminium monoiodide is the cyclic adduct formed with triethylamine, .