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Aluminium iodide
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Formula
AlI3
Melting point
189.4 °C
Density
3.98 g/cm³
Molar mass
407.695 g/mol
Boiling point
360 °C
Appearance
white powder; but impure samples; are often brown
Aluminium iodide is any chemical compound containing only aluminium and iodine. Invariably, the name refers to a compound of the composition AlI3, formed by the reaction of aluminium and iodine or the action of HI on Al metal. The hexahydrate is obtained from a reaction between metallic aluminum or aluminum hydroxide with hydrogen iodide or hydroiodic acid. Like the related chloride and bromide, AlI3 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.
Solid AlI3 is dimeric, consisting of Al2I6, similar to that of AlBr3. The structure of monomeric and dimeric forms have been characterized in the gas phase. The monomer, AlI3 is trigonal planar with a bond length of 2.448(6) Å, and the bridged dimer, Al2I6 at 430 K is a similar to Al2Cl6 and Al2Br6 with Al−I bond lengths of 2.456(6) Å (terminal) and 2.670(8) Å (bridging). The dimer is described as floppy with an equilibrium geometry of D2h.
Aluminium(I) iodide
The name "aluminium iodide" is widely assumed to describe the triiodide or its dimer. In fact, a monoiodide also enjoys a role in the Al−I system, although the compound AlI is unstable at room temperature relative to the triiodide
3AlI⟶AlI3+2Al
An illustrative derivative of aluminium monoiodide is the cyclic adduct formed with triethylamine, Al4I4(NEt3)4.
