Aluminium iodide

Aluminium iodide is a chemical compound containing aluminium and iodine. Invariably, the name refers to a compound of the composition AlI
₃, formed by the reaction of aluminium and iodine^[4] 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, AlI
₃ 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.^[5]

Aluminium iodide

Names
Preferred IUPAC name Aluminium iodide
Other names Aluminium(III) iodide Aluminum iodide Aluminium triiodide Aluminum triiodide
Identifiers
CAS Number	7784-23-8 (anhydrate) Y 10090-53-6 (hexahydrate) Y
3D model (JSmol)	Interactive image dimer: Interactive image
ChemSpider	74202 (anhydrate) Y
ECHA InfoCard	100.029.140
EC Number	232-054-8
PubChem CID	82222 (anhydrate)
UNII	L903Z8J9VR (anhydrate) Y VWS43EUO9V (hexahydrate) Y
UN number	UN 3260
CompTox Dashboard (EPA)	DTXSID0064838
InChI Key: CECABOMBVQNBEC-UHFFFAOYSA-K Y Key: CECABOMBVQNBEC-DFZHHIFOAE
SMILES I[Al](I)I dimer: I[Al-]1(I)[I+][Al-]([I+]1)(I)I
Properties
Chemical formula	AlI3, AlI3·6H2O (hexahydrate)
Molar mass	407.695 g/mol (anhydrous) 515.786 g/mol (hexahydrate)[1]
Appearance	white (anhydrous) or yellow powder (hexahydrate)[1]
Density	3.98 g/cm3 (anhydrous)[1] 2.63 g/cm3 (hexahydrate)[2]
Melting point	188.28 °C (370.90 °F; 461.43 K) (anhydrous) 185 °C, decomposes (hexahydrate)[1][2]
Boiling point	382 °C (720 °F; 655 K) anhydrous, sublimes[1]
Solubility in water	very soluble, partial hydrolysis
Solubility in alcohol, ether	soluble (hexahydrate)
Structure[3]
Crystal structure	Monoclinic, mP16
Space group	P21/c, No. 14
Lattice constant	a = 1.1958 nm, b = 0.6128 nm, c = 1.8307 nm α = 90°, β = 90°, γ = 90°
Formula units (Z)	8
Thermochemistry[1]
Heat capacity (C)	98.7 J/(mol·K)
Std molar entropy (S⦵298)	195.9 J/(mol·K)
Std enthalpy of formation (ΔfH⦵298)	-302.9 kJ/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Structure

Solid AlI
₃ is dimeric, consisting of Al
₂I
₆, similar to that of AlBr
₃.^[3] The structure of monomeric and dimeric forms have been characterized in the gas phase.^[6] The monomer, AlI
₃, is trigonal planar with a bond length of 2.448(6) Å, and the bridged dimer, Al
₂I
₆, at 430 K is a similar to Al
₂Cl
₆ and Al
₂Br
₆ 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 D_2h.

Aluminium(I) iodide

Main article: Aluminium monoiodide

Experiment showing a direct synthesis of aluminum iodide. Few drops of water are added to a homogenised mixture of aluminum powder and powdered iodine. After short time (an induction period) a vigorous reaction occurs followed by emission of intense colored vapors. The purple vapours are due to evaporation of iodine as a consequence of increased temperature of the system, and the brown ones are probably due to smoke of an adduct of the reaction product with excess of iodine. The exergonic reaction 2Al(s) + 3I₂(s) → 2AlI₃(s) is at the origin of the phenomenon observed.

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:^[7]

${\displaystyle {\ce {3AlI -> AlI3 + 2Al}}}$

An illustrative derivative of aluminium monoiodide is the cyclic adduct formed with triethylamine, Al
₄I
₄(NEt
₃)
₄.

References

1. Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, Florida: CRC Press. p. 4.45. ISBN 1-4398-5511-0.
2. Perry, Dale L. (19 April 2016). Handbook of Inorganic Compounds, Second Edition. CRC Press. p. 8. ISBN 978-1-4398-1462-8.
3. Troyanov, Sergey I.; Krahl, Thoralf; Kemnitz, Erhard (2004). "Crystal structures of GaX₃(X= Cl, Br, I) and AlI₃". Zeitschrift für Kristallographie. 219 (2–2004): 88–92. doi:10.1524/zkri.219.2.88.26320. S2CID 101603507.
4. Watt, George W; Hall, James L; Taylor, William Lloyd; Kleinberg, Jacob (1953). "Aluminum Iodide". Inorganic Syntheses. Vol. 4. pp. 117–119. doi:10.1002/9780470132357.ch39. ISBN 9780470132357.
5. Gugelchuk, M. (2004). "Aluminum Iodide". In L. Paquette (ed.). Encyclopedia of Reagents for Organic Synthesis. New York: J. Wiley & Sons. doi:10.1002/047084289X.ra083. ISBN 0471936235.
6. Hargittai, Magdolna; Réffy, Balázs; Kolonits, Mária (2006). "An Intricate Molecule: Aluminum Triiodide. Molecular Structure of AlI₃and Al₂I₆ from Electron Diffraction and Computation". The Journal of Physical Chemistry A. 110 (10): 3770–3777. doi:10.1021/jp056498e. PMID 16526661.
7. Dohmeier, C.; Loos, D.; Schnöckel, H. (1996). "Aluminum(I) and Gallium(I) Compounds: Syntheses, Structures, and Reactions". Angewandte Chemie International Edition. 35 (2): 129–149. doi:10.1002/anie.199601291.

External links

• Media related to Aluminium iodide at Wikimedia Commons