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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
Ball and stick model of aluminium iodide dimer
Names
Preferred IUPAC name
Aluminium iodide
Other names
Aluminium(III) iodide

Aluminum iodide
Aluminium triiodide

Aluminum triiodide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.140 Edit this at Wikidata
EC Number
  • 232-054-8
UNII
UN number UN 3260
  • Key: CECABOMBVQNBEC-UHFFFAOYSA-K checkY
  • Key: CECABOMBVQNBEC-DFZHHIFOAE
  • I[Al](I)I
  • dimer: I[Al-]1(I)[I+][Al-]([I+]1)(I)I
Properties
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]
very soluble, partial hydrolysis
Solubility in alcohol, ether soluble (hexahydrate)
Structure[3]
Monoclinic, mP16
P21/c, No. 14
a = 1.1958 nm, b = 0.6128 nm, c = 1.8307 nm
α = 90°, β = 90°, γ = 90°
8
Thermochemistry[1]
98.7 J/(mol·K)
195.9 J/(mol·K)
-302.9 kJ/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Structure

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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 D2h.

Aluminium(I) iodide

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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]

 

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

References

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  1. ^ a b c d e f Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.45. ISBN 1-4398-5511-0.
  2. ^ a b Perry, Dale L. (19 April 2016). Handbook of Inorganic Compounds, Second Edition. CRC Press. p. 8. ISBN 978-1-4398-1462-8.
  3. ^ a b 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.
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