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Diiodine tetraoxide, I₂O₄, is a chemical compound of oxygen and iodine. It belongs to the class of iodine oxides, and is a mixed oxide, consisting of iodine(III) and iodine(V) oxidation states.

Synthesis

The oxide is formed by the reaction of hot concentrated sulfuric acid on iodic acid for several days.

3HIO₃ → I₂O₄ + HIO₄ + H₂O

It is formed from diiodine pentoxide and iodine in concentrated sulfuric acid or iodosyl sulfate (IO)₂SO₄ added to water:

4(IO)₂SO₄ + 4H₂O → I₂O₄ + I₂ + 4H₂SO₄

Alternatively, excess of concentrated nitric acid oxidizes dry iodine to this salt.

Physical properties

Diiodine tetraoxide is a yellow, granular powder. At temperatures above 85 °C it decomposes to diiodine pentoxide and iodine:

5I₂O₄ → 4I₂O₅ + I₂

This process is even faster at 135 °C. It dissolves in hot water to form iodate and iodide. Structurally, the compound is an iodyl iodite O₂I-OIO (iodine(V,III) oxide) with bent IO₂ units (I–O distances 1.80 and 1.85 Å; ∠OIO angle 97°) and bent IO₂ units (IO distances 1.93 Å, OIO angle 95.8°). Both units are linked via I—O—I bridges to form polymeric zigzag chains (I₂O₄)_x.

Diiodine tetraoxide has a monoclinic crystal structure with the space group P2₁/c (space group number 14). Unit cell dimensions are a = 8.483 b = 6.696 c = 8.333 Å and β = 124.69°. Unit cell volume = 389.15 Å. Z = 4. Density is 2.57 Mg/m

Reactions

Diiodine tetroxide oxidises hydrochloric acid:

I₂O₄ + 8H + 8Cl → 2ICl + 4H₂O + 3Cl₂

It decomposes in water.

References

1. William M. Haynes, ed. (2014). CRC Handbook of Chemistry and Physics. CRC Press. p. S.4-67. ISBN 978-1482208689.
2. ^ Holleman-Wiberg inorganic chemistry. San Diego, Calif. London: Academic. 2001. pp. 465–466. ISBN 0123526515.
3. ^ Fjellvåg, Helmer; Kjekshus, Arne; Persson, Ingmar; Figgis, Brian N.; Liaaen-Jensen, Synnøve; Balzarini, Jan; Fransson, Bengt; Ragnarsson, Ulf; Francis, George W. (1994). "The Crystal Structure of I2O4 and its Relations to Other Iodine--Oxygen-Containing Compounds". Acta Chemica Scandinavica. 48: 815–822. doi:10.3891/acta.chem.scand.48-0815.
4. ^ Holmyard, E. J. (1931). Inorganic Chemistry. Edward Arnold & Co. p. 521. ISBN 978-5-87636-953-6. Retrieved 10 May 2023.
5. Wu, Zhongqing; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya (28 May 2011). "First-principles calculations of the structural and dynamic properties, and the equation of state of crystalline iodine oxides I2O4, I2O5, and I2O6". The Journal of Chemical Physics. 134 (20). doi:10.1063/1.3590278. PMID 21639450.
6. Advances in Inorganic Chemistry and Radiochemistry. Academic Press. 1 January 1963. p. 77-78. ISBN 978-0-08-057854-5.
7. Perry, Dale L. (19 April 2016). Handbook of Inorganic Compounds. CRC Press. p. 210. ISBN 978-1-4398-1462-8. Retrieved 10 May 2023.

• Iodine compounds