Diiodine tetroxide
{{Chembox
| IUPACName = iodosyl iodate
|Section1={{Chembox Identifiers
| PubChem = 54579881
| StdInChI=1S/I2O4/c3-1-6-2(4)5
| StdInChIKey = XHTWXUOEQMOFEJ-UHFFFAOYSA-N
| SMILES = O=IOI(=O)=O
| CASNo = 1024652-24-1
| CASNo_Ref = {{cascite|correct|CAS}}
}}
|Section2={{Chembox Properties
| Density = 2.57
| I=2 | O=4
}}
|Section8={{Chembox Related
}}
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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.{{cite book |title=Holleman-Wiberg inorganic chemistry |date=2001 |publisher=Academic |location=San Diego, Calif. London |isbn=0123526515|pages=465–466}}
:{{chem2|3HIO3 -> I2O4 + HIO4 + H2O}}
It is formed from diiodine pentoxide and iodine in concentrated sulfuric acid or iodosyl sulfate (IO)2SO4 added to water:{{cite journal |last1=Fjellvåg |first1=Helmer |last2=Kjekshus |first2=Arne |last3=Persson |first3=Ingmar |last4=Figgis |first4=Brian N. |last5=Liaaen-Jensen |first5=Synnøve |last6=Balzarini |first6=Jan |last7=Fransson |first7=Bengt |last8=Ragnarsson |first8=Ulf |last9=Francis |first9=George W. |title=The Crystal Structure of I2O4 and its Relations to Other Iodine--Oxygen-Containing Compounds. |journal=Acta Chemica Scandinavica |date=1994 |volume=48 |pages=815–822 |doi=10.3891/acta.chem.scand.48-0815|doi-access=free }}
:{{Chem2|4(IO)2SO4 + 4H2O -> 3I2O4 + I2 + 4H2SO4}}
Alternatively, excess of concentrated nitric acid oxidizes dry iodine to this salt.{{cite book |last1=Holmyard |first1=E. J. |title=Inorganic Chemistry |date=1931 |isbn=978-5-87636-953-6 |page=521 |publisher=Edward Arnold & Co.|url=https://books.google.com/books?id=uLsOAwAAQBAJ&dq=iodine+dioxide+IO2&pg=PA521 |access-date=10 May 2023 |language=en}}
Physical properties
Diiodine tetraoxide is a yellow, granular powder. At temperatures above 85 °C it decomposes to diiodine pentoxide and iodine:
:{{chem2|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 IVO2 units (I–O distances 1.80 and 1.85 Å; ∠OIO angle 97°) and bent IIIIO2 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 Å3. Z = 4. Density is 2.57 Mg/m3{{cite journal |last1=Wu |first1=Zhongqing |last2=Kalia |first2=Rajiv K. |last3=Nakano |first3=Aiichiro |last4=Vashishta |first4=Priya |title=First-principles calculations of the structural and dynamic properties, and the equation of state of crystalline iodine oxides I2O4, I2O5, and I2O6 |journal=The Journal of Chemical Physics |date=28 May 2011 |volume=134 |issue=20 |doi=10.1063/1.3590278|pmid=21639450 }}
Reactions
Diiodine tetroxide oxidises hydrochloric acid:{{cite book |title=Advances in Inorganic Chemistry and Radiochemistry |date=1 January 1963 |publisher=Academic Press |isbn=978-0-08-057854-5 |page=77-78 |url=https://books.google.com/books?id=pRXIwIV-hB8C |language=en}}
:{{chem2|I2O4 + 8H+ + 8Cl− -> 2ICl + 4H2O + 3Cl2}}
It decomposes{{vague|date=November 2024}} in water.{{cite book |last1=Perry |first1=Dale L. |title=Handbook of Inorganic Compounds |date=19 April 2016 |publisher=CRC Press |isbn=978-1-4398-1462-8 |page=210 |url=https://books.google.com/books?id=SFD30BvPBhoC&dq=iodine+dioxide+IO2&pg=PA210 |access-date=10 May 2023 |language=en}}
References
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