Diiodine tetroxide

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.

Diiodine tetroxide^[1]

Names
IUPAC name iodosyl iodate
Identifiers
CAS Number	1024652-24-1 Y
3D model (JSmol)	Interactive image
PubChem CID	54579881
InChI InChI=1S/I2O4/c3-1-6-2(4)5 Key: XHTWXUOEQMOFEJ-UHFFFAOYSA-N
SMILES O=IOI(=O)=O
Properties
Chemical formula	I2O4
Molar mass	317.805 g·mol−1
Density	2.57
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Synthesis

The oxide is formed by the reaction of hot concentrated sulfuric acid on iodic acid for several days.^[2]

3HIO₃ → I₂O₄ + HIO₄ + H₂O

It is formed from diiodine pentoxide and iodine in concentrated sulfuric acid or iodosyl sulfate (IO)₂SO₄ added to water:^[3]

4(IO)₂SO₄ + 4H₂O → 3I₂O₄ + I₂ + 4H₂SO₄

Alternatively, excess of concentrated nitric acid oxidizes dry iodine to this salt.^[4]

Physical properties

Diiodine tetraoxide is a yellow, granular powder. At temperatures above 85 °C it decomposes to diiodine pentoxide and iodine:^[2]

5I₂O₄ → 4I₂O₅ + I₂

This process is even faster at 135 °C. It dissolves in hot water to form iodate and iodide.^[2] Structurally, the compound is an iodyl iodite O₂I-OIO (iodine(V,III) oxide)^[2] with bent I^VO₂ units (I–O distances 1.80 and 1.85 Å; ∠OIO angle 97°) and bent I^IIIO₂ 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.^[2]

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/m^3[3][5]

Reactions

Diiodine tetroxide oxidises hydrochloric acid:^[6]

I₂O₄ + 8H⁺ + 8Cl⁻ → 2ICl + 4H₂O + 3Cl₂

It decomposes^[vague] in water.^[4][7]