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 and iodine oxidation states.

Synthesis

The oxide is formed by the reaction of hot concentrated sulfuric acid on iodic acid for several days.
It is formed from diiodine pentoxide and iodine in concentrated sulfuric acid or iodosyl sulfate ₂SO₄ added to water:
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:
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 with bent I^VO₂ units and bent I^IIIO₂ units. Both units are linked via I—O—I bridges to form polymeric zigzag chains _x.
Diiodine tetraoxide has a monoclinic crystal structure with the space group P2₁/c. 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

Reactions

Diiodine tetroxide oxidises hydrochloric acid:
It decomposes in water.