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.

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 (IO)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 iodyl iodite O₂I-OIO (iodine(V,III) oxide) 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°). The structure is a polymeric zigzag chain of I–O–I-O–... alternating as I^VO₂ and I^III.

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 ÃƒÂ… and β = 124.69°. Unit cell volume = 389.15 ÃƒÂ…³. Z = 4. Density is 2.57 Mg/m³

Reactions

Diiodine tetroxide oxidises hydrochloric acid:

It decomposes in water.

References