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.
The oxide is formed by the reaction of hot concentrated sulfuric acid on iodic acid for several days.[1]
It is formed from diiodine pentoxide and iodine in concentrated sulfuric acid or iodosyl sulfate (IO)2SO4 added to water:[2]
Diiodine tetraoxide is a yellow, granular powder. At temperatures above 85 °C it decomposes to diiodine pentoxide and iodine:[1]
This process is even faster at 135 °C. It dissolves in hot water to form iodate and iodide.[1] Structurally, the compound is an iodyl iodite O2I-OIO (iodine(V,III) oxide)[1] 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.[1]
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[2] [3]
Diiodine tetroxide oxidises hydrochloric acid:[4]