Diiodine hexaoxide, is a chemical compound of oxygen and iodine with the chemical formula I<sub>2</sub>O<sub>6</sub>. It belongs to the class of iodine oxides, and is a mixed oxide, consisting of iodine(V) and iodine(VII) oxidation states.
Reaction of periodic acid with iodic acid in sulfuric acid:
The thermal decomposition of meta-periodic acid in vacuum also leads to the formation of diiodine hexoxide.
Below 100 ðC, diiodine hexaoxide can be stored stably in the absence of moisture. When dissolved in water, an exothermic reaction to form iodine and periodic acid takes place. When heated above 179 ðC, decomposition into diiodine pentoxide can be observed, with the reaction going to completion at 197 ðC:
Structurally, the compound is a polymeric iodine(V,VII) oxide consisting of repeating I<sub>4</sub>O<sub>12</sub>, units contradicting previous sources describing it as "iodyl periodate" (IO<sub>2</sub><sup>+</sup>IO<sub>4</sub><sup>-</sup>). As a solid, the compound crystallizes in the space group P1 (space group no. 2) with the lattice constants a = 500.6 pm, b = 674.1 pm, c = 679.5 pm, ñ = 97.1ð, ò = 96.43ð, ó = 105.36ð with one formula unit per unit cell.
Diiodine hexaoxide has been investigated for potential use as a neutralizer for chemical and biological agents in combination with aluminium powder.