Iodine oxide


Iodine oxides are chemical compounds of oxygen and iodine. Iodine has only two stable oxides which are isolatable in bulk, iodine tetroxide and iodine pentoxide, but a number of other oxides are formed in trace quantities or have been hypothesized to exist.
The chemistry of these compounds is complicated with only a few having been well characterized. Many have been detected in the atmosphere and are believed to be particularly important in the marine boundary layer.
Molecular formulaI2OIOIO2I2O4I2O5I4O9
Namediiodine monoxideiodine monoxideiodine dioxideiodine tetroxide
Iodine pentoxide
tetraiodine nonoxide
StructureI2OIOIO22O2I3
CAS registry39319-71-614696-98-113494-92-31024652-24-112029-98-066523-94-2
AppearanceUnknownpurple gasyellow solidyellow solidwhite crystalline soliddark yellow solid
Oxidation state+1+2+4+3 and +5+5+3 and +5
Melting pointnot isolablenot isolablenot isolabledecomp. 100 °Cdecomp. 300-350 °Cdecomp. 75 °C
Specific gravity4.24.8
Solubility in waterdecomp. to HIO3 + I2187 g/100 mLdecomp. to HIO3 + I2

Diiodine monoxide has largely been the subject of theoretical study, but there is some evidence that it may be prepared in a similar manner to dichlorine monoxide, via a reaction between HgO and I2. The compound appears to be highly unstable but can react with alkenes to give halogenated products.
Radical iodine oxide, iodine dioxide and iodine tetroxide all possess significant and interconnected atmospheric chemistry. They are formed, in very small quantities, at the marine boundary layer by the photooxidation of diiodomethane, which is produced by macroalga such as seaweed or through the oxidation of molecular iodine, produced by the reaction of gaseous ozone and iodide present at the seasurface. Despite the small quantities produced they are thought to be powerful ozone depletion agents.
Diiodine pentoxide is the anhydride of iodic acid and the only stable anhydride of an iodine oxoacid.
Tetraiodine nonoxide has been prepared by the gas-phase reaction of I2 with O3 but has not been extensively studied.

Iodate anions

Iodine oxides also form negatively charged anions, which are components of acids or salts. These include the iodates and periodates.
In acid form, these anions are:
Iodine oxidation state−1+1+3+5+7
NameHydrogen iodide*Hypoiodous acidIodous acidIodic acidPeriodic acid
FormulaHIHIOHIO2HIO3HIO4 or H5IO6

The periodates include two variants: metaperiodate and orthoperiodate.