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.

Iodine oxides
Molecular formula I2O IO IO2 I2O4 I2O5 I4O9
Name diiodine oxide iodine monoxide iodine dioxide iodine tetroxide

(diiodine tetroxide)

 Iodine pentoxide

(diiodine pentoxide)

 tetraiodine nonoxide
Structure I2O IO IO2 (IO2)2 O(IO2)2 I(OIO2)3
Molecular model
CAS registry 39319-71-6 14696-98-1 13494-92-3 1024652-24-1 12029-98-0 66523-94-2
Appearance Unknown purple gas yellow solid yellow solid white crystalline solid dark yellow solid
Oxidation state +1 +2 +4 +3 and +5 +5 +3 and +5
Melting point not isolable not isolable not isolable decomp. 100 °C decomp. 300–350 °C decomp. 75 °C
Specific gravity 4.2 4.8
Solubility in water decomp. to HIO3 + I2 187 g/100 mL decomp. 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 (IO), iodine dioxide (IO2) and iodine tetroxide ((IO2)2) 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 (typically below ppt) they are thought to be powerful ozone depletion agents.

Diiodine pentoxide (I2O5) is the anhydride of iodic acid and the only stable anhydride of an iodine oxoacid.

Tetraiodine nonoxide (I4O9) has been prepared by the gas-phase reaction of I2 with O3 but has not been extensively studied.

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