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.^[1]

Iodine pentoxide (I₂O₅)

Molecular compounds

Iodine oxides^[2]

Molecular formula	I2O	IO[3]	IO2	I2O4	I4O9	I2O5	I2O6
Name	diiodine oxide	iodine monoxide	iodine dioxide	iodine tetroxide (diiodine tetroxide)	tetraiodine nonoxide	Iodine pentoxide (diiodine pentoxide)	Diiodine hexaoxide
Structure	I2O	IO	IO2	O2IOIO	I(OIO2)3	O(IO2)2	[IO2]+[IO4]−
Molecular model
CAS registry	39319-71-6	14696-98-1	13494-92-3	1024652-24-1	66523-94-2	12029-98-0	65355-99-9
Appearance	Unknown	purple gas	dilute gas; condenses to I2O4[4]	yellow solid	dark yellow solid	white crystalline solid	yellow solid
Oxidation state	+1	+2	+4	+3 and +5	+3 and +5	+5	+5 and +7
Melting point	not isolable	not isolable	not isolable	decomp. 100 °C	decomp. 75 °C	decomp. 300–350 °C	decomp 150 °C
Specific gravity			4.2	4.8			4.53
Solubility in water				decomp. to HIO3 + I2	decomp. to HIO3 + I2	187 g/100 mL

Diiodine monoxide has largely been the subject of theoretical study,^[5] but there is some evidence that it may be prepared in a similar manner to dichlorine monoxide, via a reaction between HgO and I₂.^[6] The compound appears to be highly unstable but can react with alkenes to give halogenated products.^[7]

Radical iodine oxide (IO), iodine dioxide (IO₂), collectively referred to as I_xO_y and iodine tetroxide (I₂O₄) all possess significant and interconnected atmospheric chemistry. They are formed, in very small quantities, in 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.^[4][8] Despite the small quantities produced (typically below ppt) they are thought to be powerful ozone depletion agents.^[9][10]

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.^[11]

Iodate anions

Iodine oxides also form negatively charged anions, which (associated with complementary cations) are components of acids or salts. These include the iodates and periodates.

Their conjugate acids are:

Iodine oxidation state	−1	+1	+3	+5	+7
Name	Hydrogen iodide*	Hypoiodous acid	Iodous acid	Iodic acid	Periodic acid
Formula	HI	HIO	HIO2	HIO3	HIO4 or H5IO6

 • The −1 oxidation state, hydrogen iodide, is not an oxide, but it is included in this table for completeness.

The periodates include two variants: metaperiodate IO⁻
₄ and orthoperiodate IO⁵⁻
₆.

See also

• Oxygen fluoride
• Chlorine oxide
• Bromine oxide