Iodine oxides are chemical compounds of oxygen and iodine. Iodine has two well-established bulk-isolable stable oxides: iodine pentoxide (I2O5) and diiodine tetroxide (I2O4). A third oxide, diiodine hexaoxide (I2O6) has been reported but is not generally accepted as a well-established stable bulk oxide. Several other oxides have been formed in trace quantities or hypothesized to exist. The most significant of the stable oxides is iodine pentoxide, which is the most thermodynamically and kinetically stable of all halogen oxides.
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 compounds +Iodine oxidesMolecular formulaI2OIOIO2I2O4I4O9I2O5I2O6I2O7NameDiiodine oxideIodine monoxideIodine dioxideDiiodine tetroxide(Iodine tetroxide)Tetraiodine nonoxideIodine pentoxide(Diiodine pentoxide)Diiodine hexaoxideDiiodine heptoxideStructureI2OIOIO2O2IOIOI(OIO2)3O(IO2)2(I4O12)npolymericMolecular model CAS registry39319-71-614696-98-113494-92-31024652-24-166523-94-212029-98-065355-99-9 Appearancered solutions in CH2Cl2 dilute gas; condenses to I2O4yellow soliddark yellow solidwhite crystalline solidyellow solidunstable yellow solidOxidation state +1 +2 +4 +3 and +5 +3 and +5 +5 +5 and +7 +7Melting pointnot isolablenot isolablenot isolabledecomp. 100 °Cdecomp. 75 °Cdecomp. 300–350 °Cdecomp. 179–197 °CChriste, K. O., Haiges, R., & Vashista, P. (2013). Synthesis, Characterization, and Multimillion-Atom Simulation of Halogen-Based Energetic Materials for Agent Defeat (No. USCDTRAF2012).decomp. <60 °CSolubility in water decomp. to HIO3 + I2decomp. to HIO3 + I2187 g/100 mL (hydrolyzes into HIO3)
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.
As of 2019, diiodine monoxide has finally been synthesized by comproportionation of suspensions of HIO3 and elemental iodine in concentrated sulfuric acid. The compound was extracted using dichloromethane and its presence was confirmed by spectroscopy.
Radical iodine oxide (IO) and iodine dioxide (IO2), collectively referred to as IO, and also iodine tetroxide (I2O4) all possess significant and interconnected atmospheric chemistry. They are formed, in very small quantities, in the marine boundary layer by the photochemical reaction of ozone with diiodomethane, 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 all the halogen oxoacids. Unlike other halogen oxides, it can be synthesized by thermal dehydration of iodic acid and is highly resilient to thermal decomposition. Iodine pentoxide adopts multiple polymorphs that can be synthesized by varying pressures.
Tetraiodine nonoxide (I4O9) has been prepared by the gas-phase reaction of I2 with O3 but has not been extensively studied.
Diiodine hexaoxide (I2O6), also known as iodine trioxide or diiodine(V,VII) oxide, is a hygroscopic yellow solid. It has been isolated in bulk and has been studied as a mix with aluminium for destroying chemical and biological agents. It can be synthesized in hot concentrated sulfuric acid, starting either with pure H5IO6 or a mix of H5IO6 and HIO3 It adopts a polymeric structure consisting of IV and IVII centers.
Diiodine heptoxide (I2O7) has been reported as a yellow solid that slowly decomposes into oxygen at room temperature with rapid decomposition beginning at 60 °C, converting it into I2O6.
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, which can form multinuclear structures such as [I2O9]4-.
The conjugate acids of the iodine oxides are:
Iodine oxidation state +1 +3 +5 +7 Name Hypoiodous acid Iodous acid Iodic acid Periodic acid Formula HIO HIO2 HIO3 HIO4 or H5IO6
The periodates include two main variants: metaperiodate and orthoperiodate .
See also Oxygen fluoride Chlorine oxide Bromine oxide References