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.
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==