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]
| 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 IxOy 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]
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: metaperiodateIO−
4 and orthoperiodateIO5−
6.
Osmium tetroxide (also osmium(VIII) oxide) is the chemical compound with the formula OsO4. The compound is noteworthy for its many uses, despite its toxicity and the rarity of osmium. It also has a number of unusual properties, one being that the solid is volatile. The compound is colourless, but most samples appear yellow. This is most likely due to the presence of the impurity OsO2, which is yellow-brown in colour. In biology, its property of binding to lipids has made it a widely-used stain in electron microscopy.
Nitrogen dioxide is a chemical compound with the formula NO2. One of several nitrogen oxides, nitrogen dioxide is a reddish-brown gas. It is a paramagnetic, bent molecule with C2v point group symmetry. Industrially, NO2 is an intermediate in the synthesis of nitric acid, millions of tons of which are produced each year, primarily for the production of fertilizers.
Dinitrogen pentoxide is the chemical compound with the formula N2O5. It is one of the binary nitrogen oxides, a family of compounds that contain only nitrogen and oxygen. It exists as colourless crystals that sublime slightly above room temperature, yielding a colorless gas.
Dichlorine heptoxide is the chemical compound with the formula Cl2O7. This chlorine oxide is the anhydride of perchloric acid. It is produced by the careful distillation of perchloric acid in the presence of the dehydrating agent phosphorus pentoxide:
Periodate is an anion composed of iodine and oxygen. It is one of a number of oxyanions of iodine and is the highest in the series, with iodine existing in oxidation state +7. Unlike other perhalogenates, such as perchlorate, it can exist in two forms: metaperiodateIO−
4 and orthoperiodateIO5−
6. In this regard it is comparable to the tellurate ion from the adjacent group. It can combine with a number of counter ions to form periodates, which may also be regarded as the salts of periodic acid.
Periodic acid is the highest oxoacid of iodine, in which the iodine exists in oxidation state +7. It can exist in two forms: orthoperiodic acid, with the chemical formula H5IO6, and metaperiodic acid, which has the formula HIO4.
Ruthenium tetroxide is the inorganic compound with the formula RuO4. It is a yellow volatile solid that melts near room temperature. It has the odor of ozone. Samples are typically black due to impurities. The analogous OsO4 is more widely used and better known. It is also the anhydride of hyperruthenic acid (H2RuO5). One of the few solvents in which RuO4 forms stable solutions is CCl4.
Iodine compounds are compounds containing the element iodine. Iodine can form compounds using multiple oxidation states. Iodine is quite reactive, but it is much less reactive than the other halogens. For example, while chlorine gas will halogenate carbon monoxide, nitric oxide, and sulfur dioxide, iodine will not do so. Furthermore, iodination of metals tends to result in lower oxidation states than chlorination or bromination; for example, rhenium metal reacts with chlorine to form rhenium hexachloride, but with bromine it forms only rhenium pentabromide and iodine can achieve only rhenium tetraiodide. By the same token, however, since iodine has the lowest ionisation energy among the halogens and is the most easily oxidised of them, it has a more significant cationic chemistry and its higher oxidation states are rather more stable than those of bromine and chlorine, for example in iodine heptafluoride.
Deoxygenation is a chemical reaction involving the removal of oxygen atoms from a molecule. The term also refers to the removal of molecular oxygen (O2) from gases and solvents, a step in air-free technique and gas purifiers. As applied to organic compounds, deoxygenation is a component of fuels production as well a type of reaction employed in organic synthesis, e.g. of pharmaceuticals.
Iodine pentoxide is the chemical compound with the formula I2O5. This iodine oxide is the anhydride of iodic acid, and one of the few iodine oxides that is stable. It is produced by dehydrating iodic acid at 200 °C in a stream of dry air:
Carbon pentaoxide, carbon pentoxide or tetraoxolan-5-one is an unstable molecular oxide of carbon. The molecule has been produced and studied at cryogenic temperatures. The molecule is important in atmospheric chemistry and in the study of cold ices in the outer solar system and interstellar space. The substance could form and be present on Ganymede or Triton, moons in the outer solar system.
Diiodine oxide, also known as iodo hypoiodite, is an oxide of iodine that is equivalent to an acid anhydride of hypoiodous acid. This substance is unstable and it is very difficult to isolate.
Tetraiodine nonoxide is an iodine oxide with the chemical formula I4O9.
Astatine compounds are compounds that contain the element astatine (At). As this element is very radioactive, few compounds have been studied. Less reactive than iodine, astatine is the least reactive of the halogens. Its compounds have been synthesized in nano-scale amounts and studied as intensively as possible before their radioactive disintegration. The reactions involved have been typically tested with dilute solutions of astatine mixed with larger amounts of iodine. Acting as a carrier, the iodine ensures there is sufficient material for laboratory techniques to work. Like iodine, astatine has been shown to adopt odd-numbered oxidation states ranging from −1 to +7.
Iodine monoxide is a binary inorganic compound of iodine and oxygen with the chemical formula IO•. A free radical, this compound is the simplest of many iodine oxides. It is similar to the oxygen monofluoride, chlorine monoxide and bromine monoxide radicals.
Iodine dioxide is a binary inorganic compound of iodine and oxygen with the chemical formula IO
2. Only stable as a dilute gas, this compound is one of many iodine oxides, and "iodine dioxide" is sometimes used to describe its formal dimer, the salt diiodine tetroxide (I2O4, [IO]+[IO3]−).
Iodosyl trifluoride is an inorganic compound of iodine, fluorine, and oxygen with the chemical formula IOF3.
Samarium iodate is an inorganic compound with the chemical formula Sm(IO3)3.
Diiodine tetraoxide, I2O4, is a chemical compound of oxygen and iodine. It belongs to the class of iodine oxides, and is a mixed oxide, consisting of iodine(III) and iodine(V) oxidation states.
Diiodine hexaoxide, is a chemical compound of oxygen and iodine with the chemical formula I2O6. It belongs to the class of iodine oxides, and is a mixed oxide, consisting of iodine(V) and iodine(VII) oxidation states.