Iodine pentoxide
# Iodine pentoxide

Iodine pentoxide is the chemical compound with the formula $I_2O_5.$ This iodine oxide is the anhydride of iodic acid, and the only stable oxide of iodine. It is produced by dehydrating iodic acid at 200 °C in a stream of dry air:

    $2HIO_3$ → $I_2O_5$ + $H_2O$

## Structure

$I_2O_5$ is bent with an I–O–I angle of 139.2°, but the molecule has no mirror plane so its symmetry is $C_2$ rather than $C_{2v}.$ The terminal I–O distances are around 1.80 Å and the bridging I–O distances are around 1.95 Å.

## Reactions

Iodine pentoxide easily oxidises carbon monoxide to carbon dioxide at room temperature:

    5 CO + $I_2O_5$ → $I_2$ + 5 $CO_2$

This reaction can be used to analyze the concentration of CO in a gaseous sample.

$I_2O_5$ forms iodyl salts, $[IO_2^+],$ with $SO_3$ and $S_2O_6F_2,$ but iodosyl salts, $[IO^+],$ with concentrated sulfuric acid.

Iodine pentoxide decomposes to iodine (vapor) and oxygen when heated to about 350 °C.

