Iodine pentoxide explained

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:

2HIO₃ → I₂O₅ + H₂O

Structure

I₂O₅ is bent with an I–O–I angle of 139.2°, but the molecule has no mirror plane so its symmetry is C₂ 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.^[1]

Reactions

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

5 CO + I₂O₅ → I₂ + 5 CO₂

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

I₂O₅ forms iodyl salts, [IO₂⁺], with SO₃ and S₂O₆F₂, but iodosyl salts, [IO⁺], with concentrated sulfuric acid.

Iodine pentoxide decomposes to iodine (vapor) and oxygen when heated to about 350 °C.^[2]

Notes and References

1. Selte, K. . Kjekshus, A. . 1970 . Iodine Oxides: Part III. The Crystal Structure of I₂O₅ . Acta Chemica Scandinavica . 24 . 6 . 1912–1924 . 10.3891/acta.chem.scand.24-1912 . free .
2. G. Baxter and G. Tilley, "A Revision of the Atomic Weights of Iodine and Silver," The Chemical News and Journal of Industrial Science; Volumes 99-100, Royal Society Anniversary Meeting, December 3, 1909, p. 276. (Google Books)