Ferric iodide, FeI₃

Ferric iodide, FeI₃, has not as yet been prepared, but the possibility of its existence is perhaps indicated by the fact that hydrated ferric oxide dissolves in hydriodic acid, yielding a brown solution.

Two ferrous per-iodates are described by Kimmins, namely Fe₅(IO₆)₂ and FeH₃(IO₆). The former is a brick-red crystalline salt produced on adding ferrous sulphate to a solution of K₄I₂O₉.FeH₃(IO₆) results as a light brown powder on adding a solution of Na₂H₃IO₆ to ferrous sulphate.

Two ferric per-iodates have been prepared, namely FeHI₂O₉ and Fe(IO₄)₃. The former is obtained by drying at 100° C. the light brown precipitate resulting from the interaction of solutions of ferric chloride and Na₂H₃IO₆. It is also formed when K₄I₂O₉ is used instead of the sodium salt. It is a reddish-brown powder, stable towards boiling dilute nitric acid. With concentrated nitric acid, however, Fe(IO₄)₃ is formed as a bright yellow powder.