Bismuth Oxyiodide, BiOI

Bismuth Oxyiodide, or Bismuthyl Iodide, BiOI, is most readily obtained by the hydrolysis of bismuth triiodide. Various other methods for its preparation have been described, including the oxidation of bismuth triiodide, the action of heat upon a mixture of bismuth triiodide and bismuth trioxide, or the direct combination of those compounds in a solution of potassium iodide at the ordinary temperature, and the distillation of methyl iodide through bismuth trioxide.

It is a red, crystalline powder; the crystals are variously described as brick-red, cubic microcrystals, or as copper-red, rhombic leaflets. The density at 15° C. is 7.922.

The oxyiodide is stable in air, melting at red heat without decomposition. When heated in the absence of air it sublimes with partial decomposition, and when more strongly heated it is converted to bismuth trioxide. It is only slightly attacked by water, but readily by dilute mineral acids with the formation of bismuth triiodide. It dissolves in concentrated hydrochloric acid, forming a yellow solution. It is decomposed by both concentrated sulphuric acid and concentrated nitric acid with evolution of iodine. It is not attacked to any appreciable extent by dilute alkaline solutions, even on warming; but it is converted to trioxide by the action of a concentrated solution of potassium hydroxide. It is not attacked by a solution of potassium chloride. It is completely converted into trisulphide by the action of a mixture of potassium hydroxide and ammonium sulphide.

Various other oxyiodides have been reported from time to time, but their existence has not been confirmed.