Antimony Oxyiodide, or Antimonyl Iodide, SbOI

Antimony Oxyiodide, or Antimonyl Iodide, SbOI, is obtained when a solution of antimony triiodide in carbon disulphide is exposed to bright sunlight in the presence of air. No action takes place in the dark unless ozone is present. It is an amorphous yellow powder, which decomposes at 150° C., at which temperature antimony triiodide sublimes; sublimation ceases at 200° C., the residue, another oxyiodide, Sb₄O₅I₂, remaining stable up to 350° C. The oxyiodide Sb₄O₅I₂ is also obtained when a solution of antimony triiodide in hydriodic acid is poured into boiling water. It is a yellow powder which dissolves slowly in tartaric acid. It is decomposed when heated to a red heat, antimony triiodide being removed by sublimation, leaving a residue of antimony trioxide. If a solution of potassium iodide is added to a very dilute solution of antimony trichloride in water containing a little sulphuric acid, a bright red precipitate of antimony triiodide is obtained. If insufficient sulphuric acid is present, however, an orange precipitate of 2Sb₂O₃.SbI₃ is obtained by hydrolysis.

The product obtained by the action of water upon antimony triiodide is of variable composition depending upon the temperature and concentration. There is some indication that a complex acid, H₂(SbOI₃), is formed, the mercuric and cupric salts of this acid having been obtained. Mercuric antimony oxyiodide, HgSbOI₃, is prepared by warming a mixture of equimolecular proportions of mercuric cyanide and antimony triiodide in moist amyl alcohol upon a water-bath for four or six hours. It melts at 78° C. and is decomposed by concentrated acids and by alkalis. It can, however, be recrystallised from solution in cold, dilute, hydrochloric acid. Cupric antimony oxyiodide, CuSbOI₃, is obtained by a similar reaction between cupric acetate and antimony triiodide.

Another complex acid, [Sb(IO₃)₃(OH)₃]H, is stated to have been obtained by the action of antimony pentachloride upon an excess of iodic acid.