Osmium Tetra-iodide, OsI₄

Osmium Tetra-iodide, OsI₄, was obtained by Moraht and Wischin by heating on the water-bath osmic acid, H₂OsO₄, and a concentrated aqueous solution of hydrogen iodide. The osmic acid slowly dissolves, yielding a deep brown solution, which is stable in the cold. Concentration in vacuo over sulphuric acid and caustic potash (to absorb the hydrogen iodide), and subsequent recrystallisation, yields rhombohedral crystals violet-black in colour, and of metallic appearance. They are hygroscopic, readily soluble in alcohol and water, yielding a reddish brown solution stable in the cold, but one that readily decomposes on warming with precipitation of a dark oxy-iodide.