Mercury(I) iodide

Mercury(I) iodide, also known as mercurous iodide, is a chemical compound. Its chemical formula is Hg2I2. It has mercury and iodide ions in it. The mercury is in its +1 oxidation state.
Properties.
It is a yellow solid. When light is shined on it, it breaks down (by disproportionation) to mercury(II) iodide and iodine. It is toxic, as are all mercury compounds.
Preparation and use.
It is made by reacting mercury and iodine. It was once used as a medicine.