Boron pentasulphide, B₂S₅

When sulphur reacts upon boron tri-iodide without the intervention of a solvent, boron sesquisulphide is produced, but when the reaction occurs in carbon disulphide solution, crystals of boron pentasulphide are said to separate from the liquid. The substance dissociates into sesquisulphide and sulphur when heated in vacuo. It has not been obtained with less than 10 to 15 per cent, of admixed iodine.