Tetraphosphorus Triselenide, P₄Se₃

Tetraphosphorus Triselenide, P₄Se₃, is readily prepared by the action of yellow phosphorus on powdered selenium in boiling tetrahydronaphthalene. The crude substance crystallises from the solution and may be purified by extraction with a mixture of light petroleum and carbon disulphide. The colour of the selenide varies from yellow to orange-red, according to the thickness of the layer under observation. The density at 22° C. is 3.161. On being heated the selenide exhibits distinct phosphorescence above 160° C. and melts at about 242° C.; at 280° C. the phosphorescence is very marked. The compound is slowly decomposed by moisture, and reacts with alkali hydroxides, sulphides and carbonates to form alkali selenide.