Molybdenum Tribromide, MoBr₃

Molybdenum Tribromide, MoBr₃, is formed when bromine- vapour is passed over moderately heated molybdenum or over a mixture of the dioxide with carbon. The compound sublimes, recondensing to dark green crystals, which tend on heating to decompose into bromine and the dibromide, and which are insoluble in water, dilute acids, or alkalies; they dissolve, however, in concentrated alkalies, the bromide undergoing hydrolysis.

By electrolysis of a solution of molybdic anhydride in hydrobromic acid, using a mercury cathode, a purplish-red solution is obtained, which, on addition of ammonium chloride and subsequent evaporation, deposits deep blood-red crystals of the double bromide (NH₄)₂MoBr₅.2H₂O.