Arsenic tribromide
Arsenic tribromide is the inorganic compound with the formula AsBr. This pyramidal molecule is the only known binary arsenic bromide. AsBr is noteworthy for its very high refractive index of approximately 2.3. It also has a very high diamagnetic susceptibility. The compound exists as colourless deliquescent crystals that fume in moist air. Preparation. Arsenic tribromide can be prepared by the direct bromination of arsenic powder. Alternatively arsenic(III) oxide can be used as the precursor in the presence of elemental sulfur: Bromides of arsenic. AsBr is not known, although the corresponding phosphorus compound PBr is well characterized. AsBr is  the parent for a series of hypervalent anionic bromoarsenates including [AsBr], [AsBr], and [AsBr]. Organoarsenic bromides, (CH)AsBr and (CH)AsBr are formed efficiently by the copper-catalyzed reaction of methyl bromide with hot arsenic metal. This synthesis is similar to the direct process used for the synthesis of methyl chlorosilanes. Safety. Arsenic tribromide is toxic, as are most all arsenic compounds.