Copper(I) bromide is the chemical compound with the formula CuBr. This white diamagnetic solid adopts a polymeric structure akin to that for zinc sulfide. The compound is widely used in the synthesis of organic compounds and as a lasing medium in copper bromide lasers.
The compound is white, although samples are often colored due to the presence of copper(II) impurities.[1] The copper(I) ion also oxidizes easily in air. It is commonly prepared by the reduction of cupric salts with sulfite in the presence of bromide.[2] For example, the reduction of copper(II) bromide with sulfite yields copper(I) bromide and hydrogen bromide:
2 CuBr2 + H2O + → 2 CuBr + + 2 HBr
CuBr is insoluble in most solvents due to its polymeric structure, which features four-coordinated, tetrahedral Cu centers interconnected by bromide ligands (ZnS structure). Upon treatment with Lewis bases, CuBr converts to molecular adducts. For example, with dimethyl sulfide, the colorless complex is formed:
CuBr + S(CH3)2 → CuBr(S(CH3)2)In this coordination complex, the copper is two-coordinate, with a linear geometry. Other soft ligands afford related complexes. For example, triphenylphosphine gives CuBr(P(C6H5)3), although this species has a more complex structure.Thermal excitation of copper(I) bromide vapour yields a blue-violet emission which is of greater saturation than known copper(I) chloride emission.[3] Copper(I) bromide is hence an advantageous emitter in pyrotechnic flames.
In the Sandmeyer reaction, CuBr is employed to convert diazonium salts into the corresponding aryl bromides:[2]
+ CuBr → ArBr + N2 + Cu+The aforementioned complex CuBr(S(CH3)2) is widely used to generate organocopper reagents. Related CuBr complexes are catalysts for atom transfer radical polymerization and copper-catalyzed cross-dehydrogenative couplings (CDC).