Mercury(I) bromide or mercurous bromide is the chemical compound composed of mercury and bromine with the formula Hg2Br2. It changes color from white to yellow when heated and fluoresces a salmon color when exposed to ultraviolet light. It has applications in acousto-optical devices.
A very rare mineral form is called kuzminite and has the chemical formula .
Mercury(I) bromide is prepared by the oxidation of elemental mercury with elemental bromine or by adding sodium bromide to a solution of mercury(I) nitrate. It decomposes to mercury(II) bromide and elemental mercury.
In common with other Hg(I) (mercurous) compounds which contain linear X-Hg-Hg-X units, Hg2Br2 contains linear BrHg2Br units with an Hg-Hg bond length of 249 pm (Hg-Hg in the metal is 300 pm) and an Hg-Br bond length of 271 pm.[1] The overall coordination of each Hg atom is octahedral as, in addition to the two nearest neighbours, there are four other Br atoms at 332 pm.[1] The compound is often formulated as Hg22+ 2Br−, although it is actually a molecular compound.