Gallium(III) bromide (GaBr3) is a chemical compound, and one of four gallium trihalides. Introduction Gallium(III) bromide is, at room temperature and atmospheric pressure, a white, crystalline powder which reacts favorably and exothermically with water. Solid gallium tribromide is stable at room temperature and can be found primarily in its dimeric form. GaBr3 can form an intermediate halide, Ga2Br7; however, this is not as common as with GaCl3. It is a member of the gallium trihalide group and is similar to GaCl3, and GaI3, but not GaF3, in its preparation and uses. GaBr3 is a milder Lewis acid than AlBr3, and has more versatile chemistry due to the comparative ease of reducing gallium, but is more reactive than GaCl3. GaBr3 is similar spectroscopically to aluminum, indium, and thallium trihalides excluding trifluorides. Preparation One method of preparing GaBr3 is to heat elemental gallium in the presence of bromine liquid under vacuum. Following the highly exothermic reaction, the mixture is allowed to rest and then subjected to various purifying steps. This method from the turn of the twentieth century remains a useful way of preparing GaBr3. Historically, gallium was obtained by electrolysis of its hydroxide in solution of potassium hydroxide, however today it is obtained as a byproduct of aluminium and zinc production. GaBr3 can be synthesized by exposing gallium to bromine in an environment free of water, oxygen and grease. The result is a gas which must be crystallized in order to form bromide purchased by laboratories. Below is the equation: 2 Ga(s) + 3 Br2(l) ⟶ 2 GaBr3(g) Structure The GaBr3 monomer has trigonal planar geometry, but when it forms the dimer Ga2Br6 the geometry around the gallium center distorts to become roughly tetrahedral. As a solid, GaBr3 forms a monoclinic crystalline structure with a unit cell volume of 524.16 Å3. Additional specifications for this unit cell are as follows: a = 8.87 Å, b = 5.64 Å, c =11.01 Å, α = 90˚, β = 107.81˚, γ = 90˚. Complexes Gallium is the lightest group 13 metal with a filled d-shell, and has an electronic configuration of ([Ar] 3d10 4s2 4p1) below the valence electrons that could take part in d-π bonding with ligands. The somewhat high oxidation state of Ga in Ga(III)Br3, low electronegativity, and high polarizability allow GaBr3 to behave as a "soft acid" in terms of the Hard-Soft-Acid-Base (HSAB) theory. The Lewis acidity of all the gallium