Lanthanide tribromides are a family of inorganic compounds with the formula LnBr3, where Ln stands for a lanthanide metal. The tribromides are similar to the more widely used lanthanide trichlorides. They exist as anhydrous solids and as hydrates. For the hydrates, three structural motifs are recognized: [Ln2(μ-Br)2(H2O)14]Br4, [LnBr2(H2O)6]Br, and [Ln(H2O)8]Br3. The former two are also observed for the lanthanum trichlorides, but the last motif is unique to the bromides.
They can be prepared by heating the hydrated lanthanide bromides with excess ammonium bromide under an atmosphere of hydrogen bromide.
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![Lanthanide tribromide: Structure of La2(μ-X)2(H2O)14]4+ (X = Cl, Br).](https://upload.wikimedia.org/wikipedia/commons/thumb/4/4d/Ln2x2%28aq%2914_4%2B.svg/500px-Ln2x2%28aq%2914_4%2B.svg.png?utm_source=en.wikipedia.org&utm_campaign=parser&utm_content=thumbnail)
