Indium(III) bromide, (indium tribromide), InBr<sub>3</sub>, is a chemical compound of indium and bromine. It is a Lewis acid and has been used in organic synthesis.
It has the same crystal structure as aluminium trichloride, with 6 coordinate indium atoms. When molten it is dimeric, In<sub>2</sub>Br<sub>6</sub>, and predominantly dimeric in the gas phase. The dimer has bridging bromine atoms with a structure similar to dimeric aluminium trichloride Al<sub>2</sub>Cl<sub>6</sub>.
It is formed by the reaction of indium and bromine. InBr<sub>3</sub> forms complexes with ligands, L, InBr<sub>3</sub>L, InBr<sub>3</sub>L<sub>2</sub>, InBr<sub>3</sub>L<sub>3</sub>.
Reaction with indium metal forms lower valent indium bromides, InBr<sub>2</sub>, In<sub>4</sub>Br<sub>7</sub>, In<sub>2</sub>Br<sub>3</sub>, In<sub>5</sub>Br<sub>7</sub>, In<sub>7</sub>Br<sub>9</sub>, indium(I) bromide. In refluxing xylene solution InBr<sub>3</sub> and In metal react to form InBr<sub>2</sub>.