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TmBr3 crystallizes in the hexagonal P6_3/mmc space group. The structure is one-dimensional and consists of two TmBr3 ribbons oriented in the (0, 0, 1) direction. Tm3+ is bonded to six equivalent Br1- atoms to form distorted face-sharing TmBr6 pentagonal pyramids. All Tm–Br bond lengths are 2.80 Å. Br1- is bonded in an L-shaped geometry to two equivalent Tm3+ atoms.
TmBr2 is Baddeleyite-like structured and crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. Tm is bonded in a 7-coordinate geometry to seven Br atoms. There are a spread of Tm–Br bond distances ranging from 2.89–3.11 Å. There are two inequivalent Br sites. In the first Br site, Br is bonded in a trigonal planar geometry to three equivalent Tm atoms. In the second Br site, Br is bonded to four equivalent Tm atoms to form a mixture of distorted edge and corner-sharing BrTm4 tetrahedra.