TmCoGa5 crystallizes in the tetragonal P4/mmm space group. Tm(1) is bonded to four equivalent Ga(2) and eight equivalent Ga(1) atoms to form TmGa12 cuboctahedra that share corners with four equivalent Tm(1)Ga12 cuboctahedra, faces with four equivalent Tm(1)Ga12 cuboctahedra, and faces with four equivalent Ga(2)Tm4Ga8 cuboctahedra. Co(1) is bonded in a body-centered cubic geometry to eight equivalent Ga(1) atoms. There are two inequivalent Ga sites. In the first Ga site, Ga(1) is bonded in a 11-coordinate geometry to two equivalent Tm(1), two equivalent Co(1), two equivalent Ga(2), and five equivalent Ga(1) atoms. In the second Ga site, Ga(2) is bonded to four equivalent Tm(1) and eight equivalent Ga(1) atoms to form distorted GaTm4Ga8 cuboctahedra that share corners with four equivalent Ga(2)Tm4Ga8 cuboctahedra, faces with four equivalent Tm(1)Ga12 cuboctahedra, and faces with four equivalent Ga(2)Tm4Ga8 cuboctahedra.
TmCoGa5 crystallizes in the tetragonal P4/mmm space group. Tm(1) is bonded to four equivalent Ga(2) and eight equivalent Ga(1) atoms to form TmGa12 cuboctahedra that share corners with four equivalent Tm(1)Ga12 cuboctahedra, faces with four equivalent Tm(1)Ga12 cuboctahedra, and faces with four equivalent Ga(2)Tm4Ga8 cuboctahedra. All Tm(1)-Ga(2) bond lengths are 2.94 Å. All Tm(1)-Ga(1) bond lengths are 2.94 Å. Co(1) is bonded in a body-centered cubic geometry to eight equivalent Ga(1) atoms. All Co(1)-Ga(1) bond lengths are 2.44 Å. There are two inequivalent Ga sites. In the first Ga site, Ga(1) is bonded in a 11-coordinate geometry to two equivalent Tm(1), two equivalent Co(1), two equivalent Ga(2), and five equivalent Ga(1) atoms. Both Ga(1)-Ga(2) bond lengths are 2.94 Å. There is one shorter (2.55 Å) and four longer (2.94 Å) Ga(1)-Ga(1) bond lengths. In the second Ga site, Ga(2) is bonded to four equivalent Tm(1) and eight equivalent Ga(1) atoms to form distorted GaTm4Ga8 cuboctahedra that share corners with four equivalent Ga(2)Tm4Ga8 cuboctahedra, faces with four equivalent Tm(1)Ga12 cuboctahedra, and faces with four equivalent Ga(2)Tm4Ga8 cuboctahedra.