TmCoSi2 crystallizes in the orthorhombic Cmcm space group. Tm(1) is bonded in a 14-coordinate geometry to four equivalent Co(1), four equivalent Si(2), and six equivalent Si(1) atoms. Co(1) is bonded in a 9-coordinate geometry to four equivalent Tm(1), one Si(1), and four equivalent Si(2) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to six equivalent Tm(1), one Co(1), and two equivalent Si(1) atoms. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to four equivalent Tm(1) and four equivalent Co(1) atoms.
TmCoSi2 crystallizes in the orthorhombic Cmcm space group. Tm(1) is bonded in a 14-coordinate geometry to four equivalent Co(1), four equivalent Si(2), and six equivalent Si(1) atoms. All Tm(1)-Co(1) bond lengths are 3.03 Å. There are two shorter (3.04 Å) and two longer (3.05 Å) Tm(1)-Si(2) bond lengths. There are four shorter (2.99 Å) and two longer (3.12 Å) Tm(1)-Si(1) bond lengths. Co(1) is bonded in a 9-coordinate geometry to four equivalent Tm(1), one Si(1), and four equivalent Si(2) atoms. The Co(1)-Si(1) bond length is 2.21 Å. There are two shorter (2.29 Å) and two longer (2.30 Å) Co(1)-Si(2) bond lengths. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to six equivalent Tm(1), one Co(1), and two equivalent Si(1) atoms. Both Si(1)-Si(1) bond lengths are 2.40 Å. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to four equivalent Tm(1) and four equivalent Co(1) atoms.