Tm5Si3C crystallizes in the orthorhombic Cmcm space group. There are three inequivalent Tm sites. In the first Tm site, Tm(1) is bonded in a 6-coordinate geometry to two equivalent Si(1) and four equivalent Si(2) atoms. In the second Tm site, Tm(2) is bonded in a 2-coordinate geometry to two equivalent Si(2), three equivalent Si(1), and two equivalent C(1) atoms. In the third Tm site, Tm(3) is bonded in a 2-coordinate geometry to one Si(1), four equivalent Si(2), and two equivalent C(1) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Tm(3), three equivalent Tm(2), and four equivalent Tm(1) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Tm(2), four equivalent Tm(1), and four equivalent Tm(3) atoms. C(1) is bonded to two equivalent Tm(2) and four equivalent Tm(3) atoms to form face-sharing CTm6 octahedra.
Tm5Si3C crystallizes in the orthorhombic Cmcm space group. There are three inequivalent Tm sites. In the first Tm site, Tm(1) is bonded in a 6-coordinate geometry to two equivalent Si(1) and four equivalent Si(2) atoms. Both Tm(1)-Si(1) bond lengths are 2.98 Å. All Tm(1)-Si(2) bond lengths are 2.97 Å. In the second Tm site, Tm(2) is bonded in a 2-coordinate geometry to two equivalent Si(2), three equivalent Si(1), and two equivalent C(1) atoms. Both Tm(2)-Si(2) bond lengths are 2.94 Å. There is one shorter (3.09 Å) and two longer (3.47 Å) Tm(2)-Si(1) bond lengths. Both Tm(2)-C(1) bond lengths are 2.43 Å. In the third Tm site, Tm(3) is bonded in a 2-coordinate geometry to one Si(1), four equivalent Si(2), and two equivalent C(1) atoms. The Tm(3)-Si(1) bond length is 2.94 Å. There are a spread of Tm(3)-Si(2) bond distances ranging from 2.93-3.47 Å. Both Tm(3)-C(1) bond lengths are 2.44 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Tm(3), three equivalent Tm(2), and four equivalent Tm(1) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Tm(2), four equivalent Tm(1), and four equivalent Tm(3) atoms. C(1) is bonded to two equivalent Tm(2) and four equivalent Tm(3) atoms to form face-sharing CTm6 octahedra.