Tm3FeSi3 crystallizes in the monoclinic C2/m 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 Fe(1), one Si(1), two equivalent Si(2), and three equivalent Si(3) atoms. In the second Tm site, Tm(2) is bonded in a 10-coordinate geometry to four equivalent Fe(1), two equivalent Si(3), and five equivalent Si(1) atoms. In the third Tm site, Tm(3) is bonded in a 7-coordinate geometry to two equivalent Si(3) and five equivalent Si(2) atoms. Fe(1) is bonded in a 10-coordinate geometry to two equivalent Tm(1), four equivalent Tm(2), one Si(3), and three equivalent Si(1) atoms. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 10-coordinate geometry to one Tm(1), five equivalent Tm(2), three equivalent Fe(1), and one Si(1) atom. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Tm(1), five equivalent Tm(3), one Si(2), and one Si(3) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to two equivalent Tm(2), two equivalent Tm(3), three equivalent Tm(1), one Fe(1), and one Si(2) atom.
Tm3FeSi3 crystallizes in the monoclinic C2/m 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 Fe(1), one Si(1), two equivalent Si(2), and three equivalent Si(3) atoms. Both Tm(1)-Fe(1) bond lengths are 3.22 Å. The Tm(1)-Si(1) bond length is 2.81 Å. Both Tm(1)-Si(2) bond lengths are 2.87 Å. There are two shorter (2.91 Å) and one longer (3.10 Å) Tm(1)-Si(3) bond length. In the second Tm site, Tm(2) is bonded in a 10-coordinate geometry to four equivalent Fe(1), two equivalent Si(3), and five equivalent Si(1) atoms. There are a spread of Tm(2)-Fe(1) bond distances ranging from 2.87-3.07 Å. Both Tm(2)-Si(3) bond lengths are 2.84 Å. There are a spread of Tm(2)-Si(1) bond distances ranging from 2.91-3.18 Å. In the third Tm site, Tm(3) is bonded in a 7-coordinate geometry to two equivalent Si(3) and five equivalent Si(2) atoms. Both Tm(3)-Si(3) bond lengths are 2.98 Å. There are a spread of Tm(3)-Si(2) bond distances ranging from 2.89-3.04 Å. Fe(1) is bonded in a 10-coordinate geometry to two equivalent Tm(1), four equivalent Tm(2), one Si(3), and three equivalent Si(1) atoms. The Fe(1)-Si(3) bond length is 2.43 Å. All Fe(1)-Si(1) bond lengths are 2.30 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 10-coordinate geometry to one Tm(1), five equivalent Tm(2), three equivalent Fe(1), and one Si(1) atom. The Si(1)-Si(1) bond length is 2.78 Å. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Tm(1), five equivalent Tm(3), one Si(2), and one Si(3) atom. The Si(2)-Si(2) bond length is 2.50 Å. The Si(2)-Si(3) bond length is 2.51 Å. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to two equivalent Tm(2), two equivalent Tm(3), three equivalent Tm(1), one Fe(1), and one Si(2) atom.