TbFeSi2 crystallizes in the monoclinic P2_1/m space group. Tb(1) is bonded in a 12-coordinate geometry to three equivalent Fe(1), three equivalent Si(2), and six equivalent Si(1) atoms. Fe(1) is bonded in a 5-coordinate geometry to three equivalent Tb(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 Tb(1), one Fe(1), and two equivalent Si(1) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to three equivalent Tb(1), four equivalent Fe(1), and two equivalent Si(2) atoms.
TbFeSi2 crystallizes in the monoclinic P2_1/m space group. Tb(1) is bonded in a 12-coordinate geometry to three equivalent Fe(1), three equivalent Si(2), and six equivalent Si(1) atoms. There are two shorter (3.04 Å) and one longer (3.12 Å) Tb(1)-Fe(1) bond length. There is one shorter (2.87 Å) and two longer (2.98 Å) Tb(1)-Si(2) bond lengths. There are a spread of Tb(1)-Si(1) bond distances ranging from 2.98-3.22 Å. Fe(1) is bonded in a 5-coordinate geometry to three equivalent Tb(1), one Si(1), and four equivalent Si(2) atoms. The Fe(1)-Si(1) bond length is 2.26 Å. There are a spread of Fe(1)-Si(2) bond distances ranging from 2.23-2.32 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to six equivalent Tb(1), one Fe(1), and two equivalent Si(1) atoms. Both Si(1)-Si(1) bond lengths are 2.49 Å. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to three equivalent Tb(1), four equivalent Fe(1), and two equivalent Si(2) atoms. Both Si(2)-Si(2) bond lengths are 2.47 Å.