Tb2Si3 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 4-coordinate geometry to four equivalent Si(2) atoms. In the second Tb site, Tb(2) is bonded in a 11-coordinate geometry to three equivalent Si(1), four equivalent Si(2), and four equivalent Si(3) atoms. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to three equivalent Tb(2), two equivalent Si(1), and two equivalent Si(3) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to four equivalent Tb(1), four equivalent Tb(2), and one Si(3) atom. In the third Si site, Si(3) is bonded in a 7-coordinate geometry to four equivalent Tb(2), one Si(2), and two equivalent Si(1) atoms.
Tb2Si3 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 4-coordinate geometry to four equivalent Si(2) atoms. There are two shorter (2.90 Å) and two longer (3.04 Å) Tb(1)-Si(2) bond lengths. In the second Tb site, Tb(2) is bonded in a 11-coordinate geometry to three equivalent Si(1), four equivalent Si(2), and four equivalent Si(3) atoms. There are two shorter (3.16 Å) and one longer (3.35 Å) Tb(2)-Si(1) bond length. All Tb(2)-Si(2) bond lengths are 3.21 Å. All Tb(2)-Si(3) bond lengths are 3.24 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to three equivalent Tb(2), two equivalent Si(1), and two equivalent Si(3) atoms. Both Si(1)-Si(1) bond lengths are 2.38 Å. Both Si(1)-Si(3) bond lengths are 2.40 Å. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to four equivalent Tb(1), four equivalent Tb(2), and one Si(3) atom. The Si(2)-Si(3) bond length is 2.31 Å. In the third Si site, Si(3) is bonded in a 7-coordinate geometry to four equivalent Tb(2), one Si(2), and two equivalent Si(1) atoms.