Tb3Co2Si3 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 9-coordinate geometry to four equivalent Co(1), two equivalent Si(2), and three equivalent Si(1) atoms. In the second Tb site, Tb(2) is bonded in a 10-coordinate geometry to four equivalent Co(1), two equivalent Si(1), and five equivalent Si(2) atoms. Co(1) is bonded in a 10-coordinate geometry to two equivalent Tb(1), four equivalent Tb(2), one Si(1), and three 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 three equivalent Tb(1), four equivalent Tb(2), and two equivalent Co(1) atoms. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to one Tb(1), five equivalent Tb(2), three equivalent Co(1), and one Si(2) atom.
Tb3Co2Si3 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 9-coordinate geometry to four equivalent Co(1), two equivalent Si(2), and three equivalent Si(1) atoms. All Tb(1)-Co(1) bond lengths are 3.21 Å. Both Tb(1)-Si(2) bond lengths are 2.88 Å. There are two shorter (2.88 Å) and one longer (3.24 Å) Tb(1)-Si(1) bond length. In the second Tb site, Tb(2) is bonded in a 10-coordinate geometry to four equivalent Co(1), two equivalent Si(1), and five equivalent Si(2) atoms. There are a spread of Tb(2)-Co(1) bond distances ranging from 2.98-3.13 Å. Both Tb(2)-Si(1) bond lengths are 2.95 Å. There are a spread of Tb(2)-Si(2) bond distances ranging from 2.96-3.27 Å. Co(1) is bonded in a 10-coordinate geometry to two equivalent Tb(1), four equivalent Tb(2), one Si(1), and three equivalent Si(2) atoms. The Co(1)-Si(1) bond length is 2.63 Å. There are two shorter (2.33 Å) and one longer (2.38 Å) Co(1)-Si(2) bond length. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to three equivalent Tb(1), four equivalent Tb(2), and two equivalent Co(1) atoms. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to one Tb(1), five equivalent Tb(2), three equivalent Co(1), and one Si(2) atom. The Si(2)-Si(2) bond length is 2.81 Å.