Tb3Cu4Si4 crystallizes in the orthorhombic Immm space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 12-coordinate geometry to six equivalent Cu(1), two equivalent Si(2), and four equivalent Si(1) atoms. In the second Tb site, Tb(2) is bonded to two equivalent Si(2) and four equivalent Si(1) atoms to form distorted edge-sharing TbSi6 octahedra. Cu(1) is bonded in a 8-coordinate geometry to three equivalent Tb(1), one Cu(1), 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 two equivalent Tb(2), four equivalent Tb(1), two equivalent Cu(1), and one Si(1) atom. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Tb(2), two equivalent Tb(1), and six equivalent Cu(1) atoms.
Tb3Cu4Si4 crystallizes in the orthorhombic Immm space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 12-coordinate geometry to six equivalent Cu(1), two equivalent Si(2), and four equivalent Si(1) atoms. There are four shorter (2.94 Å) and two longer (3.02 Å) Tb(1)-Cu(1) bond lengths. Both Tb(1)-Si(2) bond lengths are 2.95 Å. All Tb(1)-Si(1) bond lengths are 2.99 Å. In the second Tb site, Tb(2) is bonded to two equivalent Si(2) and four equivalent Si(1) atoms to form distorted edge-sharing TbSi6 octahedra. Both Tb(2)-Si(2) bond lengths are 2.95 Å. All Tb(2)-Si(1) bond lengths are 2.92 Å. Cu(1) is bonded in a 8-coordinate geometry to three equivalent Tb(1), one Cu(1), one Si(1), and three equivalent Si(2) atoms. The Cu(1)-Cu(1) bond length is 2.47 Å. The Cu(1)-Si(1) bond length is 2.44 Å. There are two shorter (2.50 Å) and one longer (2.58 Å) Cu(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 two equivalent Tb(2), four equivalent Tb(1), two equivalent Cu(1), and one Si(1) atom. The Si(1)-Si(1) bond length is 2.40 Å. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Tb(2), two equivalent Tb(1), and six equivalent Cu(1) atoms.