Tb2RhSi3 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to twelve equivalent Si(1) atoms to form TbSi12 cuboctahedra that share edges with twelve equivalent Tb(2)Si8Rh4 cuboctahedra, faces with two equivalent Tb(1)Si12 cuboctahedra, and faces with six equivalent Tb(2)Si8Rh4 cuboctahedra. In the second Tb site, Tb(2) is bonded to four equivalent Rh(1) and eight equivalent Si(1) atoms to form TbSi8Rh4 cuboctahedra that share edges with four equivalent Tb(1)Si12 cuboctahedra, edges with eight equivalent Tb(2)Si8Rh4 cuboctahedra, faces with two equivalent Tb(1)Si12 cuboctahedra, and faces with six equivalent Tb(2)Si8Rh4 cuboctahedra. Rh(1) is bonded in a 9-coordinate geometry to six equivalent Tb(2) and three equivalent Si(1) atoms. Si(1) is bonded in a 9-coordinate geometry to two equivalent Tb(1), four equivalent Tb(2), one Rh(1), and two equivalent Si(1) atoms.
Tb2RhSi3 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to twelve equivalent Si(1) atoms to form TbSi12 cuboctahedra that share edges with twelve equivalent Tb(2)Si8Rh4 cuboctahedra, faces with two equivalent Tb(1)Si12 cuboctahedra, and faces with six equivalent Tb(2)Si8Rh4 cuboctahedra. There are six shorter (3.08 Å) and six longer (3.09 Å) Tb(1)-Si(1) bond lengths. In the second Tb site, Tb(2) is bonded to four equivalent Rh(1) and eight equivalent Si(1) atoms to form TbSi8Rh4 cuboctahedra that share edges with four equivalent Tb(1)Si12 cuboctahedra, edges with eight equivalent Tb(2)Si8Rh4 cuboctahedra, faces with two equivalent Tb(1)Si12 cuboctahedra, and faces with six equivalent Tb(2)Si8Rh4 cuboctahedra. There are two shorter (3.06 Å) and two longer (3.13 Å) Tb(2)-Rh(1) bond lengths. There are four shorter (3.08 Å) and four longer (3.11 Å) Tb(2)-Si(1) bond lengths. Rh(1) is bonded in a 9-coordinate geometry to six equivalent Tb(2) and three equivalent Si(1) atoms. All Rh(1)-Si(1) bond lengths are 2.37 Å. Si(1) is bonded in a 9-coordinate geometry to two equivalent Tb(1), four equivalent Tb(2), one Rh(1), and two equivalent Si(1) atoms. Both Si(1)-Si(1) bond lengths are 2.35 Å.