Er2RhSi3 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to four equivalent Rh(1) and eight equivalent Si(1) atoms to form distorted ErSi8Rh4 cuboctahedra that share edges with four equivalent Er(2)Si12 cuboctahedra, edges with eight equivalent Er(1)Si8Rh4 cuboctahedra, faces with two equivalent Er(2)Si12 cuboctahedra, and faces with six equivalent Er(1)Si8Rh4 cuboctahedra. In the second Er site, Er(2) is bonded to twelve equivalent Si(1) atoms to form ErSi12 cuboctahedra that share edges with twelve equivalent Er(1)Si8Rh4 cuboctahedra, faces with two equivalent Er(2)Si12 cuboctahedra, and faces with six equivalent Er(1)Si8Rh4 cuboctahedra. Rh(1) is bonded in a 9-coordinate geometry to six equivalent Er(1) and three equivalent Si(1) atoms. Si(1) is bonded in a 9-coordinate geometry to two equivalent Er(2), four equivalent Er(1), one Rh(1), and two equivalent Si(1) atoms.
Er2RhSi3 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to four equivalent Rh(1) and eight equivalent Si(1) atoms to form distorted ErSi8Rh4 cuboctahedra that share edges with four equivalent Er(2)Si12 cuboctahedra, edges with eight equivalent Er(1)Si8Rh4 cuboctahedra, faces with two equivalent Er(2)Si12 cuboctahedra, and faces with six equivalent Er(1)Si8Rh4 cuboctahedra. There are two shorter (2.99 Å) and two longer (3.12 Å) Er(1)-Rh(1) bond lengths. There are four shorter (3.00 Å) and four longer (3.09 Å) Er(1)-Si(1) bond lengths. In the second Er site, Er(2) is bonded to twelve equivalent Si(1) atoms to form ErSi12 cuboctahedra that share edges with twelve equivalent Er(1)Si8Rh4 cuboctahedra, faces with two equivalent Er(2)Si12 cuboctahedra, and faces with six equivalent Er(1)Si8Rh4 cuboctahedra. All Er(2)-Si(1) bond lengths are 3.05 Å. Rh(1) is bonded in a 9-coordinate geometry to six equivalent Er(1) and three equivalent Si(1) atoms. All Rh(1)-Si(1) bond lengths are 2.35 Å. Si(1) is bonded in a 9-coordinate geometry to two equivalent Er(2), four equivalent Er(1), one Rh(1), and two equivalent Si(1) atoms. Both Si(1)-Si(1) bond lengths are 2.34 Å.