ErRh2Si crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 9-coordinate geometry to one Er(2) and nine equivalent Rh(1) atoms. In the second Er site, Er(2) is bonded in a 20-coordinate geometry to two equivalent Er(1), twelve equivalent Rh(1), three equivalent Si(1), and three equivalent Si(2) atoms. Rh(1) is bonded in a 12-coordinate geometry to two equivalent Er(2), three equivalent Er(1), four equivalent Rh(1), one Si(1), one Si(2), and one Si(3) atom. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 6-coordinate geometry to three equivalent Er(2) and six equivalent Rh(1) atoms. In the second Si site, Si(2) is bonded in a 6-coordinate geometry to three equivalent Er(2) and six equivalent Rh(1) atoms. In the third Si site, Si(3) is bonded in a distorted cuboctahedral geometry to six equivalent Rh(1) atoms.
ErRh2Si crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 9-coordinate geometry to one Er(2) and nine equivalent Rh(1) atoms. The Er(1)-Er(2) bond length is 3.19 Å. There are three shorter (2.96 Å) and six longer (3.08 Å) Er(1)-Rh(1) bond lengths. In the second Er site, Er(2) is bonded in a 20-coordinate geometry to two equivalent Er(1), twelve equivalent Rh(1), three equivalent Si(1), and three equivalent Si(2) atoms. All Er(2)-Rh(1) bond lengths are 3.28 Å. All Er(2)-Si(1) bond lengths are 3.17 Å. All Er(2)-Si(2) bond lengths are 3.17 Å. Rh(1) is bonded in a 12-coordinate geometry to two equivalent Er(2), three equivalent Er(1), four equivalent Rh(1), one Si(1), one Si(2), and one Si(3) atom. All Rh(1)-Rh(1) bond lengths are 2.75 Å. The Rh(1)-Si(1) bond length is 2.39 Å. The Rh(1)-Si(2) bond length is 2.39 Å. The Rh(1)-Si(3) bond length is 2.51 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 6-coordinate geometry to three equivalent Er(2) and six equivalent Rh(1) atoms. In the second Si site, Si(2) is bonded in a 6-coordinate geometry to three equivalent Er(2) and six equivalent Rh(1) atoms. In the third Si site, Si(3) is bonded in a distorted cuboctahedral geometry to six equivalent Rh(1) atoms.