ErNi10Si2 crystallizes in the tetragonal P4/nmm space group. Er(1) is bonded in a 20-coordinate geometry to four equivalent Ni(1), four equivalent Ni(3), eight equivalent Ni(2), and four equivalent Si(1) atoms. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent Er(1), four equivalent Ni(2), four equivalent Ni(3), and two equivalent Si(1) atoms to form NiEr2Si2Ni8 cuboctahedra that share corners with four equivalent Ni(1)Er2Si2Ni8 cuboctahedra, corners with six equivalent Si(1)Er2Ni10 cuboctahedra, corners with eight equivalent Ni(2)Er2Si2Ni8 cuboctahedra, edges with four equivalent Ni(2)Er2Si2Ni8 cuboctahedra, edges with four equivalent Si(1)Er2Ni10 cuboctahedra, faces with two equivalent Si(1)Er2Ni10 cuboctahedra, faces with four equivalent Ni(1)Er2Si2Ni8 cuboctahedra, and faces with eight equivalent Ni(2)Er2Si2Ni8 cuboctahedra. In the second Ni site, Ni(2) is bonded to two equivalent Er(1), two equivalent Ni(1), two equivalent Ni(2), four equivalent Ni(3), and two equivalent Si(1) atoms to form distorted NiEr2Si2Ni8 cuboctahedra that share corners with four equivalent Ni(1)Er2Si2Ni8 cuboctahedra, corners with four equivalent Si(1)Er2Ni10 cuboctahedra, corners with ten equivalent Ni(2)Er2Si2Ni8 cuboctahedra, edges with two equivalent Ni(1)Er2Si2Ni8 cuboctahedra, edges with two equivalent Si(1)Er2Ni10 cuboctahedra, edges with three equivalent Ni(2)Er2Si2Ni8 cuboctahedra, faces with four equivalent Ni(1)Er2Si2Ni8 cuboctahedra, faces with four equivalent Si(1)Er2Ni10 cuboctahedra, and faces with seven equivalent Ni(2)Er2Si2Ni8 cuboctahedra. In the third Ni site, Ni(3) is bonded in a 14-coordinate geometry to one Er(1), two equivalent Ni(1), four equivalent Ni(2), five equivalent Ni(3), and two equivalent Si(1) atoms. Si(1) is bonded to two equivalent Er(1), two equivalent Ni(1), four equivalent Ni(2), and four equivalent Ni(3) atoms to form distorted SiEr2Ni10 cuboctahedra that share corners with four equivalent Si(1)Er2Ni10 cuboctahedra, corners with six equivalent Ni(1)Er2Si2Ni8 cuboctahedra, corners with eight equivalent Ni(2)Er2Si2Ni8 cuboctahedra, edges with four equivalent Ni(1)Er2Si2Ni8 cuboctahedra, edges with four equivalent Ni(2)Er2Si2Ni8 cuboctahedra, faces with two equivalent Ni(1)Er2Si2Ni8 cuboctahedra, faces with four equivalent Si(1)Er2Ni10 cuboctahedra, and faces with eight equivalent Ni(2)Er2Si2Ni8 cuboctahedra.
ErNi10Si2 crystallizes in the tetragonal P4/nmm space group. Er(1) is bonded in a 20-coordinate geometry to four equivalent Ni(1), four equivalent Ni(3), eight equivalent Ni(2), and four equivalent Si(1) atoms. All Er(1)-Ni(1) bond lengths are 3.03 Å. All Er(1)-Ni(3) bond lengths are 2.84 Å. There are four shorter (2.90 Å) and four longer (2.96 Å) Er(1)-Ni(2) bond lengths. All Er(1)-Si(1) bond lengths are 3.13 Å. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent Er(1), four equivalent Ni(2), four equivalent Ni(3), and two equivalent Si(1) atoms to form NiEr2Si2Ni8 cuboctahedra that share corners with four equivalent Ni(1)Er2Si2Ni8 cuboctahedra, corners with six equivalent Si(1)Er2Ni10 cuboctahedra, corners with eight equivalent Ni(2)Er2Si2Ni8 cuboctahedra, edges with four equivalent Ni(2)Er2Si2Ni8 cuboctahedra, edges with four equivalent Si(1)Er2Ni10 cuboctahedra, faces with two equivalent Si(1)Er2Ni10 cuboctahedra, faces with four equivalent Ni(1)Er2Si2Ni8 cuboctahedra, and faces with eight equivalent Ni(2)Er2Si2Ni8 cuboctahedra. All Ni(1)-Ni(2) bond lengths are 2.38 Å. All Ni(1)-Ni(3) bond lengths are 2.44 Å. Both Ni(1)-Si(1) bond lengths are 2.31 Å. In the second Ni site, Ni(2) is bonded to two equivalent Er(1), two equivalent Ni(1), two equivalent Ni(2), four equivalent Ni(3), and two equivalent Si(1) atoms to form distorted NiEr2Si2Ni8 cuboctahedra that share corners with four equivalent Ni(1)Er2Si2Ni8 cuboctahedra, corners with four equivalent Si(1)Er2Ni10 cuboctahedra, corners with ten equivalent Ni(2)Er2Si2Ni8 cuboctahedra, edges with two equivalent Ni(1)Er2Si2Ni8 cuboctahedra, edges with two equivalent Si(1)Er2Ni10 cuboctahedra, edges with three equivalent Ni(2)Er2Si2Ni8 cuboctahedra, faces with four equivalent Ni(1)Er2Si2Ni8 cuboctahedra, faces with four equivalent Si(1)Er2Ni10 cuboctahedra, and faces with seven equivalent Ni(2)Er2Si2Ni8 cuboctahedra. Both Ni(2)-Ni(2) bond lengths are 2.54 Å. There are a spread of Ni(2)-Ni(3) bond distances ranging from 2.50-2.58 Å. Both Ni(2)-Si(1) bond lengths are 2.29 Å. In the third Ni site, Ni(3) is bonded in a 14-coordinate geometry to one Er(1), two equivalent Ni(1), four equivalent Ni(2), five equivalent Ni(3), and two equivalent Si(1) atoms. There are a spread of Ni(3)-Ni(3) bond distances ranging from 2.38-2.94 Å. Both Ni(3)-Si(1) bond lengths are 2.49 Å. Si(1) is bonded to two equivalent Er(1), two equivalent Ni(1), four equivalent Ni(2), and four equivalent Ni(3) atoms to form distorted SiEr2Ni10 cuboctahedra that share corners with four equivalent Si(1)Er2Ni10 cuboctahedra, corners with six equivalent Ni(1)Er2Si2Ni8 cuboctahedra, corners with eight equivalent Ni(2)Er2Si2Ni8 cuboctahedra, edges with four equivalent Ni(1)Er2Si2Ni8 cuboctahedra, edges with four equivalent Ni(2)Er2Si2Ni8 cuboctahedra, faces with two equivalent Ni(1)Er2Si2Ni8 cuboctahedra, faces with four equivalent Si(1)Er2Ni10 cuboctahedra, and faces with eight equivalent Ni(2)Er2Si2Ni8 cuboctahedra.