Er2Ni17 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 20-coordinate geometry to two equivalent Ni(2), six equivalent Ni(1), six equivalent Ni(3), and six equivalent Ni(4) atoms. In the second Er site, Er(2) is bonded in a 18-coordinate geometry to six equivalent Ni(4) and twelve equivalent Ni(1) atoms. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one Er(1), two equivalent Er(2), one Ni(2), two equivalent Ni(1), two equivalent Ni(3), and four equivalent Ni(4) atoms to form distorted NiEr3Ni9 cuboctahedra that share corners with five equivalent Ni(3)Er2Ni10 cuboctahedra, corners with ten equivalent Ni(1)Er3Ni9 cuboctahedra, edges with three equivalent Ni(3)Er2Ni10 cuboctahedra, edges with five equivalent Ni(1)Er3Ni9 cuboctahedra, faces with two equivalent Ni(3)Er2Ni10 cuboctahedra, and faces with eight equivalent Ni(1)Er3Ni9 cuboctahedra. In the second Ni site, Ni(2) is bonded in a 14-coordinate geometry to one Er(1), one Ni(2), three equivalent Ni(1), three equivalent Ni(3), and six equivalent Ni(4) atoms. In the third Ni site, Ni(3) is bonded to two equivalent Er(1), two equivalent Ni(2), four equivalent Ni(1), and four equivalent Ni(4) atoms to form NiEr2Ni10 cuboctahedra that share corners with four equivalent Ni(3)Er2Ni10 cuboctahedra, corners with ten equivalent Ni(1)Er3Ni9 cuboctahedra, edges with six equivalent Ni(1)Er3Ni9 cuboctahedra, faces with four equivalent Ni(1)Er3Ni9 cuboctahedra, and faces with six equivalent Ni(3)Er2Ni10 cuboctahedra. In the fourth Ni site, Ni(4) is bonded in a 12-coordinate geometry to one Er(1), one Er(2), two equivalent Ni(2), two equivalent Ni(3), two equivalent Ni(4), and four equivalent Ni(1) atoms.
Er2Ni17 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 20-coordinate geometry to two equivalent Ni(2), six equivalent Ni(1), six equivalent Ni(3), and six equivalent Ni(4) atoms. Both Er(1)-Ni(2) bond lengths are 2.81 Å. All Er(1)-Ni(1) bond lengths are 3.02 Å. All Er(1)-Ni(3) bond lengths are 3.11 Å. All Er(1)-Ni(4) bond lengths are 2.96 Å. In the second Er site, Er(2) is bonded in a 18-coordinate geometry to six equivalent Ni(4) and twelve equivalent Ni(1) atoms. All Er(2)-Ni(4) bond lengths are 2.89 Å. There are six shorter (2.99 Å) and six longer (3.21 Å) Er(2)-Ni(1) bond lengths. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one Er(1), two equivalent Er(2), one Ni(2), two equivalent Ni(1), two equivalent Ni(3), and four equivalent Ni(4) atoms to form distorted NiEr3Ni9 cuboctahedra that share corners with five equivalent Ni(3)Er2Ni10 cuboctahedra, corners with ten equivalent Ni(1)Er3Ni9 cuboctahedra, edges with three equivalent Ni(3)Er2Ni10 cuboctahedra, edges with five equivalent Ni(1)Er3Ni9 cuboctahedra, faces with two equivalent Ni(3)Er2Ni10 cuboctahedra, and faces with eight equivalent Ni(1)Er3Ni9 cuboctahedra. The Ni(1)-Ni(2) bond length is 2.59 Å. Both Ni(1)-Ni(1) bond lengths are 2.39 Å. Both Ni(1)-Ni(3) bond lengths are 2.40 Å. There are two shorter (2.48 Å) and two longer (2.49 Å) Ni(1)-Ni(4) bond lengths. In the second Ni site, Ni(2) is bonded in a 14-coordinate geometry to one Er(1), one Ni(2), three equivalent Ni(1), three equivalent Ni(3), and six equivalent Ni(4) atoms. The Ni(2)-Ni(2) bond length is 2.38 Å. All Ni(2)-Ni(3) bond lengths are 2.52 Å. All Ni(2)-Ni(4) bond lengths are 2.70 Å. In the third Ni site, Ni(3) is bonded to two equivalent Er(1), two equivalent Ni(2), four equivalent Ni(1), and four equivalent Ni(4) atoms to form NiEr2Ni10 cuboctahedra that share corners with four equivalent Ni(3)Er2Ni10 cuboctahedra, corners with ten equivalent Ni(1)Er3Ni9 cuboctahedra, edges with six equivalent Ni(1)Er3Ni9 cuboctahedra, faces with four equivalent Ni(1)Er3Ni9 cuboctahedra, and faces with six equivalent Ni(3)Er2Ni10 cuboctahedra. All Ni(3)-Ni(4) bond lengths are 2.38 Å. In the fourth Ni site, Ni(4) is bonded in a 12-coordinate geometry to one Er(1), one Er(2), two equivalent Ni(2), two equivalent Ni(3), two equivalent Ni(4), and four equivalent Ni(1) atoms. There is one shorter (2.35 Å) and one longer (2.50 Å) Ni(4)-Ni(4) bond length.