Er2Ni7 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 12-coordinate geometry to three equivalent Ni(1) and nine equivalent Ni(3) atoms. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to three equivalent Ni(4), three equivalent Ni(5), six equivalent Ni(2), and six equivalent Ni(3) atoms. There are five inequivalent Ni sites. In the first Ni site, Ni(5) is bonded in a 9-coordinate geometry to three equivalent Er(2), three equivalent Ni(2), and three equivalent Ni(3) atoms. In the second Ni site, Ni(1) is bonded to six equivalent Er(1) and six equivalent Ni(3) atoms to form NiEr6Ni6 cuboctahedra that share corners with twelve equivalent Ni(3)Er5Ni7 cuboctahedra, edges with six equivalent Ni(1)Er6Ni6 cuboctahedra, and faces with eighteen equivalent Ni(3)Er5Ni7 cuboctahedra. In the third Ni site, Ni(2) is bonded to four equivalent Er(2), two equivalent Ni(4), two equivalent Ni(5), and four equivalent Ni(2) atoms to form NiEr4Ni8 cuboctahedra that share corners with four equivalent Ni(2)Er4Ni8 cuboctahedra, corners with twelve equivalent Ni(3)Er5Ni7 cuboctahedra, edges with two equivalent Ni(2)Er4Ni8 cuboctahedra, edges with eight equivalent Ni(3)Er5Ni7 cuboctahedra, faces with two equivalent Ni(3)Er5Ni7 cuboctahedra, and faces with eight equivalent Ni(2)Er4Ni8 cuboctahedra. In the fourth Ni site, Ni(3) is bonded to two equivalent Er(2), three equivalent Er(1), one Ni(1), one Ni(4), one Ni(5), and four equivalent Ni(3) atoms to form distorted NiEr5Ni7 cuboctahedra that share corners with two equivalent Ni(1)Er6Ni6 cuboctahedra, corners with six equivalent Ni(2)Er4Ni8 cuboctahedra, corners with nine equivalent Ni(3)Er5Ni7 cuboctahedra, edges with four equivalent Ni(2)Er4Ni8 cuboctahedra, edges with four equivalent Ni(3)Er5Ni7 cuboctahedra,  a faceface with one Ni(2)Er4Ni8 cuboctahedra, faces with three equivalent Ni(1)Er6Ni6 cuboctahedra, and faces with ten equivalent Ni(3)Er5Ni7 cuboctahedra. In the fifth Ni site, Ni(4) is bonded in a 9-coordinate geometry to three equivalent Er(2), three equivalent Ni(2), and three equivalent Ni(3) atoms.
Er2Ni7 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 12-coordinate geometry to three equivalent Ni(1) and nine equivalent Ni(3) atoms. All Er(1)-Ni(1) bond lengths are 2.92 Å. There are six shorter (2.80 Å) and three longer (3.07 Å) Er(1)-Ni(3) bond lengths. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to three equivalent Ni(4), three equivalent Ni(5), six equivalent Ni(2), and six equivalent Ni(3) atoms. All Er(2)-Ni(4) bond lengths are 2.84 Å. All Er(2)-Ni(5) bond lengths are 2.84 Å. All Er(2)-Ni(2) bond lengths are 3.07 Å. All Er(2)-Ni(3) bond lengths are 3.24 Å. There are five inequivalent Ni sites. In the first Ni site, Ni(5) is bonded in a 9-coordinate geometry to three equivalent Er(2), three equivalent Ni(2), and three equivalent Ni(3) atoms. All Ni(5)-Ni(2) bond lengths are 2.45 Å. All Ni(5)-Ni(3) bond lengths are 2.42 Å. In the second Ni site, Ni(1) is bonded to six equivalent Er(1) and six equivalent Ni(3) atoms to form NiEr6Ni6 cuboctahedra that share corners with twelve equivalent Ni(3)Er5Ni7 cuboctahedra, edges with six equivalent Ni(1)Er6Ni6 cuboctahedra, and faces with eighteen equivalent Ni(3)Er5Ni7 cuboctahedra. All Ni(1)-Ni(3) bond lengths are 2.48 Å. In the third Ni site, Ni(2) is bonded to four equivalent Er(2), two equivalent Ni(4), two equivalent Ni(5), and four equivalent Ni(2) atoms to form NiEr4Ni8 cuboctahedra that share corners with four equivalent Ni(2)Er4Ni8 cuboctahedra, corners with twelve equivalent Ni(3)Er5Ni7 cuboctahedra, edges with two equivalent Ni(2)Er4Ni8 cuboctahedra, edges with eight equivalent Ni(3)Er5Ni7 cuboctahedra, faces with two equivalent Ni(3)Er5Ni7 cuboctahedra, and faces with eight equivalent Ni(2)Er4Ni8 cuboctahedra. Both Ni(2)-Ni(4) bond lengths are 2.44 Å. There are two shorter (2.45 Å) and two longer (2.46 Å) Ni(2)-Ni(2) bond lengths. In the fourth Ni site, Ni(3) is bonded to two equivalent Er(2), three equivalent Er(1), one Ni(1), one Ni(4), one Ni(5), and four equivalent Ni(3) atoms to form distorted NiEr5Ni7 cuboctahedra that share corners with two equivalent Ni(1)Er6Ni6 cuboctahedra, corners with six equivalent Ni(2)Er4Ni8 cuboctahedra, corners with nine equivalent Ni(3)Er5Ni7 cuboctahedra, edges with four equivalent Ni(2)Er4Ni8 cuboctahedra, edges with four equivalent Ni(3)Er5Ni7 cuboctahedra,  a faceface with one Ni(2)Er4Ni8 cuboctahedra, faces with three equivalent Ni(1)Er6Ni6 cuboctahedra, and faces with ten equivalent Ni(3)Er5Ni7 cuboctahedra. The Ni(3)-Ni(4) bond length is 2.44 Å. There are two shorter (2.44 Å) and two longer (2.47 Å) Ni(3)-Ni(3) bond lengths. In the fifth Ni site, Ni(4) is bonded in a 9-coordinate geometry to three equivalent Er(2), three equivalent Ni(2), and three equivalent Ni(3) atoms.