ErNi3 crystallizes in the trigonal R-3m 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(2) and nine equivalent Ni(1) atoms. In the second Er site, Er(2) is bonded in a distorted hexagonal planar geometry to six equivalent Ni(3) and twelve equivalent Ni(1) atoms. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent Er(2), three equivalent Er(1), one Ni(2), two equivalent Ni(3), and four equivalent Ni(1) atoms to form distorted NiEr5Ni7 cuboctahedra that share corners with two equivalent Ni(2)Er6Ni6 cuboctahedra, corners with fifteen equivalent Ni(1)Er5Ni7 cuboctahedra, edges with eight equivalent Ni(1)Er5Ni7 cuboctahedra, faces with three equivalent Ni(2)Er6Ni6 cuboctahedra, and faces with eleven equivalent Ni(1)Er5Ni7 cuboctahedra. In the second Ni site, Ni(2) is bonded to six equivalent Er(1) and six equivalent Ni(1) atoms to form NiEr6Ni6 cuboctahedra that share corners with twelve equivalent Ni(1)Er5Ni7 cuboctahedra, edges with six equivalent Ni(2)Er6Ni6 cuboctahedra, and faces with eighteen equivalent Ni(1)Er5Ni7 cuboctahedra. In the third Ni site, Ni(3) is bonded in a 9-coordinate geometry to three equivalent Er(2) and six equivalent Ni(1) atoms.
ErNi3 crystallizes in the trigonal R-3m 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(2) and nine equivalent Ni(1) atoms. All Er(1)-Ni(2) bond lengths are 2.90 Å. There are six shorter (2.80 Å) and three longer (3.04 Å) Er(1)-Ni(1) bond lengths. In the second Er site, Er(2) is bonded in a distorted hexagonal planar geometry to six equivalent Ni(3) and twelve equivalent Ni(1) atoms. All Er(2)-Ni(3) bond lengths are 2.82 Å. All Er(2)-Ni(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(2), three equivalent Er(1), one Ni(2), two equivalent Ni(3), and four equivalent Ni(1) atoms to form distorted NiEr5Ni7 cuboctahedra that share corners with two equivalent Ni(2)Er6Ni6 cuboctahedra, corners with fifteen equivalent Ni(1)Er5Ni7 cuboctahedra, edges with eight equivalent Ni(1)Er5Ni7 cuboctahedra, faces with three equivalent Ni(2)Er6Ni6 cuboctahedra, and faces with eleven equivalent Ni(1)Er5Ni7 cuboctahedra. The Ni(1)-Ni(2) bond length is 2.48 Å. There is one shorter (2.41 Å) and one longer (2.42 Å) Ni(1)-Ni(3) bond length. There are two shorter (2.43 Å) and two longer (2.46 Å) Ni(1)-Ni(1) bond lengths. In the second Ni site, Ni(2) is bonded to six equivalent Er(1) and six equivalent Ni(1) atoms to form NiEr6Ni6 cuboctahedra that share corners with twelve equivalent Ni(1)Er5Ni7 cuboctahedra, edges with six equivalent Ni(2)Er6Ni6 cuboctahedra, and faces with eighteen equivalent Ni(1)Er5Ni7 cuboctahedra. In the third Ni site, Ni(3) is bonded in a 9-coordinate geometry to three equivalent Er(2) and six equivalent Ni(1) atoms.