ErFeNi4 crystallizes in the hexagonal P-6m2 space group. Er(1) is bonded in a 18-coordinate geometry to three equivalent Fe(1), three equivalent Ni(1), and twelve equivalent Ni(2) atoms. Fe(1) is bonded to three equivalent Er(1), three equivalent Ni(1), and six equivalent Ni(2) atoms to form distorted FeEr3Ni9 cuboctahedra that share corners with nine equivalent Ni(1)Er3Fe3Ni6 cuboctahedra, corners with twelve equivalent Ni(2)Er4Fe2Ni6 cuboctahedra, edges with six equivalent Fe(1)Er3Ni9 cuboctahedra, faces with two equivalent Fe(1)Er3Ni9 cuboctahedra, faces with three equivalent Ni(1)Er3Fe3Ni6 cuboctahedra, and faces with eighteen equivalent Ni(2)Er4Fe2Ni6 cuboctahedra. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to three equivalent Er(1), three equivalent Fe(1), and six equivalent Ni(2) atoms to form distorted NiEr3Fe3Ni6 cuboctahedra that share corners with nine equivalent Fe(1)Er3Ni9 cuboctahedra, corners with twelve equivalent Ni(2)Er4Fe2Ni6 cuboctahedra, edges with six equivalent Ni(1)Er3Fe3Ni6 cuboctahedra, faces with two equivalent Ni(1)Er3Fe3Ni6 cuboctahedra, faces with three equivalent Fe(1)Er3Ni9 cuboctahedra, and faces with eighteen equivalent Ni(2)Er4Fe2Ni6 cuboctahedra. In the second Ni site, Ni(2) is bonded to four equivalent Er(1), two equivalent Fe(1), two equivalent Ni(1), and four equivalent Ni(2) atoms to form distorted NiEr4Fe2Ni6 cuboctahedra that share corners with four equivalent Fe(1)Er3Ni9 cuboctahedra, corners with four equivalent Ni(1)Er3Fe3Ni6 cuboctahedra, corners with sixteen equivalent Ni(2)Er4Fe2Ni6 cuboctahedra, edges with ten equivalent Ni(2)Er4Fe2Ni6 cuboctahedra, faces with six equivalent Fe(1)Er3Ni9 cuboctahedra, faces with six equivalent Ni(1)Er3Fe3Ni6 cuboctahedra, and faces with ten equivalent Ni(2)Er4Fe2Ni6 cuboctahedra.
ErFeNi4 crystallizes in the hexagonal P-6m2 space group. Er(1) is bonded in a 18-coordinate geometry to three equivalent Fe(1), three equivalent Ni(1), and twelve equivalent Ni(2) atoms. All Er(1)-Fe(1) bond lengths are 2.82 Å. All Er(1)-Ni(1) bond lengths are 2.82 Å. All Er(1)-Ni(2) bond lengths are 3.13 Å. Fe(1) is bonded to three equivalent Er(1), three equivalent Ni(1), and six equivalent Ni(2) atoms to form distorted FeEr3Ni9 cuboctahedra that share corners with nine equivalent Ni(1)Er3Fe3Ni6 cuboctahedra, corners with twelve equivalent Ni(2)Er4Fe2Ni6 cuboctahedra, edges with six equivalent Fe(1)Er3Ni9 cuboctahedra, faces with two equivalent Fe(1)Er3Ni9 cuboctahedra, faces with three equivalent Ni(1)Er3Fe3Ni6 cuboctahedra, and faces with eighteen equivalent Ni(2)Er4Fe2Ni6 cuboctahedra. All Fe(1)-Ni(1) bond lengths are 2.82 Å. All Fe(1)-Ni(2) bond lengths are 2.41 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to three equivalent Er(1), three equivalent Fe(1), and six equivalent Ni(2) atoms to form distorted NiEr3Fe3Ni6 cuboctahedra that share corners with nine equivalent Fe(1)Er3Ni9 cuboctahedra, corners with twelve equivalent Ni(2)Er4Fe2Ni6 cuboctahedra, edges with six equivalent Ni(1)Er3Fe3Ni6 cuboctahedra, faces with two equivalent Ni(1)Er3Fe3Ni6 cuboctahedra, faces with three equivalent Fe(1)Er3Ni9 cuboctahedra, and faces with eighteen equivalent Ni(2)Er4Fe2Ni6 cuboctahedra. All Ni(1)-Ni(2) bond lengths are 2.41 Å. In the second Ni site, Ni(2) is bonded to four equivalent Er(1), two equivalent Fe(1), two equivalent Ni(1), and four equivalent Ni(2) atoms to form distorted NiEr4Fe2Ni6 cuboctahedra that share corners with four equivalent Fe(1)Er3Ni9 cuboctahedra, corners with four equivalent Ni(1)Er3Fe3Ni6 cuboctahedra, corners with sixteen equivalent Ni(2)Er4Fe2Ni6 cuboctahedra, edges with ten equivalent Ni(2)Er4Fe2Ni6 cuboctahedra, faces with six equivalent Fe(1)Er3Ni9 cuboctahedra, faces with six equivalent Ni(1)Er3Fe3Ni6 cuboctahedra, and faces with ten equivalent Ni(2)Er4Fe2Ni6 cuboctahedra. There are two shorter (2.44 Å) and two longer (2.45 Å) Ni(2)-Ni(2) bond lengths.