ErCo3Ni2 crystallizes in the hexagonal P6/mmm space group. Er(1) is bonded in a distorted hexagonal planar geometry to twelve equivalent Co(1) and six equivalent Ni(1) atoms. Co(1) is bonded to four equivalent Er(1), four equivalent Co(1), and four equivalent Ni(1) atoms to form CoEr4Co4Ni4 cuboctahedra that share corners with eight equivalent Ni(1)Er3Co6 cuboctahedra, corners with sixteen equivalent Co(1)Er4Co4Ni4 cuboctahedra, edges with eight equivalent Ni(1)Er3Co6 cuboctahedra, edges with ten equivalent Co(1)Er4Co4Ni4 cuboctahedra, faces with four equivalent Ni(1)Er3Co6 cuboctahedra, and faces with ten equivalent Co(1)Er4Co4Ni4 cuboctahedra. Ni(1) is bonded to three equivalent Er(1) and six equivalent Co(1) atoms to form distorted NiEr3Co6 cuboctahedra that share corners with twelve equivalent Co(1)Er4Co4Ni4 cuboctahedra, corners with fifteen equivalent Ni(1)Er3Co6 cuboctahedra, edges with twelve equivalent Co(1)Er4Co4Ni4 cuboctahedra, faces with five equivalent Ni(1)Er3Co6 cuboctahedra, and faces with six equivalent Co(1)Er4Co4Ni4 cuboctahedra.
ErCo3Ni2 crystallizes in the hexagonal P6/mmm space group. Er(1) is bonded in a distorted hexagonal planar geometry to twelve equivalent Co(1) and six equivalent Ni(1) atoms. All Er(1)-Co(1) bond lengths are 3.14 Å. All Er(1)-Ni(1) bond lengths are 2.78 Å. Co(1) is bonded to four equivalent Er(1), four equivalent Co(1), and four equivalent Ni(1) atoms to form CoEr4Co4Ni4 cuboctahedra that share corners with eight equivalent Ni(1)Er3Co6 cuboctahedra, corners with sixteen equivalent Co(1)Er4Co4Ni4 cuboctahedra, edges with eight equivalent Ni(1)Er3Co6 cuboctahedra, edges with ten equivalent Co(1)Er4Co4Ni4 cuboctahedra, faces with four equivalent Ni(1)Er3Co6 cuboctahedra, and faces with ten equivalent Co(1)Er4Co4Ni4 cuboctahedra. All Co(1)-Co(1) bond lengths are 2.41 Å. All Co(1)-Ni(1) bond lengths are 2.45 Å. Ni(1) is bonded to three equivalent Er(1) and six equivalent Co(1) atoms to form distorted NiEr3Co6 cuboctahedra that share corners with twelve equivalent Co(1)Er4Co4Ni4 cuboctahedra, corners with fifteen equivalent Ni(1)Er3Co6 cuboctahedra, edges with twelve equivalent Co(1)Er4Co4Ni4 cuboctahedra, faces with five equivalent Ni(1)Er3Co6 cuboctahedra, and faces with six equivalent Co(1)Er4Co4Ni4 cuboctahedra.