Tm3Er is Magnesium-derived structured and crystallizes in the hexagonal P6_3/mmc space group. Tm(1) is bonded to eight equivalent Tm(1) and four equivalent Er(1) atoms to form TmEr4Tm8 cuboctahedra that share corners with four equivalent Er(1)Tm12 cuboctahedra, corners with fourteen equivalent Tm(1)Er4Tm8 cuboctahedra, edges with six equivalent Er(1)Tm12 cuboctahedra, edges with twelve equivalent Tm(1)Er4Tm8 cuboctahedra, faces with four equivalent Er(1)Tm12 cuboctahedra, and faces with sixteen equivalent Tm(1)Er4Tm8 cuboctahedra. Er(1) is bonded to twelve equivalent Tm(1) atoms to form ErTm12 cuboctahedra that share corners with six equivalent Er(1)Tm12 cuboctahedra, corners with twelve equivalent Tm(1)Er4Tm8 cuboctahedra, edges with eighteen equivalent Tm(1)Er4Tm8 cuboctahedra, faces with eight equivalent Er(1)Tm12 cuboctahedra, and faces with twelve equivalent Tm(1)Er4Tm8 cuboctahedra.
Tm3Er is Magnesium-derived structured and crystallizes in the hexagonal P6_3/mmc space group. Tm(1) is bonded to eight equivalent Tm(1) and four equivalent Er(1) atoms to form TmEr4Tm8 cuboctahedra that share corners with four equivalent Er(1)Tm12 cuboctahedra, corners with fourteen equivalent Tm(1)Er4Tm8 cuboctahedra, edges with six equivalent Er(1)Tm12 cuboctahedra, edges with twelve equivalent Tm(1)Er4Tm8 cuboctahedra, faces with four equivalent Er(1)Tm12 cuboctahedra, and faces with sixteen equivalent Tm(1)Er4Tm8 cuboctahedra. There are a spread of Tm(1)-Tm(1) bond distances ranging from 3.50-3.54 Å. There are two shorter (3.50 Å) and two longer (3.53 Å) Tm(1)-Er(1) bond lengths. Er(1) is bonded to twelve equivalent Tm(1) atoms to form ErTm12 cuboctahedra that share corners with six equivalent Er(1)Tm12 cuboctahedra, corners with twelve equivalent Tm(1)Er4Tm8 cuboctahedra, edges with eighteen equivalent Tm(1)Er4Tm8 cuboctahedra, faces with eight equivalent Er(1)Tm12 cuboctahedra, and faces with twelve equivalent Tm(1)Er4Tm8 cuboctahedra.