MgTb3 is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. Mg(1) is bonded to twelve equivalent Tb(1) atoms to form MgTb12 cuboctahedra that share corners with six equivalent Mg(1)Tb12 cuboctahedra, corners with twelve equivalent Tb(1)Tb8Mg4 cuboctahedra, edges with eighteen equivalent Tb(1)Tb8Mg4 cuboctahedra, faces with eight equivalent Mg(1)Tb12 cuboctahedra, and faces with twelve equivalent Tb(1)Tb8Mg4 cuboctahedra. Tb(1) is bonded to four equivalent Mg(1) and eight equivalent Tb(1) atoms to form distorted TbTb8Mg4 cuboctahedra that share corners with four equivalent Mg(1)Tb12 cuboctahedra, corners with fourteen equivalent Tb(1)Tb8Mg4 cuboctahedra, edges with six equivalent Mg(1)Tb12 cuboctahedra, edges with twelve equivalent Tb(1)Tb8Mg4 cuboctahedra, faces with four equivalent Mg(1)Tb12 cuboctahedra, and faces with sixteen equivalent Tb(1)Tb8Mg4 cuboctahedra.
MgTb3 is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. Mg(1) is bonded to twelve equivalent Tb(1) atoms to form MgTb12 cuboctahedra that share corners with six equivalent Mg(1)Tb12 cuboctahedra, corners with twelve equivalent Tb(1)Tb8Mg4 cuboctahedra, edges with eighteen equivalent Tb(1)Tb8Mg4 cuboctahedra, faces with eight equivalent Mg(1)Tb12 cuboctahedra, and faces with twelve equivalent Tb(1)Tb8Mg4 cuboctahedra. There are six shorter (3.40 Å) and six longer (3.52 Å) Mg(1)-Tb(1) bond lengths. Tb(1) is bonded to four equivalent Mg(1) and eight equivalent Tb(1) atoms to form distorted TbTb8Mg4 cuboctahedra that share corners with four equivalent Mg(1)Tb12 cuboctahedra, corners with fourteen equivalent Tb(1)Tb8Mg4 cuboctahedra, edges with six equivalent Mg(1)Tb12 cuboctahedra, edges with twelve equivalent Tb(1)Tb8Mg4 cuboctahedra, faces with four equivalent Mg(1)Tb12 cuboctahedra, and faces with sixteen equivalent Tb(1)Tb8Mg4 cuboctahedra. There are a spread of Tb(1)-Tb(1) bond distances ranging from 3.43-3.61 Å.