Mg4Ti3 is beta-derived structured and crystallizes in the hexagonal P6_3/m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Mg(2), six equivalent Mg(1), and five equivalent Ti(1) atoms to form distorted MgMg7Ti5 cuboctahedra that share corners with three equivalent Mg(2)Mg3Ti9 cuboctahedra, corners with six equivalent Mg(1)Mg7Ti5 cuboctahedra, corners with nine equivalent Ti(1)Mg8Ti4 cuboctahedra, edges with three equivalent Mg(2)Mg3Ti9 cuboctahedra, edges with four equivalent Mg(1)Mg7Ti5 cuboctahedra, edges with eleven equivalent Ti(1)Mg8Ti4 cuboctahedra, faces with three equivalent Mg(2)Mg3Ti9 cuboctahedra, faces with seven equivalent Ti(1)Mg8Ti4 cuboctahedra, and faces with ten equivalent Mg(1)Mg7Ti5 cuboctahedra. In the second Mg site, Mg(2) is bonded to three equivalent Mg(1) and nine equivalent Ti(1) atoms to form MgMg3Ti9 cuboctahedra that share corners with nine equivalent Mg(1)Mg7Ti5 cuboctahedra, corners with nine equivalent Ti(1)Mg8Ti4 cuboctahedra, edges with three equivalent Ti(1)Mg8Ti4 cuboctahedra, edges with six equivalent Mg(2)Mg3Ti9 cuboctahedra, edges with nine equivalent Mg(1)Mg7Ti5 cuboctahedra, faces with two equivalent Mg(2)Mg3Ti9 cuboctahedra, faces with nine equivalent Mg(1)Mg7Ti5 cuboctahedra, and faces with nine equivalent Ti(1)Mg8Ti4 cuboctahedra. Ti(1) is bonded to three equivalent Mg(2), five equivalent Mg(1), and four equivalent Ti(1) atoms to form distorted TiMg8Ti4 cuboctahedra that share corners with three equivalent Mg(2)Mg3Ti9 cuboctahedra, corners with six equivalent Ti(1)Mg8Ti4 cuboctahedra, corners with nine equivalent Mg(1)Mg7Ti5 cuboctahedra,  an edgeedge with one Mg(2)Mg3Ti9 cuboctahedra, edges with six equivalent Ti(1)Mg8Ti4 cuboctahedra, edges with eleven equivalent Mg(1)Mg7Ti5 cuboctahedra, faces with three equivalent Mg(2)Mg3Ti9 cuboctahedra, faces with seven equivalent Mg(1)Mg7Ti5 cuboctahedra, and faces with ten equivalent Ti(1)Mg8Ti4 cuboctahedra.
Mg4Ti3 is beta-derived structured and crystallizes in the hexagonal P6_3/m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Mg(2), six equivalent Mg(1), and five equivalent Ti(1) atoms to form distorted MgMg7Ti5 cuboctahedra that share corners with three equivalent Mg(2)Mg3Ti9 cuboctahedra, corners with six equivalent Mg(1)Mg7Ti5 cuboctahedra, corners with nine equivalent Ti(1)Mg8Ti4 cuboctahedra, edges with three equivalent Mg(2)Mg3Ti9 cuboctahedra, edges with four equivalent Mg(1)Mg7Ti5 cuboctahedra, edges with eleven equivalent Ti(1)Mg8Ti4 cuboctahedra, faces with three equivalent Mg(2)Mg3Ti9 cuboctahedra, faces with seven equivalent Ti(1)Mg8Ti4 cuboctahedra, and faces with ten equivalent Mg(1)Mg7Ti5 cuboctahedra. The Mg(1)-Mg(2) bond length is 2.97 Å. There are four shorter (3.08 Å) and two longer (3.17 Å) Mg(1)-Mg(1) bond lengths. There are a spread of Mg(1)-Ti(1) bond distances ranging from 3.00-3.12 Å. In the second Mg site, Mg(2) is bonded to three equivalent Mg(1) and nine equivalent Ti(1) atoms to form MgMg3Ti9 cuboctahedra that share corners with nine equivalent Mg(1)Mg7Ti5 cuboctahedra, corners with nine equivalent Ti(1)Mg8Ti4 cuboctahedra, edges with three equivalent Ti(1)Mg8Ti4 cuboctahedra, edges with six equivalent Mg(2)Mg3Ti9 cuboctahedra, edges with nine equivalent Mg(1)Mg7Ti5 cuboctahedra, faces with two equivalent Mg(2)Mg3Ti9 cuboctahedra, faces with nine equivalent Mg(1)Mg7Ti5 cuboctahedra, and faces with nine equivalent Ti(1)Mg8Ti4 cuboctahedra. There are six shorter (2.98 Å) and three longer (3.14 Å) Mg(2)-Ti(1) bond lengths. Ti(1) is bonded to three equivalent Mg(2), five equivalent Mg(1), and four equivalent Ti(1) atoms to form distorted TiMg8Ti4 cuboctahedra that share corners with three equivalent Mg(2)Mg3Ti9 cuboctahedra, corners with six equivalent Ti(1)Mg8Ti4 cuboctahedra, corners with nine equivalent Mg(1)Mg7Ti5 cuboctahedra,  an edgeedge with one Mg(2)Mg3Ti9 cuboctahedra, edges with six equivalent Ti(1)Mg8Ti4 cuboctahedra, edges with eleven equivalent Mg(1)Mg7Ti5 cuboctahedra, faces with three equivalent Mg(2)Mg3Ti9 cuboctahedra, faces with seven equivalent Mg(1)Mg7Ti5 cuboctahedra, and faces with ten equivalent Ti(1)Mg8Ti4 cuboctahedra. There are two shorter (2.87 Å) and two longer (3.10 Å) Ti(1)-Ti(1) bond lengths.