MgY is beta-derived structured and crystallizes in the hexagonal P-6m2 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent Mg(2), six equivalent Mg(1), and three equivalent Y(2) atoms to form MgY3Mg9 cuboctahedra that share corners with six equivalent Y(1)Y12 cuboctahedra, corners with twelve equivalent Mg(1)Y3Mg9 cuboctahedra, edges with six equivalent Mg(2)Mg12 cuboctahedra, edges with six equivalent Mg(1)Y3Mg9 cuboctahedra, edges with six equivalent Y(2)Y9Mg3 cuboctahedra,  a faceface with one Y(1)Y12 cuboctahedra, faces with six equivalent Mg(2)Mg12 cuboctahedra, faces with six equivalent Y(2)Y9Mg3 cuboctahedra, and faces with seven equivalent Mg(1)Y3Mg9 cuboctahedra. In the second Mg site, Mg(2) is bonded to six equivalent Mg(1) and six equivalent Mg(2) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(2)Mg12 cuboctahedra, corners with twelve equivalent Y(2)Y9Mg3 cuboctahedra, edges with six equivalent Mg(2)Mg12 cuboctahedra, edges with twelve equivalent Mg(1)Y3Mg9 cuboctahedra, faces with two equivalent Y(2)Y9Mg3 cuboctahedra, faces with six equivalent Mg(2)Mg12 cuboctahedra, and faces with twelve equivalent Mg(1)Y3Mg9 cuboctahedra. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded to six equivalent Y(1) and six equivalent Y(2) atoms to form YY12 cuboctahedra that share corners with six equivalent Y(1)Y12 cuboctahedra, corners with twelve equivalent Mg(1)Y3Mg9 cuboctahedra, edges with six equivalent Y(1)Y12 cuboctahedra, edges with twelve equivalent Y(2)Y9Mg3 cuboctahedra, faces with two equivalent Mg(1)Y3Mg9 cuboctahedra, faces with six equivalent Y(1)Y12 cuboctahedra, and faces with twelve equivalent Y(2)Y9Mg3 cuboctahedra. In the second Y site, Y(2) is bonded to three equivalent Mg(1), three equivalent Y(1), and six equivalent Y(2) atoms to form YY9Mg3 cuboctahedra that share corners with six equivalent Mg(2)Mg12 cuboctahedra, corners with twelve equivalent Y(2)Y9Mg3 cuboctahedra, edges with six equivalent Mg(1)Y3Mg9 cuboctahedra, edges with six equivalent Y(1)Y12 cuboctahedra, edges with six equivalent Y(2)Y9Mg3 cuboctahedra,  a faceface with one Mg(2)Mg12 cuboctahedra, faces with six equivalent Mg(1)Y3Mg9 cuboctahedra, faces with six equivalent Y(1)Y12 cuboctahedra, and faces with seven equivalent Y(2)Y9Mg3 cuboctahedra.
MgY is beta-derived structured and crystallizes in the hexagonal P-6m2 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent Mg(2), six equivalent Mg(1), and three equivalent Y(2) atoms to form MgY3Mg9 cuboctahedra that share corners with six equivalent Y(1)Y12 cuboctahedra, corners with twelve equivalent Mg(1)Y3Mg9 cuboctahedra, edges with six equivalent Mg(2)Mg12 cuboctahedra, edges with six equivalent Mg(1)Y3Mg9 cuboctahedra, edges with six equivalent Y(2)Y9Mg3 cuboctahedra,  a faceface with one Y(1)Y12 cuboctahedra, faces with six equivalent Mg(2)Mg12 cuboctahedra, faces with six equivalent Y(2)Y9Mg3 cuboctahedra, and faces with seven equivalent Mg(1)Y3Mg9 cuboctahedra. All Mg(1)-Mg(2) bond lengths are 3.25 Å. All Mg(1)-Mg(1) bond lengths are 3.45 Å. All Mg(1)-Y(2) bond lengths are 3.42 Å. In the second Mg site, Mg(2) is bonded to six equivalent Mg(1) and six equivalent Mg(2) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(2)Mg12 cuboctahedra, corners with twelve equivalent Y(2)Y9Mg3 cuboctahedra, edges with six equivalent Mg(2)Mg12 cuboctahedra, edges with twelve equivalent Mg(1)Y3Mg9 cuboctahedra, faces with two equivalent Y(2)Y9Mg3 cuboctahedra, faces with six equivalent Mg(2)Mg12 cuboctahedra, and faces with twelve equivalent Mg(1)Y3Mg9 cuboctahedra. All Mg(2)-Mg(2) bond lengths are 3.45 Å. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded to six equivalent Y(1) and six equivalent Y(2) atoms to form YY12 cuboctahedra that share corners with six equivalent Y(1)Y12 cuboctahedra, corners with twelve equivalent Mg(1)Y3Mg9 cuboctahedra, edges with six equivalent Y(1)Y12 cuboctahedra, edges with twelve equivalent Y(2)Y9Mg3 cuboctahedra, faces with two equivalent Mg(1)Y3Mg9 cuboctahedra, faces with six equivalent Y(1)Y12 cuboctahedra, and faces with twelve equivalent Y(2)Y9Mg3 cuboctahedra. All Y(1)-Y(1) bond lengths are 3.45 Å. All Y(1)-Y(2) bond lengths are 3.58 Å. In the second Y site, Y(2) is bonded to three equivalent Mg(1), three equivalent Y(1), and six equivalent Y(2) atoms to form YY9Mg3 cuboctahedra that share corners with six equivalent Mg(2)Mg12 cuboctahedra, corners with twelve equivalent Y(2)Y9Mg3 cuboctahedra, edges with six equivalent Mg(1)Y3Mg9 cuboctahedra, edges with six equivalent Y(1)Y12 cuboctahedra, edges with six equivalent Y(2)Y9Mg3 cuboctahedra,  a faceface with one Mg(2)Mg12 cuboctahedra, faces with six equivalent Mg(1)Y3Mg9 cuboctahedra, faces with six equivalent Y(1)Y12 cuboctahedra, and faces with seven equivalent Y(2)Y9Mg3 cuboctahedra. All Y(2)-Y(2) bond lengths are 3.45 Å.