Mg5SmSb4 crystallizes in the trigonal P-3m1 space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Sb(1) and three equivalent Sb(2) atoms to form MgSb4 tetrahedra that share corners with three equivalent Mg(2)Sb6 octahedra, corners with three equivalent Sm(1)Sb6 octahedra, corners with six equivalent Mg(1)Sb4 tetrahedra, edges with three equivalent Mg(2)Sb6 octahedra, and edges with three equivalent Mg(3)Sb4 tetrahedra. The corner-sharing octahedral tilt angles range from 13-56°. In the second Mg site, Mg(2) is bonded to six equivalent Sb(2) atoms to form MgSb6 octahedra that share corners with six equivalent Mg(1)Sb4 tetrahedra, corners with six equivalent Mg(3)Sb4 tetrahedra, edges with six equivalent Mg(2)Sb6 octahedra, and edges with six equivalent Mg(1)Sb4 tetrahedra. In the third Mg site, Mg(3) is bonded to one Sb(2) and three equivalent Sb(1) atoms to form MgSb4 tetrahedra that share corners with three equivalent Mg(2)Sb6 octahedra, corners with three equivalent Sm(1)Sb6 octahedra, corners with six equivalent Mg(3)Sb4 tetrahedra, edges with three equivalent Sm(1)Sb6 octahedra, and edges with three equivalent Mg(1)Sb4 tetrahedra. The corner-sharing octahedral tilt angles range from 15-59°. Sm(1) is bonded to six equivalent Sb(1) atoms to form SmSb6 octahedra that share corners with six equivalent Mg(1)Sb4 tetrahedra, corners with six equivalent Mg(3)Sb4 tetrahedra, edges with six equivalent Sm(1)Sb6 octahedra, and edges with six equivalent Mg(3)Sb4 tetrahedra. There are two inequivalent Sb sites. In the first Sb site, Sb(1) is bonded to one Mg(1), three equivalent Mg(3), and three equivalent Sm(1) atoms to form a mixture of distorted edge and corner-sharing SbSm3Mg4 pentagonal bipyramids. In the second Sb site, Sb(2) is bonded in a 7-coordinate geometry to one Mg(3), three equivalent Mg(1), and three equivalent Mg(2) atoms.
Mg5SmSb4 crystallizes in the trigonal P-3m1 space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Sb(1) and three equivalent Sb(2) atoms to form MgSb4 tetrahedra that share corners with three equivalent Mg(2)Sb6 octahedra, corners with three equivalent Sm(1)Sb6 octahedra, corners with six equivalent Mg(1)Sb4 tetrahedra, edges with three equivalent Mg(2)Sb6 octahedra, and edges with three equivalent Mg(3)Sb4 tetrahedra. The corner-sharing octahedral tilt angles range from 13-56°. The Mg(1)-Sb(1) bond length is 2.96 Å. All Mg(1)-Sb(2) bond lengths are 2.81 Å. In the second Mg site, Mg(2) is bonded to six equivalent Sb(2) atoms to form MgSb6 octahedra that share corners with six equivalent Mg(1)Sb4 tetrahedra, corners with six equivalent Mg(3)Sb4 tetrahedra, edges with six equivalent Mg(2)Sb6 octahedra, and edges with six equivalent Mg(1)Sb4 tetrahedra. All Mg(2)-Sb(2) bond lengths are 3.13 Å. In the third Mg site, Mg(3) is bonded to one Sb(2) and three equivalent Sb(1) atoms to form MgSb4 tetrahedra that share corners with three equivalent Mg(2)Sb6 octahedra, corners with three equivalent Sm(1)Sb6 octahedra, corners with six equivalent Mg(3)Sb4 tetrahedra, edges with three equivalent Sm(1)Sb6 octahedra, and edges with three equivalent Mg(1)Sb4 tetrahedra. The corner-sharing octahedral tilt angles range from 15-59°. The Mg(3)-Sb(2) bond length is 2.90 Å. All Mg(3)-Sb(1) bond lengths are 2.83 Å. Sm(1) is bonded to six equivalent Sb(1) atoms to form SmSb6 octahedra that share corners with six equivalent Mg(1)Sb4 tetrahedra, corners with six equivalent Mg(3)Sb4 tetrahedra, edges with six equivalent Sm(1)Sb6 octahedra, and edges with six equivalent Mg(3)Sb4 tetrahedra. All Sm(1)-Sb(1) bond lengths are 3.24 Å. There are two inequivalent Sb sites. In the first Sb site, Sb(1) is bonded to one Mg(1), three equivalent Mg(3), and three equivalent Sm(1) atoms to form a mixture of distorted edge and corner-sharing SbSm3Mg4 pentagonal bipyramids. In the second Sb site, Sb(2) is bonded in a 7-coordinate geometry to one Mg(3), three equivalent Mg(1), and three equivalent Mg(2) atoms.