MgYb2Se4 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded in a rectangular see-saw-like geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. There are two inequivalent Yb sites. In the first Yb site, Yb(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form YbSe6 octahedra that share corners with two equivalent Yb(2)Se7 pentagonal bipyramids, edges with two equivalent Yb(1)Se6 octahedra, and edges with four equivalent Yb(2)Se7 pentagonal bipyramids. In the second Yb site, Yb(2) is bonded to one Se(2), two equivalent Se(3), and four equivalent Se(1) atoms to form distorted YbSe7 pentagonal bipyramids that share corners with two equivalent Yb(1)Se6 octahedra, corners with six equivalent Yb(2)Se7 pentagonal bipyramids, and edges with four equivalent Yb(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 48°. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to one Mg(1), one Yb(1), and two equivalent Yb(2) atoms. In the second Se site, Se(2) is bonded to one Mg(1), one Yb(2), and two equivalent Yb(1) atoms to form distorted SeYb3Mg trigonal pyramids that share corners with three equivalent Se(3)Yb4Mg trigonal bipyramids, corners with two equivalent Se(2)Yb3Mg trigonal pyramids, and edges with two equivalent Se(3)Yb4Mg trigonal bipyramids. In the third Se site, Se(3) is bonded to one Mg(1), two equivalent Yb(1), and two equivalent Yb(2) atoms to form SeYb4Mg trigonal bipyramids that share corners with four equivalent Se(3)Yb4Mg trigonal bipyramids, corners with three equivalent Se(2)Yb3Mg trigonal pyramids, and edges with two equivalent Se(2)Yb3Mg trigonal pyramids.
MgYb2Se4 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded in a rectangular see-saw-like geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. The Mg(1)-Se(2) bond length is 2.63 Å. The Mg(1)-Se(3) bond length is 2.52 Å. Both Mg(1)-Se(1) bond lengths are 2.53 Å. There are two inequivalent Yb sites. In the first Yb site, Yb(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form YbSe6 octahedra that share corners with two equivalent Yb(2)Se7 pentagonal bipyramids, edges with two equivalent Yb(1)Se6 octahedra, and edges with four equivalent Yb(2)Se7 pentagonal bipyramids. Both Yb(1)-Se(1) bond lengths are 2.96 Å. Both Yb(1)-Se(2) bond lengths are 3.06 Å. Both Yb(1)-Se(3) bond lengths are 2.91 Å. In the second Yb site, Yb(2) is bonded to one Se(2), two equivalent Se(3), and four equivalent Se(1) atoms to form distorted YbSe7 pentagonal bipyramids that share corners with two equivalent Yb(1)Se6 octahedra, corners with six equivalent Yb(2)Se7 pentagonal bipyramids, and edges with four equivalent Yb(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 48°. The Yb(2)-Se(2) bond length is 2.91 Å. There is one shorter (2.99 Å) and one longer (3.21 Å) Yb(2)-Se(3) bond length. There are two shorter (3.00 Å) and two longer (3.20 Å) Yb(2)-Se(1) bond lengths. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to one Mg(1), one Yb(1), and two equivalent Yb(2) atoms. In the second Se site, Se(2) is bonded to one Mg(1), one Yb(2), and two equivalent Yb(1) atoms to form distorted SeYb3Mg trigonal pyramids that share corners with three equivalent Se(3)Yb4Mg trigonal bipyramids, corners with two equivalent Se(2)Yb3Mg trigonal pyramids, and edges with two equivalent Se(3)Yb4Mg trigonal bipyramids. In the third Se site, Se(3) is bonded to one Mg(1), two equivalent Yb(1), and two equivalent Yb(2) atoms to form SeYb4Mg trigonal bipyramids that share corners with four equivalent Se(3)Yb4Mg trigonal bipyramids, corners with three equivalent Se(2)Yb3Mg trigonal pyramids, and edges with two equivalent Se(2)Yb3Mg trigonal pyramids.