MgY2Se4 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded in a trigonal pyramidal geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 7-coordinate geometry to one Se(2), two equivalent Se(3), and four equivalent Se(1) atoms. In the second Y site, Y(2) is bonded in a 6-coordinate geometry to one Se(2), one Se(3), and four equivalent Se(1) atoms. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Y(1), and two equivalent Y(2) atoms. In the second Se site, Se(2) is bonded in a T-shaped geometry to one Mg(1), one Y(1), and one Y(2) atom. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Y(2), and two equivalent Y(1) atoms.
MgY2Se4 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded in a trigonal pyramidal geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. The Mg(1)-Se(2) bond length is 2.45 Å. The Mg(1)-Se(3) bond length is 2.58 Å. Both Mg(1)-Se(1) bond lengths are 2.60 Å. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 7-coordinate geometry to one Se(2), two equivalent Se(3), and four equivalent Se(1) atoms. The Y(1)-Se(2) bond length is 2.87 Å. There is one shorter (2.82 Å) and one longer (2.83 Å) Y(1)-Se(3) bond length. There are two shorter (3.06 Å) and two longer (3.28 Å) Y(1)-Se(1) bond lengths. In the second Y site, Y(2) is bonded in a 6-coordinate geometry to one Se(2), one Se(3), and four equivalent Se(1) atoms. The Y(2)-Se(2) bond length is 2.71 Å. The Y(2)-Se(3) bond length is 2.90 Å. There are two shorter (2.90 Å) and two longer (3.00 Å) Y(2)-Se(1) bond lengths. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Y(1), and two equivalent Y(2) atoms. In the second Se site, Se(2) is bonded in a T-shaped geometry to one Mg(1), one Y(1), and one Y(2) atom. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Y(2), and two equivalent Y(1) atoms.