MgSm2Se4 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 Sm sites. In the first Sm site, Sm(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 Sm site, Sm(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 to one Mg(1), two equivalent Sm(1), and two equivalent Sm(2) atoms to form a mixture of distorted face, corner, and edge-sharing SeSm4Mg square pyramids. In the second Se site, Se(2) is bonded in a T-shaped geometry to one Mg(1), one Sm(1), and one Sm(2) atom. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Sm(2), and two equivalent Sm(1) atoms.
MgSm2Se4 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 2.62 Å. Both Mg(1)-Se(1) bond lengths are 2.60 Å. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 7-coordinate geometry to one Se(2), two equivalent Se(3), and four equivalent Se(1) atoms. The Sm(1)-Se(2) bond length is 2.90 Å. There is one shorter (2.85 Å) and one longer (2.88 Å) Sm(1)-Se(3) bond length. There are two shorter (3.16 Å) and two longer (3.25 Å) Sm(1)-Se(1) bond lengths. In the second Sm site, Sm(2) is bonded in a 6-coordinate geometry to one Se(2), one Se(3), and four equivalent Se(1) atoms. The Sm(2)-Se(2) bond length is 2.75 Å. The Sm(2)-Se(3) bond length is 2.93 Å. There are two shorter (2.99 Å) and two longer (3.04 Å) Sm(2)-Se(1) bond lengths. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Mg(1), two equivalent Sm(1), and two equivalent Sm(2) atoms to form a mixture of distorted face, corner, and edge-sharing SeSm4Mg square pyramids. In the second Se site, Se(2) is bonded in a T-shaped geometry to one Mg(1), one Sm(1), and one Sm(2) atom. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Sm(2), and two equivalent Sm(1) atoms.