MgPm2Se4 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded in a distorted trigonal pyramidal geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. There are two inequivalent Pm sites. In the first Pm site, Pm(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 Pm site, Pm(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 Pm(1), and two equivalent Pm(2) atoms to form a mixture of distorted corner, edge, and face-sharing SePm4Mg square pyramids. In the second Se site, Se(2) is bonded in a T-shaped geometry to one Mg(1), one Pm(1), and one Pm(2) atom. In the third Se site, Se(3) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Pm(2), and two equivalent Pm(1) atoms.
MgPm2Se4 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded in a distorted trigonal pyramidal geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. The Mg(1)-Se(2) bond length is 2.44 Å. The Mg(1)-Se(3) bond length is 2.55 Å. Both Mg(1)-Se(1) bond lengths are 2.57 Å. There are two inequivalent Pm sites. In the first Pm site, Pm(1) is bonded in a 7-coordinate geometry to one Se(2), two equivalent Se(3), and four equivalent Se(1) atoms. The Pm(1)-Se(2) bond length is 2.97 Å. Both Pm(1)-Se(3) bond lengths are 2.92 Å. There are two shorter (3.12 Å) and two longer (3.30 Å) Pm(1)-Se(1) bond lengths. In the second Pm site, Pm(2) is bonded in a 6-coordinate geometry to one Se(2), one Se(3), and four equivalent Se(1) atoms. The Pm(2)-Se(2) bond length is 2.79 Å. The Pm(2)-Se(3) bond length is 3.05 Å. There are two shorter (2.97 Å) and two longer (3.07 Å) Pm(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 Pm(1), and two equivalent Pm(2) atoms to form a mixture of distorted corner, edge, and face-sharing SePm4Mg square pyramids. In the second Se site, Se(2) is bonded in a T-shaped geometry to one Mg(1), one Pm(1), and one Pm(2) atom. In the third Se site, Se(3) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Pm(2), and two equivalent Pm(1) atoms.