Mg2SnSe4 is Spinel-like structured and crystallizes in the orthorhombic Pnma space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form MgSe6 octahedra that share corners with four equivalent Mg(2)Se6 octahedra, corners with two equivalent Sn(1)Se4 tetrahedra, edges with two equivalent Mg(1)Se6 octahedra, edges with two equivalent Mg(2)Se6 octahedra, and edges with two equivalent Sn(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-54°. In the second Mg site, Mg(2) is bonded to one Se(1), one Se(2), and four equivalent Se(3) atoms to form MgSe6 octahedra that share corners with four equivalent Mg(1)Se6 octahedra, corners with four equivalent Mg(2)Se6 octahedra, corners with four equivalent Sn(1)Se4 tetrahedra, edges with two equivalent Mg(1)Se6 octahedra, and  an edgeedge with one Sn(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 46-54°. Sn(1) is bonded to one Se(1), one Se(2), and two equivalent Se(3) atoms to form SnSe4 tetrahedra that share corners with two equivalent Mg(1)Se6 octahedra, corners with four equivalent Mg(2)Se6 octahedra,  an edgeedge with one Mg(2)Se6 octahedra, and edges with two equivalent Mg(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 61-66°. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Mg(2), two equivalent Mg(1), and one Sn(1) atom to form corner-sharing SeMg3Sn tetrahedra. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Mg(2), two equivalent Mg(1), and one Sn(1) atom. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), two equivalent Mg(2), and one Sn(1) atom.
Mg2SnSe4 is Spinel-like structured and crystallizes in the orthorhombic Pnma space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form MgSe6 octahedra that share corners with four equivalent Mg(2)Se6 octahedra, corners with two equivalent Sn(1)Se4 tetrahedra, edges with two equivalent Mg(1)Se6 octahedra, edges with two equivalent Mg(2)Se6 octahedra, and edges with two equivalent Sn(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-54°. Both Mg(1)-Se(1) bond lengths are 2.69 Å. Both Mg(1)-Se(2) bond lengths are 2.76 Å. Both Mg(1)-Se(3) bond lengths are 2.79 Å. In the second Mg site, Mg(2) is bonded to one Se(1), one Se(2), and four equivalent Se(3) atoms to form MgSe6 octahedra that share corners with four equivalent Mg(1)Se6 octahedra, corners with four equivalent Mg(2)Se6 octahedra, corners with four equivalent Sn(1)Se4 tetrahedra, edges with two equivalent Mg(1)Se6 octahedra, and  an edgeedge with one Sn(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 46-54°. The Mg(2)-Se(1) bond length is 2.74 Å. The Mg(2)-Se(2) bond length is 2.68 Å. There are two shorter (2.76 Å) and two longer (2.86 Å) Mg(2)-Se(3) bond lengths. Sn(1) is bonded to one Se(1), one Se(2), and two equivalent Se(3) atoms to form SnSe4 tetrahedra that share corners with two equivalent Mg(1)Se6 octahedra, corners with four equivalent Mg(2)Se6 octahedra,  an edgeedge with one Mg(2)Se6 octahedra, and edges with two equivalent Mg(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 61-66°. The Sn(1)-Se(1) bond length is 2.50 Å. The Sn(1)-Se(2) bond length is 2.55 Å. Both Sn(1)-Se(3) bond lengths are 2.54 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Mg(2), two equivalent Mg(1), and one Sn(1) atom to form corner-sharing SeMg3Sn tetrahedra. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Mg(2), two equivalent Mg(1), and one Sn(1) atom. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), two equivalent Mg(2), and one Sn(1) atom.