MgCe2Se4 is Spinel-like structured and crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded to one Se(2), one Se(3), and two equivalent Se(1) atoms to form MgSe4 tetrahedra that share corners with two equivalent Ce(1)Se6 octahedra, corners with four equivalent Ce(2)Se6 octahedra,  an edgeedge with one Ce(2)Se6 octahedra, and edges with two equivalent Ce(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 59-63°. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form CeSe6 octahedra that share corners with four equivalent Ce(2)Se6 octahedra, corners with two equivalent Mg(1)Se4 tetrahedra, edges with two equivalent Ce(1)Se6 octahedra, edges with two equivalent Ce(2)Se6 octahedra, and edges with two equivalent Mg(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-56°. In the second Ce site, Ce(2) is bonded to one Se(2), one Se(3), and four equivalent Se(1) atoms to form CeSe6 octahedra that share corners with four equivalent Ce(1)Se6 octahedra, corners with four equivalent Ce(2)Se6 octahedra, corners with four equivalent Mg(1)Se4 tetrahedra, edges with two equivalent Ce(1)Se6 octahedra, and  an edgeedge with one Mg(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 47-56°. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Ce(1), and two equivalent Ce(2) atoms. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Ce(2), and two equivalent Ce(1) atoms. In the third Se site, Se(3) is bonded to one Mg(1), one Ce(2), and two equivalent Ce(1) atoms to form distorted corner-sharing SeCe3Mg trigonal pyramids.
MgCe2Se4 is Spinel-like structured and crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded to one Se(2), one Se(3), and two equivalent Se(1) atoms to form MgSe4 tetrahedra that share corners with two equivalent Ce(1)Se6 octahedra, corners with four equivalent Ce(2)Se6 octahedra,  an edgeedge with one Ce(2)Se6 octahedra, and edges with two equivalent Ce(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 59-63°. The Mg(1)-Se(2) bond length is 2.62 Å. The Mg(1)-Se(3) bond length is 2.56 Å. Both Mg(1)-Se(1) bond lengths are 2.61 Å. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form CeSe6 octahedra that share corners with four equivalent Ce(2)Se6 octahedra, corners with two equivalent Mg(1)Se4 tetrahedra, edges with two equivalent Ce(1)Se6 octahedra, edges with two equivalent Ce(2)Se6 octahedra, and edges with two equivalent Mg(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-56°. Both Ce(1)-Se(1) bond lengths are 3.01 Å. Both Ce(1)-Se(2) bond lengths are 2.97 Å. Both Ce(1)-Se(3) bond lengths are 2.97 Å. In the second Ce site, Ce(2) is bonded to one Se(2), one Se(3), and four equivalent Se(1) atoms to form CeSe6 octahedra that share corners with four equivalent Ce(1)Se6 octahedra, corners with four equivalent Ce(2)Se6 octahedra, corners with four equivalent Mg(1)Se4 tetrahedra, edges with two equivalent Ce(1)Se6 octahedra, and  an edgeedge with one Mg(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 47-56°. The Ce(2)-Se(2) bond length is 2.97 Å. The Ce(2)-Se(3) bond length is 2.99 Å. All Ce(2)-Se(1) bond lengths are 3.04 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Ce(1), and two equivalent Ce(2) atoms. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Ce(2), and two equivalent Ce(1) atoms. In the third Se site, Se(3) is bonded to one Mg(1), one Ce(2), and two equivalent Ce(1) atoms to form distorted corner-sharing SeCe3Mg trigonal pyramids.