MgCeSe3 is Ilmenite structured and crystallizes in the trigonal R-3 space group. Mg(1) is bonded to six equivalent Se(1) atoms to form MgSe6 octahedra that share corners with nine equivalent Ce(1)Se6 octahedra, edges with three equivalent Mg(1)Se6 octahedra, and  a faceface with one Ce(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. Ce(1) is bonded to six equivalent Se(1) atoms to form CeSe6 octahedra that share corners with nine equivalent Mg(1)Se6 octahedra, edges with three equivalent Ce(1)Se6 octahedra, and  a faceface with one Mg(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. Se(1) is bonded to two equivalent Mg(1) and two equivalent Ce(1) atoms to form a mixture of distorted corner and edge-sharing SeCe2Mg2 trigonal pyramids.
MgCeSe3 is Ilmenite structured and crystallizes in the trigonal R-3 space group. Mg(1) is bonded to six equivalent Se(1) atoms to form MgSe6 octahedra that share corners with nine equivalent Ce(1)Se6 octahedra, edges with three equivalent Mg(1)Se6 octahedra, and  a faceface with one Ce(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. There are three shorter (2.75 Å) and three longer (2.83 Å) Mg(1)-Se(1) bond lengths. Ce(1) is bonded to six equivalent Se(1) atoms to form CeSe6 octahedra that share corners with nine equivalent Mg(1)Se6 octahedra, edges with three equivalent Ce(1)Se6 octahedra, and  a faceface with one Mg(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. There are three shorter (2.87 Å) and three longer (2.88 Å) Ce(1)-Se(1) bond lengths. Se(1) is bonded to two equivalent Mg(1) and two equivalent Ce(1) atoms to form a mixture of distorted corner and edge-sharing SeCe2Mg2 trigonal pyramids.