MgYbSe3 is Ilmenite-like structured and crystallizes in the trigonal R-3 space group. Mg(1) is bonded to six equivalent Se(1) atoms to form distorted MgSe6 octahedra that share corners with nine equivalent Yb(1)Se6 pentagonal pyramids, edges with three equivalent Mg(1)Se6 octahedra, and  a faceface with one Yb(1)Se6 pentagonal pyramid. Yb(1) is bonded to six equivalent Se(1) atoms to form distorted YbSe6 pentagonal pyramids that share corners with nine equivalent Mg(1)Se6 octahedra, edges with three equivalent Yb(1)Se6 pentagonal pyramids, and  a faceface with one Mg(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 39-67°. Se(1) is bonded to two equivalent Mg(1) and two equivalent Yb(1) atoms to form a mixture of distorted corner and edge-sharing SeYb2Mg2 tetrahedra.
MgYbSe3 is Ilmenite-like structured and crystallizes in the trigonal R-3 space group. Mg(1) is bonded to six equivalent Se(1) atoms to form distorted MgSe6 octahedra that share corners with nine equivalent Yb(1)Se6 pentagonal pyramids, edges with three equivalent Mg(1)Se6 octahedra, and  a faceface with one Yb(1)Se6 pentagonal pyramid. There are three shorter (2.60 Å) and three longer (2.79 Å) Mg(1)-Se(1) bond lengths. Yb(1) is bonded to six equivalent Se(1) atoms to form distorted YbSe6 pentagonal pyramids that share corners with nine equivalent Mg(1)Se6 octahedra, edges with three equivalent Yb(1)Se6 pentagonal pyramids, and  a faceface with one Mg(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 39-67°. There are three shorter (2.94 Å) and three longer (2.98 Å) Yb(1)-Se(1) bond lengths. Se(1) is bonded to two equivalent Mg(1) and two equivalent Yb(1) atoms to form a mixture of distorted corner and edge-sharing SeYb2Mg2 tetrahedra.