MgLuSe3 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded in a 4-coordinate geometry to two equivalent Se(2) and four equivalent Se(1) atoms. Lu(1) is bonded in a 6-coordinate geometry to two equivalent Se(2) and four equivalent Se(1) atoms. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to two equivalent Mg(1) and two equivalent Lu(1) atoms. In the second Se site, Se(2) is bonded to two equivalent Mg(1) and two equivalent Lu(1) atoms to form edge-sharing SeLu2Mg2 trigonal pyramids.
MgLuSe3 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded in a 4-coordinate geometry to two equivalent Se(2) and four equivalent Se(1) atoms. Both Mg(1)-Se(2) bond lengths are 2.60 Å. There are two shorter (2.63 Å) and two longer (3.28 Å) Mg(1)-Se(1) bond lengths. Lu(1) is bonded in a 6-coordinate geometry to two equivalent Se(2) and four equivalent Se(1) atoms. There is one shorter (2.68 Å) and one longer (2.70 Å) Lu(1)-Se(2) bond length. There are two shorter (2.76 Å) and two longer (3.02 Å) Lu(1)-Se(1) bond lengths. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to two equivalent Mg(1) and two equivalent Lu(1) atoms. In the second Se site, Se(2) is bonded to two equivalent Mg(1) and two equivalent Lu(1) atoms to form edge-sharing SeLu2Mg2 trigonal pyramids.