LuSmSe3 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Lu sites. In the first Lu site, Lu(1) is bonded to one Se(1), two equivalent Se(3), and three equivalent Se(4) atoms to form LuSe6 octahedra that share corners with three equivalent Lu(2)Se6 octahedra, corners with two equivalent Sm(1)Se7 pentagonal bipyramids, and edges with four equivalent Lu(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 56-59°. In the second Lu site, Lu(2) is bonded to one Se(6), two equivalent Se(2), and three equivalent Se(1) atoms to form LuSe6 octahedra that share corners with three equivalent Lu(1)Se6 octahedra,  a cornercorner with one Sm(1)Se7 pentagonal bipyramid, edges with four equivalent Lu(2)Se6 octahedra, and edges with two equivalent Sm(1)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 56-59°. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded to one Se(2), one Se(3), two equivalent Se(5), and three equivalent Se(6) atoms to form distorted SmSe7 pentagonal bipyramids that share  a cornercorner with one Lu(2)Se6 octahedra, corners with two equivalent Lu(1)Se6 octahedra, edges with two equivalent Lu(2)Se6 octahedra, and edges with four equivalent Sm(1)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 34-51°. In the second Sm site, Sm(2) is bonded in a 8-coordinate geometry to one Se(3), two equivalent Se(2), two equivalent Se(4), and three equivalent Se(5) atoms. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded to one Lu(1) and three equivalent Lu(2) atoms to form distorted SeLu4 trigonal pyramids that share corners with three equivalent Se(4)Sm2Lu3 square pyramids, corners with four equivalent Se(2)Sm3Lu2 trigonal bipyramids, corners with two equivalent Se(1)Lu4 trigonal pyramids, corners with two equivalent Se(3)Sm2Lu2 trigonal pyramids, corners with three equivalent Se(6)Sm3Lu trigonal pyramids,  an edgeedge with one Se(2)Sm3Lu2 trigonal bipyramid, and edges with two equivalent Se(1)Lu4 trigonal pyramids. In the second Se site, Se(2) is bonded to two equivalent Lu(2), one Sm(1), and two equivalent Sm(2) atoms to form SeSm3Lu2 trigonal bipyramids that share corners with two equivalent Se(4)Sm2Lu3 square pyramids, corners with two equivalent Se(5)Sm5 trigonal bipyramids,  a cornercorner with one Se(6)Sm3Lu trigonal pyramid, corners with three equivalent Se(3)Sm2Lu2 trigonal pyramids, corners with four equivalent Se(1)Lu4 trigonal pyramids,  an edgeedge with one Se(4)Sm2Lu3 square pyramid, edges with two equivalent Se(2)Sm3Lu2 trigonal bipyramids, edges with three equivalent Se(5)Sm5 trigonal bipyramids,  an edgeedge with one Se(1)Lu4 trigonal pyramid, and edges with two equivalent Se(6)Sm3Lu trigonal pyramids. In the third Se site, Se(3) is bonded to two equivalent Lu(1), one Sm(1), and one Sm(2) atom to form distorted SeSm2Lu2 trigonal pyramids that share corners with two equivalent Se(4)Sm2Lu3 square pyramids,  a cornercorner with one Se(5)Sm5 trigonal bipyramid, corners with three equivalent Se(2)Sm3Lu2 trigonal bipyramids, corners with two equivalent Se(1)Lu4 trigonal pyramids, corners with two equivalent Se(3)Sm2Lu2 trigonal pyramids, corners with three equivalent Se(6)Sm3Lu trigonal pyramids, edges with three equivalent Se(4)Sm2Lu3 square pyramids, and edges with two equivalent Se(5)Sm5 trigonal bipyramids. In the fourth Se site, Se(4) is bonded to three equivalent Lu(1) and two equivalent Sm(2) atoms to form SeSm2Lu3 square pyramids that share corners with two equivalent Se(2)Sm3Lu2 trigonal bipyramids, corners with four equivalent Se(5)Sm5 trigonal bipyramids, corners with two equivalent Se(3)Sm2Lu2 trigonal pyramids, corners with three equivalent Se(1)Lu4 trigonal pyramids, edges with four equivalent Se(4)Sm2Lu3 square pyramids,  an edgeedge with one Se(2)Sm3Lu2 trigonal bipyramid,  an edgeedge with one Se(5)Sm5 trigonal bipyramid, and edges with three equivalent Se(3)Sm2Lu2 trigonal pyramids. In the fifth Se site, Se(5) is bonded to two equivalent Sm(1) and three equivalent Sm(2) atoms to form distorted SeSm5 trigonal bipyramids that share corners with four equivalent Se(4)Sm2Lu3 square pyramids, corners with two equivalent Se(2)Sm3Lu2 trigonal bipyramids,  a cornercorner with one Se(3)Sm2Lu2 trigonal pyramid, corners with four equivalent Se(6)Sm3Lu trigonal pyramids,  an edgeedge with one Se(4)Sm2Lu3 square pyramid, edges with three equivalent Se(2)Sm3Lu2 trigonal bipyramids, edges with four equivalent Se(5)Sm5 trigonal bipyramids,  an edgeedge with one Se(6)Sm3Lu trigonal pyramid, and edges with two equivalent Se(3)Sm2Lu2 trigonal pyramids. In the sixth Se site, Se(6) is bonded to one Lu(2) and three equivalent Sm(1) atoms to form distorted SeSm3Lu trigonal pyramids that share  a cornercorner with one Se(2)Sm3Lu2 trigonal bipyramid, corners with four equivalent Se(5)Sm5 trigonal bipyramids, corners with two equivalent Se(6)Sm3Lu trigonal pyramids, corners with three equivalent Se(1)Lu4 trigonal pyramids, corners with three equivalent Se(3)Sm2Lu2 trigonal pyramids,  an edgeedge with one Se(5)Sm5 trigonal bipyramid, edges with two equivalent Se(2)Sm3Lu2 trigonal bipyramids, and edges with two equivalent Se(6)Sm3Lu trigonal pyramids.
LuSmSe3 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Lu sites. In the first Lu site, Lu(1) is bonded to one Se(1), two equivalent Se(3), and three equivalent Se(4) atoms to form LuSe6 octahedra that share corners with three equivalent Lu(2)Se6 octahedra, corners with two equivalent Sm(1)Se7 pentagonal bipyramids, and edges with four equivalent Lu(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 56-59°. The Lu(1)-Se(1) bond length is 2.80 Å. Both Lu(1)-Se(3) bond lengths are 2.72 Å. There is one shorter (2.80 Å) and two longer (2.83 Å) Lu(1)-Se(4) bond lengths. In the second Lu site, Lu(2) is bonded to one Se(6), two equivalent Se(2), and three equivalent Se(1) atoms to form LuSe6 octahedra that share corners with three equivalent Lu(1)Se6 octahedra,  a cornercorner with one Sm(1)Se7 pentagonal bipyramid, edges with four equivalent Lu(2)Se6 octahedra, and edges with two equivalent Sm(1)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 56-59°. The Lu(2)-Se(6) bond length is 2.74 Å. Both Lu(2)-Se(2) bond lengths are 2.84 Å. There are two shorter (2.80 Å) and one longer (2.83 Å) Lu(2)-Se(1) bond length. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded to one Se(2), one Se(3), two equivalent Se(5), and three equivalent Se(6) atoms to form distorted SmSe7 pentagonal bipyramids that share  a cornercorner with one Lu(2)Se6 octahedra, corners with two equivalent Lu(1)Se6 octahedra, edges with two equivalent Lu(2)Se6 octahedra, and edges with four equivalent Sm(1)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 34-51°. The Sm(1)-Se(2) bond length is 3.04 Å. The Sm(1)-Se(3) bond length is 2.88 Å. Both Sm(1)-Se(5) bond lengths are 3.06 Å. There are two shorter (2.86 Å) and one longer (3.01 Å) Sm(1)-Se(6) bond length. In the second Sm site, Sm(2) is bonded in a 8-coordinate geometry to one Se(3), two equivalent Se(2), two equivalent Se(4), and three equivalent Se(5) atoms. The Sm(2)-Se(3) bond length is 3.06 Å. Both Sm(2)-Se(2) bond lengths are 3.12 Å. Both Sm(2)-Se(4) bond lengths are 3.13 Å. There are two shorter (2.98 Å) and one longer (3.07 Å) Sm(2)-Se(5) bond length. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded to one Lu(1) and three equivalent Lu(2) atoms to form distorted SeLu4 trigonal pyramids that share corners with three equivalent Se(4)Sm2Lu3 square pyramids, corners with four equivalent Se(2)Sm3Lu2 trigonal bipyramids, corners with two equivalent Se(1)Lu4 trigonal pyramids, corners with two equivalent Se(3)Sm2Lu2 trigonal pyramids, corners with three equivalent Se(6)Sm3Lu trigonal pyramids,  an edgeedge with one Se(2)Sm3Lu2 trigonal bipyramid, and edges with two equivalent Se(1)Lu4 trigonal pyramids. In the second Se site, Se(2) is bonded to two equivalent Lu(2), one Sm(1), and two equivalent Sm(2) atoms to form SeSm3Lu2 trigonal bipyramids that share corners with two equivalent Se(4)Sm2Lu3 square pyramids, corners with two equivalent Se(5)Sm5 trigonal bipyramids,  a cornercorner with one Se(6)Sm3Lu trigonal pyramid, corners with three equivalent Se(3)Sm2Lu2 trigonal pyramids, corners with four equivalent Se(1)Lu4 trigonal pyramids,  an edgeedge with one Se(4)Sm2Lu3 square pyramid, edges with two equivalent Se(2)Sm3Lu2 trigonal bipyramids, edges with three equivalent Se(5)Sm5 trigonal bipyramids,  an edgeedge with one Se(1)Lu4 trigonal pyramid, and edges with two equivalent Se(6)Sm3Lu trigonal pyramids. In the third Se site, Se(3) is bonded to two equivalent Lu(1), one Sm(1), and one Sm(2) atom to form distorted SeSm2Lu2 trigonal pyramids that share corners with two equivalent Se(4)Sm2Lu3 square pyramids,  a cornercorner with one Se(5)Sm5 trigonal bipyramid, corners with three equivalent Se(2)Sm3Lu2 trigonal bipyramids, corners with two equivalent Se(1)Lu4 trigonal pyramids, corners with two equivalent Se(3)Sm2Lu2 trigonal pyramids, corners with three equivalent Se(6)Sm3Lu trigonal pyramids, edges with three equivalent Se(4)Sm2Lu3 square pyramids, and edges with two equivalent Se(5)Sm5 trigonal bipyramids. In the fourth Se site, Se(4) is bonded to three equivalent Lu(1) and two equivalent Sm(2) atoms to form SeSm2Lu3 square pyramids that share corners with two equivalent Se(2)Sm3Lu2 trigonal bipyramids, corners with four equivalent Se(5)Sm5 trigonal bipyramids, corners with two equivalent Se(3)Sm2Lu2 trigonal pyramids, corners with three equivalent Se(1)Lu4 trigonal pyramids, edges with four equivalent Se(4)Sm2Lu3 square pyramids,  an edgeedge with one Se(2)Sm3Lu2 trigonal bipyramid,  an edgeedge with one Se(5)Sm5 trigonal bipyramid, and edges with three equivalent Se(3)Sm2Lu2 trigonal pyramids. In the fifth Se site, Se(5) is bonded to two equivalent Sm(1) and three equivalent Sm(2) atoms to form distorted SeSm5 trigonal bipyramids that share corners with four equivalent Se(4)Sm2Lu3 square pyramids, corners with two equivalent Se(2)Sm3Lu2 trigonal bipyramids,  a cornercorner with one Se(3)Sm2Lu2 trigonal pyramid, corners with four equivalent Se(6)Sm3Lu trigonal pyramids,  an edgeedge with one Se(4)Sm2Lu3 square pyramid, edges with three equivalent Se(2)Sm3Lu2 trigonal bipyramids, edges with four equivalent Se(5)Sm5 trigonal bipyramids,  an edgeedge with one Se(6)Sm3Lu trigonal pyramid, and edges with two equivalent Se(3)Sm2Lu2 trigonal pyramids. In the sixth Se site, Se(6) is bonded to one Lu(2) and three equivalent Sm(1) atoms to form distorted SeSm3Lu trigonal pyramids that share  a cornercorner with one Se(2)Sm3Lu2 trigonal bipyramid, corners with four equivalent Se(5)Sm5 trigonal bipyramids, corners with two equivalent Se(6)Sm3Lu trigonal pyramids, corners with three equivalent Se(1)Lu4 trigonal pyramids, corners with three equivalent Se(3)Sm2Lu2 trigonal pyramids,  an edgeedge with one Se(5)Sm5 trigonal bipyramid, edges with two equivalent Se(2)Sm3Lu2 trigonal bipyramids, and edges with two equivalent Se(6)Sm3Lu trigonal pyramids.