Yb11(Sm2Se11)2 crystallizes in the monoclinic C2/m space group. There are six inequivalent Yb sites. In the first Yb site, Yb(1) is bonded in a 6-coordinate geometry to one Se(1), one Se(4), two equivalent Se(8), and two equivalent Se(9) atoms. In the second Yb site, Yb(2) is bonded in a 6-coordinate geometry to one Se(10), one Se(7), two equivalent Se(11), and three equivalent Se(2) atoms. In the third Yb site, Yb(3) is bonded in a 6-coordinate geometry to one Se(5), one Se(8), two equivalent Se(4), and two equivalent Se(6) atoms. In the fourth Yb site, Yb(4) is bonded to one Se(2), two equivalent Se(10), and three equivalent Se(3) atoms to form YbSe6 octahedra that share corners with two equivalent Se(1)Yb3Sm2Se octahedra, corners with three equivalent Yb(5)Se6 octahedra, and edges with four equivalent Yb(4)Se6 octahedra. The corner-sharing octahedral tilt angles range from 56-71°. In the fifth Yb site, Yb(5) is bonded to one Se(3), one Se(9), two equivalent Se(1), and two equivalent Se(7) atoms to form distorted YbSe6 octahedra that share  a cornercorner with one Se(5)Yb3Sm2Se octahedra, corners with three equivalent Yb(4)Se6 octahedra, and edges with two equivalent Yb(5)Se6 octahedra. The corner-sharing octahedral tilt angles range from 28-71°. In the sixth Yb site, Yb(6) is bonded to two equivalent Se(4) and four equivalent Se(5) atoms to form YbSe6 octahedra that share corners with four equivalent Se(9)Yb3Sm2Se octahedra and edges with two equivalent Yb(6)Se6 octahedra. The corner-sharing octahedral tilt angles are 69°. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 8-coordinate geometry to one Se(11), one Se(8), two equivalent Se(1), two equivalent Se(10), and two equivalent Se(6) atoms. In the second Sm site, Sm(2) is bonded in a 8-coordinate geometry to one Se(6), one Se(7), two equivalent Se(11), two equivalent Se(5), and two equivalent Se(9) atoms. There are eleven inequivalent Se sites. In the first Se site, Se(1) is bonded to one Yb(1), two equivalent Yb(5), two equivalent Sm(1), and one Se(10) atom to form distorted SeYb3Sm2Se octahedra that share corners with two equivalent Yb(4)Se6 octahedra,  a cornercorner with one Se(4)Yb4 tetrahedra, corners with two equivalent Se(7)Yb3Sm tetrahedra, corners with two equivalent Se(3)Yb4 tetrahedra, corners with two equivalent Se(11)Yb2Sm3 trigonal bipyramids, corners with two equivalent Se(6)Yb2Sm3 trigonal bipyramids, edges with two equivalent Se(1)Yb3Sm2Se octahedra, edges with two equivalent Se(9)Yb3Sm2Se octahedra,  an edgeedge with one Se(7)Yb3Sm tetrahedra, edges with two equivalent Se(8)Yb3Sm tetrahedra, and  an edgeedge with one Se(6)Yb2Sm3 trigonal bipyramid. The corner-sharing octahedral tilt angles are 70°. In the second Se site, Se(2) is bonded to one Yb(4) and three equivalent Yb(2) atoms to form SeYb4 tetrahedra that share corners with two equivalent Se(2)Yb4 tetrahedra, corners with three equivalent Se(7)Yb3Sm tetrahedra, corners with three equivalent Se(3)Yb4 tetrahedra, corners with four equivalent Se(11)Yb2Sm3 trigonal bipyramids, edges with two equivalent Se(2)Yb4 tetrahedra, and  an edgeedge with one Se(11)Yb2Sm3 trigonal bipyramid. In the third Se site, Se(3) is bonded to one Yb(5) and three equivalent Yb(4) atoms to form SeYb4 tetrahedra that share  a cornercorner with one Se(9)Yb3Sm2Se octahedra, corners with two equivalent Se(1)Yb3Sm2Se octahedra, corners with two equivalent Se(7)Yb3Sm tetrahedra, corners with two equivalent Se(3)Yb4 tetrahedra, corners with three equivalent Se(2)Yb4 tetrahedra, and edges with two equivalent Se(3)Yb4 tetrahedra. The corner-sharing octahedral tilt angles range from 11-83°. In the fourth Se site, Se(4) is bonded to one Yb(1), one Yb(6), and two equivalent Yb(3) atoms to form SeYb4 tetrahedra that share  a cornercorner with one Se(1)Yb3Sm2Se octahedra, corners with two equivalent Se(5)Yb3Sm2Se octahedra, corners with two equivalent Se(9)Yb3Sm2Se octahedra, corners with three equivalent Se(4)Yb4 tetrahedra, corners with four equivalent Se(8)Yb3Sm tetrahedra, corners with two equivalent Se(6)Yb2Sm3 trigonal bipyramids, edges with two equivalent Se(5)Yb3Sm2Se octahedra, and  an edgeedge with one Se(6)Yb2Sm3 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 4-84°. In the fifth Se site, Se(5) is bonded to one Yb(3), two equivalent Yb(6), two equivalent Sm(2), and one Se(9) atom to form distorted SeYb3Sm2Se octahedra that share  a cornercorner with one Yb(5)Se6 octahedra, corners with two equivalent Se(5)Yb3Sm2Se octahedra, corners with two equivalent Se(9)Yb3Sm2Se octahedra,  a cornercorner with one Se(8)Yb3Sm tetrahedra, corners with two equivalent Se(7)Yb3Sm tetrahedra, corners with two equivalent Se(4)Yb4 tetrahedra, corners with two equivalent Se(11)Yb2Sm3 trigonal bipyramids,  an edgeedge with one Se(9)Yb3Sm2Se octahedra, edges with three equivalent Se(5)Yb3Sm2Se octahedra, edges with two equivalent Se(4)Yb4 tetrahedra,  an edgeedge with one Se(11)Yb2Sm3 trigonal bipyramid, and edges with two equivalent Se(6)Yb2Sm3 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 0-80°. In the sixth Se site, Se(6) is bonded to two equivalent Yb(3), one Sm(2), and two equivalent Sm(1) atoms to form distorted SeYb2Sm3 trigonal bipyramids that share corners with two equivalent Se(1)Yb3Sm2Se octahedra, corners with two equivalent Se(9)Yb3Sm2Se octahedra,  a cornercorner with one Se(7)Yb3Sm tetrahedra, corners with two equivalent Se(4)Yb4 tetrahedra,  an edgeedge with one Se(1)Yb3Sm2Se octahedra, edges with two equivalent Se(5)Yb3Sm2Se octahedra,  an edgeedge with one Se(4)Yb4 tetrahedra, edges with two equivalent Se(8)Yb3Sm tetrahedra, edges with two equivalent Se(11)Yb2Sm3 trigonal bipyramids, and edges with two equivalent Se(6)Yb2Sm3 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 23-55°. In the seventh Se site, Se(7) is bonded to one Yb(2), two equivalent Yb(5), and one Sm(2) atom to form SeYb3Sm tetrahedra that share corners with two equivalent Se(1)Yb3Sm2Se octahedra, corners with two equivalent Se(5)Yb3Sm2Se octahedra, corners with two equivalent Se(7)Yb3Sm tetrahedra, corners with two equivalent Se(3)Yb4 tetrahedra, corners with three equivalent Se(2)Yb4 tetrahedra,  a cornercorner with one Se(6)Yb2Sm3 trigonal bipyramid,  an edgeedge with one Se(1)Yb3Sm2Se octahedra, edges with two equivalent Se(9)Yb3Sm2Se octahedra, and edges with two equivalent Se(11)Yb2Sm3 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 13-55°. In the eighth Se site, Se(8) is bonded to one Yb(3), two equivalent Yb(1), and one Sm(1) atom to form distorted SeYb3Sm tetrahedra that share  a cornercorner with one Se(5)Yb3Sm2Se octahedra, corners with two equivalent Se(9)Yb3Sm2Se octahedra, corners with two equivalent Se(8)Yb3Sm tetrahedra, corners with four equivalent Se(4)Yb4 tetrahedra,  a cornercorner with one Se(11)Yb2Sm3 trigonal bipyramid,  an edgeedge with one Se(9)Yb3Sm2Se octahedra, edges with two equivalent Se(1)Yb3Sm2Se octahedra, and edges with two equivalent Se(6)Yb2Sm3 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 22-32°. In the ninth Se site, Se(9) is bonded to one Yb(5), two equivalent Yb(1), two equivalent Sm(2), and one Se(5) atom to form distorted SeYb3Sm2Se octahedra that share corners with two equivalent Yb(6)Se6 octahedra, corners with two equivalent Se(5)Yb3Sm2Se octahedra,  a cornercorner with one Se(3)Yb4 tetrahedra, corners with two equivalent Se(8)Yb3Sm tetrahedra, corners with two equivalent Se(4)Yb4 tetrahedra, corners with two equivalent Se(11)Yb2Sm3 trigonal bipyramids, corners with two equivalent Se(6)Yb2Sm3 trigonal bipyramids,  an edgeedge with one Se(5)Yb3Sm2Se octahedra, edges with two equivalent Se(1)Yb3Sm2Se octahedra, edges with two equivalent Se(9)Yb3Sm2Se octahedra,  an edgeedge with one Se(8)Yb3Sm tetrahedra, edges with two equivalent Se(7)Yb3Sm tetrahedra, and  an edgeedge with one Se(11)Yb2Sm3 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 69-80°. In the tenth Se site, Se(10) is bonded in a 6-coordinate geometry to one Yb(2), two equivalent Yb(4), two equivalent Sm(1), and one Se(1) atom. In the eleventh Se site, Se(11) is bonded to two equivalent Yb(2), one Sm(1), and two equivalent Sm(2) atoms to form distorted SeYb2Sm3 trigonal bipyramids that share corners with two equivalent Se(1)Yb3Sm2Se octahedra, corners with two equivalent Se(5)Yb3Sm2Se octahedra, corners with two equivalent Se(9)Yb3Sm2Se octahedra,  a cornercorner with one Se(8)Yb3Sm tetrahedra, corners with four equivalent Se(2)Yb4 tetrahedra,  an edgeedge with one Se(5)Yb3Sm2Se octahedra,  an edgeedge with one Se(9)Yb3Sm2Se octahedra,  an edgeedge with one Se(2)Yb4 tetrahedra, edges with two equivalent Se(7)Yb3Sm tetrahedra, edges with two equivalent Se(11)Yb2Sm3 trigonal bipyramids, and edges with two equivalent Se(6)Yb2Sm3 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 21-53°.
Yb11(Sm2Se11)2 crystallizes in the monoclinic C2/m space group. There are six inequivalent Yb sites. In the first Yb site, Yb(1) is bonded in a 6-coordinate geometry to one Se(1), one Se(4), two equivalent Se(8), and two equivalent Se(9) atoms. The Yb(1)-Se(1) bond length is 3.57 Å. The Yb(1)-Se(4) bond length is 2.78 Å. Both Yb(1)-Se(8) bond lengths are 2.81 Å. Both Yb(1)-Se(9) bond lengths are 3.15 Å. In the second Yb site, Yb(2) is bonded in a 6-coordinate geometry to one Se(10), one Se(7), two equivalent Se(11), and three equivalent Se(2) atoms. The Yb(2)-Se(10) bond length is 3.75 Å. The Yb(2)-Se(7) bond length is 2.89 Å. Both Yb(2)-Se(11) bond lengths are 3.16 Å. There are two shorter (2.91 Å) and one longer (2.98 Å) Yb(2)-Se(2) bond length. In the third Yb site, Yb(3) is bonded in a 6-coordinate geometry to one Se(5), one Se(8), two equivalent Se(4), and two equivalent Se(6) atoms. The Yb(3)-Se(5) bond length is 3.46 Å. The Yb(3)-Se(8) bond length is 2.84 Å. Both Yb(3)-Se(4) bond lengths are 2.85 Å. Both Yb(3)-Se(6) bond lengths are 2.99 Å. In the fourth Yb site, Yb(4) is bonded to one Se(2), two equivalent Se(10), and three equivalent Se(3) atoms to form YbSe6 octahedra that share corners with two equivalent Se(1)Yb3Sm2Se octahedra, corners with three equivalent Yb(5)Se6 octahedra, and edges with four equivalent Yb(4)Se6 octahedra. The corner-sharing octahedral tilt angles range from 56-71°. The Yb(4)-Se(2) bond length is 2.85 Å. Both Yb(4)-Se(10) bond lengths are 3.15 Å. There are two shorter (2.83 Å) and one longer (2.86 Å) Yb(4)-Se(3) bond length. In the fifth Yb site, Yb(5) is bonded to one Se(3), one Se(9), two equivalent Se(1), and two equivalent Se(7) atoms to form distorted YbSe6 octahedra that share  a cornercorner with one Se(5)Yb3Sm2Se octahedra, corners with three equivalent Yb(4)Se6 octahedra, and edges with two equivalent Yb(5)Se6 octahedra. The corner-sharing octahedral tilt angles range from 28-71°. The Yb(5)-Se(3) bond length is 2.74 Å. The Yb(5)-Se(9) bond length is 3.36 Å. Both Yb(5)-Se(1) bond lengths are 3.12 Å. Both Yb(5)-Se(7) bond lengths are 2.80 Å. In the sixth Yb site, Yb(6) is bonded to two equivalent Se(4) and four equivalent Se(5) atoms to form YbSe6 octahedra that share corners with four equivalent Se(9)Yb3Sm2Se octahedra and edges with two equivalent Yb(6)Se6 octahedra. The corner-sharing octahedral tilt angles are 69°. Both Yb(6)-Se(4) bond lengths are 2.80 Å. All Yb(6)-Se(5) bond lengths are 3.06 Å. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 8-coordinate geometry to one Se(11), one Se(8), two equivalent Se(1), two equivalent Se(10), and two equivalent Se(6) atoms. The Sm(1)-Se(11) bond length is 3.04 Å. The Sm(1)-Se(8) bond length is 3.03 Å. Both Sm(1)-Se(1) bond lengths are 3.06 Å. Both Sm(1)-Se(10) bond lengths are 3.13 Å. Both Sm(1)-Se(6) bond lengths are 2.94 Å. In the second Sm site, Sm(2) is bonded in a 8-coordinate geometry to one Se(6), one Se(7), two equivalent Se(11), two equivalent Se(5), and two equivalent Se(9) atoms. The Sm(2)-Se(6) bond length is 2.99 Å. The Sm(2)-Se(7) bond length is 2.90 Å. Both Sm(2)-Se(11) bond lengths are 2.93 Å. Both Sm(2)-Se(5) bond lengths are 3.22 Å. Both Sm(2)-Se(9) bond lengths are 3.15 Å. There are eleven inequivalent Se sites. In the first Se site, Se(1) is bonded to one Yb(1), two equivalent Yb(5), two equivalent Sm(1), and one Se(10) atom to form distorted SeYb3Sm2Se octahedra that share corners with two equivalent Yb(4)Se6 octahedra,  a cornercorner with one Se(4)Yb4 tetrahedra, corners with two equivalent Se(7)Yb3Sm tetrahedra, corners with two equivalent Se(3)Yb4 tetrahedra, corners with two equivalent Se(11)Yb2Sm3 trigonal bipyramids, corners with two equivalent Se(6)Yb2Sm3 trigonal bipyramids, edges with two equivalent Se(1)Yb3Sm2Se octahedra, edges with two equivalent Se(9)Yb3Sm2Se octahedra,  an edgeedge with one Se(7)Yb3Sm tetrahedra, edges with two equivalent Se(8)Yb3Sm tetrahedra, and  an edgeedge with one Se(6)Yb2Sm3 trigonal bipyramid. The corner-sharing octahedral tilt angles are 70°. The Se(1)-Se(10) bond length is 2.47 Å. In the second Se site, Se(2) is bonded to one Yb(4) and three equivalent Yb(2) atoms to form SeYb4 tetrahedra that share corners with two equivalent Se(2)Yb4 tetrahedra, corners with three equivalent Se(7)Yb3Sm tetrahedra, corners with three equivalent Se(3)Yb4 tetrahedra, corners with four equivalent Se(11)Yb2Sm3 trigonal bipyramids, edges with two equivalent Se(2)Yb4 tetrahedra, and  an edgeedge with one Se(11)Yb2Sm3 trigonal bipyramid. In the third Se site, Se(3) is bonded to one Yb(5) and three equivalent Yb(4) atoms to form SeYb4 tetrahedra that share  a cornercorner with one Se(9)Yb3Sm2Se octahedra, corners with two equivalent Se(1)Yb3Sm2Se octahedra, corners with two equivalent Se(7)Yb3Sm tetrahedra, corners with two equivalent Se(3)Yb4 tetrahedra, corners with three equivalent Se(2)Yb4 tetrahedra, and edges with two equivalent Se(3)Yb4 tetrahedra. The corner-sharing octahedral tilt angles range from 11-83°. In the fourth Se site, Se(4) is bonded to one Yb(1), one Yb(6), and two equivalent Yb(3) atoms to form SeYb4 tetrahedra that share  a cornercorner with one Se(1)Yb3Sm2Se octahedra, corners with two equivalent Se(5)Yb3Sm2Se octahedra, corners with two equivalent Se(9)Yb3Sm2Se octahedra, corners with three equivalent Se(4)Yb4 tetrahedra, corners with four equivalent Se(8)Yb3Sm tetrahedra, corners with two equivalent Se(6)Yb2Sm3 trigonal bipyramids, edges with two equivalent Se(5)Yb3Sm2Se octahedra, and  an edgeedge with one Se(6)Yb2Sm3 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 4-84°. In the fifth Se site, Se(5) is bonded to one Yb(3), two equivalent Yb(6), two equivalent Sm(2), and one Se(9) atom to form distorted SeYb3Sm2Se octahedra that share  a cornercorner with one Yb(5)Se6 octahedra, corners with two equivalent Se(5)Yb3Sm2Se octahedra, corners with two equivalent Se(9)Yb3Sm2Se octahedra,  a cornercorner with one Se(8)Yb3Sm tetrahedra, corners with two equivalent Se(7)Yb3Sm tetrahedra, corners with two equivalent Se(4)Yb4 tetrahedra, corners with two equivalent Se(11)Yb2Sm3 trigonal bipyramids,  an edgeedge with one Se(9)Yb3Sm2Se octahedra, edges with three equivalent Se(5)Yb3Sm2Se octahedra, edges with two equivalent Se(4)Yb4 tetrahedra,  an edgeedge with one Se(11)Yb2Sm3 trigonal bipyramid, and edges with two equivalent Se(6)Yb2Sm3 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 0-80°. The Se(5)-Se(9) bond length is 2.45 Å. In the sixth Se site, Se(6) is bonded to two equivalent Yb(3), one Sm(2), and two equivalent Sm(1) atoms to form distorted SeYb2Sm3 trigonal bipyramids that share corners with two equivalent Se(1)Yb3Sm2Se octahedra, corners with two equivalent Se(9)Yb3Sm2Se octahedra,  a cornercorner with one Se(7)Yb3Sm tetrahedra, corners with two equivalent Se(4)Yb4 tetrahedra,  an edgeedge with one Se(1)Yb3Sm2Se octahedra, edges with two equivalent Se(5)Yb3Sm2Se octahedra,  an edgeedge with one Se(4)Yb4 tetrahedra, edges with two equivalent Se(8)Yb3Sm tetrahedra, edges with two equivalent Se(11)Yb2Sm3 trigonal bipyramids, and edges with two equivalent Se(6)Yb2Sm3 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 23-55°. In the seventh Se site, Se(7) is bonded to one Yb(2), two equivalent Yb(5), and one Sm(2) atom to form SeYb3Sm tetrahedra that share corners with two equivalent Se(1)Yb3Sm2Se octahedra, corners with two equivalent Se(5)Yb3Sm2Se octahedra, corners with two equivalent Se(7)Yb3Sm tetrahedra, corners with two equivalent Se(3)Yb4 tetrahedra, corners with three equivalent Se(2)Yb4 tetrahedra,  a cornercorner with one Se(6)Yb2Sm3 trigonal bipyramid,  an edgeedge with one Se(1)Yb3Sm2Se octahedra, edges with two equivalent Se(9)Yb3Sm2Se octahedra, and edges with two equivalent Se(11)Yb2Sm3 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 13-55°. In the eighth Se site, Se(8) is bonded to one Yb(3), two equivalent Yb(1), and one Sm(1) atom to form distorted SeYb3Sm tetrahedra that share  a cornercorner with one Se(5)Yb3Sm2Se octahedra, corners with two equivalent Se(9)Yb3Sm2Se octahedra, corners with two equivalent Se(8)Yb3Sm tetrahedra, corners with four equivalent Se(4)Yb4 tetrahedra,  a cornercorner with one Se(11)Yb2Sm3 trigonal bipyramid,  an edgeedge with one Se(9)Yb3Sm2Se octahedra, edges with two equivalent Se(1)Yb3Sm2Se octahedra, and edges with two equivalent Se(6)Yb2Sm3 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 22-32°. In the ninth Se site, Se(9) is bonded to one Yb(5), two equivalent Yb(1), two equivalent Sm(2), and one Se(5) atom to form distorted SeYb3Sm2Se octahedra that share corners with two equivalent Yb(6)Se6 octahedra, corners with two equivalent Se(5)Yb3Sm2Se octahedra,  a cornercorner with one Se(3)Yb4 tetrahedra, corners with two equivalent Se(8)Yb3Sm tetrahedra, corners with two equivalent Se(4)Yb4 tetrahedra, corners with two equivalent Se(11)Yb2Sm3 trigonal bipyramids, corners with two equivalent Se(6)Yb2Sm3 trigonal bipyramids,  an edgeedge with one Se(5)Yb3Sm2Se octahedra, edges with two equivalent Se(1)Yb3Sm2Se octahedra, edges with two equivalent Se(9)Yb3Sm2Se octahedra,  an edgeedge with one Se(8)Yb3Sm tetrahedra, edges with two equivalent Se(7)Yb3Sm tetrahedra, and  an edgeedge with one Se(11)Yb2Sm3 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 69-80°. In the tenth Se site, Se(10) is bonded in a 6-coordinate geometry to one Yb(2), two equivalent Yb(4), two equivalent Sm(1), and one Se(1) atom. In the eleventh Se site, Se(11) is bonded to two equivalent Yb(2), one Sm(1), and two equivalent Sm(2) atoms to form distorted SeYb2Sm3 trigonal bipyramids that share corners with two equivalent Se(1)Yb3Sm2Se octahedra, corners with two equivalent Se(5)Yb3Sm2Se octahedra, corners with two equivalent Se(9)Yb3Sm2Se octahedra,  a cornercorner with one Se(8)Yb3Sm tetrahedra, corners with four equivalent Se(2)Yb4 tetrahedra,  an edgeedge with one Se(5)Yb3Sm2Se octahedra,  an edgeedge with one Se(9)Yb3Sm2Se octahedra,  an edgeedge with one Se(2)Yb4 tetrahedra, edges with two equivalent Se(7)Yb3Sm tetrahedra, edges with two equivalent Se(11)Yb2Sm3 trigonal bipyramids, and edges with two equivalent Se(6)Yb2Sm3 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 21-53°.