Yb11(Ce2Se11)2 crystallizes in the monoclinic C2/m space group. There are six inequivalent Yb sites. In the first Yb site, Yb(1) is bonded to one Se(4), one Se(8), two equivalent Se(3), and two equivalent Se(5) atoms to form YbSe6 octahedra that share corners with three equivalent Yb(2)Se6 octahedra, corners with two equivalent Yb(5)Se7 pentagonal bipyramids, edges with two equivalent Yb(1)Se6 octahedra, and edges with two equivalent Yb(4)Se6 octahedra. The corner-sharing octahedral tilt angles range from 57-60°. In the second Yb site, Yb(2) is bonded to one Se(10), two equivalent Se(9), and three equivalent Se(8) atoms to form YbSe6 octahedra that share corners with three equivalent Yb(1)Se6 octahedra,  a cornercorner with one Yb(5)Se7 pentagonal bipyramid, edges with four equivalent Yb(2)Se6 octahedra, and edges with two equivalent Yb(5)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 57-60°. In the third Yb site, Yb(3) is bonded to one Se(1), one Se(6), two equivalent Se(11), and two equivalent Se(7) atoms to form a mixture of distorted corner and edge-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles range from 50-60°. In the fourth Yb site, Yb(4) is bonded to one Se(3), one Se(7), two equivalent Se(4), and two equivalent Se(6) atoms to form a mixture of corner and edge-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles range from 50-60°. In the fifth Yb site, Yb(5) is bonded to one Se(5), one Se(9), two equivalent Se(2), and three equivalent Se(10) atoms to form distorted YbSe7 pentagonal bipyramids that share  a cornercorner with one Yb(2)Se6 octahedra, corners with two equivalent Yb(1)Se6 octahedra, edges with two equivalent Yb(2)Se6 octahedra, and edges with four equivalent Yb(5)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 43-49°. In the sixth Yb site, Yb(6) is bonded to two equivalent Se(7) and four equivalent Se(1) atoms to form a mixture of corner and edge-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles are 59°. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded in a 8-coordinate geometry to one Se(2), one Se(6), two equivalent Se(11), two equivalent Se(3), and two equivalent Se(9) atoms. In the second Ce site, Ce(2) is bonded in a 8-coordinate geometry to one Se(11), one Se(5), two equivalent Se(1), two equivalent Se(2), and two equivalent Se(4) atoms. There are eleven inequivalent Se sites. In the first Se site, Se(1) is bonded to one Yb(3), two equivalent Yb(6), and two equivalent Ce(2) atoms to form distorted SeYb3Ce2 square pyramids that share corners with two equivalent Se(1)Yb3Ce2 square pyramids, corners with two equivalent Se(4)Yb3Ce2 square pyramids, corners with two equivalent Se(2)Yb2Ce3 trigonal bipyramids,  a cornercorner with one Se(6)Yb3Ce trigonal pyramid, corners with two equivalent Se(5)Yb3Ce trigonal pyramids, corners with two equivalent Se(7)Yb4 trigonal pyramids,  an edgeedge with one Se(4)Yb3Ce2 square pyramid, edges with three equivalent Se(1)Yb3Ce2 square pyramids,  an edgeedge with one Se(2)Yb2Ce3 trigonal bipyramid, edges with two equivalent Se(11)Yb2Ce3 trigonal bipyramids, and edges with two equivalent Se(7)Yb4 trigonal pyramids. In the second Se site, Se(2) is bonded to two equivalent Yb(5), one Ce(1), and two equivalent Ce(2) atoms to form distorted SeYb2Ce3 trigonal bipyramids that share corners with two equivalent Se(1)Yb3Ce2 square pyramids, corners with two equivalent Se(3)Yb3Ce2 square pyramids, corners with two equivalent Se(4)Yb3Ce2 square pyramids,  a cornercorner with one Se(6)Yb3Ce trigonal pyramid,  an edgeedge with one Se(1)Yb3Ce2 square pyramid,  an edgeedge with one Se(4)Yb3Ce2 square pyramid, edges with two equivalent Se(11)Yb2Ce3 trigonal bipyramids, edges with two equivalent Se(2)Yb2Ce3 trigonal bipyramids, edges with two equivalent Se(9)Yb3Ce2 trigonal bipyramids, and edges with two equivalent Se(5)Yb3Ce trigonal pyramids. In the third Se site, Se(3) is bonded to one Yb(4), two equivalent Yb(1), and two equivalent Ce(1) atoms to form SeYb3Ce2 square pyramids that share corners with two equivalent Se(11)Yb2Ce3 trigonal bipyramids, corners with two equivalent Se(2)Yb2Ce3 trigonal bipyramids, corners with two equivalent Se(9)Yb3Ce2 trigonal bipyramids,  a cornercorner with one Se(7)Yb4 trigonal pyramid, corners with two equivalent Se(5)Yb3Ce trigonal pyramids, edges with two equivalent Se(3)Yb3Ce2 square pyramids, edges with two equivalent Se(4)Yb3Ce2 square pyramids,  an edgeedge with one Se(11)Yb2Ce3 trigonal bipyramid,  an edgeedge with one Se(9)Yb3Ce2 trigonal bipyramid,  an edgeedge with one Se(5)Yb3Ce trigonal pyramid, and edges with two equivalent Se(6)Yb3Ce trigonal pyramids. In the fourth Se site, Se(4) is bonded to one Yb(1), two equivalent Yb(4), and two equivalent Ce(2) atoms to form distorted SeYb3Ce2 square pyramids that share corners with two equivalent Se(1)Yb3Ce2 square pyramids, corners with two equivalent Se(11)Yb2Ce3 trigonal bipyramids, corners with two equivalent Se(2)Yb2Ce3 trigonal bipyramids, corners with two equivalent Se(6)Yb3Ce trigonal pyramids, corners with two equivalent Se(7)Yb4 trigonal pyramids,  an edgeedge with one Se(1)Yb3Ce2 square pyramid, edges with two equivalent Se(3)Yb3Ce2 square pyramids, edges with two equivalent Se(4)Yb3Ce2 square pyramids,  an edgeedge with one Se(2)Yb2Ce3 trigonal bipyramid,  an edgeedge with one Se(6)Yb3Ce trigonal pyramid, and edges with two equivalent Se(5)Yb3Ce trigonal pyramids. In the fifth Se site, Se(5) is bonded to one Yb(5), two equivalent Yb(1), and one Ce(2) atom to form distorted SeYb3Ce trigonal pyramids that share corners with two equivalent Se(1)Yb3Ce2 square pyramids, corners with two equivalent Se(3)Yb3Ce2 square pyramids,  a cornercorner with one Se(11)Yb2Ce3 trigonal bipyramid,  a cornercorner with one Se(9)Yb3Ce2 trigonal bipyramid, corners with two equivalent Se(5)Yb3Ce trigonal pyramids,  an edgeedge with one Se(3)Yb3Ce2 square pyramid, edges with two equivalent Se(4)Yb3Ce2 square pyramids, and edges with two equivalent Se(2)Yb2Ce3 trigonal bipyramids. In the sixth Se site, Se(6) is bonded to one Yb(3), two equivalent Yb(4), and one Ce(1) atom to form distorted SeYb3Ce trigonal pyramids that share  a cornercorner with one Se(1)Yb3Ce2 square pyramid, corners with two equivalent Se(4)Yb3Ce2 square pyramids,  a cornercorner with one Se(2)Yb2Ce3 trigonal bipyramid, corners with two equivalent Se(9)Yb3Ce2 trigonal bipyramids, corners with two equivalent Se(6)Yb3Ce trigonal pyramids, corners with four equivalent Se(7)Yb4 trigonal pyramids,  an edgeedge with one Se(4)Yb3Ce2 square pyramid, edges with two equivalent Se(3)Yb3Ce2 square pyramids, and edges with two equivalent Se(11)Yb2Ce3 trigonal bipyramids. In the seventh Se site, Se(7) is bonded to one Yb(4), one Yb(6), and two equivalent Yb(3) atoms to form distorted SeYb4 trigonal pyramids that share  a cornercorner with one Se(3)Yb3Ce2 square pyramid, corners with two equivalent Se(1)Yb3Ce2 square pyramids, corners with two equivalent Se(4)Yb3Ce2 square pyramids, corners with two equivalent Se(11)Yb2Ce3 trigonal bipyramids, corners with three equivalent Se(7)Yb4 trigonal pyramids, corners with four equivalent Se(6)Yb3Ce trigonal pyramids, edges with two equivalent Se(1)Yb3Ce2 square pyramids, and  an edgeedge with one Se(11)Yb2Ce3 trigonal bipyramid. In the eighth Se site, Se(8) is bonded in a rectangular see-saw-like geometry to one Yb(1) and three equivalent Yb(2) atoms. In the ninth Se site, Se(9) is bonded to one Yb(5), two equivalent Yb(2), and two equivalent Ce(1) atoms to form SeYb3Ce2 trigonal bipyramids that share corners with two equivalent Se(3)Yb3Ce2 square pyramids, corners with two equivalent Se(11)Yb2Ce3 trigonal bipyramids,  a cornercorner with one Se(5)Yb3Ce trigonal pyramid, corners with two equivalent Se(6)Yb3Ce trigonal pyramids,  an edgeedge with one Se(3)Yb3Ce2 square pyramid,  an edgeedge with one Se(11)Yb2Ce3 trigonal bipyramid, edges with two equivalent Se(2)Yb2Ce3 trigonal bipyramids, and edges with two equivalent Se(9)Yb3Ce2 trigonal bipyramids. In the tenth Se site, Se(10) is bonded in a rectangular see-saw-like geometry to one Yb(2) and three equivalent Yb(5) atoms. In the eleventh Se site, Se(11) is bonded to two equivalent Yb(3), one Ce(2), and two equivalent Ce(1) atoms to form distorted SeYb2Ce3 trigonal bipyramids that share corners with two equivalent Se(3)Yb3Ce2 square pyramids, corners with two equivalent Se(4)Yb3Ce2 square pyramids, corners with two equivalent Se(9)Yb3Ce2 trigonal bipyramids,  a cornercorner with one Se(5)Yb3Ce trigonal pyramid, corners with two equivalent Se(7)Yb4 trigonal pyramids,  an edgeedge with one Se(3)Yb3Ce2 square pyramid, edges with two equivalent Se(1)Yb3Ce2 square pyramids,  an edgeedge with one Se(9)Yb3Ce2 trigonal bipyramid, edges with two equivalent Se(11)Yb2Ce3 trigonal bipyramids, edges with two equivalent Se(2)Yb2Ce3 trigonal bipyramids,  an edgeedge with one Se(7)Yb4 trigonal pyramid, and edges with two equivalent Se(6)Yb3Ce trigonal pyramids.
Yb11(Ce2Se11)2 crystallizes in the monoclinic C2/m space group. There are six inequivalent Yb sites. In the first Yb site, Yb(1) is bonded to one Se(4), one Se(8), two equivalent Se(3), and two equivalent Se(5) atoms to form YbSe6 octahedra that share corners with three equivalent Yb(2)Se6 octahedra, corners with two equivalent Yb(5)Se7 pentagonal bipyramids, edges with two equivalent Yb(1)Se6 octahedra, and edges with two equivalent Yb(4)Se6 octahedra. The corner-sharing octahedral tilt angles range from 57-60°. The Yb(1)-Se(4) bond length is 2.97 Å. The Yb(1)-Se(8) bond length is 2.78 Å. Both Yb(1)-Se(3) bond lengths are 2.99 Å. Both Yb(1)-Se(5) bond lengths are 2.86 Å. In the second Yb site, Yb(2) is bonded to one Se(10), two equivalent Se(9), and three equivalent Se(8) atoms to form YbSe6 octahedra that share corners with three equivalent Yb(1)Se6 octahedra,  a cornercorner with one Yb(5)Se7 pentagonal bipyramid, edges with four equivalent Yb(2)Se6 octahedra, and edges with two equivalent Yb(5)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 57-60°. The Yb(2)-Se(10) bond length is 2.94 Å. Both Yb(2)-Se(9) bond lengths are 3.06 Å. There is one shorter (2.85 Å) and two longer (2.88 Å) Yb(2)-Se(8) bond lengths. In the third Yb site, Yb(3) is bonded to one Se(1), one Se(6), two equivalent Se(11), and two equivalent Se(7) atoms to form a mixture of distorted corner and edge-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles range from 50-60°. The Yb(3)-Se(1) bond length is 2.98 Å. The Yb(3)-Se(6) bond length is 2.82 Å. Both Yb(3)-Se(11) bond lengths are 3.05 Å. Both Yb(3)-Se(7) bond lengths are 2.82 Å. In the fourth Yb site, Yb(4) is bonded to one Se(3), one Se(7), two equivalent Se(4), and two equivalent Se(6) atoms to form a mixture of corner and edge-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles range from 50-60°. The Yb(4)-Se(3) bond length is 2.97 Å. The Yb(4)-Se(7) bond length is 2.82 Å. Both Yb(4)-Se(4) bond lengths are 3.09 Å. Both Yb(4)-Se(6) bond lengths are 2.85 Å. In the fifth Yb site, Yb(5) is bonded to one Se(5), one Se(9), two equivalent Se(2), and three equivalent Se(10) atoms to form distorted YbSe7 pentagonal bipyramids that share  a cornercorner with one Yb(2)Se6 octahedra, corners with two equivalent Yb(1)Se6 octahedra, edges with two equivalent Yb(2)Se6 octahedra, and edges with four equivalent Yb(5)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 43-49°. The Yb(5)-Se(5) bond length is 2.91 Å. The Yb(5)-Se(9) bond length is 2.99 Å. Both Yb(5)-Se(2) bond lengths are 3.06 Å. There are two shorter (2.93 Å) and one longer (2.96 Å) Yb(5)-Se(10) bond length. In the sixth Yb site, Yb(6) is bonded to two equivalent Se(7) and four equivalent Se(1) atoms to form a mixture of corner and edge-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles are 59°. Both Yb(6)-Se(7) bond lengths are 2.82 Å. All Yb(6)-Se(1) bond lengths are 3.01 Å. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded in a 8-coordinate geometry to one Se(2), one Se(6), two equivalent Se(11), two equivalent Se(3), and two equivalent Se(9) atoms. The Ce(1)-Se(2) bond length is 3.13 Å. The Ce(1)-Se(6) bond length is 2.99 Å. Both Ce(1)-Se(11) bond lengths are 2.98 Å. Both Ce(1)-Se(3) bond lengths are 3.00 Å. Both Ce(1)-Se(9) bond lengths are 3.05 Å. In the second Ce site, Ce(2) is bonded in a 8-coordinate geometry to one Se(11), one Se(5), two equivalent Se(1), two equivalent Se(2), and two equivalent Se(4) atoms. The Ce(2)-Se(11) bond length is 3.07 Å. The Ce(2)-Se(5) bond length is 2.85 Å. Both Ce(2)-Se(1) bond lengths are 3.07 Å. Both Ce(2)-Se(2) bond lengths are 2.95 Å. Both Ce(2)-Se(4) bond lengths are 3.03 Å. There are eleven inequivalent Se sites. In the first Se site, Se(1) is bonded to one Yb(3), two equivalent Yb(6), and two equivalent Ce(2) atoms to form distorted SeYb3Ce2 square pyramids that share corners with two equivalent Se(1)Yb3Ce2 square pyramids, corners with two equivalent Se(4)Yb3Ce2 square pyramids, corners with two equivalent Se(2)Yb2Ce3 trigonal bipyramids,  a cornercorner with one Se(6)Yb3Ce trigonal pyramid, corners with two equivalent Se(5)Yb3Ce trigonal pyramids, corners with two equivalent Se(7)Yb4 trigonal pyramids,  an edgeedge with one Se(4)Yb3Ce2 square pyramid, edges with three equivalent Se(1)Yb3Ce2 square pyramids,  an edgeedge with one Se(2)Yb2Ce3 trigonal bipyramid, edges with two equivalent Se(11)Yb2Ce3 trigonal bipyramids, and edges with two equivalent Se(7)Yb4 trigonal pyramids. In the second Se site, Se(2) is bonded to two equivalent Yb(5), one Ce(1), and two equivalent Ce(2) atoms to form distorted SeYb2Ce3 trigonal bipyramids that share corners with two equivalent Se(1)Yb3Ce2 square pyramids, corners with two equivalent Se(3)Yb3Ce2 square pyramids, corners with two equivalent Se(4)Yb3Ce2 square pyramids,  a cornercorner with one Se(6)Yb3Ce trigonal pyramid,  an edgeedge with one Se(1)Yb3Ce2 square pyramid,  an edgeedge with one Se(4)Yb3Ce2 square pyramid, edges with two equivalent Se(11)Yb2Ce3 trigonal bipyramids, edges with two equivalent Se(2)Yb2Ce3 trigonal bipyramids, edges with two equivalent Se(9)Yb3Ce2 trigonal bipyramids, and edges with two equivalent Se(5)Yb3Ce trigonal pyramids. In the third Se site, Se(3) is bonded to one Yb(4), two equivalent Yb(1), and two equivalent Ce(1) atoms to form SeYb3Ce2 square pyramids that share corners with two equivalent Se(11)Yb2Ce3 trigonal bipyramids, corners with two equivalent Se(2)Yb2Ce3 trigonal bipyramids, corners with two equivalent Se(9)Yb3Ce2 trigonal bipyramids,  a cornercorner with one Se(7)Yb4 trigonal pyramid, corners with two equivalent Se(5)Yb3Ce trigonal pyramids, edges with two equivalent Se(3)Yb3Ce2 square pyramids, edges with two equivalent Se(4)Yb3Ce2 square pyramids,  an edgeedge with one Se(11)Yb2Ce3 trigonal bipyramid,  an edgeedge with one Se(9)Yb3Ce2 trigonal bipyramid,  an edgeedge with one Se(5)Yb3Ce trigonal pyramid, and edges with two equivalent Se(6)Yb3Ce trigonal pyramids. In the fourth Se site, Se(4) is bonded to one Yb(1), two equivalent Yb(4), and two equivalent Ce(2) atoms to form distorted SeYb3Ce2 square pyramids that share corners with two equivalent Se(1)Yb3Ce2 square pyramids, corners with two equivalent Se(11)Yb2Ce3 trigonal bipyramids, corners with two equivalent Se(2)Yb2Ce3 trigonal bipyramids, corners with two equivalent Se(6)Yb3Ce trigonal pyramids, corners with two equivalent Se(7)Yb4 trigonal pyramids,  an edgeedge with one Se(1)Yb3Ce2 square pyramid, edges with two equivalent Se(3)Yb3Ce2 square pyramids, edges with two equivalent Se(4)Yb3Ce2 square pyramids,  an edgeedge with one Se(2)Yb2Ce3 trigonal bipyramid,  an edgeedge with one Se(6)Yb3Ce trigonal pyramid, and edges with two equivalent Se(5)Yb3Ce trigonal pyramids. In the fifth Se site, Se(5) is bonded to one Yb(5), two equivalent Yb(1), and one Ce(2) atom to form distorted SeYb3Ce trigonal pyramids that share corners with two equivalent Se(1)Yb3Ce2 square pyramids, corners with two equivalent Se(3)Yb3Ce2 square pyramids,  a cornercorner with one Se(11)Yb2Ce3 trigonal bipyramid,  a cornercorner with one Se(9)Yb3Ce2 trigonal bipyramid, corners with two equivalent Se(5)Yb3Ce trigonal pyramids,  an edgeedge with one Se(3)Yb3Ce2 square pyramid, edges with two equivalent Se(4)Yb3Ce2 square pyramids, and edges with two equivalent Se(2)Yb2Ce3 trigonal bipyramids. In the sixth Se site, Se(6) is bonded to one Yb(3), two equivalent Yb(4), and one Ce(1) atom to form distorted SeYb3Ce trigonal pyramids that share  a cornercorner with one Se(1)Yb3Ce2 square pyramid, corners with two equivalent Se(4)Yb3Ce2 square pyramids,  a cornercorner with one Se(2)Yb2Ce3 trigonal bipyramid, corners with two equivalent Se(9)Yb3Ce2 trigonal bipyramids, corners with two equivalent Se(6)Yb3Ce trigonal pyramids, corners with four equivalent Se(7)Yb4 trigonal pyramids,  an edgeedge with one Se(4)Yb3Ce2 square pyramid, edges with two equivalent Se(3)Yb3Ce2 square pyramids, and edges with two equivalent Se(11)Yb2Ce3 trigonal bipyramids. In the seventh Se site, Se(7) is bonded to one Yb(4), one Yb(6), and two equivalent Yb(3) atoms to form distorted SeYb4 trigonal pyramids that share  a cornercorner with one Se(3)Yb3Ce2 square pyramid, corners with two equivalent Se(1)Yb3Ce2 square pyramids, corners with two equivalent Se(4)Yb3Ce2 square pyramids, corners with two equivalent Se(11)Yb2Ce3 trigonal bipyramids, corners with three equivalent Se(7)Yb4 trigonal pyramids, corners with four equivalent Se(6)Yb3Ce trigonal pyramids, edges with two equivalent Se(1)Yb3Ce2 square pyramids, and  an edgeedge with one Se(11)Yb2Ce3 trigonal bipyramid. In the eighth Se site, Se(8) is bonded in a rectangular see-saw-like geometry to one Yb(1) and three equivalent Yb(2) atoms. In the ninth Se site, Se(9) is bonded to one Yb(5), two equivalent Yb(2), and two equivalent Ce(1) atoms to form SeYb3Ce2 trigonal bipyramids that share corners with two equivalent Se(3)Yb3Ce2 square pyramids, corners with two equivalent Se(11)Yb2Ce3 trigonal bipyramids,  a cornercorner with one Se(5)Yb3Ce trigonal pyramid, corners with two equivalent Se(6)Yb3Ce trigonal pyramids,  an edgeedge with one Se(3)Yb3Ce2 square pyramid,  an edgeedge with one Se(11)Yb2Ce3 trigonal bipyramid, edges with two equivalent Se(2)Yb2Ce3 trigonal bipyramids, and edges with two equivalent Se(9)Yb3Ce2 trigonal bipyramids. In the tenth Se site, Se(10) is bonded in a rectangular see-saw-like geometry to one Yb(2) and three equivalent Yb(5) atoms. In the eleventh Se site, Se(11) is bonded to two equivalent Yb(3), one Ce(2), and two equivalent Ce(1) atoms to form distorted SeYb2Ce3 trigonal bipyramids that share corners with two equivalent Se(3)Yb3Ce2 square pyramids, corners with two equivalent Se(4)Yb3Ce2 square pyramids, corners with two equivalent Se(9)Yb3Ce2 trigonal bipyramids,  a cornercorner with one Se(5)Yb3Ce trigonal pyramid, corners with two equivalent Se(7)Yb4 trigonal pyramids,  an edgeedge with one Se(3)Yb3Ce2 square pyramid, edges with two equivalent Se(1)Yb3Ce2 square pyramids,  an edgeedge with one Se(9)Yb3Ce2 trigonal bipyramid, edges with two equivalent Se(11)Yb2Ce3 trigonal bipyramids, edges with two equivalent Se(2)Yb2Ce3 trigonal bipyramids,  an edgeedge with one Se(7)Yb4 trigonal pyramid, and edges with two equivalent Se(6)Yb3Ce trigonal pyramids.