Mo9Tl2Se11 crystallizes in the trigonal R-3 space group. There are three inequivalent Mo sites. In the first Mo site, Mo(1) is bonded to one Se(2), one Se(4), and three equivalent Se(1) atoms to form distorted MoSe5 square pyramids that share corners with three equivalent Mo(2)Se5 square pyramids,  a cornercorner with one Tl(2)Se4 trigonal pyramid,  an edgeedge with one Mo(2)Se5 square pyramid, and edges with four equivalent Mo(1)Se5 square pyramids. In the second Mo site, Mo(2) is bonded to one Se(1), one Se(3), one Se(5), and two equivalent Se(2) atoms to form distorted MoSe5 square pyramids that share corners with three equivalent Mo(1)Se5 square pyramids, corners with three equivalent Tl(2)Se4 trigonal pyramids,  an edgeedge with one Mo(1)Se5 square pyramid, and edges with two equivalent Mo(2)Se5 square pyramids. In the third Mo site, Mo(3) is bonded in a distorted see-saw-like geometry to one Se(2) and three equivalent Se(3) atoms. There are two inequivalent Tl sites. In the first Tl site, Tl(1) is bonded in a single-bond geometry to one Se(4) atom. In the second Tl site, Tl(2) is bonded to one Se(5) and three equivalent Se(2) atoms to form distorted TlSe4 trigonal pyramids that share corners with three equivalent Mo(1)Se5 square pyramids and corners with nine equivalent Mo(2)Se5 square pyramids. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted rectangular see-saw-like geometry to one Mo(2) and three equivalent Mo(1) atoms. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to one Mo(1), one Mo(3), two equivalent Mo(2), and one Tl(2) atom. In the third Se site, Se(3) is bonded in a 4-coordinate geometry to one Mo(2) and three equivalent Mo(3) atoms. In the fourth Se site, Se(4) is bonded in a 4-coordinate geometry to three equivalent Mo(1) and one Tl(1) atom. In the fifth Se site, Se(5) is bonded in a 4-coordinate geometry to three equivalent Mo(2) and one Tl(2) atom.
Mo9Tl2Se11 crystallizes in the trigonal R-3 space group. There are three inequivalent Mo sites. In the first Mo site, Mo(1) is bonded to one Se(2), one Se(4), and three equivalent Se(1) atoms to form distorted MoSe5 square pyramids that share corners with three equivalent Mo(2)Se5 square pyramids,  a cornercorner with one Tl(2)Se4 trigonal pyramid,  an edgeedge with one Mo(2)Se5 square pyramid, and edges with four equivalent Mo(1)Se5 square pyramids. The Mo(1)-Se(2) bond length is 2.70 Å. The Mo(1)-Se(4) bond length is 2.55 Å. There are a spread of Mo(1)-Se(1) bond distances ranging from 2.58-2.63 Å. In the second Mo site, Mo(2) is bonded to one Se(1), one Se(3), one Se(5), and two equivalent Se(2) atoms to form distorted MoSe5 square pyramids that share corners with three equivalent Mo(1)Se5 square pyramids, corners with three equivalent Tl(2)Se4 trigonal pyramids,  an edgeedge with one Mo(1)Se5 square pyramid, and edges with two equivalent Mo(2)Se5 square pyramids. The Mo(2)-Se(1) bond length is 2.73 Å. The Mo(2)-Se(3) bond length is 2.70 Å. The Mo(2)-Se(5) bond length is 2.53 Å. There is one shorter (2.63 Å) and one longer (2.65 Å) Mo(2)-Se(2) bond length. In the third Mo site, Mo(3) is bonded in a distorted see-saw-like geometry to one Se(2) and three equivalent Se(3) atoms. The Mo(3)-Se(2) bond length is 2.60 Å. There are two shorter (2.63 Å) and one longer (2.73 Å) Mo(3)-Se(3) bond length. There are two inequivalent Tl sites. In the first Tl site, Tl(1) is bonded in a single-bond geometry to one Se(4) atom. The Tl(1)-Se(4) bond length is 3.12 Å. In the second Tl site, Tl(2) is bonded to one Se(5) and three equivalent Se(2) atoms to form distorted TlSe4 trigonal pyramids that share corners with three equivalent Mo(1)Se5 square pyramids and corners with nine equivalent Mo(2)Se5 square pyramids. The Tl(2)-Se(5) bond length is 3.10 Å. All Tl(2)-Se(2) bond lengths are 3.24 Å. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted rectangular see-saw-like geometry to one Mo(2) and three equivalent Mo(1) atoms. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to one Mo(1), one Mo(3), two equivalent Mo(2), and one Tl(2) atom. In the third Se site, Se(3) is bonded in a 4-coordinate geometry to one Mo(2) and three equivalent Mo(3) atoms. In the fourth Se site, Se(4) is bonded in a 4-coordinate geometry to three equivalent Mo(1) and one Tl(1) atom. In the fifth Se site, Se(5) is bonded in a 4-coordinate geometry to three equivalent Mo(2) and one Tl(2) atom.