Cs3Tl2Br9 crystallizes in the monoclinic P2_1 space group. There are three inequivalent Cs sites. In the first Cs site, Cs(1) is bonded to one Br(1), one Br(2), one Br(3), two equivalent Br(4), two equivalent Br(5), two equivalent Br(8), and three equivalent Br(7) atoms to form CsBr12 cuboctahedra that share corners with four equivalent Cs(1)Br12 cuboctahedra,  an edgeedge with one Tl(1)Br4 tetrahedra, faces with two equivalent Cs(1)Br12 cuboctahedra, and faces with four equivalent Tl(2)Br6 octahedra. In the second Cs site, Cs(2) is bonded in a 9-coordinate geometry to one Br(1), one Br(2), one Br(3), one Br(4), one Br(5), one Br(9), and three equivalent Br(6) atoms. In the third Cs site, Cs(3) is bonded in a distorted q6 geometry to one Br(1), one Br(2), one Br(4), one Br(5), one Br(6), one Br(7), one Br(9), two equivalent Br(3), and two equivalent Br(8) atoms. There are two inequivalent Tl sites. In the first Tl site, Tl(1) is bonded to one Br(1), one Br(2), one Br(6), and one Br(9) atom to form TlBr4 tetrahedra that share  an edgeedge with one Cs(1)Br12 cuboctahedra. In the second Tl site, Tl(2) is bonded to one Br(3), one Br(4), one Br(5), one Br(7), and two equivalent Br(8) atoms to form TlBr6 octahedra that share corners with two equivalent Tl(2)Br6 octahedra and faces with four equivalent Cs(1)Br12 cuboctahedra. The corner-sharing octahedra are not tilted. There are nine inequivalent Br sites. In the first Br site, Br(1) is bonded in a distorted single-bond geometry to one Cs(1), one Cs(2), one Cs(3), and one Tl(1) atom. In the second Br site, Br(2) is bonded in a distorted single-bond geometry to one Cs(1), one Cs(2), one Cs(3), and one Tl(1) atom. In the third Br site, Br(3) is bonded in a distorted single-bond geometry to one Cs(1), one Cs(2), two equivalent Cs(3), and one Tl(2) atom. In the fourth Br site, Br(4) is bonded to one Cs(2), one Cs(3), two equivalent Cs(1), and one Tl(2) atom to form distorted BrCs4Tl square pyramids that share corners with three equivalent Br(8)Cs4Tl2 octahedra, corners with two equivalent Br(4)Cs4Tl square pyramids,  an edgeedge with one Br(8)Cs4Tl2 octahedra, edges with two equivalent Br(5)Cs4Tl square pyramids,  a faceface with one Br(8)Cs4Tl2 octahedra, and  a faceface with one Br(5)Cs4Tl square pyramid. The corner-sharing octahedral tilt angles range from 1-60°. In the fifth Br site, Br(5) is bonded to one Cs(2), one Cs(3), two equivalent Cs(1), and one Tl(2) atom to form distorted BrCs4Tl square pyramids that share corners with three equivalent Br(8)Cs4Tl2 octahedra, corners with two equivalent Br(5)Cs4Tl square pyramids,  an edgeedge with one Br(8)Cs4Tl2 octahedra, edges with two equivalent Br(4)Cs4Tl square pyramids,  a faceface with one Br(8)Cs4Tl2 octahedra, and  a faceface with one Br(4)Cs4Tl square pyramid. The corner-sharing octahedral tilt angles range from 2-61°. In the sixth Br site, Br(6) is bonded in a distorted single-bond geometry to one Cs(3), three equivalent Cs(2), and one Tl(1) atom. In the seventh Br site, Br(7) is bonded in a distorted single-bond geometry to one Cs(3), three equivalent Cs(1), and one Tl(2) atom. In the eighth Br site, Br(8) is bonded to two equivalent Cs(1), two equivalent Cs(3), and two equivalent Tl(2) atoms to form distorted BrCs4Tl2 octahedra that share corners with three equivalent Br(4)Cs4Tl square pyramids, corners with three equivalent Br(5)Cs4Tl square pyramids,  an edgeedge with one Br(4)Cs4Tl square pyramid,  an edgeedge with one Br(5)Cs4Tl square pyramid, faces with two equivalent Br(8)Cs4Tl2 octahedra,  a faceface with one Br(4)Cs4Tl square pyramid, and  a faceface with one Br(5)Cs4Tl square pyramid. In the ninth Br site, Br(9) is bonded in a 3-coordinate geometry to one Cs(2), one Cs(3), and one Tl(1) atom.
Cs3Tl2Br9 crystallizes in the monoclinic P2_1 space group. There are three inequivalent Cs sites. In the first Cs site, Cs(1) is bonded to one Br(1), one Br(2), one Br(3), two equivalent Br(4), two equivalent Br(5), two equivalent Br(8), and three equivalent Br(7) atoms to form CsBr12 cuboctahedra that share corners with four equivalent Cs(1)Br12 cuboctahedra,  an edgeedge with one Tl(1)Br4 tetrahedra, faces with two equivalent Cs(1)Br12 cuboctahedra, and faces with four equivalent Tl(2)Br6 octahedra. The Cs(1)-Br(1) bond length is 4.10 Å. The Cs(1)-Br(2) bond length is 4.10 Å. The Cs(1)-Br(3) bond length is 4.01 Å. There is one shorter (3.86 Å) and one longer (3.95 Å) Cs(1)-Br(4) bond length. There is one shorter (3.86 Å) and one longer (3.95 Å) Cs(1)-Br(5) bond length. There is one shorter (3.95 Å) and one longer (3.96 Å) Cs(1)-Br(8) bond length. There are two shorter (3.94 Å) and one longer (4.04 Å) Cs(1)-Br(7) bond length. In the second Cs site, Cs(2) is bonded in a 9-coordinate geometry to one Br(1), one Br(2), one Br(3), one Br(4), one Br(5), one Br(9), and three equivalent Br(6) atoms. The Cs(2)-Br(1) bond length is 3.95 Å. The Cs(2)-Br(2) bond length is 3.95 Å. The Cs(2)-Br(3) bond length is 3.83 Å. The Cs(2)-Br(4) bond length is 3.75 Å. The Cs(2)-Br(5) bond length is 3.74 Å. The Cs(2)-Br(9) bond length is 3.69 Å. There are a spread of Cs(2)-Br(6) bond distances ranging from 3.82-3.98 Å. In the third Cs site, Cs(3) is bonded in a distorted q6 geometry to one Br(1), one Br(2), one Br(4), one Br(5), one Br(6), one Br(7), one Br(9), two equivalent Br(3), and two equivalent Br(8) atoms. The Cs(3)-Br(1) bond length is 4.05 Å. The Cs(3)-Br(2) bond length is 4.05 Å. The Cs(3)-Br(4) bond length is 3.85 Å. The Cs(3)-Br(5) bond length is 3.87 Å. The Cs(3)-Br(6) bond length is 4.01 Å. The Cs(3)-Br(7) bond length is 3.83 Å. The Cs(3)-Br(9) bond length is 3.81 Å. Both Cs(3)-Br(3) bond lengths are 3.94 Å. There is one shorter (3.76 Å) and one longer (3.77 Å) Cs(3)-Br(8) bond length. There are two inequivalent Tl sites. In the first Tl site, Tl(1) is bonded to one Br(1), one Br(2), one Br(6), and one Br(9) atom to form TlBr4 tetrahedra that share  an edgeedge with one Cs(1)Br12 cuboctahedra. The Tl(1)-Br(1) bond length is 2.60 Å. The Tl(1)-Br(2) bond length is 2.60 Å. The Tl(1)-Br(6) bond length is 2.66 Å. The Tl(1)-Br(9) bond length is 2.57 Å. In the second Tl site, Tl(2) is bonded to one Br(3), one Br(4), one Br(5), one Br(7), and two equivalent Br(8) atoms to form TlBr6 octahedra that share corners with two equivalent Tl(2)Br6 octahedra and faces with four equivalent Cs(1)Br12 cuboctahedra. The corner-sharing octahedra are not tilted. The Tl(2)-Br(3) bond length is 2.73 Å. The Tl(2)-Br(4) bond length is 2.70 Å. The Tl(2)-Br(5) bond length is 2.70 Å. The Tl(2)-Br(7) bond length is 2.67 Å. There is one shorter (2.94 Å) and one longer (2.95 Å) Tl(2)-Br(8) bond length. There are nine inequivalent Br sites. In the first Br site, Br(1) is bonded in a distorted single-bond geometry to one Cs(1), one Cs(2), one Cs(3), and one Tl(1) atom. In the second Br site, Br(2) is bonded in a distorted single-bond geometry to one Cs(1), one Cs(2), one Cs(3), and one Tl(1) atom. In the third Br site, Br(3) is bonded in a distorted single-bond geometry to one Cs(1), one Cs(2), two equivalent Cs(3), and one Tl(2) atom. In the fourth Br site, Br(4) is bonded to one Cs(2), one Cs(3), two equivalent Cs(1), and one Tl(2) atom to form distorted BrCs4Tl square pyramids that share corners with three equivalent Br(8)Cs4Tl2 octahedra, corners with two equivalent Br(4)Cs4Tl square pyramids,  an edgeedge with one Br(8)Cs4Tl2 octahedra, edges with two equivalent Br(5)Cs4Tl square pyramids,  a faceface with one Br(8)Cs4Tl2 octahedra, and  a faceface with one Br(5)Cs4Tl square pyramid. The corner-sharing octahedral tilt angles range from 1-60°. In the fifth Br site, Br(5) is bonded to one Cs(2), one Cs(3), two equivalent Cs(1), and one Tl(2) atom to form distorted BrCs4Tl square pyramids that share corners with three equivalent Br(8)Cs4Tl2 octahedra, corners with two equivalent Br(5)Cs4Tl square pyramids,  an edgeedge with one Br(8)Cs4Tl2 octahedra, edges with two equivalent Br(4)Cs4Tl square pyramids,  a faceface with one Br(8)Cs4Tl2 octahedra, and  a faceface with one Br(4)Cs4Tl square pyramid. The corner-sharing octahedral tilt angles range from 2-61°. In the sixth Br site, Br(6) is bonded in a distorted single-bond geometry to one Cs(3), three equivalent Cs(2), and one Tl(1) atom. In the seventh Br site, Br(7) is bonded in a distorted single-bond geometry to one Cs(3), three equivalent Cs(1), and one Tl(2) atom. In the eighth Br site, Br(8) is bonded to two equivalent Cs(1), two equivalent Cs(3), and two equivalent Tl(2) atoms to form distorted BrCs4Tl2 octahedra that share corners with three equivalent Br(4)Cs4Tl square pyramids, corners with three equivalent Br(5)Cs4Tl square pyramids,  an edgeedge with one Br(4)Cs4Tl square pyramid,  an edgeedge with one Br(5)Cs4Tl square pyramid, faces with two equivalent Br(8)Cs4Tl2 octahedra,  a faceface with one Br(4)Cs4Tl square pyramid, and  a faceface with one Br(5)Cs4Tl square pyramid. In the ninth Br site, Br(9) is bonded in a 3-coordinate geometry to one Cs(2), one Cs(3), and one Tl(1) atom.