Cs3LaBr6 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 8-coordinate geometry to one Br(1), one Br(3), one Br(5), one Br(6), two equivalent Br(2), and two equivalent Br(4) atoms. In the second Cs site, Cs(2) is bonded in a 9-coordinate geometry to one Br(2), one Br(3), two equivalent Br(1), two equivalent Br(5), and three equivalent Br(6) atoms. In the third Cs site, Cs(3) is bonded in a 8-coordinate geometry to one Br(1), one Br(2), one Br(5), one Br(6), two equivalent Br(3), and two equivalent Br(4) atoms. There are two inequivalent La sites. In the first La site, La(1) is bonded in an octahedral geometry to two equivalent Br(2), two equivalent Br(3), and two equivalent Br(4) atoms. In the second La site, La(2) is bonded in an octahedral geometry to two equivalent Br(1), two equivalent Br(5), and two equivalent Br(6) atoms. There are six inequivalent Br sites. In the first Br site, Br(5) is bonded in a 5-coordinate geometry to one Cs(1), one Cs(3), two equivalent Cs(2), and one La(2) atom. In the second Br site, Br(6) is bonded to one Cs(1), one Cs(3), three equivalent Cs(2), and one La(2) atom to form distorted BrCs5La octahedra that share corners with five equivalent Br(6)Cs5La octahedra, corners with two equivalent Br(1)Cs4La square pyramids,  a cornercorner with one Br(3)Cs4La trigonal bipyramid,  an edgeedge with one Br(6)Cs5La octahedra,  an edgeedge with one Br(1)Cs4La square pyramid,  an edgeedge with one Br(3)Cs4La trigonal bipyramid, faces with two equivalent Br(1)Cs4La square pyramids, and  a faceface with one Br(3)Cs4La trigonal bipyramid. The corner-sharing octahedral tilt angles range from 0-54°. In the third Br site, Br(1) is bonded to one Cs(1), one Cs(3), two equivalent Cs(2), and one La(2) atom to form distorted BrCs4La square pyramids that share corners with two equivalent Br(6)Cs5La octahedra, corners with three equivalent Br(1)Cs4La square pyramids, corners with two equivalent Br(3)Cs4La trigonal bipyramids,  an edgeedge with one Br(6)Cs5La octahedra, faces with two equivalent Br(6)Cs5La octahedra, and  a faceface with one Br(3)Cs4La trigonal bipyramid. The corner-sharing octahedral tilt angles range from 47-54°. In the fourth Br site, Br(2) is bonded in a 5-coordinate geometry to one Cs(2), one Cs(3), two equivalent Cs(1), and one La(1) atom. In the fifth Br site, Br(3) is bonded to one Cs(1), one Cs(2), two equivalent Cs(3), and one La(1) atom to form distorted BrCs4La trigonal bipyramids that share  a cornercorner with one Br(6)Cs5La octahedra, corners with two equivalent Br(1)Cs4La square pyramids, corners with three equivalent Br(3)Cs4La trigonal bipyramids,  an edgeedge with one Br(6)Cs5La octahedra,  a faceface with one Br(6)Cs5La octahedra, and  a faceface with one Br(1)Cs4La square pyramid. The corner-sharing octahedral tilt angles are 22°. In the sixth Br site, Br(4) is bonded in a 5-coordinate geometry to two equivalent Cs(1), two equivalent Cs(3), and one La(1) atom.
Cs3LaBr6 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 8-coordinate geometry to one Br(1), one Br(3), one Br(5), one Br(6), two equivalent Br(2), and two equivalent Br(4) atoms. The Cs(1)-Br(1) bond length is 3.67 Å. The Cs(1)-Br(3) bond length is 3.58 Å. The Cs(1)-Br(5) bond length is 3.49 Å. The Cs(1)-Br(6) bond length is 4.17 Å. There is one shorter (3.88 Å) and one longer (3.92 Å) Cs(1)-Br(2) bond length. There is one shorter (3.67 Å) and one longer (3.69 Å) Cs(1)-Br(4) bond length. In the second Cs site, Cs(2) is bonded in a 9-coordinate geometry to one Br(2), one Br(3), two equivalent Br(1), two equivalent Br(5), and three equivalent Br(6) atoms. The Cs(2)-Br(2) bond length is 4.29 Å. The Cs(2)-Br(3) bond length is 3.87 Å. There is one shorter (3.85 Å) and one longer (3.95 Å) Cs(2)-Br(1) bond length. There is one shorter (3.70 Å) and one longer (4.07 Å) Cs(2)-Br(5) bond length. There are a spread of Cs(2)-Br(6) bond distances ranging from 3.76-4.05 Å. In the third Cs site, Cs(3) is bonded in a 8-coordinate geometry to one Br(1), one Br(2), one Br(5), one Br(6), two equivalent Br(3), and two equivalent Br(4) atoms. The Cs(3)-Br(1) bond length is 3.76 Å. The Cs(3)-Br(2) bond length is 3.63 Å. The Cs(3)-Br(5) bond length is 3.76 Å. The Cs(3)-Br(6) bond length is 3.71 Å. There is one shorter (3.81 Å) and one longer (3.93 Å) Cs(3)-Br(3) bond length. There is one shorter (3.63 Å) and one longer (3.66 Å) Cs(3)-Br(4) bond length. There are two inequivalent La sites. In the first La site, La(1) is bonded in an octahedral geometry to two equivalent Br(2), two equivalent Br(3), and two equivalent Br(4) atoms. Both La(1)-Br(2) bond lengths are 2.94 Å. Both La(1)-Br(3) bond lengths are 2.95 Å. Both La(1)-Br(4) bond lengths are 2.96 Å. In the second La site, La(2) is bonded in an octahedral geometry to two equivalent Br(1), two equivalent Br(5), and two equivalent Br(6) atoms. Both La(2)-Br(1) bond lengths are 2.91 Å. Both La(2)-Br(5) bond lengths are 2.92 Å. Both La(2)-Br(6) bond lengths are 2.98 Å. There are six inequivalent Br sites. In the first Br site, Br(5) is bonded in a 5-coordinate geometry to one Cs(1), one Cs(3), two equivalent Cs(2), and one La(2) atom. In the second Br site, Br(6) is bonded to one Cs(1), one Cs(3), three equivalent Cs(2), and one La(2) atom to form distorted BrCs5La octahedra that share corners with five equivalent Br(6)Cs5La octahedra, corners with two equivalent Br(1)Cs4La square pyramids,  a cornercorner with one Br(3)Cs4La trigonal bipyramid,  an edgeedge with one Br(6)Cs5La octahedra,  an edgeedge with one Br(1)Cs4La square pyramid,  an edgeedge with one Br(3)Cs4La trigonal bipyramid, faces with two equivalent Br(1)Cs4La square pyramids, and  a faceface with one Br(3)Cs4La trigonal bipyramid. The corner-sharing octahedral tilt angles range from 0-54°. In the third Br site, Br(1) is bonded to one Cs(1), one Cs(3), two equivalent Cs(2), and one La(2) atom to form distorted BrCs4La square pyramids that share corners with two equivalent Br(6)Cs5La octahedra, corners with three equivalent Br(1)Cs4La square pyramids, corners with two equivalent Br(3)Cs4La trigonal bipyramids,  an edgeedge with one Br(6)Cs5La octahedra, faces with two equivalent Br(6)Cs5La octahedra, and  a faceface with one Br(3)Cs4La trigonal bipyramid. The corner-sharing octahedral tilt angles range from 47-54°. In the fourth Br site, Br(2) is bonded in a 5-coordinate geometry to one Cs(2), one Cs(3), two equivalent Cs(1), and one La(1) atom. In the fifth Br site, Br(3) is bonded to one Cs(1), one Cs(2), two equivalent Cs(3), and one La(1) atom to form distorted BrCs4La trigonal bipyramids that share  a cornercorner with one Br(6)Cs5La octahedra, corners with two equivalent Br(1)Cs4La square pyramids, corners with three equivalent Br(3)Cs4La trigonal bipyramids,  an edgeedge with one Br(6)Cs5La octahedra,  a faceface with one Br(6)Cs5La octahedra, and  a faceface with one Br(1)Cs4La square pyramid. The corner-sharing octahedral tilt angles are 22°. In the sixth Br site, Br(4) is bonded in a 5-coordinate geometry to two equivalent Cs(1), two equivalent Cs(3), and one La(1) atom.