Sr3LaBr9 crystallizes in the monoclinic Pc space group. There are six inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to one Br(1), one Br(10), one Br(13), one Br(14), one Br(4), one Br(5), and one Br(9) atom to form distorted SrBr7 pentagonal bipyramids that share corners with two equivalent Sr(6)Br7 pentagonal bipyramids, corners with two equivalent La(2)Br7 pentagonal bipyramids,  an edgeedge with one Sr(3)Br7 pentagonal bipyramid, and edges with two equivalent Sr(6)Br7 pentagonal bipyramids. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to one Br(11), one Br(12), one Br(15), one Br(2), one Br(3), one Br(6), one Br(7), and one Br(8) atom. In the third Sr site, Sr(3) is bonded to one Br(12), one Br(13), one Br(17), one Br(18), one Br(3), one Br(8), and one Br(9) atom to form distorted SrBr7 pentagonal bipyramids that share corners with two equivalent Sr(6)Br7 pentagonal bipyramids, corners with two equivalent La(2)Br7 pentagonal bipyramids,  an edgeedge with one Sr(1)Br7 pentagonal bipyramid, and edges with two equivalent La(2)Br7 pentagonal bipyramids. In the fourth Sr site, Sr(4) is bonded in a 8-coordinate geometry to one Br(1), one Br(10), one Br(11), one Br(14), one Br(15), one Br(16), one Br(2), and one Br(7) atom. In the fifth Sr site, Sr(5) is bonded in a 8-coordinate geometry to one Br(11), one Br(12), one Br(15), one Br(16), one Br(17), one Br(2), one Br(3), and one Br(6) atom. In the sixth Sr site, Sr(6) is bonded to one Br(1), one Br(10), one Br(13), one Br(14), one Br(18), one Br(4), and one Br(5) atom to form distorted SrBr7 pentagonal bipyramids that share corners with two equivalent Sr(1)Br7 pentagonal bipyramids, corners with two equivalent Sr(3)Br7 pentagonal bipyramids,  an edgeedge with one La(2)Br7 pentagonal bipyramid, and edges with two equivalent Sr(1)Br7 pentagonal bipyramids. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 8-coordinate geometry to one Br(1), one Br(10), one Br(11), one Br(16), one Br(2), one Br(5), one Br(6), and one Br(7) atom. In the second La site, La(2) is bonded to one Br(12), one Br(17), one Br(18), one Br(3), one Br(4), one Br(8), and one Br(9) atom to form distorted LaBr7 pentagonal bipyramids that share corners with two equivalent Sr(1)Br7 pentagonal bipyramids, corners with two equivalent Sr(3)Br7 pentagonal bipyramids,  an edgeedge with one Sr(6)Br7 pentagonal bipyramid, and edges with two equivalent Sr(3)Br7 pentagonal bipyramids. There are eighteen inequivalent Br sites. In the first Br site, Br(1) is bonded to one Sr(1), one Sr(4), one Sr(6), and one La(1) atom to form a mixture of corner and edge-sharing BrSr3La tetrahedra. In the second Br site, Br(2) is bonded to one Sr(2), one Sr(4), one Sr(5), and one La(1) atom to form a mixture of distorted corner and edge-sharing BrSr3La tetrahedra. In the third Br site, Br(3) is bonded to one Sr(2), one Sr(3), one Sr(5), and one La(2) atom to form a mixture of corner and edge-sharing BrSr3La tetrahedra. In the fourth Br site, Br(4) is bonded in a trigonal non-coplanar geometry to one Sr(1), one Sr(6), and one La(2) atom. In the fifth Br site, Br(5) is bonded in a trigonal planar geometry to one Sr(1), one Sr(6), and one La(1) atom. In the sixth Br site, Br(6) is bonded in a distorted trigonal non-coplanar geometry to one Sr(2), one Sr(5), and one La(1) atom. In the seventh Br site, Br(7) is bonded in a distorted trigonal non-coplanar geometry to one Sr(2), one Sr(4), and one La(1) atom. In the eighth Br site, Br(8) is bonded in a trigonal planar geometry to one Sr(2), one Sr(3), and one La(2) atom. In the ninth Br site, Br(9) is bonded in a trigonal non-coplanar geometry to one Sr(1), one Sr(3), and one La(2) atom. In the tenth Br site, Br(10) is bonded to one Sr(1), one Sr(4), one Sr(6), and one La(1) atom to form a mixture of corner and edge-sharing BrSr3La tetrahedra. In the eleventh Br site, Br(11) is bonded to one Sr(2), one Sr(4), one Sr(5), and one La(1) atom to form a mixture of corner and edge-sharing BrSr3La tetrahedra. In the twelfth Br site, Br(12) is bonded to one Sr(2), one Sr(3), one Sr(5), and one La(2) atom to form a mixture of corner and edge-sharing BrSr3La tetrahedra. In the thirteenth Br site, Br(13) is bonded in a trigonal non-coplanar geometry to one Sr(1), one Sr(3), and one Sr(6) atom. In the fourteenth Br site, Br(14) is bonded in a trigonal planar geometry to one Sr(1), one Sr(4), and one Sr(6) atom. In the fifteenth Br site, Br(15) is bonded in a distorted trigonal non-coplanar geometry to one Sr(2), one Sr(4), and one Sr(5) atom. In the sixteenth Br site, Br(16) is bonded in a distorted trigonal non-coplanar geometry to one Sr(4), one Sr(5), and one La(1) atom. In the seventeenth Br site, Br(17) is bonded in a trigonal planar geometry to one Sr(3), one Sr(5), and one La(2) atom. In the eighteenth Br site, Br(18) is bonded in a trigonal non-coplanar geometry to one Sr(3), one Sr(6), and one La(2) atom.
Sr3LaBr9 crystallizes in the monoclinic Pc space group. There are six inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to one Br(1), one Br(10), one Br(13), one Br(14), one Br(4), one Br(5), and one Br(9) atom to form distorted SrBr7 pentagonal bipyramids that share corners with two equivalent Sr(6)Br7 pentagonal bipyramids, corners with two equivalent La(2)Br7 pentagonal bipyramids,  an edgeedge with one Sr(3)Br7 pentagonal bipyramid, and edges with two equivalent Sr(6)Br7 pentagonal bipyramids. The Sr(1)-Br(1) bond length is 3.30 Å. The Sr(1)-Br(10) bond length is 3.20 Å. The Sr(1)-Br(13) bond length is 3.12 Å. The Sr(1)-Br(14) bond length is 3.09 Å. The Sr(1)-Br(4) bond length is 3.15 Å. The Sr(1)-Br(5) bond length is 3.15 Å. The Sr(1)-Br(9) bond length is 3.17 Å. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to one Br(11), one Br(12), one Br(15), one Br(2), one Br(3), one Br(6), one Br(7), and one Br(8) atom. The Sr(2)-Br(11) bond length is 3.23 Å. The Sr(2)-Br(12) bond length is 3.30 Å. The Sr(2)-Br(15) bond length is 3.05 Å. The Sr(2)-Br(2) bond length is 3.21 Å. The Sr(2)-Br(3) bond length is 3.25 Å. The Sr(2)-Br(6) bond length is 3.07 Å. The Sr(2)-Br(7) bond length is 3.37 Å. The Sr(2)-Br(8) bond length is 3.21 Å. In the third Sr site, Sr(3) is bonded to one Br(12), one Br(13), one Br(17), one Br(18), one Br(3), one Br(8), and one Br(9) atom to form distorted SrBr7 pentagonal bipyramids that share corners with two equivalent Sr(6)Br7 pentagonal bipyramids, corners with two equivalent La(2)Br7 pentagonal bipyramids,  an edgeedge with one Sr(1)Br7 pentagonal bipyramid, and edges with two equivalent La(2)Br7 pentagonal bipyramids. The Sr(3)-Br(12) bond length is 3.22 Å. The Sr(3)-Br(13) bond length is 3.08 Å. The Sr(3)-Br(17) bond length is 3.13 Å. The Sr(3)-Br(18) bond length is 3.14 Å. The Sr(3)-Br(3) bond length is 3.29 Å. The Sr(3)-Br(8) bond length is 3.17 Å. The Sr(3)-Br(9) bond length is 3.20 Å. In the fourth Sr site, Sr(4) is bonded in a 8-coordinate geometry to one Br(1), one Br(10), one Br(11), one Br(14), one Br(15), one Br(16), one Br(2), and one Br(7) atom. The Sr(4)-Br(1) bond length is 3.22 Å. The Sr(4)-Br(10) bond length is 3.35 Å. The Sr(4)-Br(11) bond length is 3.24 Å. The Sr(4)-Br(14) bond length is 3.11 Å. The Sr(4)-Br(15) bond length is 3.52 Å. The Sr(4)-Br(16) bond length is 3.12 Å. The Sr(4)-Br(2) bond length is 3.17 Å. The Sr(4)-Br(7) bond length is 3.08 Å. In the fifth Sr site, Sr(5) is bonded in a 8-coordinate geometry to one Br(11), one Br(12), one Br(15), one Br(16), one Br(17), one Br(2), one Br(3), and one Br(6) atom. The Sr(5)-Br(11) bond length is 3.21 Å. The Sr(5)-Br(12) bond length is 3.29 Å. The Sr(5)-Br(15) bond length is 3.06 Å. The Sr(5)-Br(16) bond length is 3.38 Å. The Sr(5)-Br(17) bond length is 3.19 Å. The Sr(5)-Br(2) bond length is 3.31 Å. The Sr(5)-Br(3) bond length is 3.39 Å. The Sr(5)-Br(6) bond length is 3.06 Å. In the sixth Sr site, Sr(6) is bonded to one Br(1), one Br(10), one Br(13), one Br(14), one Br(18), one Br(4), and one Br(5) atom to form distorted SrBr7 pentagonal bipyramids that share corners with two equivalent Sr(1)Br7 pentagonal bipyramids, corners with two equivalent Sr(3)Br7 pentagonal bipyramids,  an edgeedge with one La(2)Br7 pentagonal bipyramid, and edges with two equivalent Sr(1)Br7 pentagonal bipyramids. The Sr(6)-Br(1) bond length is 3.22 Å. The Sr(6)-Br(10) bond length is 3.38 Å. The Sr(6)-Br(13) bond length is 3.07 Å. The Sr(6)-Br(14) bond length is 3.06 Å. The Sr(6)-Br(18) bond length is 3.19 Å. The Sr(6)-Br(4) bond length is 3.17 Å. The Sr(6)-Br(5) bond length is 3.15 Å. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 8-coordinate geometry to one Br(1), one Br(10), one Br(11), one Br(16), one Br(2), one Br(5), one Br(6), and one Br(7) atom. The La(1)-Br(1) bond length is 3.19 Å. The La(1)-Br(10) bond length is 3.14 Å. The La(1)-Br(11) bond length is 3.15 Å. The La(1)-Br(16) bond length is 2.97 Å. The La(1)-Br(2) bond length is 3.13 Å. The La(1)-Br(5) bond length is 3.08 Å. The La(1)-Br(6) bond length is 3.24 Å. The La(1)-Br(7) bond length is 2.96 Å. In the second La site, La(2) is bonded to one Br(12), one Br(17), one Br(18), one Br(3), one Br(4), one Br(8), and one Br(9) atom to form distorted LaBr7 pentagonal bipyramids that share corners with two equivalent Sr(1)Br7 pentagonal bipyramids, corners with two equivalent Sr(3)Br7 pentagonal bipyramids,  an edgeedge with one Sr(6)Br7 pentagonal bipyramid, and edges with two equivalent Sr(3)Br7 pentagonal bipyramids. The La(2)-Br(12) bond length is 3.18 Å. The La(2)-Br(17) bond length is 3.01 Å. The La(2)-Br(18) bond length is 3.04 Å. The La(2)-Br(3) bond length is 3.10 Å. The La(2)-Br(4) bond length is 3.01 Å. The La(2)-Br(8) bond length is 3.00 Å. The La(2)-Br(9) bond length is 3.00 Å. There are eighteen inequivalent Br sites. In the first Br site, Br(1) is bonded to one Sr(1), one Sr(4), one Sr(6), and one La(1) atom to form a mixture of corner and edge-sharing BrSr3La tetrahedra. In the second Br site, Br(2) is bonded to one Sr(2), one Sr(4), one Sr(5), and one La(1) atom to form a mixture of distorted corner and edge-sharing BrSr3La tetrahedra. In the third Br site, Br(3) is bonded to one Sr(2), one Sr(3), one Sr(5), and one La(2) atom to form a mixture of corner and edge-sharing BrSr3La tetrahedra. In the fourth Br site, Br(4) is bonded in a trigonal non-coplanar geometry to one Sr(1), one Sr(6), and one La(2) atom. In the fifth Br site, Br(5) is bonded in a trigonal planar geometry to one Sr(1), one Sr(6), and one La(1) atom. In the sixth Br site, Br(6) is bonded in a distorted trigonal non-coplanar geometry to one Sr(2), one Sr(5), and one La(1) atom. In the seventh Br site, Br(7) is bonded in a distorted trigonal non-coplanar geometry to one Sr(2), one Sr(4), and one La(1) atom. In the eighth Br site, Br(8) is bonded in a trigonal planar geometry to one Sr(2), one Sr(3), and one La(2) atom. In the ninth Br site, Br(9) is bonded in a trigonal non-coplanar geometry to one Sr(1), one Sr(3), and one La(2) atom. In the tenth Br site, Br(10) is bonded to one Sr(1), one Sr(4), one Sr(6), and one La(1) atom to form a mixture of corner and edge-sharing BrSr3La tetrahedra. In the eleventh Br site, Br(11) is bonded to one Sr(2), one Sr(4), one Sr(5), and one La(1) atom to form a mixture of corner and edge-sharing BrSr3La tetrahedra. In the twelfth Br site, Br(12) is bonded to one Sr(2), one Sr(3), one Sr(5), and one La(2) atom to form a mixture of corner and edge-sharing BrSr3La tetrahedra. In the thirteenth Br site, Br(13) is bonded in a trigonal non-coplanar geometry to one Sr(1), one Sr(3), and one Sr(6) atom. In the fourteenth Br site, Br(14) is bonded in a trigonal planar geometry to one Sr(1), one Sr(4), and one Sr(6) atom. In the fifteenth Br site, Br(15) is bonded in a distorted trigonal non-coplanar geometry to one Sr(2), one Sr(4), and one Sr(5) atom. In the sixteenth Br site, Br(16) is bonded in a distorted trigonal non-coplanar geometry to one Sr(4), one Sr(5), and one La(1) atom. In the seventeenth Br site, Br(17) is bonded in a trigonal planar geometry to one Sr(3), one Sr(5), and one La(2) atom. In the eighteenth Br site, Br(18) is bonded in a trigonal non-coplanar geometry to one Sr(3), one Sr(6), and one La(2) atom.