Ba3YI9 crystallizes in the monoclinic Pc space group. There are six inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to one I(1), one I(10), one I(13), one I(14), one I(4), one I(5), and one I(9) atom to form distorted BaI7 pentagonal bipyramids that share corners with two equivalent Y(2)I7 pentagonal bipyramids and  an edgeedge with one Ba(3)I7 pentagonal bipyramid. In the second Ba site, Ba(2) is bonded in a 8-coordinate geometry to one I(11), one I(12), one I(15), one I(2), one I(3), one I(6), one I(7), and one I(8) atom. In the third Ba site, Ba(3) is bonded to one I(12), one I(13), one I(17), one I(18), one I(3), one I(8), and one I(9) atom to form distorted BaI7 pentagonal bipyramids that share corners with two equivalent Y(2)I7 pentagonal bipyramids,  an edgeedge with one Ba(1)I7 pentagonal bipyramid, and edges with two equivalent Y(2)I7 pentagonal bipyramids. In the fourth Ba site, Ba(4) is bonded in a 8-coordinate geometry to one I(1), one I(10), one I(11), one I(14), one I(15), one I(16), one I(2), and one I(7) atom. In the fifth Ba site, Ba(5) is bonded in a 8-coordinate geometry to one I(11), one I(12), one I(15), one I(16), one I(17), one I(2), one I(3), and one I(6) atom. In the sixth Ba site, Ba(6) is bonded in a 7-coordinate geometry to one I(1), one I(10), one I(13), one I(14), one I(18), one I(4), and one I(5) atom. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 8-coordinate geometry to one I(1), one I(10), one I(11), one I(16), one I(2), one I(5), one I(6), and one I(7) atom. In the second Y site, Y(2) is bonded to one I(12), one I(17), one I(18), one I(3), one I(4), one I(8), and one I(9) atom to form distorted YI7 pentagonal bipyramids that share corners with two equivalent Ba(1)I7 pentagonal bipyramids, corners with two equivalent Ba(3)I7 pentagonal bipyramids, and edges with two equivalent Ba(3)I7 pentagonal bipyramids. There are eighteen inequivalent I sites. In the first I site, I(1) is bonded to one Ba(1), one Ba(4), one Ba(6), and one Y(1) atom to form edge-sharing IBa3Y tetrahedra. In the second I site, I(2) is bonded to one Ba(2), one Ba(4), one Ba(5), and one Y(1) atom to form a mixture of edge and corner-sharing IBa3Y tetrahedra. In the third I site, I(3) is bonded to one Ba(2), one Ba(3), one Ba(5), and one Y(2) atom to form edge-sharing IBa3Y tetrahedra. In the fourth I site, I(4) is bonded in a distorted trigonal non-coplanar geometry to one Ba(1), one Ba(6), and one Y(2) atom. In the fifth I site, I(5) is bonded in a trigonal planar geometry to one Ba(1), one Ba(6), and one Y(1) atom. In the sixth I site, I(6) is bonded in a trigonal non-coplanar geometry to one Ba(2), one Ba(5), and one Y(1) atom. In the seventh I site, I(7) is bonded in a 3-coordinate geometry to one Ba(2), one Ba(4), and one Y(1) atom. In the eighth I site, I(8) is bonded in a distorted trigonal planar geometry to one Ba(2), one Ba(3), and one Y(2) atom. In the ninth I site, I(9) is bonded in a distorted trigonal non-coplanar geometry to one Ba(1), one Ba(3), and one Y(2) atom. In the tenth I site, I(10) is bonded to one Ba(1), one Ba(4), one Ba(6), and one Y(1) atom to form a mixture of distorted edge and corner-sharing IBa3Y tetrahedra. In the eleventh I site, I(11) is bonded in a distorted rectangular see-saw-like geometry to one Ba(2), one Ba(4), one Ba(5), and one Y(1) atom. In the twelfth I site, I(12) is bonded to one Ba(2), one Ba(3), one Ba(5), and one Y(2) atom to form a mixture of distorted edge and corner-sharing IBa3Y tetrahedra. In the thirteenth I site, I(13) is bonded in a trigonal non-coplanar geometry to one Ba(1), one Ba(3), and one Ba(6) atom. In the fourteenth I site, I(14) is bonded in a trigonal planar geometry to one Ba(1), one Ba(4), and one Ba(6) atom. In the fifteenth I site, I(15) is bonded in a distorted trigonal non-coplanar geometry to one Ba(2), one Ba(4), and one Ba(5) atom. In the sixteenth I site, I(16) is bonded in a distorted trigonal non-coplanar geometry to one Ba(4), one Ba(5), and one Y(1) atom. In the seventeenth I site, I(17) is bonded in a trigonal planar geometry to one Ba(3), one Ba(5), and one Y(2) atom. In the eighteenth I site, I(18) is bonded in a trigonal non-coplanar geometry to one Ba(3), one Ba(6), and one Y(2) atom.
Ba3YI9 crystallizes in the monoclinic Pc space group. There are six inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to one I(1), one I(10), one I(13), one I(14), one I(4), one I(5), and one I(9) atom to form distorted BaI7 pentagonal bipyramids that share corners with two equivalent Y(2)I7 pentagonal bipyramids and  an edgeedge with one Ba(3)I7 pentagonal bipyramid. The Ba(1)-I(1) bond length is 3.59 Å. The Ba(1)-I(10) bond length is 3.61 Å. The Ba(1)-I(13) bond length is 3.47 Å. The Ba(1)-I(14) bond length is 3.45 Å. The Ba(1)-I(4) bond length is 3.54 Å. The Ba(1)-I(5) bond length is 3.52 Å. The Ba(1)-I(9) bond length is 3.62 Å. In the second Ba site, Ba(2) is bonded in a 8-coordinate geometry to one I(11), one I(12), one I(15), one I(2), one I(3), one I(6), one I(7), and one I(8) atom. The Ba(2)-I(11) bond length is 3.60 Å. The Ba(2)-I(12) bond length is 3.63 Å. The Ba(2)-I(15) bond length is 3.44 Å. The Ba(2)-I(2) bond length is 3.53 Å. The Ba(2)-I(3) bond length is 3.57 Å. The Ba(2)-I(6) bond length is 3.44 Å. The Ba(2)-I(7) bond length is 3.80 Å. The Ba(2)-I(8) bond length is 3.65 Å. In the third Ba site, Ba(3) is bonded to one I(12), one I(13), one I(17), one I(18), one I(3), one I(8), and one I(9) atom to form distorted BaI7 pentagonal bipyramids that share corners with two equivalent Y(2)I7 pentagonal bipyramids,  an edgeedge with one Ba(1)I7 pentagonal bipyramid, and edges with two equivalent Y(2)I7 pentagonal bipyramids. The Ba(3)-I(12) bond length is 3.56 Å. The Ba(3)-I(13) bond length is 3.42 Å. The Ba(3)-I(17) bond length is 3.55 Å. The Ba(3)-I(18) bond length is 3.55 Å. The Ba(3)-I(3) bond length is 3.63 Å. The Ba(3)-I(8) bond length is 3.62 Å. The Ba(3)-I(9) bond length is 3.63 Å. In the fourth Ba site, Ba(4) is bonded in a 8-coordinate geometry to one I(1), one I(10), one I(11), one I(14), one I(15), one I(16), one I(2), and one I(7) atom. The Ba(4)-I(1) bond length is 3.60 Å. The Ba(4)-I(10) bond length is 3.74 Å. The Ba(4)-I(11) bond length is 3.57 Å. The Ba(4)-I(14) bond length is 3.45 Å. The Ba(4)-I(15) bond length is 3.84 Å. The Ba(4)-I(16) bond length is 3.55 Å. The Ba(4)-I(2) bond length is 3.53 Å. The Ba(4)-I(7) bond length is 3.49 Å. In the fifth Ba site, Ba(5) is bonded in a 8-coordinate geometry to one I(11), one I(12), one I(15), one I(16), one I(17), one I(2), one I(3), and one I(6) atom. The Ba(5)-I(11) bond length is 3.62 Å. The Ba(5)-I(12) bond length is 3.67 Å. The Ba(5)-I(15) bond length is 3.49 Å. The Ba(5)-I(16) bond length is 3.76 Å. The Ba(5)-I(17) bond length is 3.58 Å. The Ba(5)-I(2) bond length is 3.65 Å. The Ba(5)-I(3) bond length is 3.74 Å. The Ba(5)-I(6) bond length is 3.42 Å. In the sixth Ba site, Ba(6) is bonded in a 7-coordinate geometry to one I(1), one I(10), one I(13), one I(14), one I(18), one I(4), and one I(5) atom. The Ba(6)-I(1) bond length is 3.56 Å. The Ba(6)-I(10) bond length is 3.78 Å. The Ba(6)-I(13) bond length is 3.42 Å. The Ba(6)-I(14) bond length is 3.40 Å. The Ba(6)-I(18) bond length is 3.59 Å. The Ba(6)-I(4) bond length is 3.56 Å. The Ba(6)-I(5) bond length is 3.51 Å. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 8-coordinate geometry to one I(1), one I(10), one I(11), one I(16), one I(2), one I(5), one I(6), and one I(7) atom. The Y(1)-I(1) bond length is 3.41 Å. The Y(1)-I(10) bond length is 3.35 Å. The Y(1)-I(11) bond length is 3.33 Å. The Y(1)-I(16) bond length is 3.08 Å. The Y(1)-I(2) bond length is 3.30 Å. The Y(1)-I(5) bond length is 3.23 Å. The Y(1)-I(6) bond length is 3.43 Å. The Y(1)-I(7) bond length is 3.06 Å. In the second Y site, Y(2) is bonded to one I(12), one I(17), one I(18), one I(3), one I(4), one I(8), and one I(9) atom to form distorted YI7 pentagonal bipyramids that share corners with two equivalent Ba(1)I7 pentagonal bipyramids, corners with two equivalent Ba(3)I7 pentagonal bipyramids, and edges with two equivalent Ba(3)I7 pentagonal bipyramids. The Y(2)-I(12) bond length is 3.42 Å. The Y(2)-I(17) bond length is 3.13 Å. The Y(2)-I(18) bond length is 3.17 Å. The Y(2)-I(3) bond length is 3.25 Å. The Y(2)-I(4) bond length is 3.11 Å. The Y(2)-I(8) bond length is 3.13 Å. The Y(2)-I(9) bond length is 3.11 Å. There are eighteen inequivalent I sites. In the first I site, I(1) is bonded to one Ba(1), one Ba(4), one Ba(6), and one Y(1) atom to form edge-sharing IBa3Y tetrahedra. In the second I site, I(2) is bonded to one Ba(2), one Ba(4), one Ba(5), and one Y(1) atom to form a mixture of edge and corner-sharing IBa3Y tetrahedra. In the third I site, I(3) is bonded to one Ba(2), one Ba(3), one Ba(5), and one Y(2) atom to form edge-sharing IBa3Y tetrahedra. In the fourth I site, I(4) is bonded in a distorted trigonal non-coplanar geometry to one Ba(1), one Ba(6), and one Y(2) atom. In the fifth I site, I(5) is bonded in a trigonal planar geometry to one Ba(1), one Ba(6), and one Y(1) atom. In the sixth I site, I(6) is bonded in a trigonal non-coplanar geometry to one Ba(2), one Ba(5), and one Y(1) atom. In the seventh I site, I(7) is bonded in a 3-coordinate geometry to one Ba(2), one Ba(4), and one Y(1) atom. In the eighth I site, I(8) is bonded in a distorted trigonal planar geometry to one Ba(2), one Ba(3), and one Y(2) atom. In the ninth I site, I(9) is bonded in a distorted trigonal non-coplanar geometry to one Ba(1), one Ba(3), and one Y(2) atom. In the tenth I site, I(10) is bonded to one Ba(1), one Ba(4), one Ba(6), and one Y(1) atom to form a mixture of distorted edge and corner-sharing IBa3Y tetrahedra. In the eleventh I site, I(11) is bonded in a distorted rectangular see-saw-like geometry to one Ba(2), one Ba(4), one Ba(5), and one Y(1) atom. In the twelfth I site, I(12) is bonded to one Ba(2), one Ba(3), one Ba(5), and one Y(2) atom to form a mixture of distorted edge and corner-sharing IBa3Y tetrahedra. In the thirteenth I site, I(13) is bonded in a trigonal non-coplanar geometry to one Ba(1), one Ba(3), and one Ba(6) atom. In the fourteenth I site, I(14) is bonded in a trigonal planar geometry to one Ba(1), one Ba(4), and one Ba(6) atom. In the fifteenth I site, I(15) is bonded in a distorted trigonal non-coplanar geometry to one Ba(2), one Ba(4), and one Ba(5) atom. In the sixteenth I site, I(16) is bonded in a distorted trigonal non-coplanar geometry to one Ba(4), one Ba(5), and one Y(1) atom. In the seventeenth I site, I(17) is bonded in a trigonal planar geometry to one Ba(3), one Ba(5), and one Y(2) atom. In the eighteenth I site, I(18) is bonded in a trigonal non-coplanar geometry to one Ba(3), one Ba(6), and one Y(2) atom.