Ba3CaSb2O9 crystallizes in the monoclinic C2/c space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 10-coordinate geometry to two equivalent O(2), two equivalent O(3), two equivalent O(5), and four equivalent O(1) atoms. In the second Ba site, Ba(2) is bonded in a 12-coordinate geometry to one O(5), two equivalent O(1), three equivalent O(2), three equivalent O(3), and three equivalent O(4) atoms. Ca(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form CaO6 octahedra that share corners with six equivalent Sb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 11-22°. Sb(1) is bonded to one O(2), one O(3), one O(4), one O(5), and two equivalent O(1) atoms to form SbO6 octahedra that share corners with three equivalent Ca(1)O6 octahedra and  a faceface with one Sb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 11-22°. There are five inequivalent O sites. In the first O site, O(5) is bonded in a distorted L-shaped geometry to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Sb(1) atoms. In the second O site, O(1) is bonded in a 2-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Sb(1) atoms. In the third O site, O(2) is bonded in a 2-coordinate geometry to one Ba(1), three equivalent Ba(2), one Ca(1), and one Sb(1) atom. In the fourth O site, O(3) is bonded in a 2-coordinate geometry to one Ba(1), three equivalent Ba(2), one Ca(1), and one Sb(1) atom. In the fifth O site, O(4) is bonded in a 2-coordinate geometry to three equivalent Ba(2), one Ca(1), and one Sb(1) atom.
Ba3CaSb2O9 crystallizes in the monoclinic C2/c space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 10-coordinate geometry to two equivalent O(2), two equivalent O(3), two equivalent O(5), and four equivalent O(1) atoms. Both Ba(1)-O(2) bond lengths are 3.04 Å. Both Ba(1)-O(3) bond lengths are 2.72 Å. Both Ba(1)-O(5) bond lengths are 3.07 Å. There are two shorter (2.98 Å) and two longer (3.13 Å) Ba(1)-O(1) bond lengths. In the second Ba site, Ba(2) is bonded in a 12-coordinate geometry to one O(5), two equivalent O(1), three equivalent O(2), three equivalent O(3), and three equivalent O(4) atoms. The Ba(2)-O(5) bond length is 3.11 Å. There is one shorter (2.91 Å) and one longer (3.38 Å) Ba(2)-O(1) bond length. There are a spread of Ba(2)-O(2) bond distances ranging from 2.85-3.26 Å. There are a spread of Ba(2)-O(3) bond distances ranging from 2.93-3.48 Å. There are a spread of Ba(2)-O(4) bond distances ranging from 2.87-3.22 Å. Ca(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form CaO6 octahedra that share corners with six equivalent Sb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 11-22°. Both Ca(1)-O(2) bond lengths are 2.30 Å. Both Ca(1)-O(3) bond lengths are 2.29 Å. Both Ca(1)-O(4) bond lengths are 2.31 Å. Sb(1) is bonded to one O(2), one O(3), one O(4), one O(5), and two equivalent O(1) atoms to form SbO6 octahedra that share corners with three equivalent Ca(1)O6 octahedra and  a faceface with one Sb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 11-22°. The Sb(1)-O(2) bond length is 1.96 Å. The Sb(1)-O(3) bond length is 1.96 Å. The Sb(1)-O(4) bond length is 1.96 Å. The Sb(1)-O(5) bond length is 2.11 Å. There is one shorter (2.08 Å) and one longer (2.14 Å) Sb(1)-O(1) bond length. There are five inequivalent O sites. In the first O site, O(5) is bonded in a distorted L-shaped geometry to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Sb(1) atoms. In the second O site, O(1) is bonded in a 2-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Sb(1) atoms. In the third O site, O(2) is bonded in a 2-coordinate geometry to one Ba(1), three equivalent Ba(2), one Ca(1), and one Sb(1) atom. In the fourth O site, O(3) is bonded in a 2-coordinate geometry to one Ba(1), three equivalent Ba(2), one Ca(1), and one Sb(1) atom. In the fifth O site, O(4) is bonded in a 2-coordinate geometry to three equivalent Ba(2), one Ca(1), and one Sb(1) atom.