Ba8CaU4Y2O24 crystallizes in the tetragonal I4/mmm space group. Ba(1) is bonded to one O(1), one O(2), two equivalent O(3), two equivalent O(4), two equivalent O(5), and four equivalent O(6) atoms to form BaO12 cuboctahedra that share corners with twelve equivalent Ba(1)O12 cuboctahedra, faces with six equivalent Ba(1)O12 cuboctahedra,  a faceface with one Ca(1)O6 octahedra, faces with two equivalent U(1)O6 octahedra, faces with two equivalent U(2)O6 octahedra, and faces with two equivalent Y(1)O6 octahedra. Ca(1) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form CaO6 octahedra that share corners with two equivalent U(1)O6 octahedra, corners with four equivalent U(2)O6 octahedra, and faces with eight equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. There are two inequivalent U sites. In the first U site, U(1) is bonded to one O(1), one O(2), and four equivalent O(6) atoms to form UO6 octahedra that share  a cornercorner with one Ca(1)O6 octahedra, corners with four equivalent Y(1)O6 octahedra, and faces with eight equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-2°. In the second U site, U(2) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms to form UO6 octahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Y(1)O6 octahedra, and faces with eight equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. Y(1) is bonded to two equivalent O(5) and four equivalent O(6) atoms to form YO6 octahedra that share corners with two equivalent U(2)O6 octahedra, corners with four equivalent U(1)O6 octahedra, and faces with eight equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-2°. There are six inequivalent O sites. In the first O site, O(2) is bonded in a distorted linear geometry to four equivalent Ba(1), one Ca(1), and one U(1) atom. In the second O site, O(3) is bonded in a distorted single-bond geometry to four equivalent Ba(1) and one U(2) atom. In the third O site, O(4) is bonded in a distorted linear geometry to four equivalent Ba(1), one Ca(1), and one U(2) atom. In the fourth O site, O(5) is bonded in a distorted linear geometry to four equivalent Ba(1), one U(2), and one Y(1) atom. In the fifth O site, O(6) is bonded in a distorted linear geometry to four equivalent Ba(1), one U(1), and one Y(1) atom. In the sixth O site, O(1) is bonded in a distorted single-bond geometry to four equivalent Ba(1) and one U(1) atom.
Ba8CaU4Y2O24 crystallizes in the tetragonal I4/mmm space group. Ba(1) is bonded to one O(1), one O(2), two equivalent O(3), two equivalent O(4), two equivalent O(5), and four equivalent O(6) atoms to form BaO12 cuboctahedra that share corners with twelve equivalent Ba(1)O12 cuboctahedra, faces with six equivalent Ba(1)O12 cuboctahedra,  a faceface with one Ca(1)O6 octahedra, faces with two equivalent U(1)O6 octahedra, faces with two equivalent U(2)O6 octahedra, and faces with two equivalent Y(1)O6 octahedra. The Ba(1)-O(1) bond length is 2.99 Å. The Ba(1)-O(2) bond length is 3.25 Å. Both Ba(1)-O(3) bond lengths are 2.96 Å. Both Ba(1)-O(4) bond lengths are 3.09 Å. Both Ba(1)-O(5) bond lengths are 3.10 Å. There are two shorter (3.12 Å) and two longer (3.28 Å) Ba(1)-O(6) bond lengths. Ca(1) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form CaO6 octahedra that share corners with two equivalent U(1)O6 octahedra, corners with four equivalent U(2)O6 octahedra, and faces with eight equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. Both Ca(1)-O(2) bond lengths are 2.32 Å. All Ca(1)-O(4) bond lengths are 2.29 Å. There are two inequivalent U sites. In the first U site, U(1) is bonded to one O(1), one O(2), and four equivalent O(6) atoms to form UO6 octahedra that share  a cornercorner with one Ca(1)O6 octahedra, corners with four equivalent Y(1)O6 octahedra, and faces with eight equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-2°. The U(1)-O(1) bond length is 2.01 Å. The U(1)-O(2) bond length is 2.03 Å. All U(1)-O(6) bond lengths are 2.13 Å. In the second U site, U(2) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms to form UO6 octahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Y(1)O6 octahedra, and faces with eight equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. Both U(2)-O(3) bond lengths are 2.01 Å. Both U(2)-O(4) bond lengths are 2.10 Å. Both U(2)-O(5) bond lengths are 2.16 Å. Y(1) is bonded to two equivalent O(5) and four equivalent O(6) atoms to form YO6 octahedra that share corners with two equivalent U(2)O6 octahedra, corners with four equivalent U(1)O6 octahedra, and faces with eight equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-2°. Both Y(1)-O(5) bond lengths are 2.25 Å. All Y(1)-O(6) bond lengths are 2.25 Å. There are six inequivalent O sites. In the first O site, O(2) is bonded in a distorted linear geometry to four equivalent Ba(1), one Ca(1), and one U(1) atom. In the second O site, O(3) is bonded in a distorted single-bond geometry to four equivalent Ba(1) and one U(2) atom. In the third O site, O(4) is bonded in a distorted linear geometry to four equivalent Ba(1), one Ca(1), and one U(2) atom. In the fourth O site, O(5) is bonded in a distorted linear geometry to four equivalent Ba(1), one U(2), and one Y(1) atom. In the fifth O site, O(6) is bonded in a distorted linear geometry to four equivalent Ba(1), one U(1), and one Y(1) atom. In the sixth O site, O(1) is bonded in a distorted single-bond geometry to four equivalent Ba(1) and one U(1) atom.