Ca3(CaTa2)O9 crystallizes in the triclinic P-1 space group. There are five inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 3-coordinate geometry to one O(1), one O(2), one O(4), one O(6), one O(7), and one O(9) atom. In the second Ca site, Ca(2) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(9) atoms to form CaO6 octahedra that share corners with six equivalent Ca(4)O6 octahedra and corners with six equivalent Ta(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 41-62°. In the third Ca site, Ca(3) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(8) atoms to form CaO6 octahedra that share corners with six equivalent Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 35-37°. In the fourth Ca site, Ca(4) is bonded to one O(1), one O(2), one O(4), one O(6), one O(7), and one O(9) atom to form distorted CaO6 octahedra that share corners with three equivalent Ca(2)O6 octahedra, corners with three equivalent Ta(1)O6 octahedra, and edges with three equivalent Ta(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 29-62°. In the fifth Ca site, Ca(5) is bonded in a distorted trigonal planar geometry to one O(3), one O(5), one O(7), and one O(8) atom. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form TaO6 octahedra that share corners with three equivalent Ca(3)O6 octahedra, corners with three equivalent Ca(4)O6 octahedra, and  a faceface with one Ta(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 29-37°. In the second Ta site, Ta(2) is bonded to one O(1), one O(2), one O(4), one O(6), one O(7), and one O(9) atom to form distorted TaO6 octahedra that share corners with three equivalent Ca(2)O6 octahedra, edges with three equivalent Ca(4)O6 octahedra, and  a faceface with one Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 41-42°. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(4), one Ta(1), and one Ta(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(4), and one Ta(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(3), one Ca(5), and one Ta(1) atom. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(2), one Ca(4), and one Ta(2) atom to form distorted corner-sharing OCa3Ta trigonal pyramids. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(3), one Ca(5), and one Ta(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(4), one Ta(1), and one Ta(2) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one Ca(1), one Ca(4), one Ca(5), one Ta(1), and one Ta(2) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Ca(3), one Ca(5), and one Ta(1) atom. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(4), and one Ta(2) atom.
Ca3(CaTa2)O9 crystallizes in the triclinic P-1 space group. There are five inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 3-coordinate geometry to one O(1), one O(2), one O(4), one O(6), one O(7), and one O(9) atom. The Ca(1)-O(1) bond length is 2.33 Å. The Ca(1)-O(2) bond length is 2.87 Å. The Ca(1)-O(4) bond length is 2.83 Å. The Ca(1)-O(6) bond length is 2.33 Å. The Ca(1)-O(7) bond length is 2.33 Å. The Ca(1)-O(9) bond length is 2.86 Å. In the second Ca site, Ca(2) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(9) atoms to form CaO6 octahedra that share corners with six equivalent Ca(4)O6 octahedra and corners with six equivalent Ta(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 41-62°. Both Ca(2)-O(2) bond lengths are 2.37 Å. Both Ca(2)-O(4) bond lengths are 2.38 Å. Both Ca(2)-O(9) bond lengths are 2.38 Å. In the third Ca site, Ca(3) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(8) atoms to form CaO6 octahedra that share corners with six equivalent Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 35-37°. Both Ca(3)-O(3) bond lengths are 2.29 Å. Both Ca(3)-O(5) bond lengths are 2.31 Å. Both Ca(3)-O(8) bond lengths are 2.30 Å. In the fourth Ca site, Ca(4) is bonded to one O(1), one O(2), one O(4), one O(6), one O(7), and one O(9) atom to form distorted CaO6 octahedra that share corners with three equivalent Ca(2)O6 octahedra, corners with three equivalent Ta(1)O6 octahedra, and edges with three equivalent Ta(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 29-62°. The Ca(4)-O(1) bond length is 2.41 Å. The Ca(4)-O(2) bond length is 2.34 Å. The Ca(4)-O(4) bond length is 2.35 Å. The Ca(4)-O(6) bond length is 2.43 Å. The Ca(4)-O(7) bond length is 2.43 Å. The Ca(4)-O(9) bond length is 2.34 Å. In the fifth Ca site, Ca(5) is bonded in a distorted trigonal planar geometry to one O(3), one O(5), one O(7), and one O(8) atom. The Ca(5)-O(3) bond length is 2.25 Å. The Ca(5)-O(5) bond length is 2.25 Å. The Ca(5)-O(7) bond length is 2.95 Å. The Ca(5)-O(8) bond length is 2.25 Å. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form TaO6 octahedra that share corners with three equivalent Ca(3)O6 octahedra, corners with three equivalent Ca(4)O6 octahedra, and  a faceface with one Ta(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 29-37°. The Ta(1)-O(1) bond length is 2.12 Å. The Ta(1)-O(3) bond length is 1.92 Å. The Ta(1)-O(5) bond length is 1.92 Å. The Ta(1)-O(6) bond length is 2.12 Å. The Ta(1)-O(7) bond length is 2.11 Å. The Ta(1)-O(8) bond length is 1.92 Å. In the second Ta site, Ta(2) is bonded to one O(1), one O(2), one O(4), one O(6), one O(7), and one O(9) atom to form distorted TaO6 octahedra that share corners with three equivalent Ca(2)O6 octahedra, edges with three equivalent Ca(4)O6 octahedra, and  a faceface with one Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 41-42°. The Ta(2)-O(1) bond length is 2.20 Å. The Ta(2)-O(2) bond length is 1.90 Å. The Ta(2)-O(4) bond length is 1.90 Å. The Ta(2)-O(6) bond length is 2.19 Å. The Ta(2)-O(7) bond length is 2.21 Å. The Ta(2)-O(9) bond length is 1.90 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(4), one Ta(1), and one Ta(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(4), and one Ta(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(3), one Ca(5), and one Ta(1) atom. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(2), one Ca(4), and one Ta(2) atom to form distorted corner-sharing OCa3Ta trigonal pyramids. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(3), one Ca(5), and one Ta(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(4), one Ta(1), and one Ta(2) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one Ca(1), one Ca(4), one Ca(5), one Ta(1), and one Ta(2) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Ca(3), one Ca(5), and one Ta(1) atom. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(4), and one Ta(2) atom.