CaBi2Ta2O9 crystallizes in the triclinic P-1 space group. Ca(1) is bonded to four equivalent O(2), four equivalent O(4), and four equivalent O(5) atoms to form CaO12 cuboctahedra that share corners with four equivalent Ca(1)O12 cuboctahedra, faces with four equivalent Ca(1)O12 cuboctahedra, and faces with eight equivalent Ta(1)O6 octahedra. Ta(1) is bonded to one O(1), one O(5), two equivalent O(2), and two equivalent O(4) atoms to form TaO6 octahedra that share corners with five equivalent Ta(1)O6 octahedra and faces with four equivalent Ca(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-14°. Bi(1) is bonded in a 5-coordinate geometry to one O(1) and four equivalent O(3) atoms. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Ta(1) and one Bi(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Ca(1) and two equivalent Ta(1) atoms. In the third O site, O(3) is bonded to four equivalent Bi(1) atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Ca(1) and two equivalent Ta(1) atoms. In the fifth O site, O(5) is bonded in a distorted linear geometry to four equivalent Ca(1) and two equivalent Ta(1) atoms.
CaBi2Ta2O9 crystallizes in the triclinic P-1 space group. Ca(1) is bonded to four equivalent O(2), four equivalent O(4), and four equivalent O(5) atoms to form CaO12 cuboctahedra that share corners with four equivalent Ca(1)O12 cuboctahedra, faces with four equivalent Ca(1)O12 cuboctahedra, and faces with eight equivalent Ta(1)O6 octahedra. There are two shorter (2.70 Å) and two longer (2.71 Å) Ca(1)-O(2) bond lengths. There are two shorter (2.67 Å) and two longer (2.72 Å) Ca(1)-O(4) bond lengths. All Ca(1)-O(5) bond lengths are 2.79 Å. Ta(1) is bonded to one O(1), one O(5), two equivalent O(2), and two equivalent O(4) atoms to form TaO6 octahedra that share corners with five equivalent Ta(1)O6 octahedra and faces with four equivalent Ca(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-14°. The Ta(1)-O(1) bond length is 1.92 Å. The Ta(1)-O(5) bond length is 2.07 Å. There is one shorter (1.96 Å) and one longer (2.00 Å) Ta(1)-O(2) bond length. There is one shorter (1.97 Å) and one longer (2.02 Å) Ta(1)-O(4) bond length. Bi(1) is bonded in a 5-coordinate geometry to one O(1) and four equivalent O(3) atoms. The Bi(1)-O(1) bond length is 2.36 Å. There are a spread of Bi(1)-O(3) bond distances ranging from 2.21-2.49 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Ta(1) and one Bi(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Ca(1) and two equivalent Ta(1) atoms. In the third O site, O(3) is bonded to four equivalent Bi(1) atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Ca(1) and two equivalent Ta(1) atoms. In the fifth O site, O(5) is bonded in a distorted linear geometry to four equivalent Ca(1) and two equivalent Ta(1) atoms.