Ca2Bi3O8 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form CaO6 octahedra that share corners with six equivalent Bi(1)O6 octahedra, corners with three equivalent Ca(2)O4 trigonal pyramids, and edges with three equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. In the second Ca site, Ca(2) is bonded to one O(4) and three equivalent O(2) atoms to form CaO4 trigonal pyramids that share corners with three equivalent Ca(1)O6 octahedra and corners with nine equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 52-67°. Bi(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form BiO6 octahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with three equivalent Ca(2)O4 trigonal pyramids,  an edgeedge with one Ca(1)O6 octahedra, and edges with four equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Bi(1) atoms. In the second O site, O(2) is bonded to one Ca(1), one Ca(2), and two equivalent Bi(1) atoms to form OCa2Bi2 tetrahedra that share corners with two equivalent O(2)Ca2Bi2 tetrahedra,  a cornercorner with one O(4)CaBi3 trigonal pyramid, edges with two equivalent O(2)Ca2Bi2 tetrahedra, and  an edgeedge with one O(4)CaBi3 trigonal pyramid. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to three equivalent Bi(1) atoms. In the fourth O site, O(4) is bonded to one Ca(2) and three equivalent Bi(1) atoms to form a mixture of distorted corner and edge-sharing OCaBi3 trigonal pyramids.
Ca2Bi3O8 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form CaO6 octahedra that share corners with six equivalent Bi(1)O6 octahedra, corners with three equivalent Ca(2)O4 trigonal pyramids, and edges with three equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. All Ca(1)-O(1) bond lengths are 2.37 Å. All Ca(1)-O(2) bond lengths are 2.43 Å. In the second Ca site, Ca(2) is bonded to one O(4) and three equivalent O(2) atoms to form CaO4 trigonal pyramids that share corners with three equivalent Ca(1)O6 octahedra and corners with nine equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 52-67°. The Ca(2)-O(4) bond length is 2.38 Å. All Ca(2)-O(2) bond lengths are 2.30 Å. Bi(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form BiO6 octahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with three equivalent Ca(2)O4 trigonal pyramids,  an edgeedge with one Ca(1)O6 octahedra, and edges with four equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. The Bi(1)-O(3) bond length is 2.27 Å. The Bi(1)-O(4) bond length is 2.38 Å. Both Bi(1)-O(1) bond lengths are 2.23 Å. Both Bi(1)-O(2) bond lengths are 2.30 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Bi(1) atoms. In the second O site, O(2) is bonded to one Ca(1), one Ca(2), and two equivalent Bi(1) atoms to form OCa2Bi2 tetrahedra that share corners with two equivalent O(2)Ca2Bi2 tetrahedra,  a cornercorner with one O(4)CaBi3 trigonal pyramid, edges with two equivalent O(2)Ca2Bi2 tetrahedra, and  an edgeedge with one O(4)CaBi3 trigonal pyramid. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to three equivalent Bi(1) atoms. In the fourth O site, O(4) is bonded to one Ca(2) and three equivalent Bi(1) atoms to form a mixture of distorted corner and edge-sharing OCaBi3 trigonal pyramids.