Ca3Bi2O7 crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 6-coordinate geometry to two equivalent O(4) and four equivalent O(3) atoms. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to one O(3), two equivalent O(2), and three equivalent O(1) atoms. Bi(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form corner-sharing BiO6 octahedra. The corner-sharing octahedral tilt angles range from 38-46°. There are four inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ca(2) and one Bi(1) atom to form distorted OCa3Bi tetrahedra that share corners with six equivalent O(1)Ca3Bi tetrahedra,  a cornercorner with one O(3)Ca3Bi2 trigonal bipyramid,  a cornercorner with one O(4)Ca2Bi2 trigonal pyramid, and edges with two equivalent O(3)Ca3Bi2 trigonal bipyramids. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Ca(2) and two equivalent Bi(1) atoms. In the third O site, O(3) is bonded to one Ca(2), two equivalent Ca(1), and two equivalent Bi(1) atoms to form distorted OCa3Bi2 trigonal bipyramids that share  a cornercorner with one O(1)Ca3Bi tetrahedra, corners with two equivalent O(3)Ca3Bi2 trigonal bipyramids, corners with four equivalent O(4)Ca2Bi2 trigonal pyramids, edges with two equivalent O(1)Ca3Bi tetrahedra, edges with three equivalent O(3)Ca3Bi2 trigonal bipyramids, and  an edgeedge with one O(4)Ca2Bi2 trigonal pyramid. In the fourth O site, O(4) is bonded to two equivalent Ca(1) and two equivalent Bi(1) atoms to form distorted OCa2Bi2 trigonal pyramids that share corners with two equivalent O(1)Ca3Bi tetrahedra, corners with eight equivalent O(3)Ca3Bi2 trigonal bipyramids, corners with two equivalent O(4)Ca2Bi2 trigonal pyramids, and edges with two equivalent O(3)Ca3Bi2 trigonal bipyramids.
Ca3Bi2O7 crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 6-coordinate geometry to two equivalent O(4) and four equivalent O(3) atoms. There is one shorter (2.36 Å) and one longer (2.43 Å) Ca(1)-O(4) bond length. There are two shorter (2.38 Å) and two longer (2.76 Å) Ca(1)-O(3) bond lengths. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to one O(3), two equivalent O(2), and three equivalent O(1) atoms. The Ca(2)-O(3) bond length is 2.71 Å. There is one shorter (2.36 Å) and one longer (2.61 Å) Ca(2)-O(2) bond length. There are a spread of Ca(2)-O(1) bond distances ranging from 2.27-2.37 Å. Bi(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form corner-sharing BiO6 octahedra. The corner-sharing octahedral tilt angles range from 38-46°. The Bi(1)-O(1) bond length is 2.19 Å. The Bi(1)-O(4) bond length is 2.28 Å. There is one shorter (2.21 Å) and one longer (2.23 Å) Bi(1)-O(2) bond length. There is one shorter (2.23 Å) and one longer (2.26 Å) Bi(1)-O(3) bond length. There are four inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ca(2) and one Bi(1) atom to form distorted OCa3Bi tetrahedra that share corners with six equivalent O(1)Ca3Bi tetrahedra,  a cornercorner with one O(3)Ca3Bi2 trigonal bipyramid,  a cornercorner with one O(4)Ca2Bi2 trigonal pyramid, and edges with two equivalent O(3)Ca3Bi2 trigonal bipyramids. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Ca(2) and two equivalent Bi(1) atoms. In the third O site, O(3) is bonded to one Ca(2), two equivalent Ca(1), and two equivalent Bi(1) atoms to form distorted OCa3Bi2 trigonal bipyramids that share  a cornercorner with one O(1)Ca3Bi tetrahedra, corners with two equivalent O(3)Ca3Bi2 trigonal bipyramids, corners with four equivalent O(4)Ca2Bi2 trigonal pyramids, edges with two equivalent O(1)Ca3Bi tetrahedra, edges with three equivalent O(3)Ca3Bi2 trigonal bipyramids, and  an edgeedge with one O(4)Ca2Bi2 trigonal pyramid. In the fourth O site, O(4) is bonded to two equivalent Ca(1) and two equivalent Bi(1) atoms to form distorted OCa2Bi2 trigonal pyramids that share corners with two equivalent O(1)Ca3Bi tetrahedra, corners with eight equivalent O(3)Ca3Bi2 trigonal bipyramids, corners with two equivalent O(4)Ca2Bi2 trigonal pyramids, and edges with two equivalent O(3)Ca3Bi2 trigonal bipyramids.