Ca3Sn2O7 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 8-coordinate geometry to two equivalent O(2), 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. Sn(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form corner-sharing SnO6 octahedra. The corner-sharing octahedral tilt angles range from 33-34°. There are four inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ca(2) and one Sn(1) atom to form OCa3Sn tetrahedra that share  a cornercorner with one O(4)Ca2Sn2 tetrahedra and corners with six equivalent O(1)Ca3Sn tetrahedra. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Ca(1), two equivalent Ca(2), and two equivalent Sn(1) atoms. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Ca(2), two equivalent Ca(1), and two equivalent Sn(1) atoms. In the fourth O site, O(4) is bonded to two equivalent Ca(1) and two equivalent Sn(1) atoms to form distorted OCa2Sn2 tetrahedra that share corners with two equivalent O(4)Ca2Sn2 tetrahedra and corners with two equivalent O(1)Ca3Sn tetrahedra.
Ca3Sn2O7 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 8-coordinate geometry to two equivalent O(2), two equivalent O(4), and four equivalent O(3) atoms. Both Ca(1)-O(2) bond lengths are 2.79 Å. There is one shorter (2.36 Å) and one longer (2.43 Å) Ca(1)-O(4) bond length. There are two shorter (2.37 Å) and two longer (2.73 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 2.59 Å. There is one shorter (2.35 Å) and one longer (2.72 Å) Ca(2)-O(2) bond length. There are a spread of Ca(2)-O(1) bond distances ranging from 2.29-2.39 Å. Sn(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form corner-sharing SnO6 octahedra. The corner-sharing octahedral tilt angles range from 33-34°. The Sn(1)-O(1) bond length is 2.07 Å. The Sn(1)-O(4) bond length is 2.09 Å. There is one shorter (2.10 Å) and one longer (2.11 Å) Sn(1)-O(2) bond length. Both Sn(1)-O(3) bond lengths are 2.12 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ca(2) and one Sn(1) atom to form OCa3Sn tetrahedra that share  a cornercorner with one O(4)Ca2Sn2 tetrahedra and corners with six equivalent O(1)Ca3Sn tetrahedra. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Ca(1), two equivalent Ca(2), and two equivalent Sn(1) atoms. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Ca(2), two equivalent Ca(1), and two equivalent Sn(1) atoms. In the fourth O site, O(4) is bonded to two equivalent Ca(1) and two equivalent Sn(1) atoms to form distorted OCa2Sn2 tetrahedra that share corners with two equivalent O(4)Ca2Sn2 tetrahedra and corners with two equivalent O(1)Ca3Sn tetrahedra.