Ca3W2O7 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. W(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form corner-sharing WO6 octahedra. The corner-sharing octahedral tilt angles range from 32-35°. There are four inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ca(2) and one W(1) atom to form OCa3W tetrahedra that share  a cornercorner with one O(4)Ca2W2 tetrahedra, corners with six equivalent O(1)Ca3W tetrahedra,  a cornercorner with one O(3)Ca3W2 trigonal bipyramid, and edges with two equivalent O(3)Ca3W2 trigonal bipyramids. 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 W(1) atoms. In the third O site, O(3) is bonded to one Ca(2), two equivalent Ca(1), and two equivalent W(1) atoms to form distorted OCa3W2 trigonal bipyramids that share  a cornercorner with one O(1)Ca3W tetrahedra, corners with four equivalent O(4)Ca2W2 tetrahedra, corners with two equivalent O(3)Ca3W2 trigonal bipyramids,  an edgeedge with one O(4)Ca2W2 tetrahedra, edges with two equivalent O(1)Ca3W tetrahedra, and edges with three equivalent O(3)Ca3W2 trigonal bipyramids. In the fourth O site, O(4) is bonded to two equivalent Ca(1) and two equivalent W(1) atoms to form OCa2W2 tetrahedra that share corners with two equivalent O(4)Ca2W2 tetrahedra, corners with two equivalent O(1)Ca3W tetrahedra, corners with eight equivalent O(3)Ca3W2 trigonal bipyramids, and edges with two equivalent O(3)Ca3W2 trigonal bipyramids.
Ca3W2O7 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 2.76 Å. There is one shorter (2.36 Å) and one longer (2.43 Å) Ca(1)-O(4) bond length. There are two shorter (2.38 Å) and two longer (2.74 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 2.54 Å. There is one shorter (2.33 Å) and one longer (2.70 Å) Ca(2)-O(2) bond length. There are a spread of Ca(2)-O(1) bond distances ranging from 2.29-2.42 Å. W(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form corner-sharing WO6 octahedra. The corner-sharing octahedral tilt angles range from 32-35°. The W(1)-O(1) bond length is 2.05 Å. The W(1)-O(4) bond length is 2.08 Å. There is one shorter (2.06 Å) and one longer (2.14 Å) W(1)-O(2) bond length. There is one shorter (2.07 Å) and one longer (2.16 Å) W(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 W(1) atom to form OCa3W tetrahedra that share  a cornercorner with one O(4)Ca2W2 tetrahedra, corners with six equivalent O(1)Ca3W tetrahedra,  a cornercorner with one O(3)Ca3W2 trigonal bipyramid, and edges with two equivalent O(3)Ca3W2 trigonal bipyramids. 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 W(1) atoms. In the third O site, O(3) is bonded to one Ca(2), two equivalent Ca(1), and two equivalent W(1) atoms to form distorted OCa3W2 trigonal bipyramids that share  a cornercorner with one O(1)Ca3W tetrahedra, corners with four equivalent O(4)Ca2W2 tetrahedra, corners with two equivalent O(3)Ca3W2 trigonal bipyramids,  an edgeedge with one O(4)Ca2W2 tetrahedra, edges with two equivalent O(1)Ca3W tetrahedra, and edges with three equivalent O(3)Ca3W2 trigonal bipyramids. In the fourth O site, O(4) is bonded to two equivalent Ca(1) and two equivalent W(1) atoms to form OCa2W2 tetrahedra that share corners with two equivalent O(4)Ca2W2 tetrahedra, corners with two equivalent O(1)Ca3W tetrahedra, corners with eight equivalent O(3)Ca3W2 trigonal bipyramids, and edges with two equivalent O(3)Ca3W2 trigonal bipyramids.