CaSnP2O7 crystallizes in the monoclinic P2_1/c space group. Ca(1) is bonded to one O(2), one O(3), one O(5), one O(6), and one O(7) atom to form CaO5 trigonal bipyramids that share  a cornercorner with one Sn(1)O5 square pyramid, corners with two equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and  an edgeedge with one Sn(1)O5 square pyramid. Sn(1) is bonded to one O(5), one O(6), one O(7), and two equivalent O(4) atoms to form distorted SnO5 square pyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra,  a cornercorner with one Ca(1)O5 trigonal bipyramid,  an edgeedge with one Sn(1)O5 square pyramid, and  an edgeedge with one Ca(1)O5 trigonal bipyramid. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(4), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Sn(1)O5 square pyramids,  a cornercorner with one P(2)O4 tetrahedra, and corners with two equivalent Ca(1)O5 trigonal bipyramids. In the second P site, P(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with two equivalent Sn(1)O5 square pyramids,  a cornercorner with one P(1)O4 tetrahedra, and corners with three equivalent Ca(1)O5 trigonal bipyramids. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Ca(1) and one P(1) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ca(1) and one P(2) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to two equivalent Sn(1) and one P(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Sn(1), and one P(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(1), one Sn(1), and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(1), one Sn(1), and one P(1) atom.
CaSnP2O7 crystallizes in the monoclinic P2_1/c space group. Ca(1) is bonded to one O(2), one O(3), one O(5), one O(6), and one O(7) atom to form CaO5 trigonal bipyramids that share  a cornercorner with one Sn(1)O5 square pyramid, corners with two equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and  an edgeedge with one Sn(1)O5 square pyramid. The Ca(1)-O(2) bond length is 2.25 Å. The Ca(1)-O(3) bond length is 2.32 Å. The Ca(1)-O(5) bond length is 2.34 Å. The Ca(1)-O(6) bond length is 2.30 Å. The Ca(1)-O(7) bond length is 2.39 Å. Sn(1) is bonded to one O(5), one O(6), one O(7), and two equivalent O(4) atoms to form distorted SnO5 square pyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra,  a cornercorner with one Ca(1)O5 trigonal bipyramid,  an edgeedge with one Sn(1)O5 square pyramid, and  an edgeedge with one Ca(1)O5 trigonal bipyramid. The Sn(1)-O(5) bond length is 2.47 Å. The Sn(1)-O(6) bond length is 2.48 Å. The Sn(1)-O(7) bond length is 2.29 Å. There is one shorter (2.48 Å) and one longer (2.59 Å) Sn(1)-O(4) bond length. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(4), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Sn(1)O5 square pyramids,  a cornercorner with one P(2)O4 tetrahedra, and corners with two equivalent Ca(1)O5 trigonal bipyramids. The P(1)-O(1) bond length is 1.62 Å. The P(1)-O(2) bond length is 1.52 Å. The P(1)-O(4) bond length is 1.53 Å. The P(1)-O(7) bond length is 1.56 Å. In the second P site, P(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with two equivalent Sn(1)O5 square pyramids,  a cornercorner with one P(1)O4 tetrahedra, and corners with three equivalent Ca(1)O5 trigonal bipyramids. The P(2)-O(1) bond length is 1.62 Å. The P(2)-O(3) bond length is 1.53 Å. The P(2)-O(5) bond length is 1.54 Å. The P(2)-O(6) bond length is 1.54 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Ca(1) and one P(1) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ca(1) and one P(2) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to two equivalent Sn(1) and one P(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Sn(1), and one P(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(1), one Sn(1), and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(1), one Sn(1), and one P(1) atom.