Sn2P2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded to one O(1), one O(2), one O(3), one O(5), and one O(7) atom to form distorted SnO5 square pyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and edges with two equivalent Sn(2)O5 square pyramids. In the second Sn site, Sn(2) is bonded to one O(1), one O(2), one O(3), one O(5), and one O(6) atom to form distorted SnO5 square pyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and edges with two equivalent Sn(1)O5 square pyramids. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with three equivalent Sn(1)O5 square pyramids, corners with three equivalent Sn(2)O5 square pyramids, and  a cornercorner with one P(2)O4 tetrahedra. In the second P site, P(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Sn(1)O5 square pyramids, corners with two equivalent Sn(2)O5 square pyramids, and  a cornercorner with one P(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one Sn(1), one Sn(2), and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Sn(1), one Sn(2), and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Sn(1), one Sn(2), and one P(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Sn(1), one Sn(2), and one P(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Sn(2) and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Sn(1) and one P(2) atom.
Sn2P2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded to one O(1), one O(2), one O(3), one O(5), and one O(7) atom to form distorted SnO5 square pyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and edges with two equivalent Sn(2)O5 square pyramids. The Sn(1)-O(1) bond length is 2.55 Å. The Sn(1)-O(2) bond length is 2.68 Å. The Sn(1)-O(3) bond length is 2.25 Å. The Sn(1)-O(5) bond length is 2.37 Å. The Sn(1)-O(7) bond length is 2.36 Å. In the second Sn site, Sn(2) is bonded to one O(1), one O(2), one O(3), one O(5), and one O(6) atom to form distorted SnO5 square pyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and edges with two equivalent Sn(1)O5 square pyramids. The Sn(2)-O(1) bond length is 2.52 Å. The Sn(2)-O(2) bond length is 2.26 Å. The Sn(2)-O(3) bond length is 2.66 Å. The Sn(2)-O(5) bond length is 2.44 Å. The Sn(2)-O(6) bond length is 2.26 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with three equivalent Sn(1)O5 square pyramids, corners with three equivalent Sn(2)O5 square pyramids, and  a cornercorner with one P(2)O4 tetrahedra. The P(1)-O(1) bond length is 1.52 Å. The P(1)-O(2) bond length is 1.55 Å. The P(1)-O(3) bond length is 1.56 Å. The P(1)-O(4) bond length is 1.61 Å. In the second P site, P(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Sn(1)O5 square pyramids, corners with two equivalent Sn(2)O5 square pyramids, and  a cornercorner with one P(1)O4 tetrahedra. The P(2)-O(4) bond length is 1.65 Å. The P(2)-O(5) bond length is 1.56 Å. The P(2)-O(6) bond length is 1.52 Å. The P(2)-O(7) bond length is 1.52 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one Sn(1), one Sn(2), and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Sn(1), one Sn(2), and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Sn(1), one Sn(2), and one P(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Sn(1), one Sn(2), and one P(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Sn(2) and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Sn(1) and one P(2) atom.