Sn2P2O7 crystallizes in the monoclinic C2/c space group. Sn(1) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted SnO5 square pyramids that share corners with five equivalent P(1)O4 tetrahedra and edges with two equivalent Sn(1)O5 square pyramids. 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 five equivalent Sn(1)O5 square pyramids and  a cornercorner with one P(1)O4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Sn(1) and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Sn(1) and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Sn(1) and one P(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to two equivalent P(1) atoms.
Sn2P2O7 crystallizes in the monoclinic C2/c space group. Sn(1) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted SnO5 square pyramids that share corners with five equivalent P(1)O4 tetrahedra and edges with two equivalent Sn(1)O5 square pyramids. The Sn(1)-O(1) bond length is 2.50 Å. There is one shorter (2.29 Å) and one longer (2.56 Å) Sn(1)-O(2) bond length. There is one shorter (2.35 Å) and one longer (2.57 Å) Sn(1)-O(3) bond length. 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 five equivalent Sn(1)O5 square pyramids and  a cornercorner with one P(1)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 1.54 Å. The P(1)-O(4) bond length is 1.64 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Sn(1) and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Sn(1) and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Sn(1) and one P(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to two equivalent P(1) atoms.