W2P2O9 crystallizes in the orthorhombic Pnma space group. There are two inequivalent W sites. In the first W site, W(1) is bonded to one O(3), one O(4), one O(6), one O(7), and two equivalent O(5) atoms to form WO6 octahedra that share corners with two equivalent W(2)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. In the second W site, W(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form WO6 octahedra that share corners with two equivalent W(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and edges with two equivalent W(2)O6 octahedra. The corner-sharing octahedral tilt angles are 53°. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(6), and two equivalent O(5) atoms to form PO4 tetrahedra that share corners with two equivalent W(2)O6 octahedra and corners with three equivalent W(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 9-51°. In the second P site, P(2) is bonded to one O(4), one O(7), and two equivalent O(1) atoms to form PO4 tetrahedra that share corners with two equivalent W(2)O6 octahedra and  an edgeedge with one W(1)O6 octahedra. The corner-sharing octahedral tilt angles are 46°. There are seven inequivalent O sites. In the first O site, O(4) is bonded in an L-shaped geometry to one W(1) and one P(2) atom. In the second O site, O(5) is bonded in a bent 150 degrees geometry to one W(1) and one P(1) atom. In the third O site, O(6) is bonded in a linear geometry to one W(1) and one P(1) atom. In the fourth O site, O(7) is bonded in an L-shaped geometry to one W(1) and one P(2) atom. In the fifth O site, O(1) is bonded in a distorted bent 120 degrees geometry to one W(2) and one P(2) atom. In the sixth O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent W(2) and one P(1) atom. In the seventh O site, O(3) is bonded in a trigonal planar geometry to one W(1) and two equivalent W(2) atoms.
W2P2O9 crystallizes in the orthorhombic Pnma space group. There are two inequivalent W sites. In the first W site, W(1) is bonded to one O(3), one O(4), one O(6), one O(7), and two equivalent O(5) atoms to form WO6 octahedra that share corners with two equivalent W(2)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. The W(1)-O(3) bond length is 2.15 Å. The W(1)-O(4) bond length is 2.04 Å. The W(1)-O(6) bond length is 2.07 Å. The W(1)-O(7) bond length is 2.15 Å. Both W(1)-O(5) bond lengths are 2.04 Å. In the second W site, W(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form WO6 octahedra that share corners with two equivalent W(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and edges with two equivalent W(2)O6 octahedra. The corner-sharing octahedral tilt angles are 53°. Both W(2)-O(1) bond lengths are 2.04 Å. Both W(2)-O(2) bond lengths are 2.16 Å. Both W(2)-O(3) bond lengths are 2.07 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(6), and two equivalent O(5) atoms to form PO4 tetrahedra that share corners with two equivalent W(2)O6 octahedra and corners with three equivalent W(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 9-51°. The P(1)-O(2) bond length is 1.60 Å. The P(1)-O(6) bond length is 1.52 Å. Both P(1)-O(5) bond lengths are 1.52 Å. In the second P site, P(2) is bonded to one O(4), one O(7), and two equivalent O(1) atoms to form PO4 tetrahedra that share corners with two equivalent W(2)O6 octahedra and  an edgeedge with one W(1)O6 octahedra. The corner-sharing octahedral tilt angles are 46°. The P(2)-O(4) bond length is 1.58 Å. The P(2)-O(7) bond length is 1.55 Å. Both P(2)-O(1) bond lengths are 1.56 Å. There are seven inequivalent O sites. In the first O site, O(4) is bonded in an L-shaped geometry to one W(1) and one P(2) atom. In the second O site, O(5) is bonded in a bent 150 degrees geometry to one W(1) and one P(1) atom. In the third O site, O(6) is bonded in a linear geometry to one W(1) and one P(1) atom. In the fourth O site, O(7) is bonded in an L-shaped geometry to one W(1) and one P(2) atom. In the fifth O site, O(1) is bonded in a distorted bent 120 degrees geometry to one W(2) and one P(2) atom. In the sixth O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent W(2) and one P(1) atom. In the seventh O site, O(3) is bonded in a trigonal planar geometry to one W(1) and two equivalent W(2) atoms.