Bi2P2O9 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one O(3), one O(4), one O(6), one O(7), and two equivalent O(5) atoms to form BiO6 octahedra that share corners with two equivalent Bi(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 51°. In the second Bi site, Bi(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form BiO6 octahedra that share corners with two equivalent Bi(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and edges with two equivalent Bi(2)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. 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 Bi(2)O6 octahedra and corners with three equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 10-49°. 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 Bi(2)O6 octahedra and  an edgeedge with one Bi(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 a distorted L-shaped geometry to one Bi(1) and one P(2) atom. In the second O site, O(5) is bonded in a bent 150 degrees geometry to one Bi(1) and one P(1) atom. In the third O site, O(6) is bonded in a linear geometry to one Bi(1) and one P(1) atom. In the fourth O site, O(7) is bonded in a distorted L-shaped geometry to one Bi(1) and one P(2) atom. In the fifth O site, O(1) is bonded in a 2-coordinate geometry to one Bi(2) and one P(2) atom. In the sixth O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Bi(2) and one P(1) atom. In the seventh O site, O(3) is bonded in a trigonal planar geometry to one Bi(1) and two equivalent Bi(2) atoms.
Bi2P2O9 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one O(3), one O(4), one O(6), one O(7), and two equivalent O(5) atoms to form BiO6 octahedra that share corners with two equivalent Bi(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 51°. The Bi(1)-O(3) bond length is 2.24 Å. The Bi(1)-O(4) bond length is 2.29 Å. The Bi(1)-O(6) bond length is 2.26 Å. The Bi(1)-O(7) bond length is 2.22 Å. Both Bi(1)-O(5) bond lengths are 2.27 Å. In the second Bi site, Bi(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form BiO6 octahedra that share corners with two equivalent Bi(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and edges with two equivalent Bi(2)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. Both Bi(2)-O(1) bond lengths are 2.24 Å. Both Bi(2)-O(2) bond lengths are 2.37 Å. Both Bi(2)-O(3) bond lengths are 2.25 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 Bi(2)O6 octahedra and corners with three equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 10-49°. The P(1)-O(2) bond length is 1.62 Å. The P(1)-O(6) bond length is 1.53 Å. Both P(1)-O(5) bond lengths are 1.54 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 Bi(2)O6 octahedra and  an edgeedge with one Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles are 46°. The P(2)-O(4) bond length is 1.56 Å. The P(2)-O(7) bond length is 1.59 Å. Both P(2)-O(1) bond lengths are 1.55 Å. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a distorted L-shaped geometry to one Bi(1) and one P(2) atom. In the second O site, O(5) is bonded in a bent 150 degrees geometry to one Bi(1) and one P(1) atom. In the third O site, O(6) is bonded in a linear geometry to one Bi(1) and one P(1) atom. In the fourth O site, O(7) is bonded in a distorted L-shaped geometry to one Bi(1) and one P(2) atom. In the fifth O site, O(1) is bonded in a 2-coordinate geometry to one Bi(2) and one P(2) atom. In the sixth O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Bi(2) and one P(1) atom. In the seventh O site, O(3) is bonded in a trigonal planar geometry to one Bi(1) and two equivalent Bi(2) atoms.