BiP2O7 crystallizes in the monoclinic P2_1 space group. Bi(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form BiO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(4), one O(5), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Bi(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 33-50°. In the second P site, P(2) is bonded to one O(1), one O(3), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Bi(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 44-52°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Bi(1) and one P(2) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Bi(1) and one P(1) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Bi(1) and one P(2) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Bi(1) and one P(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Bi(1) and one P(1) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Bi(1) and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one P(1) and one P(2) atom.
BiP2O7 crystallizes in the monoclinic P2_1 space group. Bi(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form BiO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. The Bi(1)-O(1) bond length is 2.27 Å. The Bi(1)-O(2) bond length is 2.28 Å. The Bi(1)-O(3) bond length is 2.26 Å. The Bi(1)-O(4) bond length is 2.28 Å. The Bi(1)-O(5) bond length is 2.30 Å. The Bi(1)-O(6) bond length is 2.28 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(4), one O(5), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Bi(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 33-50°. The P(1)-O(2) bond length is 1.54 Å. The P(1)-O(4) bond length is 1.53 Å. The P(1)-O(5) bond length is 1.54 Å. The P(1)-O(7) bond length is 1.62 Å. In the second P site, P(2) is bonded to one O(1), one O(3), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Bi(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 44-52°. The P(2)-O(1) bond length is 1.54 Å. The P(2)-O(3) bond length is 1.54 Å. The P(2)-O(6) bond length is 1.54 Å. The P(2)-O(7) bond length is 1.61 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Bi(1) and one P(2) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Bi(1) and one P(1) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Bi(1) and one P(2) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Bi(1) and one P(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Bi(1) and one P(1) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Bi(1) and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one P(1) and one P(2) atom.