FeP2O7 crystallizes in the triclinic P-1 space group. Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(7) atom to form FeO6 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 Fe(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-40°. In the second P site, P(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 21-47°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(2) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom.
FeP2O7 crystallizes in the triclinic P-1 space group. Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(7) atom to form FeO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. The Fe(1)-O(1) bond length is 2.00 Å. The Fe(1)-O(2) bond length is 1.99 Å. The Fe(1)-O(3) bond length is 2.03 Å. The Fe(1)-O(4) bond length is 1.99 Å. The Fe(1)-O(6) bond length is 2.02 Å. The Fe(1)-O(7) bond length is 2.00 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 Fe(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-40°. The P(1)-O(2) bond length is 1.52 Å. The P(1)-O(4) bond length is 1.53 Å. The P(1)-O(5) bond length is 1.61 Å. The P(1)-O(7) bond length is 1.53 Å. In the second P site, P(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 21-47°. The P(2)-O(1) bond length is 1.52 Å. The P(2)-O(3) bond length is 1.53 Å. The P(2)-O(5) bond length is 1.60 Å. The P(2)-O(6) bond length is 1.53 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(2) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom.