Fe2P2O7 crystallizes in the triclinic P1 space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(5), one O(6), and one O(7) atom. In the second Fe site, Fe(2) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(6), and one O(7) atom. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form corner-sharing PO4 tetrahedra. In the second P site, P(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form corner-sharing PO4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one P(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Fe(2) and one P(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one P(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to one P(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one P(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Fe(1), one Fe(2), and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one P(2) atom.
Fe2P2O7 crystallizes in the triclinic P1 space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(5), one O(6), and one O(7) atom. The Fe(1)-O(1) bond length is 2.20 Å. The Fe(1)-O(3) bond length is 2.18 Å. The Fe(1)-O(5) bond length is 2.20 Å. The Fe(1)-O(6) bond length is 2.04 Å. The Fe(1)-O(7) bond length is 2.10 Å. In the second Fe site, Fe(2) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(6), and one O(7) atom. The Fe(2)-O(1) bond length is 2.08 Å. The Fe(2)-O(2) bond length is 2.01 Å. The Fe(2)-O(3) bond length is 2.19 Å. The Fe(2)-O(5) bond length is 2.18 Å. The Fe(2)-O(6) bond length is 2.55 Å. The Fe(2)-O(7) bond length is 2.20 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form corner-sharing PO4 tetrahedra. The P(1)-O(1) bond length is 1.54 Å. The P(1)-O(2) bond length is 1.53 Å. The P(1)-O(3) bond length is 1.54 Å. The P(1)-O(4) bond length is 1.59 Å. In the second P site, P(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form corner-sharing PO4 tetrahedra. The P(2)-O(4) bond length is 1.59 Å. The P(2)-O(5) 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 1.54 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one P(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Fe(2) and one P(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one P(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to one P(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one P(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Fe(1), one Fe(2), and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one P(2) atom.