FeP3O11 crystallizes in the monoclinic C2/c space group. Fe(1) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form FeO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra and corners with four equivalent P(1)O4 tetrahedra. 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 PO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 17-49°. In the second P site, P(2) is bonded to two equivalent O(1) and two equivalent O(5) atoms to form PO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra and corners with two equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 48°. There are six inequivalent O sites. In the first O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(2) atom. In the second O site, O(6) is bonded in a water-like geometry to two equivalent O(3) atoms. In the third O site, O(1) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the fourth O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(1) atom. In the fifth O site, O(3) is bonded in a distorted single-bond geometry to one P(1) and one O(6) atom. In the sixth O site, O(4) is bonded in a distorted linear geometry to one Fe(1) and one P(1) atom.
FeP3O11 crystallizes in the monoclinic C2/c space group. Fe(1) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form FeO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra and corners with four equivalent P(1)O4 tetrahedra. Both Fe(1)-O(2) bond lengths are 2.06 Å. Both Fe(1)-O(4) bond lengths are 2.00 Å. Both Fe(1)-O(5) bond lengths are 2.02 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 PO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 17-49°. The P(1)-O(1) bond length is 1.62 Å. The P(1)-O(2) bond length is 1.51 Å. The P(1)-O(3) bond length is 1.64 Å. The P(1)-O(4) bond length is 1.49 Å. In the second P site, P(2) is bonded to two equivalent O(1) and two equivalent O(5) atoms to form PO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra and corners with two equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 48°. Both P(2)-O(1) bond lengths are 1.63 Å. Both P(2)-O(5) bond lengths are 1.50 Å. There are six inequivalent O sites. In the first O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(2) atom. In the second O site, O(6) is bonded in a water-like geometry to two equivalent O(3) atoms. Both O(6)-O(3) bond lengths are 1.47 Å. In the third O site, O(1) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the fourth O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(1) atom. In the fifth O site, O(3) is bonded in a distorted single-bond geometry to one P(1) and one O(6) atom. In the sixth O site, O(4) is bonded in a distorted linear geometry to one Fe(1) and one P(1) atom.