Fe3(PO4)4 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form FeO5 trigonal bipyramids that share corners with two equivalent P(2)O4 tetrahedra and corners with three equivalent P(1)O4 tetrahedra. In the second Fe site, Fe(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra and corners with four equivalent P(2)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(3), one O(7), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra and corners with three equivalent Fe(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 39°. In the second P site, P(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with two equivalent Fe(2)O6 octahedra and corners with two equivalent Fe(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 24-42°. There are eight inequivalent O sites. In the first O site, O(7) is bonded in a bent 120 degrees geometry to one Fe(1) and one P(1) atom. In the second O site, O(8) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the third O site, O(1) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(1) atom. In the fourth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Fe(2) and one P(2) atom. In the fifth O site, O(3) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the sixth O site, O(4) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(2) atom. In the seventh O site, O(5) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the eighth O site, O(6) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom.
Fe3(PO4)4 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form FeO5 trigonal bipyramids that share corners with two equivalent P(2)O4 tetrahedra and corners with three equivalent P(1)O4 tetrahedra. The Fe(1)-O(3) bond length is 2.01 Å. The Fe(1)-O(5) bond length is 2.04 Å. The Fe(1)-O(6) bond length is 1.91 Å. The Fe(1)-O(7) bond length is 1.95 Å. The Fe(1)-O(8) bond length is 1.90 Å. In the second Fe site, Fe(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra and corners with four equivalent P(2)O4 tetrahedra. Both Fe(2)-O(1) bond lengths are 2.01 Å. Both Fe(2)-O(2) bond lengths are 2.13 Å. Both Fe(2)-O(4) bond lengths are 1.94 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(3), one O(7), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra and corners with three equivalent Fe(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 39°. The P(1)-O(1) bond length is 1.54 Å. The P(1)-O(3) bond length is 1.54 Å. The P(1)-O(7) bond length is 1.56 Å. The P(1)-O(8) bond length is 1.54 Å. In the second P site, P(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with two equivalent Fe(2)O6 octahedra and corners with two equivalent Fe(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 24-42°. The P(2)-O(2) bond length is 1.55 Å. The P(2)-O(4) bond length is 1.54 Å. The P(2)-O(5) bond length is 1.54 Å. The P(2)-O(6) bond length is 1.55 Å. There are eight inequivalent O sites. In the first O site, O(7) is bonded in a bent 120 degrees geometry to one Fe(1) and one P(1) atom. In the second O site, O(8) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the third O site, O(1) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(1) atom. In the fourth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Fe(2) and one P(2) atom. In the fifth O site, O(3) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the sixth O site, O(4) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(2) atom. In the seventh O site, O(5) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the eighth O site, O(6) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom.