Li2Fe3(P2O7)2 crystallizes in the monoclinic P2_1/c space group. Li(1) is bonded to one O(3), one O(4), one O(6), and one O(7) atom to form LiO4 tetrahedra that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and  an edgeedge with one Fe(2)O6 octahedra. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(4), and one O(7) atom. In the second Fe site, Fe(2) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form distorted FeO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra, corners with four equivalent P(1)O4 tetrahedra, and edges with two equivalent Li(1)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Fe(2)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, and corners with two equivalent Li(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-46°. In the second P site, P(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and corners with two equivalent Li(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 19°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(2) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Fe(1), one P(1), and one P(2) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to one Li(1), one Fe(2), and one P(2) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Li(1), one Fe(1), and one P(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Fe(2) and one P(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Li(1), one Fe(2), and one P(1) atom. In the seventh O site, O(7) is bonded in a trigonal non-coplanar geometry to one Li(1), one Fe(1), and one P(1) atom.
Li2Fe3(P2O7)2 crystallizes in the monoclinic P2_1/c space group. Li(1) is bonded to one O(3), one O(4), one O(6), and one O(7) atom to form LiO4 tetrahedra that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and  an edgeedge with one Fe(2)O6 octahedra. The Li(1)-O(3) bond length is 2.02 Å. The Li(1)-O(4) bond length is 1.97 Å. The Li(1)-O(6) bond length is 1.91 Å. The Li(1)-O(7) bond length is 1.96 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(4), and one O(7) atom. The Fe(1)-O(1) bond length is 1.95 Å. The Fe(1)-O(2) bond length is 2.15 Å. The Fe(1)-O(4) bond length is 1.96 Å. The Fe(1)-O(7) bond length is 2.09 Å. In the second Fe site, Fe(2) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form distorted FeO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra, corners with four equivalent P(1)O4 tetrahedra, and edges with two equivalent Li(1)O4 tetrahedra. Both Fe(2)-O(3) bond lengths are 2.53 Å. Both Fe(2)-O(5) bond lengths are 2.36 Å. Both Fe(2)-O(6) bond lengths are 2.02 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Fe(2)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, and corners with two equivalent Li(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-46°. The P(1)-O(2) bond length is 1.70 Å. The P(1)-O(5) bond length is 1.50 Å. The P(1)-O(6) bond length is 1.53 Å. The P(1)-O(7) bond length is 1.55 Å. In the second P site, P(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and corners with two equivalent Li(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 19°. The P(2)-O(1) bond length is 1.53 Å. The P(2)-O(2) bond length is 1.63 Å. The P(2)-O(3) bond length is 1.52 Å. The P(2)-O(4) bond length is 1.55 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(2) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Fe(1), one P(1), and one P(2) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to one Li(1), one Fe(2), and one P(2) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Li(1), one Fe(1), and one P(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Fe(2) and one P(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Li(1), one Fe(2), and one P(1) atom. In the seventh O site, O(7) is bonded in a trigonal non-coplanar geometry to one Li(1), one Fe(1), and one P(1) atom.