Li2Fe3(P2O7)2 crystallizes in the monoclinic P2_1/c space group. Li(1) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and one O(7) atom. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(2), one O(4), one O(7), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra, and  an edgeedge with one Fe(2)O6 octahedra. In the second Fe site, Fe(2) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra, corners with four equivalent P(2)O4 tetrahedra, and edges with two equivalent Fe(1)O6 octahedra. 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  a cornercorner with one Fe(2)O6 octahedra, 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 48-57°. 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 two equivalent Fe(2)O6 octahedra, 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 39-60°. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a distorted trigonal planar geometry to one Li(1), one Fe(1), and one P(1) atom. In the second O site, O(1) is bonded to one Li(1), one Fe(1), one Fe(2), and one P(2) atom to form distorted corner-sharing OLiFe2P trigonal pyramids. In the third O site, O(2) is bonded in a distorted trigonal planar geometry to one Li(1), one Fe(1), and one P(1) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one Li(1), one Fe(2), and one P(2) atom. In the fifth O site, O(4) is bonded in a 4-coordinate geometry to one Li(1), one Fe(1), one Fe(2), and one P(1) atom. In the sixth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one P(1) and one P(2) atom. In the seventh O site, O(6) is bonded in a distorted trigonal planar geometry to two equivalent Fe(1) and one P(2) atom.
Li2Fe3(P2O7)2 crystallizes in the monoclinic P2_1/c space group. Li(1) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and one O(7) atom. The Li(1)-O(1) bond length is 2.35 Å. The Li(1)-O(2) bond length is 2.03 Å. The Li(1)-O(3) bond length is 1.97 Å. The Li(1)-O(4) bond length is 2.60 Å. The Li(1)-O(7) bond length is 2.05 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(2), one O(4), one O(7), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra, and  an edgeedge with one Fe(2)O6 octahedra. The Fe(1)-O(1) bond length is 2.15 Å. The Fe(1)-O(2) bond length is 2.09 Å. The Fe(1)-O(4) bond length is 2.35 Å. The Fe(1)-O(7) bond length is 2.16 Å. There is one shorter (2.14 Å) and one longer (2.17 Å) Fe(1)-O(6) bond length. In the second Fe site, Fe(2) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra, corners with four equivalent P(2)O4 tetrahedra, and edges with two equivalent Fe(1)O6 octahedra. Both Fe(2)-O(1) bond lengths are 2.17 Å. Both Fe(2)-O(3) bond lengths are 2.13 Å. Both Fe(2)-O(4) bond lengths are 2.20 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  a cornercorner with one Fe(2)O6 octahedra, 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 48-57°. The P(1)-O(2) bond length is 1.54 Å. The P(1)-O(4) bond length is 1.55 Å. The P(1)-O(5) bond length is 1.63 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 two equivalent Fe(2)O6 octahedra, 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 39-60°. The P(2)-O(1) bond length is 1.55 Å. The P(2)-O(3) bond length is 1.52 Å. The P(2)-O(5) bond length is 1.60 Å. The P(2)-O(6) bond length is 1.54 Å. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a distorted trigonal planar geometry to one Li(1), one Fe(1), and one P(1) atom. In the second O site, O(1) is bonded to one Li(1), one Fe(1), one Fe(2), and one P(2) atom to form distorted corner-sharing OLiFe2P trigonal pyramids. In the third O site, O(2) is bonded in a distorted trigonal planar geometry to one Li(1), one Fe(1), and one P(1) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one Li(1), one Fe(2), and one P(2) atom. In the fifth O site, O(4) is bonded in a 4-coordinate geometry to one Li(1), one Fe(1), one Fe(2), and one P(1) atom. In the sixth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one P(1) and one P(2) atom. In the seventh O site, O(6) is bonded in a distorted trigonal planar geometry to two equivalent Fe(1) and one P(2) atom.