Li2FeP2O7 crystallizes in the monoclinic C2/c space group. There are three inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(3), one O(5), one O(6), and one O(7) atom to form LiO4 tetrahedra that share  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one Li(3)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, and corners with two equivalent P(2)O4 tetrahedra. In the second Li site, Li(2) is bonded to two equivalent O(4) and two equivalent O(7) atoms to form distorted LiO4 tetrahedra that share corners with two equivalent Li(1)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, and corners with two equivalent P(2)O4 tetrahedra. In the third Li site, Li(3) is bonded to two equivalent O(2) and two equivalent O(6) atoms to form distorted LiO4 tetrahedra that share corners with two equivalent Li(1)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, and corners with two equivalent P(2)O4 tetrahedra. Fe(1) is bonded in a square co-planar geometry to one O(2), one O(3), one O(4), and one O(5) 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(7) atom to form PO4 tetrahedra that share  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one Li(3)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra, and corners with two equivalent Li(1)O4 tetrahedra. In the second P site, P(2) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one Li(3)O4 tetrahedra,  a cornercorner with one P(1)O4 tetrahedra, and corners with two equivalent Li(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to one Li(3), one Fe(1), and one P(1) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Li(1), one Fe(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Li(2), one Fe(1), and one P(2) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Li(1), one Fe(1), and one P(2) atom. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Li(1), one Li(3), and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Li(1), one Li(2), and one P(1) atom.
Li2FeP2O7 crystallizes in the monoclinic C2/c space group. There are three inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(3), one O(5), one O(6), and one O(7) atom to form LiO4 tetrahedra that share  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one Li(3)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, and corners with two equivalent P(2)O4 tetrahedra. The Li(1)-O(3) bond length is 2.03 Å. The Li(1)-O(5) bond length is 2.03 Å. The Li(1)-O(6) bond length is 1.90 Å. The Li(1)-O(7) bond length is 1.91 Å. In the second Li site, Li(2) is bonded to two equivalent O(4) and two equivalent O(7) atoms to form distorted LiO4 tetrahedra that share corners with two equivalent Li(1)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, and corners with two equivalent P(2)O4 tetrahedra. Both Li(2)-O(4) bond lengths are 2.03 Å. Both Li(2)-O(7) bond lengths are 1.91 Å. In the third Li site, Li(3) is bonded to two equivalent O(2) and two equivalent O(6) atoms to form distorted LiO4 tetrahedra that share corners with two equivalent Li(1)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, and corners with two equivalent P(2)O4 tetrahedra. Both Li(3)-O(2) bond lengths are 2.03 Å. Both Li(3)-O(6) bond lengths are 1.91 Å. Fe(1) is bonded in a square co-planar geometry to one O(2), one O(3), one O(4), and one O(5) atom. The Fe(1)-O(2) bond length is 2.05 Å. The Fe(1)-O(3) bond length is 2.05 Å. The Fe(1)-O(4) bond length is 2.06 Å. The Fe(1)-O(5) bond length is 2.06 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(7) atom to form PO4 tetrahedra that share  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one Li(3)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra, and corners with two equivalent Li(1)O4 tetrahedra. The P(1)-O(1) bond length is 1.63 Å. The P(1)-O(2) bond length is 1.55 Å. The P(1)-O(3) bond length is 1.55 Å. The P(1)-O(7) bond length is 1.50 Å. In the second P site, P(2) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one Li(3)O4 tetrahedra,  a cornercorner with one P(1)O4 tetrahedra, and corners with two equivalent Li(1)O4 tetrahedra. The P(2)-O(1) bond length is 1.63 Å. The P(2)-O(4) bond length is 1.55 Å. The P(2)-O(5) bond length is 1.55 Å. The P(2)-O(6) bond length is 1.50 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to one Li(3), one Fe(1), and one P(1) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Li(1), one Fe(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Li(2), one Fe(1), and one P(2) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Li(1), one Fe(1), and one P(2) atom. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Li(1), one Li(3), and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Li(1), one Li(2), and one P(1) atom.