Li2FeP2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded in a 4-coordinate geometry to one O(3), one O(6), and two equivalent O(5) atoms. In the second Li site, Li(2) is bonded to one O(1), one O(7), and two equivalent O(2) atoms to form distorted LiO4 tetrahedra that share corners with two equivalent Fe(2)O6 octahedra, corners with four equivalent P(2)O4 tetrahedra,  an edgeedge with one Fe(2)O6 octahedra, and  an edgeedge with one Li(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 73-78°. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with six 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(7) atoms to form FeO6 octahedra that share corners with four equivalent Li(2)O4 tetrahedra, corners with six equivalent P(2)O4 tetrahedra, and edges with two equivalent Li(2)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share 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 32-55°. In the second P site, P(2) is bonded to one O(1), one O(2), one O(4), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Fe(2)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and corners with four equivalent Li(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-56°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Li(2), one Fe(2), and one P(2) atom. In the second O site, O(2) is bonded to two equivalent Li(2), one Fe(2), and one P(2) atom to form a mixture of distorted corner and edge-sharing OLi2FeP tetrahedra. In the third O site, O(3) 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(4) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the fifth O site, O(5) is bonded to two equivalent Li(1), one Fe(1), and one P(1) atom to form a mixture of distorted corner and edge-sharing OLi2FeP tetrahedra. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Li(1), one Fe(1), and one P(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Li(2), one Fe(2), and one P(2) atom.
Li2FeP2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded in a 4-coordinate geometry to one O(3), one O(6), and two equivalent O(5) atoms. The Li(1)-O(3) bond length is 1.93 Å. The Li(1)-O(6) bond length is 1.97 Å. There is one shorter (1.99 Å) and one longer (2.31 Å) Li(1)-O(5) bond length. In the second Li site, Li(2) is bonded to one O(1), one O(7), and two equivalent O(2) atoms to form distorted LiO4 tetrahedra that share corners with two equivalent Fe(2)O6 octahedra, corners with four equivalent P(2)O4 tetrahedra,  an edgeedge with one Fe(2)O6 octahedra, and  an edgeedge with one Li(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 73-78°. The Li(2)-O(1) bond length is 1.97 Å. The Li(2)-O(7) bond length is 1.94 Å. There is one shorter (2.00 Å) and one longer (2.29 Å) Li(2)-O(2) bond length. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra. Both Fe(1)-O(3) bond lengths are 2.32 Å. Both Fe(1)-O(5) bond lengths are 2.16 Å. Both Fe(1)-O(6) bond lengths are 2.10 Å. In the second Fe site, Fe(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with four equivalent Li(2)O4 tetrahedra, corners with six equivalent P(2)O4 tetrahedra, and edges with two equivalent Li(2)O4 tetrahedra. Both Fe(2)-O(1) bond lengths are 2.10 Å. Both Fe(2)-O(2) bond lengths are 2.15 Å. Both Fe(2)-O(7) bond lengths are 2.33 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share 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 32-55°. The P(1)-O(3) bond length is 1.53 Å. The P(1)-O(4) bond length is 1.61 Å. The P(1)-O(5) bond length is 1.54 Å. The P(1)-O(6) bond length is 1.54 Å. In the second P site, P(2) is bonded to one O(1), one O(2), one O(4), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Fe(2)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and corners with four equivalent Li(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-56°. The P(2)-O(1) bond length is 1.54 Å. The P(2)-O(2) bond length is 1.54 Å. The P(2)-O(4) bond length is 1.61 Å. The P(2)-O(7) bond length is 1.53 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Li(2), one Fe(2), and one P(2) atom. In the second O site, O(2) is bonded to two equivalent Li(2), one Fe(2), and one P(2) atom to form a mixture of distorted corner and edge-sharing OLi2FeP tetrahedra. In the third O site, O(3) 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(4) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the fifth O site, O(5) is bonded to two equivalent Li(1), one Fe(1), and one P(1) atom to form a mixture of distorted corner and edge-sharing OLi2FeP tetrahedra. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Li(1), one Fe(1), and one P(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Li(2), one Fe(2), and one P(2) atom.