Li2Fe2Si2O7 crystallizes in the monoclinic Cc space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(2), one O(5), one O(6), and one O(7) atom to form distorted LiO4 trigonal pyramids that share corners with two equivalent Fe(2)O5 square pyramids,  a cornercorner with one Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, and corners with two equivalent Li(2)O4 trigonal pyramids. In the second Li site, Li(2) is bonded to one O(3), one O(4), one O(6), and one O(7) atom to form distorted LiO4 trigonal pyramids that share corners with two equivalent Fe(2)O5 square pyramids,  a cornercorner with one Si(2)O4 tetrahedra, corners with three equivalent Si(1)O4 tetrahedra, and corners with two equivalent Li(1)O4 trigonal pyramids. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 6-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom. In the second Fe site, Fe(2) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(5) atom to form distorted FeO5 square pyramids that share corners with three equivalent Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, corners with two equivalent Li(1)O4 trigonal pyramids, and corners with two equivalent Li(2)O4 trigonal pyramids. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(4), and one O(7) atom to form SiO4 tetrahedra that share corners with three equivalent Fe(2)O5 square pyramids,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Li(1)O4 trigonal pyramid, and corners with three equivalent Li(2)O4 trigonal pyramids. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with three equivalent Fe(2)O5 square pyramids,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Li(2)O4 trigonal pyramid, and corners with three equivalent Li(1)O4 trigonal pyramids. There are seven inequivalent O sites. In the first O site, O(6) is bonded to one Li(1), one Li(2), one Fe(1), and one Si(2) atom to form distorted OLi2FeSi tetrahedra that share corners with two equivalent O(4)LiFe2Si tetrahedra, corners with three equivalent O(7)Li2FeSi tetrahedra, and corners with three equivalent O(5)LiFe2Si tetrahedra. In the second O site, O(7) is bonded to one Li(1), one Li(2), one Fe(1), and one Si(1) atom to form distorted OLi2FeSi tetrahedra that share corners with two equivalent O(5)LiFe2Si tetrahedra, corners with three equivalent O(6)Li2FeSi tetrahedra, and corners with three equivalent O(4)LiFe2Si tetrahedra. In the third O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Fe(2), one Si(1), and one Si(2) atom. In the fourth O site, O(2) is bonded in a 4-coordinate geometry to one Li(1), one Fe(1), one Fe(2), and one Si(2) atom. In the fifth O site, O(3) is bonded in a 4-coordinate geometry to one Li(2), one Fe(1), one Fe(2), and one Si(1) atom. In the sixth O site, O(4) is bonded to one Li(2), one Fe(1), one Fe(2), and one Si(1) atom to form distorted OLiFe2Si tetrahedra that share corners with two equivalent O(6)Li2FeSi tetrahedra, corners with two equivalent O(5)LiFe2Si tetrahedra, and corners with three equivalent O(7)Li2FeSi tetrahedra. In the seventh O site, O(5) is bonded to one Li(1), one Fe(1), one Fe(2), and one Si(2) atom to form distorted OLiFe2Si tetrahedra that share corners with two equivalent O(7)Li2FeSi tetrahedra, corners with two equivalent O(4)LiFe2Si tetrahedra, and corners with three equivalent O(6)Li2FeSi tetrahedra.
Li2Fe2Si2O7 crystallizes in the monoclinic Cc space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(2), one O(5), one O(6), and one O(7) atom to form distorted LiO4 trigonal pyramids that share corners with two equivalent Fe(2)O5 square pyramids,  a cornercorner with one Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, and corners with two equivalent Li(2)O4 trigonal pyramids. The Li(1)-O(2) bond length is 2.03 Å. The Li(1)-O(5) bond length is 1.95 Å. The Li(1)-O(6) bond length is 2.08 Å. The Li(1)-O(7) bond length is 2.01 Å. In the second Li site, Li(2) is bonded to one O(3), one O(4), one O(6), and one O(7) atom to form distorted LiO4 trigonal pyramids that share corners with two equivalent Fe(2)O5 square pyramids,  a cornercorner with one Si(2)O4 tetrahedra, corners with three equivalent Si(1)O4 tetrahedra, and corners with two equivalent Li(1)O4 trigonal pyramids. The Li(2)-O(3) bond length is 2.03 Å. The Li(2)-O(4) bond length is 1.95 Å. The Li(2)-O(6) bond length is 2.01 Å. The Li(2)-O(7) bond length is 2.08 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 6-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom. The Fe(1)-O(2) bond length is 2.24 Å. The Fe(1)-O(3) bond length is 2.25 Å. The Fe(1)-O(4) bond length is 2.31 Å. The Fe(1)-O(5) bond length is 2.32 Å. The Fe(1)-O(6) bond length is 2.12 Å. The Fe(1)-O(7) bond length is 2.11 Å. In the second Fe site, Fe(2) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(5) atom to form distorted FeO5 square pyramids that share corners with three equivalent Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, corners with two equivalent Li(1)O4 trigonal pyramids, and corners with two equivalent Li(2)O4 trigonal pyramids. The Fe(2)-O(1) bond length is 2.25 Å. The Fe(2)-O(2) bond length is 2.11 Å. The Fe(2)-O(3) bond length is 2.09 Å. The Fe(2)-O(4) bond length is 2.17 Å. The Fe(2)-O(5) bond length is 2.15 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(4), and one O(7) atom to form SiO4 tetrahedra that share corners with three equivalent Fe(2)O5 square pyramids,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Li(1)O4 trigonal pyramid, and corners with three equivalent Li(2)O4 trigonal pyramids. The Si(1)-O(1) bond length is 1.70 Å. The Si(1)-O(3) bond length is 1.64 Å. The Si(1)-O(4) bond length is 1.65 Å. The Si(1)-O(7) bond length is 1.62 Å. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with three equivalent Fe(2)O5 square pyramids,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Li(2)O4 trigonal pyramid, and corners with three equivalent Li(1)O4 trigonal pyramids. The Si(2)-O(1) bond length is 1.70 Å. The Si(2)-O(2) bond length is 1.64 Å. The Si(2)-O(5) bond length is 1.65 Å. The Si(2)-O(6) bond length is 1.62 Å. There are seven inequivalent O sites. In the first O site, O(6) is bonded to one Li(1), one Li(2), one Fe(1), and one Si(2) atom to form distorted OLi2FeSi tetrahedra that share corners with two equivalent O(4)LiFe2Si tetrahedra, corners with three equivalent O(7)Li2FeSi tetrahedra, and corners with three equivalent O(5)LiFe2Si tetrahedra. In the second O site, O(7) is bonded to one Li(1), one Li(2), one Fe(1), and one Si(1) atom to form distorted OLi2FeSi tetrahedra that share corners with two equivalent O(5)LiFe2Si tetrahedra, corners with three equivalent O(6)Li2FeSi tetrahedra, and corners with three equivalent O(4)LiFe2Si tetrahedra. In the third O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Fe(2), one Si(1), and one Si(2) atom. In the fourth O site, O(2) is bonded in a 4-coordinate geometry to one Li(1), one Fe(1), one Fe(2), and one Si(2) atom. In the fifth O site, O(3) is bonded in a 4-coordinate geometry to one Li(2), one Fe(1), one Fe(2), and one Si(1) atom. In the sixth O site, O(4) is bonded to one Li(2), one Fe(1), one Fe(2), and one Si(1) atom to form distorted OLiFe2Si tetrahedra that share corners with two equivalent O(6)Li2FeSi tetrahedra, corners with two equivalent O(5)LiFe2Si tetrahedra, and corners with three equivalent O(7)Li2FeSi tetrahedra. In the seventh O site, O(5) is bonded to one Li(1), one Fe(1), one Fe(2), and one Si(2) atom to form distorted OLiFe2Si tetrahedra that share corners with two equivalent O(7)Li2FeSi tetrahedra, corners with two equivalent O(4)LiFe2Si tetrahedra, and corners with three equivalent O(6)Li2FeSi tetrahedra.