Li4FeSi2O7 is Stannite-like structured and crystallizes in the monoclinic C2 space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(1), one O(2), and two equivalent O(4) atoms to form LiO4 tetrahedra that share  a cornercorner with one Fe(1)O4 tetrahedra, corners with three equivalent Li(1)O4 tetrahedra, corners with three equivalent Li(2)O4 tetrahedra, and corners with five equivalent Si(1)O4 tetrahedra. In the second Li site, Li(2) is bonded to one O(2), one O(4), and two equivalent O(3) atoms to form LiO4 tetrahedra that share corners with two equivalent Li(2)O4 tetrahedra, corners with three equivalent Li(1)O4 tetrahedra, corners with three equivalent Fe(1)O4 tetrahedra, and corners with four equivalent Si(1)O4 tetrahedra. Fe(1) is bonded to two equivalent O(2) and two equivalent O(3) atoms to form distorted FeO4 tetrahedra that share corners with two equivalent Li(1)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and corners with six equivalent Li(2)O4 tetrahedra. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Fe(1)O4 tetrahedra, corners with four equivalent Li(2)O4 tetrahedra, and corners with five equivalent Li(1)O4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Li(1) and two equivalent Si(1) atoms to form OLi2Si2 tetrahedra that share corners with two equivalent O(3)Li2FeSi tetrahedra, corners with four equivalent O(2)Li2FeSi tetrahedra, and corners with six equivalent O(4)Li3Si tetrahedra. In the second O site, O(2) is bonded to one Li(1), one Li(2), one Fe(1), and one Si(1) atom to form OLi2FeSi tetrahedra that share  a cornercorner with one O(2)Li2FeSi tetrahedra, corners with two equivalent O(1)Li2Si2 tetrahedra, corners with four equivalent O(4)Li3Si tetrahedra, and corners with five equivalent O(3)Li2FeSi tetrahedra. In the third O site, O(3) is bonded to two equivalent Li(2), one Fe(1), and one Si(1) atom to form OLi2FeSi tetrahedra that share  a cornercorner with one O(1)Li2Si2 tetrahedra, corners with three equivalent O(3)Li2FeSi tetrahedra, corners with three equivalent O(4)Li3Si tetrahedra, and corners with five equivalent O(2)Li2FeSi tetrahedra. In the fourth O site, O(4) is bonded to one Li(2), two equivalent Li(1), and one Si(1) atom to form OLi3Si tetrahedra that share corners with two equivalent O(4)Li3Si tetrahedra, corners with three equivalent O(3)Li2FeSi tetrahedra, corners with three equivalent O(1)Li2Si2 tetrahedra, and corners with four equivalent O(2)Li2FeSi tetrahedra.
Li4FeSi2O7 is Stannite-like structured and crystallizes in the monoclinic C2 space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(1), one O(2), and two equivalent O(4) atoms to form LiO4 tetrahedra that share  a cornercorner with one Fe(1)O4 tetrahedra, corners with three equivalent Li(1)O4 tetrahedra, corners with three equivalent Li(2)O4 tetrahedra, and corners with five equivalent Si(1)O4 tetrahedra. The Li(1)-O(1) bond length is 2.19 Å. The Li(1)-O(2) bond length is 1.98 Å. There is one shorter (1.94 Å) and one longer (1.96 Å) Li(1)-O(4) bond length. In the second Li site, Li(2) is bonded to one O(2), one O(4), and two equivalent O(3) atoms to form LiO4 tetrahedra that share corners with two equivalent Li(2)O4 tetrahedra, corners with three equivalent Li(1)O4 tetrahedra, corners with three equivalent Fe(1)O4 tetrahedra, and corners with four equivalent Si(1)O4 tetrahedra. The Li(2)-O(2) bond length is 2.01 Å. The Li(2)-O(4) bond length is 1.94 Å. There is one shorter (2.00 Å) and one longer (2.07 Å) Li(2)-O(3) bond length. Fe(1) is bonded to two equivalent O(2) and two equivalent O(3) atoms to form distorted FeO4 tetrahedra that share corners with two equivalent Li(1)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and corners with six equivalent Li(2)O4 tetrahedra. Both Fe(1)-O(2) bond lengths are 2.03 Å. Both Fe(1)-O(3) bond lengths are 2.04 Å. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Fe(1)O4 tetrahedra, corners with four equivalent Li(2)O4 tetrahedra, and corners with five equivalent Li(1)O4 tetrahedra. The Si(1)-O(1) bond length is 1.72 Å. The Si(1)-O(2) bond length is 1.65 Å. The Si(1)-O(3) bond length is 1.64 Å. The Si(1)-O(4) bond length is 1.62 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Li(1) and two equivalent Si(1) atoms to form OLi2Si2 tetrahedra that share corners with two equivalent O(3)Li2FeSi tetrahedra, corners with four equivalent O(2)Li2FeSi tetrahedra, and corners with six equivalent O(4)Li3Si tetrahedra. In the second O site, O(2) is bonded to one Li(1), one Li(2), one Fe(1), and one Si(1) atom to form OLi2FeSi tetrahedra that share  a cornercorner with one O(2)Li2FeSi tetrahedra, corners with two equivalent O(1)Li2Si2 tetrahedra, corners with four equivalent O(4)Li3Si tetrahedra, and corners with five equivalent O(3)Li2FeSi tetrahedra. In the third O site, O(3) is bonded to two equivalent Li(2), one Fe(1), and one Si(1) atom to form OLi2FeSi tetrahedra that share  a cornercorner with one O(1)Li2Si2 tetrahedra, corners with three equivalent O(3)Li2FeSi tetrahedra, corners with three equivalent O(4)Li3Si tetrahedra, and corners with five equivalent O(2)Li2FeSi tetrahedra. In the fourth O site, O(4) is bonded to one Li(2), two equivalent Li(1), and one Si(1) atom to form OLi3Si tetrahedra that share corners with two equivalent O(4)Li3Si tetrahedra, corners with three equivalent O(3)Li2FeSi tetrahedra, corners with three equivalent O(1)Li2Si2 tetrahedra, and corners with four equivalent O(2)Li2FeSi tetrahedra.