LiFeSiO4 crystallizes in the trigonal P31c space group. Li(1) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form distorted LiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, corners with two equivalent Li(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with three equivalent Fe(1)O5 trigonal bipyramids. Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(6) atom to form distorted FeO5 trigonal bipyramids that share  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, corners with three equivalent Li(1)O4 tetrahedra, and edges with two equivalent Fe(1)O5 trigonal bipyramids. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4) and three equivalent O(2) atoms to form SiO4 tetrahedra that share corners with three equivalent Li(1)O4 tetrahedra and corners with six equivalent Fe(1)O5 trigonal bipyramids. In the second Si site, Si(2) is bonded to one O(5) and three equivalent O(1) atoms to form SiO4 tetrahedra that share corners with six equivalent Li(1)O4 tetrahedra and corners with three equivalent Fe(1)O5 trigonal bipyramids. In the third Si site, Si(3) is bonded to one O(6) and three equivalent O(3) atoms to form SiO4 tetrahedra that share corners with three equivalent Li(1)O4 tetrahedra and corners with six equivalent Fe(1)O5 trigonal bipyramids. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Li(1), one Fe(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Li(1), one Fe(1), and one Si(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 Si(3) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to three equivalent Fe(1) and one Si(1) atom. In the fifth O site, O(5) is bonded in a tetrahedral geometry to three equivalent Li(1) and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to three equivalent Fe(1) and one Si(3) atom.
LiFeSiO4 crystallizes in the trigonal P31c space group. Li(1) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form distorted LiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, corners with two equivalent Li(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with three equivalent Fe(1)O5 trigonal bipyramids. The Li(1)-O(1) bond length is 1.94 Å. The Li(1)-O(2) bond length is 2.17 Å. The Li(1)-O(3) bond length is 2.09 Å. The Li(1)-O(5) bond length is 1.92 Å. Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(6) atom to form distorted FeO5 trigonal bipyramids that share  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, corners with three equivalent Li(1)O4 tetrahedra, and edges with two equivalent Fe(1)O5 trigonal bipyramids. The Fe(1)-O(1) bond length is 1.89 Å. The Fe(1)-O(2) bond length is 1.93 Å. The Fe(1)-O(3) bond length is 1.93 Å. The Fe(1)-O(4) bond length is 2.22 Å. The Fe(1)-O(6) bond length is 2.22 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4) and three equivalent O(2) atoms to form SiO4 tetrahedra that share corners with three equivalent Li(1)O4 tetrahedra and corners with six equivalent Fe(1)O5 trigonal bipyramids. The Si(1)-O(4) bond length is 1.69 Å. All Si(1)-O(2) bond lengths are 1.63 Å. In the second Si site, Si(2) is bonded to one O(5) and three equivalent O(1) atoms to form SiO4 tetrahedra that share corners with six equivalent Li(1)O4 tetrahedra and corners with three equivalent Fe(1)O5 trigonal bipyramids. The Si(2)-O(5) bond length is 1.61 Å. All Si(2)-O(1) bond lengths are 1.67 Å. In the third Si site, Si(3) is bonded to one O(6) and three equivalent O(3) atoms to form SiO4 tetrahedra that share corners with three equivalent Li(1)O4 tetrahedra and corners with six equivalent Fe(1)O5 trigonal bipyramids. The Si(3)-O(6) bond length is 1.71 Å. All Si(3)-O(3) bond lengths are 1.64 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Li(1), one Fe(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Li(1), one Fe(1), and one Si(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 Si(3) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to three equivalent Fe(1) and one Si(1) atom. In the fifth O site, O(5) is bonded in a tetrahedral geometry to three equivalent Li(1) and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to three equivalent Fe(1) and one Si(3) atom.