Li4Fe(SiO4)2 crystallizes in the triclinic P-1 space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(3), one O(4), and two equivalent O(2) atoms to form distorted LiO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with four equivalent Si(1)O4 tetrahedra,  a cornercorner with one Li(2)O4 trigonal pyramid,  an edgeedge with one Li(1)O4 tetrahedra, and  an edgeedge with one Li(2)O4 trigonal pyramid. The corner-sharing octahedral tilt angles range from 51-66°. In the second Li site, Li(2) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form distorted LiO4 trigonal pyramids that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Li(1)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra,  an edgeedge with one Li(1)O4 tetrahedra, and  an edgeedge with one Li(2)O4 trigonal pyramid. The corner-sharing octahedral tilt angles are 68°. Fe(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Li(1)O4 tetrahedra, corners with two equivalent Li(2)O4 trigonal pyramids, edges with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Li(2)O4 trigonal pyramids. 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 Fe(1)O6 octahedra, corners with four equivalent Li(1)O4 tetrahedra, corners with four equivalent Li(2)O4 trigonal pyramids, and  an edgeedge with one Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles are 45°. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Li(2), one Fe(1), and one Si(1) atom to form a mixture of distorted edge and corner-sharing OLi2FeSi trigonal pyramids. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Li(2), two equivalent Li(1), and one Si(1) atom. In the third O site, O(3) is bonded to one Li(1), one Li(2), one Fe(1), and one Si(1) atom to form a mixture of distorted edge and corner-sharing OLi2FeSi trigonal pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Li(1), one Fe(1), and one Si(1) atom.
Li4Fe(SiO4)2 crystallizes in the triclinic P-1 space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(3), one O(4), and two equivalent O(2) atoms to form distorted LiO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with four equivalent Si(1)O4 tetrahedra,  a cornercorner with one Li(2)O4 trigonal pyramid,  an edgeedge with one Li(1)O4 tetrahedra, and  an edgeedge with one Li(2)O4 trigonal pyramid. The corner-sharing octahedral tilt angles range from 51-66°. The Li(1)-O(3) bond length is 2.02 Å. The Li(1)-O(4) bond length is 1.99 Å. There is one shorter (2.02 Å) and one longer (2.05 Å) Li(1)-O(2) bond length. In the second Li site, Li(2) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form distorted LiO4 trigonal pyramids that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Li(1)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra,  an edgeedge with one Li(1)O4 tetrahedra, and  an edgeedge with one Li(2)O4 trigonal pyramid. The corner-sharing octahedral tilt angles are 68°. The Li(2)-O(2) bond length is 1.94 Å. The Li(2)-O(3) bond length is 2.07 Å. There is one shorter (1.96 Å) and one longer (2.21 Å) Li(2)-O(1) bond length. Fe(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Li(1)O4 tetrahedra, corners with two equivalent Li(2)O4 trigonal pyramids, edges with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Li(2)O4 trigonal pyramids. Both Fe(1)-O(1) bond lengths are 1.94 Å. Both Fe(1)-O(3) bond lengths are 2.09 Å. Both Fe(1)-O(4) bond lengths are 1.96 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 Fe(1)O6 octahedra, corners with four equivalent Li(1)O4 tetrahedra, corners with four equivalent Li(2)O4 trigonal pyramids, and  an edgeedge with one Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles are 45°. The Si(1)-O(1) bond length is 1.70 Å. The Si(1)-O(2) bond length is 1.61 Å. The Si(1)-O(3) bond length is 1.63 Å. The Si(1)-O(4) bond length is 1.68 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Li(2), one Fe(1), and one Si(1) atom to form a mixture of distorted edge and corner-sharing OLi2FeSi trigonal pyramids. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Li(2), two equivalent Li(1), and one Si(1) atom. In the third O site, O(3) is bonded to one Li(1), one Li(2), one Fe(1), and one Si(1) atom to form a mixture of distorted edge and corner-sharing OLi2FeSi trigonal pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Li(1), one Fe(1), and one Si(1) atom.