Li2FeF4 crystallizes in the monoclinic P2_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 F(2), one F(4), and two equivalent F(3) atoms. In the second Li site, Li(2) is bonded in a 5-coordinate geometry to one F(1), one F(3), one F(4), and two equivalent F(2) atoms. Fe(1) is bonded to one F(2), one F(3), two equivalent F(1), and two equivalent F(4) atoms to form corner-sharing FeF6 octahedra. The corner-sharing octahedral tilt angles range from 47-49°. There are four inequivalent F sites. In the first F site, F(1) is bonded in a 3-coordinate geometry to one Li(2) and two equivalent Fe(1) atoms. In the second F site, F(2) is bonded to one Li(1), two equivalent Li(2), and one Fe(1) atom to form distorted FLi3Fe trigonal pyramids that share corners with two equivalent F(2)Li3Fe trigonal pyramids, corners with three equivalent F(4)Li2Fe2 trigonal pyramids, corners with three equivalent F(3)Li3Fe trigonal pyramids,  an edgeedge with one F(4)Li2Fe2 trigonal pyramid, and  an edgeedge with one F(3)Li3Fe trigonal pyramid. In the third F site, F(3) is bonded to one Li(2), two equivalent Li(1), and one Fe(1) atom to form distorted FLi3Fe trigonal pyramids that share corners with two equivalent F(3)Li3Fe trigonal pyramids, corners with three equivalent F(4)Li2Fe2 trigonal pyramids, corners with three equivalent F(2)Li3Fe trigonal pyramids,  an edgeedge with one F(4)Li2Fe2 trigonal pyramid, and  an edgeedge with one F(2)Li3Fe trigonal pyramid. In the fourth F site, F(4) is bonded to one Li(1), one Li(2), and two equivalent Fe(1) atoms to form distorted FLi2Fe2 trigonal pyramids that share corners with two equivalent F(4)Li2Fe2 trigonal pyramids, corners with three equivalent F(2)Li3Fe trigonal pyramids, corners with three equivalent F(3)Li3Fe trigonal pyramids,  an edgeedge with one F(2)Li3Fe trigonal pyramid, and  an edgeedge with one F(3)Li3Fe trigonal pyramid.
Li2FeF4 crystallizes in the monoclinic P2_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 F(2), one F(4), and two equivalent F(3) atoms. The Li(1)-F(2) bond length is 2.07 Å. The Li(1)-F(4) bond length is 1.95 Å. There is one shorter (1.91 Å) and one longer (1.96 Å) Li(1)-F(3) bond length. In the second Li site, Li(2) is bonded in a 5-coordinate geometry to one F(1), one F(3), one F(4), and two equivalent F(2) atoms. The Li(2)-F(1) bond length is 1.93 Å. The Li(2)-F(3) bond length is 2.25 Å. The Li(2)-F(4) bond length is 2.35 Å. There is one shorter (1.92 Å) and one longer (1.93 Å) Li(2)-F(2) bond length. Fe(1) is bonded to one F(2), one F(3), two equivalent F(1), and two equivalent F(4) atoms to form corner-sharing FeF6 octahedra. The corner-sharing octahedral tilt angles range from 47-49°. The Fe(1)-F(2) bond length is 2.06 Å. The Fe(1)-F(3) bond length is 2.02 Å. Both Fe(1)-F(1) bond lengths are 2.14 Å. Both Fe(1)-F(4) bond lengths are 2.12 Å. There are four inequivalent F sites. In the first F site, F(1) is bonded in a 3-coordinate geometry to one Li(2) and two equivalent Fe(1) atoms. In the second F site, F(2) is bonded to one Li(1), two equivalent Li(2), and one Fe(1) atom to form distorted FLi3Fe trigonal pyramids that share corners with two equivalent F(2)Li3Fe trigonal pyramids, corners with three equivalent F(4)Li2Fe2 trigonal pyramids, corners with three equivalent F(3)Li3Fe trigonal pyramids,  an edgeedge with one F(4)Li2Fe2 trigonal pyramid, and  an edgeedge with one F(3)Li3Fe trigonal pyramid. In the third F site, F(3) is bonded to one Li(2), two equivalent Li(1), and one Fe(1) atom to form distorted FLi3Fe trigonal pyramids that share corners with two equivalent F(3)Li3Fe trigonal pyramids, corners with three equivalent F(4)Li2Fe2 trigonal pyramids, corners with three equivalent F(2)Li3Fe trigonal pyramids,  an edgeedge with one F(4)Li2Fe2 trigonal pyramid, and  an edgeedge with one F(2)Li3Fe trigonal pyramid. In the fourth F site, F(4) is bonded to one Li(1), one Li(2), and two equivalent Fe(1) atoms to form distorted FLi2Fe2 trigonal pyramids that share corners with two equivalent F(4)Li2Fe2 trigonal pyramids, corners with three equivalent F(2)Li3Fe trigonal pyramids, corners with three equivalent F(3)Li3Fe trigonal pyramids,  an edgeedge with one F(2)Li3Fe trigonal pyramid, and  an edgeedge with one F(3)Li3Fe trigonal pyramid.