Li4Fe5NiO12 crystallizes in the monoclinic C2/m space group. Li(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent O(1) and two equivalent O(2) atoms. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form edge-sharing FeO6 octahedra. In the second Fe site, Fe(2) is bonded to two equivalent O(4) and four equivalent O(1) atoms to form FeO6 octahedra that share edges with three equivalent Fe(2)O6 octahedra and edges with three equivalent Ni(1)O6 octahedra. In the third Fe site, Fe(3) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form edge-sharing FeO6 octahedra. Ni(1) is bonded to two equivalent O(4) and four equivalent O(1) atoms to form NiO6 octahedra that share edges with six equivalent Fe(2)O6 octahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Li(1), two equivalent Fe(2), and one Ni(1) atom to form distorted OLi2Fe2Ni trigonal bipyramids that share corners with two equivalent O(2)Li2Fe3 trigonal bipyramids, corners with three equivalent O(1)Li2Fe2Ni trigonal bipyramids,  an edgeedge with one O(2)Li2Fe3 trigonal bipyramid, and edges with four equivalent O(1)Li2Fe2Ni trigonal bipyramids. In the second O site, O(2) is bonded to two equivalent Li(1), one Fe(3), and two equivalent Fe(1) atoms to form distorted OLi2Fe3 trigonal bipyramids that share corners with two equivalent O(1)Li2Fe2Ni trigonal bipyramids, corners with three equivalent O(2)Li2Fe3 trigonal bipyramids,  an edgeedge with one O(1)Li2Fe2Ni trigonal bipyramid, and edges with four equivalent O(2)Li2Fe3 trigonal bipyramids. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Fe(3) and two equivalent Fe(1) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Fe(2) and one Ni(1) atom.
Li4Fe5NiO12 crystallizes in the monoclinic C2/m space group. Li(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent O(1) and two equivalent O(2) atoms. Both Li(1)-O(1) bond lengths are 2.04 Å. There is one shorter (2.05 Å) and one longer (2.09 Å) Li(1)-O(2) bond length. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form edge-sharing FeO6 octahedra. Both Fe(1)-O(3) bond lengths are 1.96 Å. There are two shorter (1.96 Å) and two longer (2.12 Å) Fe(1)-O(2) bond lengths. In the second Fe site, Fe(2) is bonded to two equivalent O(4) and four equivalent O(1) atoms to form FeO6 octahedra that share edges with three equivalent Fe(2)O6 octahedra and edges with three equivalent Ni(1)O6 octahedra. Both Fe(2)-O(4) bond lengths are 1.92 Å. There are two shorter (1.91 Å) and two longer (2.13 Å) Fe(2)-O(1) bond lengths. In the third Fe site, Fe(3) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form edge-sharing FeO6 octahedra. Both Fe(3)-O(3) bond lengths are 2.03 Å. All Fe(3)-O(2) bond lengths are 2.07 Å. Ni(1) is bonded to two equivalent O(4) and four equivalent O(1) atoms to form NiO6 octahedra that share edges with six equivalent Fe(2)O6 octahedra. Both Ni(1)-O(4) bond lengths are 2.08 Å. All Ni(1)-O(1) bond lengths are 2.12 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Li(1), two equivalent Fe(2), and one Ni(1) atom to form distorted OLi2Fe2Ni trigonal bipyramids that share corners with two equivalent O(2)Li2Fe3 trigonal bipyramids, corners with three equivalent O(1)Li2Fe2Ni trigonal bipyramids,  an edgeedge with one O(2)Li2Fe3 trigonal bipyramid, and edges with four equivalent O(1)Li2Fe2Ni trigonal bipyramids. In the second O site, O(2) is bonded to two equivalent Li(1), one Fe(3), and two equivalent Fe(1) atoms to form distorted OLi2Fe3 trigonal bipyramids that share corners with two equivalent O(1)Li2Fe2Ni trigonal bipyramids, corners with three equivalent O(2)Li2Fe3 trigonal bipyramids,  an edgeedge with one O(1)Li2Fe2Ni trigonal bipyramid, and edges with four equivalent O(2)Li2Fe3 trigonal bipyramids. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Fe(3) and two equivalent Fe(1) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Fe(2) and one Ni(1) atom.