Fe10NiN8 crystallizes in the monoclinic C2/m space group. There are five inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a distorted trigonal non-coplanar geometry to one N(1), one N(2), and one N(3) atom. In the second Fe site, Fe(2) is bonded in a 5-coordinate geometry to one N(2), two equivalent N(1), and two equivalent N(4) atoms. In the third Fe site, Fe(3) is bonded to one N(3), one N(4), and three equivalent N(2) atoms to form a mixture of distorted corner and edge-sharing FeN5 square pyramids. In the fourth Fe site, Fe(4) is bonded to one N(3), two equivalent N(1), and two equivalent N(4) atoms to form a mixture of distorted corner and edge-sharing FeN5 square pyramids. In the fifth Fe site, Fe(5) is bonded in a square co-planar geometry to one N(1), one N(2), and two equivalent N(3) atoms. Ni(1) is bonded in a distorted square co-planar geometry to two equivalent N(3) and two equivalent N(4) atoms. There are four inequivalent N sites. In the first N site, N(1) is bonded to one Fe(1), one Fe(5), two equivalent Fe(2), and two equivalent Fe(4) atoms to form distorted NFe6 octahedra that share corners with two equivalent N(1)Fe6 octahedra,  an edgeedge with one N(1)Fe6 octahedra, and edges with four equivalent N(4)Fe5Ni octahedra. The corner-sharing octahedral tilt angles are 24°. In the second N site, N(2) is bonded in a 6-coordinate geometry to one Fe(1), one Fe(2), one Fe(5), and three equivalent Fe(3) atoms. In the third N site, N(3) is bonded in a 6-coordinate geometry to one Fe(1), one Fe(3), one Fe(4), two equivalent Fe(5), and one Ni(1) atom. In the fourth N site, N(4) is bonded to one Fe(3), two equivalent Fe(2), two equivalent Fe(4), and one Ni(1) atom to form NFe5Ni octahedra that share corners with three equivalent N(4)Fe5Ni octahedra,  an edgeedge with one N(4)Fe5Ni octahedra, and edges with four equivalent N(1)Fe6 octahedra. The corner-sharing octahedral tilt angles range from 0-23°.
Fe10NiN8 crystallizes in the monoclinic C2/m space group. There are five inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a distorted trigonal non-coplanar geometry to one N(1), one N(2), and one N(3) atom. The Fe(1)-N(1) bond length is 1.81 Å. The Fe(1)-N(2) bond length is 1.81 Å. The Fe(1)-N(3) bond length is 1.86 Å. In the second Fe site, Fe(2) is bonded in a 5-coordinate geometry to one N(2), two equivalent N(1), and two equivalent N(4) atoms. The Fe(2)-N(2) bond length is 2.55 Å. There is one shorter (1.90 Å) and one longer (2.33 Å) Fe(2)-N(1) bond length. Both Fe(2)-N(4) bond lengths are 1.95 Å. In the third Fe site, Fe(3) is bonded to one N(3), one N(4), and three equivalent N(2) atoms to form a mixture of distorted corner and edge-sharing FeN5 square pyramids. The Fe(3)-N(3) bond length is 1.90 Å. The Fe(3)-N(4) bond length is 1.94 Å. There are two shorter (1.95 Å) and one longer (2.00 Å) Fe(3)-N(2) bond length. In the fourth Fe site, Fe(4) is bonded to one N(3), two equivalent N(1), and two equivalent N(4) atoms to form a mixture of distorted corner and edge-sharing FeN5 square pyramids. The Fe(4)-N(3) bond length is 2.12 Å. Both Fe(4)-N(1) bond lengths are 1.96 Å. There is one shorter (1.91 Å) and one longer (2.16 Å) Fe(4)-N(4) bond length. In the fifth Fe site, Fe(5) is bonded in a square co-planar geometry to one N(1), one N(2), and two equivalent N(3) atoms. The Fe(5)-N(1) bond length is 1.93 Å. The Fe(5)-N(2) bond length is 1.93 Å. Both Fe(5)-N(3) bond lengths are 1.93 Å. Ni(1) is bonded in a distorted square co-planar geometry to two equivalent N(3) and two equivalent N(4) atoms. Both Ni(1)-N(3) bond lengths are 2.44 Å. Both Ni(1)-N(4) bond lengths are 1.87 Å. There are four inequivalent N sites. In the first N site, N(1) is bonded to one Fe(1), one Fe(5), two equivalent Fe(2), and two equivalent Fe(4) atoms to form distorted NFe6 octahedra that share corners with two equivalent N(1)Fe6 octahedra,  an edgeedge with one N(1)Fe6 octahedra, and edges with four equivalent N(4)Fe5Ni octahedra. The corner-sharing octahedral tilt angles are 24°. In the second N site, N(2) is bonded in a 6-coordinate geometry to one Fe(1), one Fe(2), one Fe(5), and three equivalent Fe(3) atoms. In the third N site, N(3) is bonded in a 6-coordinate geometry to one Fe(1), one Fe(3), one Fe(4), two equivalent Fe(5), and one Ni(1) atom. In the fourth N site, N(4) is bonded to one Fe(3), two equivalent Fe(2), two equivalent Fe(4), and one Ni(1) atom to form NFe5Ni octahedra that share corners with three equivalent N(4)Fe5Ni octahedra,  an edgeedge with one N(4)Fe5Ni octahedra, and edges with four equivalent N(1)Fe6 octahedra. The corner-sharing octahedral tilt angles range from 0-23°.