Fe2Ni(PO4)2 crystallizes in the monoclinic P2_1 space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(8), two equivalent O(4), and two equivalent O(6) atoms to form distorted FeO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra, corners with four equivalent Fe(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra,  an edgeedge with one Fe(2)O6 octahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-64°. In the second Fe site, Fe(2) is bonded to one O(1), one O(2), one O(5), one O(6), one O(7), and one O(8) atom to form FeO6 octahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Ni(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra,  an edgeedge with one P(1)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 59-64°. Ni(1) is bonded to one O(1), one O(7), two equivalent O(3), and two equivalent O(5) atoms to form distorted NiO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra, corners with four equivalent Ni(1)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra,  an edgeedge with one Fe(2)O6 octahedra, and  an edgeedge with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-64°. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(3), one O(5), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra, corners with three equivalent Ni(1)O6 octahedra,  an edgeedge with one Fe(2)O6 octahedra, and  an edgeedge with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. In the second P site, P(2) is bonded to one O(2), one O(4), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one Ni(1)O6 octahedra, corners with three equivalent Fe(1)O6 octahedra,  an edgeedge with one Fe(1)O6 octahedra, and  an edgeedge with one Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-57°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Fe(2), one Ni(1), and one P(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one P(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Fe(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to one Fe(2), two equivalent Ni(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Fe(2), two equivalent Fe(1), and one P(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Fe(2), one Ni(1), and one P(2) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Fe(1), one Fe(2), and one P(1) atom.
Fe2Ni(PO4)2 crystallizes in the monoclinic P2_1 space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(8), two equivalent O(4), and two equivalent O(6) atoms to form distorted FeO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra, corners with four equivalent Fe(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra,  an edgeedge with one Fe(2)O6 octahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-64°. The Fe(1)-O(2) bond length is 2.19 Å. The Fe(1)-O(8) bond length is 2.13 Å. There is one shorter (2.05 Å) and one longer (2.19 Å) Fe(1)-O(4) bond length. There is one shorter (2.10 Å) and one longer (2.39 Å) Fe(1)-O(6) bond length. In the second Fe site, Fe(2) is bonded to one O(1), one O(2), one O(5), one O(6), one O(7), and one O(8) atom to form FeO6 octahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Ni(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra,  an edgeedge with one P(1)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 59-64°. The Fe(2)-O(1) bond length is 2.15 Å. The Fe(2)-O(2) bond length is 2.13 Å. The Fe(2)-O(5) bond length is 2.18 Å. The Fe(2)-O(6) bond length is 2.18 Å. The Fe(2)-O(7) bond length is 2.20 Å. The Fe(2)-O(8) bond length is 2.19 Å. Ni(1) is bonded to one O(1), one O(7), two equivalent O(3), and two equivalent O(5) atoms to form distorted NiO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra, corners with four equivalent Ni(1)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra,  an edgeedge with one Fe(2)O6 octahedra, and  an edgeedge with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-64°. The Ni(1)-O(1) bond length is 2.13 Å. The Ni(1)-O(7) bond length is 2.08 Å. There is one shorter (2.04 Å) and one longer (2.12 Å) Ni(1)-O(3) bond length. There is one shorter (2.13 Å) and one longer (2.30 Å) Ni(1)-O(5) bond length. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(3), one O(5), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra, corners with three equivalent Ni(1)O6 octahedra,  an edgeedge with one Fe(2)O6 octahedra, and  an edgeedge with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. The P(1)-O(1) bond length is 1.55 Å. The P(1)-O(3) bond length is 1.55 Å. The P(1)-O(5) bond length is 1.60 Å. The P(1)-O(8) bond length is 1.55 Å. In the second P site, P(2) is bonded to one O(2), one O(4), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one Ni(1)O6 octahedra, corners with three equivalent Fe(1)O6 octahedra,  an edgeedge with one Fe(1)O6 octahedra, and  an edgeedge with one Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-57°. The P(2)-O(2) bond length is 1.54 Å. The P(2)-O(4) bond length is 1.55 Å. The P(2)-O(6) bond length is 1.59 Å. The P(2)-O(7) bond length is 1.55 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Fe(2), one Ni(1), and one P(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one P(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Fe(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to one Fe(2), two equivalent Ni(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Fe(2), two equivalent Fe(1), and one P(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Fe(2), one Ni(1), and one P(2) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Fe(1), one Fe(2), and one P(1) atom.