FeNi3(PO4)4 crystallizes in the monoclinic Pm space group. Fe(1) is bonded to one O(1), one O(9), two equivalent O(11), and two equivalent O(5) atoms to form FeO6 octahedra that share corners with four equivalent Ni(2)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(4)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 50°. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(12), one O(4), two equivalent O(2), and two equivalent O(8) atoms to form NiO6 octahedra that share corners with four equivalent Ni(3)O6 octahedra,  a cornercorner with one P(3)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 50°. In the second Ni site, Ni(2) is bonded to one O(3), one O(7), two equivalent O(11), and two equivalent O(5) atoms to form NiO6 octahedra that share corners with four equivalent Fe(1)O6 octahedra,  a cornercorner with one P(3)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and  an edgeedge with one P(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 50°. In the third Ni site, Ni(3) is bonded to one O(10), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form NiO6 octahedra that share corners with four equivalent Ni(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(3)O4 tetrahedra, and  an edgeedge with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 50°. There are four inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(10), and two equivalent O(2) atoms to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Ni(3)O6 octahedra, corners with two equivalent Ni(1)O6 octahedra, and  an edgeedge with one Ni(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-56°. In the second P site, P(2) is bonded to one O(6), one O(9), and two equivalent O(5) atoms to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Ni(3)O6 octahedra, corners with two equivalent Ni(2)O6 octahedra, and  an edgeedge with one Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-56°. In the third P site, P(3) is bonded to one O(4), one O(7), and two equivalent O(8) atoms to form PO4 tetrahedra that share  a cornercorner with one Ni(1)O6 octahedra,  a cornercorner with one Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, and  an edgeedge with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-56°. In the fourth P site, P(4) is bonded to one O(12), one O(3), and two equivalent O(11) atoms to form PO4 tetrahedra that share  a cornercorner with one Ni(1)O6 octahedra,  a cornercorner with one Ni(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  an edgeedge with one Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-54°. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(3), and one P(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Ni(2) and one P(4) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one Ni(1) and one P(3) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Fe(1), one Ni(2), and one P(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Ni(3) and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Ni(2) and one P(3) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(3), and one P(3) atom. In the ninth O site, O(9) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(2) atom. In the tenth O site, O(10) is bonded in a bent 120 degrees geometry to one Ni(3) and one P(1) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal planar geometry to one Fe(1), one Ni(2), and one P(4) atom. In the twelfth O site, O(12) is bonded in a distorted bent 150 degrees geometry to one Ni(1) and one P(4) atom.
FeNi3(PO4)4 crystallizes in the monoclinic Pm space group. Fe(1) is bonded to one O(1), one O(9), two equivalent O(11), and two equivalent O(5) atoms to form FeO6 octahedra that share corners with four equivalent Ni(2)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(4)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 50°. The Fe(1)-O(1) bond length is 1.98 Å. The Fe(1)-O(9) bond length is 1.96 Å. Both Fe(1)-O(11) bond lengths are 2.03 Å. Both Fe(1)-O(5) bond lengths are 2.13 Å. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(12), one O(4), two equivalent O(2), and two equivalent O(8) atoms to form NiO6 octahedra that share corners with four equivalent Ni(3)O6 octahedra,  a cornercorner with one P(3)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 50°. The Ni(1)-O(12) bond length is 1.99 Å. The Ni(1)-O(4) bond length is 1.98 Å. Both Ni(1)-O(2) bond lengths are 2.04 Å. Both Ni(1)-O(8) bond lengths are 2.15 Å. In the second Ni site, Ni(2) is bonded to one O(3), one O(7), two equivalent O(11), and two equivalent O(5) atoms to form NiO6 octahedra that share corners with four equivalent Fe(1)O6 octahedra,  a cornercorner with one P(3)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and  an edgeedge with one P(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 50°. The Ni(2)-O(3) bond length is 1.97 Å. The Ni(2)-O(7) bond length is 1.99 Å. Both Ni(2)-O(11) bond lengths are 2.20 Å. Both Ni(2)-O(5) bond lengths are 2.06 Å. In the third Ni site, Ni(3) is bonded to one O(10), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form NiO6 octahedra that share corners with four equivalent Ni(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(3)O4 tetrahedra, and  an edgeedge with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 50°. The Ni(3)-O(10) bond length is 1.97 Å. The Ni(3)-O(6) bond length is 1.97 Å. Both Ni(3)-O(2) bond lengths are 2.16 Å. Both Ni(3)-O(8) bond lengths are 2.04 Å. There are four inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(10), and two equivalent O(2) atoms to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Ni(3)O6 octahedra, corners with two equivalent Ni(1)O6 octahedra, and  an edgeedge with one Ni(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-56°. The P(1)-O(1) bond length is 1.54 Å. The P(1)-O(10) bond length is 1.53 Å. Both P(1)-O(2) bond lengths are 1.57 Å. In the second P site, P(2) is bonded to one O(6), one O(9), and two equivalent O(5) atoms to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Ni(3)O6 octahedra, corners with two equivalent Ni(2)O6 octahedra, and  an edgeedge with one Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-56°. The P(2)-O(6) bond length is 1.53 Å. The P(2)-O(9) bond length is 1.53 Å. Both P(2)-O(5) bond lengths are 1.58 Å. In the third P site, P(3) is bonded to one O(4), one O(7), and two equivalent O(8) atoms to form PO4 tetrahedra that share  a cornercorner with one Ni(1)O6 octahedra,  a cornercorner with one Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, and  an edgeedge with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-56°. The P(3)-O(4) bond length is 1.53 Å. The P(3)-O(7) bond length is 1.53 Å. Both P(3)-O(8) bond lengths are 1.57 Å. In the fourth P site, P(4) is bonded to one O(12), one O(3), and two equivalent O(11) atoms to form PO4 tetrahedra that share  a cornercorner with one Ni(1)O6 octahedra,  a cornercorner with one Ni(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  an edgeedge with one Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-54°. The P(4)-O(12) bond length is 1.53 Å. The P(4)-O(3) bond length is 1.53 Å. Both P(4)-O(11) bond lengths are 1.57 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(3), and one P(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Ni(2) and one P(4) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one Ni(1) and one P(3) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Fe(1), one Ni(2), and one P(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Ni(3) and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Ni(2) and one P(3) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(3), and one P(3) atom. In the ninth O site, O(9) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(2) atom. In the tenth O site, O(10) is bonded in a bent 120 degrees geometry to one Ni(3) and one P(1) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal planar geometry to one Fe(1), one Ni(2), and one P(4) atom. In the twelfth O site, O(12) is bonded in a distorted bent 150 degrees geometry to one Ni(1) and one P(4) atom.