Fe2Ni(PO4)3 crystallizes in the trigonal R-3c space group. Fe(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form FeO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and  a faceface with one Ni(1)O6 octahedra. Ni(1) is bonded to six equivalent O(2) atoms to form distorted NiO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and faces with two equivalent Fe(1)O6 octahedra. P(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form PO4 tetrahedra that share corners with two equivalent Ni(1)O6 octahedra and corners with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 28-51°. There are two inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Fe(1), one Ni(1), and one P(1) atom.
Fe2Ni(PO4)3 crystallizes in the trigonal R-3c space group. Fe(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form FeO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and  a faceface with one Ni(1)O6 octahedra. All Fe(1)-O(1) bond lengths are 1.94 Å. All Fe(1)-O(2) bond lengths are 2.08 Å. Ni(1) is bonded to six equivalent O(2) atoms to form distorted NiO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and faces with two equivalent Fe(1)O6 octahedra. All Ni(1)-O(2) bond lengths are 2.14 Å. P(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form PO4 tetrahedra that share corners with two equivalent Ni(1)O6 octahedra and corners with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 28-51°. Both P(1)-O(1) bond lengths are 1.52 Å. Both P(1)-O(2) bond lengths are 1.56 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Fe(1), one Ni(1), and one P(1) atom.