MgTiNi(PO4)3 crystallizes in the trigonal R3c space group. Mg(1) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form distorted MgO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra,  a faceface with one Ti(1)O6 octahedra, and  a faceface with one Ni(1)O6 octahedra. Ti(1) is bonded to three equivalent O(2) and three equivalent O(4) atoms to form TiO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and  a faceface with one Mg(1)O6 octahedra. Ni(1) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form NiO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and  a faceface with one Mg(1)O6 octahedra. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Ti(1)O6 octahedra, and corners with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 23-51°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Ni(1) and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mg(1), one Ti(1), and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Ni(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Ti(1) and one P(1) atom.
MgTiNi(PO4)3 crystallizes in the trigonal R3c space group. Mg(1) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form distorted MgO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra,  a faceface with one Ti(1)O6 octahedra, and  a faceface with one Ni(1)O6 octahedra. All Mg(1)-O(2) bond lengths are 2.22 Å. All Mg(1)-O(3) bond lengths are 2.13 Å. Ti(1) is bonded to three equivalent O(2) and three equivalent O(4) atoms to form TiO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and  a faceface with one Mg(1)O6 octahedra. All Ti(1)-O(2) bond lengths are 2.08 Å. All Ti(1)-O(4) bond lengths are 1.88 Å. Ni(1) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form NiO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and  a faceface with one Mg(1)O6 octahedra. All Ni(1)-O(1) bond lengths are 1.95 Å. All Ni(1)-O(3) bond lengths are 2.05 Å. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Ti(1)O6 octahedra, and corners with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 23-51°. The P(1)-O(1) bond length is 1.51 Å. The P(1)-O(2) bond length is 1.57 Å. The P(1)-O(3) bond length is 1.55 Å. The P(1)-O(4) bond length is 1.56 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Ni(1) and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mg(1), one Ti(1), and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Ni(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Ti(1) and one P(1) atom.