KFeNi(PO4)2 crystallizes in the monoclinic P2_1/c space group. K(1) is bonded in a 9-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(7), two equivalent O(1), and two equivalent O(8) atoms. Fe(1) is bonded to one O(1), one O(2), one O(6), one O(7), and one O(8) atom to form FeO5 trigonal bipyramids that share  a cornercorner with one Ni(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, and corners with three equivalent P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. Ni(1) is bonded to one O(4), one O(6), two equivalent O(3), and two equivalent O(5) atoms to form NiO6 octahedra that share  a cornercorner with one P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra,  a cornercorner with one Fe(1)O5 trigonal bipyramid, edges with two equivalent Ni(1)O6 octahedra, and  an edgeedge with one P(2)O4 tetrahedra. There are two inequivalent P sites. In the first P site, 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 three equivalent Ni(1)O6 octahedra and corners with two equivalent Fe(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 56-58°. In the second P site, P(2) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Ni(1)O6 octahedra, corners with three equivalent Fe(1)O5 trigonal bipyramids, and  an edgeedge with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 4°. There are eight inequivalent O sites. In the first O site, O(4) is bonded in a 3-coordinate geometry to one K(1), one Ni(1), and one P(1) atom. In the second O site, O(5) is bonded in a 3-coordinate geometry to one K(1), two equivalent Ni(1), and one P(2) atom. In the third O site, O(6) is bonded in a 3-coordinate geometry to one Fe(1), one Ni(1), and one P(2) atom. In the fourth O site, O(7) is bonded in a 3-coordinate geometry to one K(1), one Fe(1), and one P(2) atom. In the fifth O site, O(8) is bonded in a 2-coordinate geometry to two equivalent K(1), one Fe(1), and one P(2) atom. In the sixth O site, O(1) is bonded in a 2-coordinate geometry to two equivalent K(1), one Fe(1), and one P(1) atom. In the seventh O site, O(2) is bonded in a distorted bent 150 degrees geometry to one K(1), one Fe(1), and one P(1) atom. In the eighth O site, O(3) is bonded in a 3-coordinate geometry to one K(1), two equivalent Ni(1), and one P(1) atom.
KFeNi(PO4)2 crystallizes in the monoclinic P2_1/c space group. K(1) is bonded in a 9-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(7), two equivalent O(1), and two equivalent O(8) atoms. The K(1)-O(2) bond length is 2.93 Å. The K(1)-O(3) bond length is 2.95 Å. The K(1)-O(4) bond length is 2.90 Å. The K(1)-O(5) bond length is 3.32 Å. The K(1)-O(7) bond length is 2.89 Å. There is one shorter (2.77 Å) and one longer (3.22 Å) K(1)-O(1) bond length. There is one shorter (2.89 Å) and one longer (3.25 Å) K(1)-O(8) bond length. Fe(1) is bonded to one O(1), one O(2), one O(6), one O(7), and one O(8) atom to form FeO5 trigonal bipyramids that share  a cornercorner with one Ni(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, and corners with three equivalent P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. The Fe(1)-O(1) bond length is 1.93 Å. The Fe(1)-O(2) bond length is 1.95 Å. The Fe(1)-O(6) bond length is 1.96 Å. The Fe(1)-O(7) bond length is 1.95 Å. The Fe(1)-O(8) bond length is 2.04 Å. Ni(1) is bonded to one O(4), one O(6), two equivalent O(3), and two equivalent O(5) atoms to form NiO6 octahedra that share  a cornercorner with one P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra,  a cornercorner with one Fe(1)O5 trigonal bipyramid, edges with two equivalent Ni(1)O6 octahedra, and  an edgeedge with one P(2)O4 tetrahedra. The Ni(1)-O(4) bond length is 2.04 Å. The Ni(1)-O(6) bond length is 2.17 Å. There is one shorter (2.05 Å) and one longer (2.10 Å) Ni(1)-O(3) bond length. There is one shorter (2.10 Å) and one longer (2.23 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(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra and corners with two equivalent Fe(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 56-58°. The P(1)-O(1) bond length is 1.56 Å. The P(1)-O(2) bond length is 1.55 Å. The P(1)-O(3) bond length is 1.57 Å. The P(1)-O(4) bond length is 1.54 Å. In the second P site, P(2) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Ni(1)O6 octahedra, corners with three equivalent Fe(1)O5 trigonal bipyramids, and  an edgeedge with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 4°. The P(2)-O(5) bond length is 1.54 Å. The P(2)-O(6) bond length is 1.58 Å. The P(2)-O(7) bond length is 1.55 Å. The P(2)-O(8) bond length is 1.54 Å. There are eight inequivalent O sites. In the first O site, O(4) is bonded in a 3-coordinate geometry to one K(1), one Ni(1), and one P(1) atom. In the second O site, O(5) is bonded in a 3-coordinate geometry to one K(1), two equivalent Ni(1), and one P(2) atom. In the third O site, O(6) is bonded in a 3-coordinate geometry to one Fe(1), one Ni(1), and one P(2) atom. In the fourth O site, O(7) is bonded in a 3-coordinate geometry to one K(1), one Fe(1), and one P(2) atom. In the fifth O site, O(8) is bonded in a 2-coordinate geometry to two equivalent K(1), one Fe(1), and one P(2) atom. In the sixth O site, O(1) is bonded in a 2-coordinate geometry to two equivalent K(1), one Fe(1), and one P(1) atom. In the seventh O site, O(2) is bonded in a distorted bent 150 degrees geometry to one K(1), one Fe(1), and one P(1) atom. In the eighth O site, O(3) is bonded in a 3-coordinate geometry to one K(1), two equivalent Ni(1), and one P(1) atom.