KNiPO4 crystallizes in the orthorhombic Pna2_1 space group. K(1) is bonded in a 7-coordinate geometry to one O(2), two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. Ni(1) is bonded to one O(1), one O(3), one O(4), and two equivalent O(2) atoms to form distorted NiO5 trigonal bipyramids that share corners with three equivalent P(1)O4 tetrahedra, corners with two equivalent Ni(1)O5 trigonal bipyramids, and  an edgeedge with one P(1)O4 tetrahedra. 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)O5 trigonal bipyramids and  an edgeedge with one Ni(1)O5 trigonal bipyramid. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to two equivalent K(1), one Ni(1), and one P(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one K(1), two equivalent Ni(1), and one P(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent K(1), one Ni(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent K(1), one Ni(1), and one P(1) atom.
KNiPO4 crystallizes in the orthorhombic Pna2_1 space group. K(1) is bonded in a 7-coordinate geometry to one O(2), two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. The K(1)-O(2) bond length is 2.77 Å. There is one shorter (2.85 Å) and one longer (3.05 Å) K(1)-O(1) bond length. There is one shorter (2.85 Å) and one longer (2.90 Å) K(1)-O(3) bond length. There is one shorter (2.64 Å) and one longer (2.71 Å) K(1)-O(4) bond length. Ni(1) is bonded to one O(1), one O(3), one O(4), and two equivalent O(2) atoms to form distorted NiO5 trigonal bipyramids that share corners with three equivalent P(1)O4 tetrahedra, corners with two equivalent Ni(1)O5 trigonal bipyramids, and  an edgeedge with one P(1)O4 tetrahedra. The Ni(1)-O(1) bond length is 2.00 Å. The Ni(1)-O(3) bond length is 2.00 Å. The Ni(1)-O(4) bond length is 2.09 Å. There is one shorter (2.03 Å) and one longer (2.17 Å) Ni(1)-O(2) bond length. 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)O5 trigonal bipyramids and  an edgeedge with one Ni(1)O5 trigonal bipyramid. The P(1)-O(1) bond length is 1.54 Å. The P(1)-O(2) bond length is 1.59 Å. The P(1)-O(3) bond length is 1.54 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 2-coordinate geometry to two equivalent K(1), one Ni(1), and one P(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one K(1), two equivalent Ni(1), and one P(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent K(1), one Ni(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent K(1), one Ni(1), and one P(1) atom.