KNiSbO4 crystallizes in the monoclinic Cm space group. K(1) is bonded in a 6-coordinate geometry to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms. Ni(1) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form NiO6 octahedra that share edges with two equivalent Ni(1)O6 octahedra and edges with four equivalent Sb(1)O6 octahedra. Sb(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form SbO6 octahedra that share edges with two equivalent Sb(1)O6 octahedra and edges with four equivalent Ni(1)O6 octahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent K(1), two equivalent Ni(1), and one Sb(1) atom. In the second O site, O(2) is bonded to one K(1), one Ni(1), and two equivalent Sb(1) atoms to form distorted OKNiSb2 trigonal pyramids that share corners with five equivalent O(3)K2NiSb2 square pyramids,  a cornercorner with one O(4)KNi2Sb trigonal pyramid, corners with two equivalent O(2)KNiSb2 trigonal pyramids,  an edgeedge with one O(3)K2NiSb2 square pyramid, and edges with two equivalent O(4)KNi2Sb trigonal pyramids. In the third O site, O(3) is bonded to two equivalent K(1), one Ni(1), and two equivalent Sb(1) atoms to form distorted OK2NiSb2 square pyramids that share corners with two equivalent O(4)KNi2Sb trigonal pyramids, corners with five equivalent O(2)KNiSb2 trigonal pyramids, edges with two equivalent O(3)K2NiSb2 square pyramids,  an edgeedge with one O(2)KNiSb2 trigonal pyramid, and edges with two equivalent O(4)KNi2Sb trigonal pyramids. In the fourth O site, O(4) is bonded to one K(1), two equivalent Ni(1), and one Sb(1) atom to form distorted OKNi2Sb trigonal pyramids that share corners with two equivalent O(3)K2NiSb2 square pyramids,  a cornercorner with one O(2)KNiSb2 trigonal pyramid, corners with two equivalent O(4)KNi2Sb trigonal pyramids, edges with two equivalent O(3)K2NiSb2 square pyramids, and edges with two equivalent O(2)KNiSb2 trigonal pyramids.
KNiSbO4 crystallizes in the monoclinic Cm space group. K(1) is bonded in a 6-coordinate geometry to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms. The K(1)-O(2) bond length is 2.82 Å. The K(1)-O(4) bond length is 2.73 Å. Both K(1)-O(1) bond lengths are 2.75 Å. Both K(1)-O(3) bond lengths are 2.83 Å. Ni(1) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form NiO6 octahedra that share edges with two equivalent Ni(1)O6 octahedra and edges with four equivalent Sb(1)O6 octahedra. The Ni(1)-O(2) bond length is 2.12 Å. The Ni(1)-O(3) bond length is 2.10 Å. Both Ni(1)-O(1) bond lengths are 2.13 Å. Both Ni(1)-O(4) bond lengths are 2.09 Å. Sb(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form SbO6 octahedra that share edges with two equivalent Sb(1)O6 octahedra and edges with four equivalent Ni(1)O6 octahedra. The Sb(1)-O(1) bond length is 1.97 Å. The Sb(1)-O(4) bond length is 1.96 Å. Both Sb(1)-O(2) bond lengths are 2.07 Å. Both Sb(1)-O(3) bond lengths are 2.10 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent K(1), two equivalent Ni(1), and one Sb(1) atom. In the second O site, O(2) is bonded to one K(1), one Ni(1), and two equivalent Sb(1) atoms to form distorted OKNiSb2 trigonal pyramids that share corners with five equivalent O(3)K2NiSb2 square pyramids,  a cornercorner with one O(4)KNi2Sb trigonal pyramid, corners with two equivalent O(2)KNiSb2 trigonal pyramids,  an edgeedge with one O(3)K2NiSb2 square pyramid, and edges with two equivalent O(4)KNi2Sb trigonal pyramids. In the third O site, O(3) is bonded to two equivalent K(1), one Ni(1), and two equivalent Sb(1) atoms to form distorted OK2NiSb2 square pyramids that share corners with two equivalent O(4)KNi2Sb trigonal pyramids, corners with five equivalent O(2)KNiSb2 trigonal pyramids, edges with two equivalent O(3)K2NiSb2 square pyramids,  an edgeedge with one O(2)KNiSb2 trigonal pyramid, and edges with two equivalent O(4)KNi2Sb trigonal pyramids. In the fourth O site, O(4) is bonded to one K(1), two equivalent Ni(1), and one Sb(1) atom to form distorted OKNi2Sb trigonal pyramids that share corners with two equivalent O(3)K2NiSb2 square pyramids,  a cornercorner with one O(2)KNiSb2 trigonal pyramid, corners with two equivalent O(4)KNi2Sb trigonal pyramids, edges with two equivalent O(3)K2NiSb2 square pyramids, and edges with two equivalent O(2)KNiSb2 trigonal pyramids.