KLa2NbO6 crystallizes in the monoclinic C2/m space group. K(1) is bonded in a 7-coordinate geometry to three equivalent O(4) and four equivalent O(1) atoms. There are two inequivalent La sites. In the first La site, La(1) is bonded in a body-centered cubic geometry to two equivalent O(1), two equivalent O(2), and four equivalent O(3) atoms. In the second La site, La(2) is bonded to one O(4), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted LaO7 hexagonal pyramids that share corners with three equivalent Nb(1)O5 trigonal bipyramids,  an edgeedge with one La(2)O7 hexagonal pyramid, and  an edgeedge with one Nb(1)O5 trigonal bipyramid. Nb(1) is bonded to one O(4), two equivalent O(1), and two equivalent O(3) atoms to form distorted NbO5 trigonal bipyramids that share corners with three equivalent La(2)O7 hexagonal pyramids and  an edgeedge with one La(2)O7 hexagonal pyramid. 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), one La(1), one La(2), and one Nb(1) atom. In the second O site, O(2) is bonded to two equivalent La(1) and two equivalent La(2) atoms to form OLa4 tetrahedra that share corners with eight equivalent O(3)La3Nb tetrahedra, edges with two equivalent O(3)La3Nb tetrahedra, and edges with two equivalent O(2)La4 tetrahedra. In the third O site, O(3) is bonded to one La(2), two equivalent La(1), and one Nb(1) atom to form distorted OLa3Nb tetrahedra that share corners with two equivalent O(3)La3Nb tetrahedra, corners with four equivalent O(2)La4 tetrahedra,  an edgeedge with one O(2)La4 tetrahedra, and edges with three equivalent O(3)La3Nb tetrahedra. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to three equivalent K(1), one La(2), and one Nb(1) atom.
KLa2NbO6 crystallizes in the monoclinic C2/m space group. K(1) is bonded in a 7-coordinate geometry to three equivalent O(4) and four equivalent O(1) atoms. There is one shorter (2.63 Å) and two longer (3.01 Å) K(1)-O(4) bond lengths. There are two shorter (2.79 Å) and two longer (2.88 Å) K(1)-O(1) bond lengths. There are two inequivalent La sites. In the first La site, La(1) is bonded in a body-centered cubic geometry to two equivalent O(1), two equivalent O(2), and four equivalent O(3) atoms. Both La(1)-O(1) bond lengths are 2.52 Å. Both La(1)-O(2) bond lengths are 2.44 Å. There are two shorter (2.59 Å) and two longer (2.64 Å) La(1)-O(3) bond lengths. In the second La site, La(2) is bonded to one O(4), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted LaO7 hexagonal pyramids that share corners with three equivalent Nb(1)O5 trigonal bipyramids,  an edgeedge with one La(2)O7 hexagonal pyramid, and  an edgeedge with one Nb(1)O5 trigonal bipyramid. The La(2)-O(4) bond length is 2.61 Å. Both La(2)-O(1) bond lengths are 2.51 Å. Both La(2)-O(2) bond lengths are 2.37 Å. Both La(2)-O(3) bond lengths are 2.55 Å. Nb(1) is bonded to one O(4), two equivalent O(1), and two equivalent O(3) atoms to form distorted NbO5 trigonal bipyramids that share corners with three equivalent La(2)O7 hexagonal pyramids and  an edgeedge with one La(2)O7 hexagonal pyramid. The Nb(1)-O(4) bond length is 1.86 Å. Both Nb(1)-O(1) bond lengths are 1.97 Å. Both Nb(1)-O(3) bond lengths are 2.03 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), one La(1), one La(2), and one Nb(1) atom. In the second O site, O(2) is bonded to two equivalent La(1) and two equivalent La(2) atoms to form OLa4 tetrahedra that share corners with eight equivalent O(3)La3Nb tetrahedra, edges with two equivalent O(3)La3Nb tetrahedra, and edges with two equivalent O(2)La4 tetrahedra. In the third O site, O(3) is bonded to one La(2), two equivalent La(1), and one Nb(1) atom to form distorted OLa3Nb tetrahedra that share corners with two equivalent O(3)La3Nb tetrahedra, corners with four equivalent O(2)La4 tetrahedra,  an edgeedge with one O(2)La4 tetrahedra, and edges with three equivalent O(3)La3Nb tetrahedra. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to three equivalent K(1), one La(2), and one Nb(1) atom.