K2NaTlO3 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(1), and two equivalent O(3) atoms. In the second K site, K(2) is bonded in a 5-coordinate geometry to one O(3), two equivalent O(1), and two equivalent O(2) atoms. Na(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form NaO4 tetrahedra that share corners with five equivalent Tl(1)O4 tetrahedra and  an edgeedge with one Na(1)O4 tetrahedra. Tl(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form distorted TlO4 tetrahedra that share corners with five equivalent Na(1)O4 tetrahedra and  an edgeedge with one Tl(1)O4 tetrahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent K(1), two equivalent K(2), one Na(1), and one Tl(1) atom to form distorted corner-sharing OK4NaTl octahedra. The corner-sharing octahedral tilt angles range from 65-68°. In the second O site, O(2) is bonded in a 6-coordinate geometry to one K(1), two equivalent K(2), two equivalent Na(1), and one Tl(1) atom. In the third O site, O(3) is bonded in a 6-coordinate geometry to one K(2), two equivalent K(1), one Na(1), and two equivalent Tl(1) atoms.
K2NaTlO3 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(1), and two equivalent O(3) atoms. The K(1)-O(2) bond length is 2.89 Å. There is one shorter (2.80 Å) and one longer (2.91 Å) K(1)-O(1) bond length. There is one shorter (2.77 Å) and one longer (3.27 Å) K(1)-O(3) bond length. In the second K site, K(2) is bonded in a 5-coordinate geometry to one O(3), two equivalent O(1), and two equivalent O(2) atoms. The K(2)-O(3) bond length is 3.05 Å. There is one shorter (2.77 Å) and one longer (2.96 Å) K(2)-O(1) bond length. There is one shorter (2.69 Å) and one longer (3.01 Å) K(2)-O(2) bond length. Na(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form NaO4 tetrahedra that share corners with five equivalent Tl(1)O4 tetrahedra and  an edgeedge with one Na(1)O4 tetrahedra. The Na(1)-O(1) bond length is 2.27 Å. The Na(1)-O(3) bond length is 2.30 Å. There is one shorter (2.34 Å) and one longer (2.35 Å) Na(1)-O(2) bond length. Tl(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form distorted TlO4 tetrahedra that share corners with five equivalent Na(1)O4 tetrahedra and  an edgeedge with one Tl(1)O4 tetrahedra. The Tl(1)-O(1) bond length is 2.13 Å. The Tl(1)-O(2) bond length is 2.14 Å. There is one shorter (2.26 Å) and one longer (2.30 Å) Tl(1)-O(3) bond length. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent K(1), two equivalent K(2), one Na(1), and one Tl(1) atom to form distorted corner-sharing OK4NaTl octahedra. The corner-sharing octahedral tilt angles range from 65-68°. In the second O site, O(2) is bonded in a 6-coordinate geometry to one K(1), two equivalent K(2), two equivalent Na(1), and one Tl(1) atom. In the third O site, O(3) is bonded in a 6-coordinate geometry to one K(2), two equivalent K(1), one Na(1), and two equivalent Tl(1) atoms.