K2Na2Sm4Ta2O13 crystallizes in the monoclinic C2/c space group. K(1) is bonded in a 10-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and four equivalent O(4) atoms. Na(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(6) atom to form distorted NaO5 trigonal bipyramids that share corners with five equivalent Ta(1)O5 trigonal bipyramids and edges with two equivalent Sm(1)O7 pentagonal bipyramids. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and two equivalent O(7) atoms to form distorted SmO7 pentagonal bipyramids that share  a cornercorner with one Sm(1)O7 pentagonal bipyramid,  an edgeedge with one Sm(1)O7 pentagonal bipyramid, edges with two equivalent Na(1)O5 trigonal bipyramids, and edges with two equivalent Ta(1)O5 trigonal bipyramids. In the second Sm site, Sm(2) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(6), and two equivalent O(7) atoms. Ta(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(6) atom to form TaO5 trigonal bipyramids that share corners with five equivalent Na(1)O5 trigonal bipyramids and edges with two equivalent Sm(1)O7 pentagonal bipyramids. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent K(1), one Na(1), one Sm(1), one Sm(2), and one Ta(1) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to two equivalent K(1), one Na(1), one Sm(1), one Sm(2), and one Ta(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent K(1), one Na(1), one Sm(1), one Sm(2), and one Ta(1) atom. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to four equivalent K(1), one Na(1), and one Ta(1) atom. In the fifth O site, O(5) is bonded to two equivalent Sm(1) and two equivalent Sm(2) atoms to form OSm4 tetrahedra that share corners with four equivalent O(6)NaSm2Ta tetrahedra, corners with four equivalent O(7)Sm4 tetrahedra, and edges with two equivalent O(7)Sm4 tetrahedra. In the sixth O site, O(6) is bonded to one Na(1), one Sm(1), one Sm(2), and one Ta(1) atom to form corner-sharing ONaSm2Ta tetrahedra. In the seventh O site, O(7) is bonded to two equivalent Sm(1) and two equivalent Sm(2) atoms to form OSm4 tetrahedra that share corners with two equivalent O(5)Sm4 tetrahedra, corners with four equivalent O(6)NaSm2Ta tetrahedra,  an edgeedge with one O(5)Sm4 tetrahedra, and edges with two equivalent O(7)Sm4 tetrahedra.
K2Na2Sm4Ta2O13 crystallizes in the monoclinic C2/c space group. K(1) is bonded in a 10-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and four equivalent O(4) atoms. There is one shorter (3.18 Å) and one longer (3.31 Å) K(1)-O(1) bond length. Both K(1)-O(2) bond lengths are 3.16 Å. There is one shorter (3.25 Å) and one longer (3.29 Å) K(1)-O(3) bond length. There are a spread of K(1)-O(4) bond distances ranging from 2.83-2.96 Å. Na(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(6) atom to form distorted NaO5 trigonal bipyramids that share corners with five equivalent Ta(1)O5 trigonal bipyramids and edges with two equivalent Sm(1)O7 pentagonal bipyramids. The Na(1)-O(1) bond length is 2.30 Å. The Na(1)-O(2) bond length is 2.33 Å. The Na(1)-O(3) bond length is 2.33 Å. The Na(1)-O(4) bond length is 2.32 Å. The Na(1)-O(6) bond length is 2.34 Å. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and two equivalent O(7) atoms to form distorted SmO7 pentagonal bipyramids that share  a cornercorner with one Sm(1)O7 pentagonal bipyramid,  an edgeedge with one Sm(1)O7 pentagonal bipyramid, edges with two equivalent Na(1)O5 trigonal bipyramids, and edges with two equivalent Ta(1)O5 trigonal bipyramids. The Sm(1)-O(1) bond length is 2.44 Å. The Sm(1)-O(2) bond length is 2.47 Å. The Sm(1)-O(3) bond length is 2.44 Å. The Sm(1)-O(5) bond length is 2.43 Å. The Sm(1)-O(6) bond length is 2.44 Å. Both Sm(1)-O(7) bond lengths are 2.38 Å. In the second Sm site, Sm(2) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(6), and two equivalent O(7) atoms. The Sm(2)-O(1) bond length is 2.40 Å. The Sm(2)-O(2) bond length is 2.59 Å. The Sm(2)-O(3) bond length is 2.42 Å. The Sm(2)-O(5) bond length is 2.38 Å. The Sm(2)-O(6) bond length is 2.45 Å. There is one shorter (2.37 Å) and one longer (2.38 Å) Sm(2)-O(7) bond length. Ta(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(6) atom to form TaO5 trigonal bipyramids that share corners with five equivalent Na(1)O5 trigonal bipyramids and edges with two equivalent Sm(1)O7 pentagonal bipyramids. The Ta(1)-O(1) bond length is 2.00 Å. The Ta(1)-O(2) bond length is 1.96 Å. The Ta(1)-O(3) bond length is 1.96 Å. The Ta(1)-O(4) bond length is 1.86 Å. The Ta(1)-O(6) bond length is 1.97 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent K(1), one Na(1), one Sm(1), one Sm(2), and one Ta(1) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to two equivalent K(1), one Na(1), one Sm(1), one Sm(2), and one Ta(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent K(1), one Na(1), one Sm(1), one Sm(2), and one Ta(1) atom. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to four equivalent K(1), one Na(1), and one Ta(1) atom. In the fifth O site, O(5) is bonded to two equivalent Sm(1) and two equivalent Sm(2) atoms to form OSm4 tetrahedra that share corners with four equivalent O(6)NaSm2Ta tetrahedra, corners with four equivalent O(7)Sm4 tetrahedra, and edges with two equivalent O(7)Sm4 tetrahedra. In the sixth O site, O(6) is bonded to one Na(1), one Sm(1), one Sm(2), and one Ta(1) atom to form corner-sharing ONaSm2Ta tetrahedra. In the seventh O site, O(7) is bonded to two equivalent Sm(1) and two equivalent Sm(2) atoms to form OSm4 tetrahedra that share corners with two equivalent O(5)Sm4 tetrahedra, corners with four equivalent O(6)NaSm2Ta tetrahedra,  an edgeedge with one O(5)Sm4 tetrahedra, and edges with two equivalent O(7)Sm4 tetrahedra.