K2Na2Eu4Ta2O13 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 Eu(1)O7 pentagonal bipyramids. There are two inequivalent Eu sites. In the first Eu site, Eu(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 EuO7 pentagonal bipyramids that share  a cornercorner with one Eu(1)O7 pentagonal bipyramid,  an edgeedge with one Eu(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 Eu site, Eu(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 Eu(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 Eu(1), one Eu(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 Eu(1), one Eu(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 Eu(1), one Eu(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 Eu(1) and two equivalent Eu(2) atoms to form OEu4 tetrahedra that share corners with four equivalent O(7)Eu4 tetrahedra, corners with four equivalent O(6)NaEu2Ta tetrahedra, and edges with two equivalent O(7)Eu4 tetrahedra. In the sixth O site, O(6) is bonded to one Na(1), one Eu(1), one Eu(2), and one Ta(1) atom to form corner-sharing ONaEu2Ta tetrahedra. In the seventh O site, O(7) is bonded to two equivalent Eu(1) and two equivalent Eu(2) atoms to form OEu4 tetrahedra that share corners with two equivalent O(5)Eu4 tetrahedra, corners with four equivalent O(6)NaEu2Ta tetrahedra,  an edgeedge with one O(5)Eu4 tetrahedra, and edges with two equivalent O(7)Eu4 tetrahedra.
K2Na2Eu4Ta2O13 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 (3.20 Å) and one longer (3.30 Å) K(1)-O(1) bond length. There is one shorter (3.17 Å) and one longer (3.18 Å) K(1)-O(2) bond length. There is one shorter (3.26 Å) and one longer (3.30 Å) K(1)-O(3) bond length. There are a spread of K(1)-O(4) bond distances ranging from 2.84-2.96 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 Eu(1)O7 pentagonal bipyramids. The Na(1)-O(1) bond length is 2.30 Å. The Na(1)-O(2) bond length is 2.34 Å. The Na(1)-O(3) bond length is 2.34 Å. The Na(1)-O(4) bond length is 2.34 Å. The Na(1)-O(6) bond length is 2.34 Å. There are two inequivalent Eu sites. In the first Eu site, Eu(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 EuO7 pentagonal bipyramids that share  a cornercorner with one Eu(1)O7 pentagonal bipyramid,  an edgeedge with one Eu(1)O7 pentagonal bipyramid, edges with two equivalent Na(1)O5 trigonal bipyramids, and edges with two equivalent Ta(1)O5 trigonal bipyramids. The Eu(1)-O(1) bond length is 2.48 Å. The Eu(1)-O(2) bond length is 2.47 Å. The Eu(1)-O(3) bond length is 2.43 Å. The Eu(1)-O(5) bond length is 2.42 Å. The Eu(1)-O(6) bond length is 2.41 Å. Both Eu(1)-O(7) bond lengths are 2.39 Å. In the second Eu site, Eu(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 Eu(2)-O(1) bond length is 2.39 Å. The Eu(2)-O(2) bond length is 2.58 Å. The Eu(2)-O(3) bond length is 2.46 Å. The Eu(2)-O(5) bond length is 2.38 Å. The Eu(2)-O(6) bond length is 2.43 Å. There is one shorter (2.38 Å) and one longer (2.40 Å) Eu(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 Eu(1)O7 pentagonal bipyramids. The Ta(1)-O(1) bond length is 1.99 Å. The Ta(1)-O(2) bond length is 1.97 Å. The Ta(1)-O(3) bond length is 1.95 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 Eu(1), one Eu(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 Eu(1), one Eu(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 Eu(1), one Eu(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 Eu(1) and two equivalent Eu(2) atoms to form OEu4 tetrahedra that share corners with four equivalent O(7)Eu4 tetrahedra, corners with four equivalent O(6)NaEu2Ta tetrahedra, and edges with two equivalent O(7)Eu4 tetrahedra. In the sixth O site, O(6) is bonded to one Na(1), one Eu(1), one Eu(2), and one Ta(1) atom to form corner-sharing ONaEu2Ta tetrahedra. In the seventh O site, O(7) is bonded to two equivalent Eu(1) and two equivalent Eu(2) atoms to form OEu4 tetrahedra that share corners with two equivalent O(5)Eu4 tetrahedra, corners with four equivalent O(6)NaEu2Ta tetrahedra,  an edgeedge with one O(5)Eu4 tetrahedra, and edges with two equivalent O(7)Eu4 tetrahedra.