K2Na2MgSm2Nb2O10 crystallizes in the monoclinic Cm space group. K(1) is bonded in a 3-coordinate geometry to one O(1), one O(2), and one O(7) atom. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 4-coordinate geometry to one O(3), one O(8), and two equivalent O(6) atoms. In the second Na site, Na(2) is bonded in a 5-coordinate geometry to one O(2), one O(5), one O(8), and two equivalent O(4) atoms. Mg(1) is bonded in a distorted trigonal planar geometry to one O(1), one O(3), and one O(7) atom. Sm(1) is bonded to one O(3), one O(5), one O(8), two equivalent O(4), and two equivalent O(6) atoms to form distorted SmO7 hexagonal pyramids that share  a cornercorner with one Sm(1)O7 hexagonal pyramid,  a cornercorner with one Nb(2)O5 trigonal bipyramid, edges with three equivalent Sm(1)O7 hexagonal pyramids, and  an edgeedge with one Nb(2)O5 trigonal bipyramid. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 5-coordinate geometry to one O(3), one O(7), one O(8), and two equivalent O(6) atoms. In the second Nb site, Nb(2) is bonded to one O(1), one O(2), one O(5), and two equivalent O(4) atoms to form NbO5 trigonal bipyramids that share corners with two equivalent Sm(1)O7 hexagonal pyramids and edges with two equivalent Sm(1)O7 hexagonal pyramids. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent K(1), one Mg(1), and one Nb(2) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent K(1), one Na(2), and one Nb(2) atom. In the third O site, O(3) is bonded to one Na(1), one Mg(1), two equivalent Sm(1), and one Nb(1) atom to form edge-sharing ONaSm2MgNb trigonal bipyramids. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Na(2), two equivalent Sm(1), and one Nb(2) atom. In the fifth O site, O(5) is bonded to one Na(2), two equivalent Sm(1), and one Nb(2) atom to form edge-sharing ONaSm2Nb tetrahedra. In the sixth O site, O(6) is bonded in a distorted see-saw-like geometry to one Na(1), two equivalent Sm(1), and one Nb(1) atom. In the seventh O site, O(7) is bonded in a distorted rectangular see-saw-like geometry to two equivalent K(1), one Mg(1), and one Nb(1) atom. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to one Na(1), one Na(2), two equivalent Sm(1), and one Nb(1) atom.
K2Na2MgSm2Nb2O10 crystallizes in the monoclinic Cm space group. K(1) is bonded in a 3-coordinate geometry to one O(1), one O(2), and one O(7) atom. The K(1)-O(1) bond length is 2.79 Å. The K(1)-O(2) bond length is 2.52 Å. The K(1)-O(7) bond length is 2.58 Å. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 4-coordinate geometry to one O(3), one O(8), and two equivalent O(6) atoms. The Na(1)-O(3) bond length is 2.35 Å. The Na(1)-O(8) bond length is 2.25 Å. Both Na(1)-O(6) bond lengths are 2.46 Å. In the second Na site, Na(2) is bonded in a 5-coordinate geometry to one O(2), one O(5), one O(8), and two equivalent O(4) atoms. The Na(2)-O(2) bond length is 2.22 Å. The Na(2)-O(5) bond length is 2.24 Å. The Na(2)-O(8) bond length is 2.85 Å. Both Na(2)-O(4) bond lengths are 2.51 Å. Mg(1) is bonded in a distorted trigonal planar geometry to one O(1), one O(3), and one O(7) atom. The Mg(1)-O(1) bond length is 1.94 Å. The Mg(1)-O(3) bond length is 1.92 Å. The Mg(1)-O(7) bond length is 1.88 Å. Sm(1) is bonded to one O(3), one O(5), one O(8), two equivalent O(4), and two equivalent O(6) atoms to form distorted SmO7 hexagonal pyramids that share  a cornercorner with one Sm(1)O7 hexagonal pyramid,  a cornercorner with one Nb(2)O5 trigonal bipyramid, edges with three equivalent Sm(1)O7 hexagonal pyramids, and  an edgeedge with one Nb(2)O5 trigonal bipyramid. The Sm(1)-O(3) bond length is 2.43 Å. The Sm(1)-O(5) bond length is 2.31 Å. The Sm(1)-O(8) bond length is 2.48 Å. There is one shorter (2.53 Å) and one longer (2.55 Å) Sm(1)-O(4) bond length. There is one shorter (2.41 Å) and one longer (2.46 Å) Sm(1)-O(6) bond length. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 5-coordinate geometry to one O(3), one O(7), one O(8), and two equivalent O(6) atoms. The Nb(1)-O(3) bond length is 2.37 Å. The Nb(1)-O(7) bond length is 2.09 Å. The Nb(1)-O(8) bond length is 1.97 Å. Both Nb(1)-O(6) bond lengths are 1.98 Å. In the second Nb site, Nb(2) is bonded to one O(1), one O(2), one O(5), and two equivalent O(4) atoms to form NbO5 trigonal bipyramids that share corners with two equivalent Sm(1)O7 hexagonal pyramids and edges with two equivalent Sm(1)O7 hexagonal pyramids. The Nb(2)-O(1) bond length is 1.95 Å. The Nb(2)-O(2) bond length is 1.88 Å. The Nb(2)-O(5) bond length is 2.10 Å. Both Nb(2)-O(4) bond lengths are 1.97 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent K(1), one Mg(1), and one Nb(2) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent K(1), one Na(2), and one Nb(2) atom. In the third O site, O(3) is bonded to one Na(1), one Mg(1), two equivalent Sm(1), and one Nb(1) atom to form edge-sharing ONaSm2MgNb trigonal bipyramids. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Na(2), two equivalent Sm(1), and one Nb(2) atom. In the fifth O site, O(5) is bonded to one Na(2), two equivalent Sm(1), and one Nb(2) atom to form edge-sharing ONaSm2Nb tetrahedra. In the sixth O site, O(6) is bonded in a distorted see-saw-like geometry to one Na(1), two equivalent Sm(1), and one Nb(1) atom. In the seventh O site, O(7) is bonded in a distorted rectangular see-saw-like geometry to two equivalent K(1), one Mg(1), and one Nb(1) atom. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to one Na(1), one Na(2), two equivalent Sm(1), and one Nb(1) atom.