K2Na2MgPr2Nb2O10 crystallizes in the monoclinic Pm space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 3-coordinate geometry to one O(4), two equivalent O(3), and two equivalent O(5) atoms. In the second K site, K(2) is bonded to two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms to form distorted KO8 hexagonal bipyramids that share corners with four equivalent K(2)O8 hexagonal bipyramids,  a cornercorner with one Na(2)O5 trigonal bipyramid,  a cornercorner with one Nb(1)O5 trigonal bipyramid, edges with two equivalent Nb(2)O5 trigonal bipyramids,  a faceface with one Na(2)O5 trigonal bipyramid, and  a faceface with one Nb(1)O5 trigonal bipyramid. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a distorted square co-planar geometry to two equivalent O(2) and two equivalent O(6) atoms. In the second Na site, Na(2) is bonded to one O(5), two equivalent O(1), and two equivalent O(3) atoms to form distorted NaO5 trigonal bipyramids that share  a cornercorner with one K(2)O8 hexagonal bipyramid,  a cornercorner with one Nb(1)O5 trigonal bipyramid, corners with four equivalent Nb(2)O5 trigonal bipyramids, and  a faceface with one K(2)O8 hexagonal bipyramid. Mg(1) is bonded in a trigonal non-coplanar geometry to one O(4) and two equivalent O(2) atoms. There are two inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(6) atoms. In the second Pr site, Pr(2) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(6) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(5), two equivalent O(2), and two equivalent O(6) atoms to form distorted NbO5 trigonal bipyramids that share  a cornercorner with one K(2)O8 hexagonal bipyramid,  a cornercorner with one Na(2)O5 trigonal bipyramid, and  a faceface with one K(2)O8 hexagonal bipyramid. In the second Nb site, Nb(2) 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 four equivalent Na(2)O5 trigonal bipyramids and edges with two equivalent K(2)O8 hexagonal bipyramids. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(2), one Pr(1), one Pr(2), and one Nb(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one K(2), one Na(1), one Mg(1), one Pr(1), and one Nb(1) atom. In the third O site, O(3) is bonded in a 6-coordinate geometry to one K(1), one K(2), one Na(2), one Pr(1), one Pr(2), and one Nb(2) atom. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one K(1), two equivalent K(2), one Mg(1), and one Nb(2) atom. In the fifth O site, O(5) is bonded in a 6-coordinate geometry to two equivalent K(1), two equivalent K(2), one Na(2), and one Nb(1) atom. In the sixth O site, O(6) is bonded to one Na(1), one Pr(1), one Pr(2), and one Nb(1) atom to form edge-sharing ONaPr2Nb tetrahedra.
K2Na2MgPr2Nb2O10 crystallizes in the monoclinic Pm space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 3-coordinate geometry to one O(4), two equivalent O(3), and two equivalent O(5) atoms. The K(1)-O(4) bond length is 2.65 Å. Both K(1)-O(3) bond lengths are 2.73 Å. Both K(1)-O(5) bond lengths are 3.21 Å. In the second K site, K(2) is bonded to two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms to form distorted KO8 hexagonal bipyramids that share corners with four equivalent K(2)O8 hexagonal bipyramids,  a cornercorner with one Na(2)O5 trigonal bipyramid,  a cornercorner with one Nb(1)O5 trigonal bipyramid, edges with two equivalent Nb(2)O5 trigonal bipyramids,  a faceface with one Na(2)O5 trigonal bipyramid, and  a faceface with one Nb(1)O5 trigonal bipyramid. Both K(2)-O(2) bond lengths are 3.11 Å. Both K(2)-O(3) bond lengths are 3.06 Å. Both K(2)-O(4) bond lengths are 2.96 Å. There is one shorter (3.00 Å) and one longer (3.04 Å) K(2)-O(5) bond length. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a distorted square co-planar geometry to two equivalent O(2) and two equivalent O(6) atoms. Both Na(1)-O(2) bond lengths are 2.44 Å. Both Na(1)-O(6) bond lengths are 2.24 Å. In the second Na site, Na(2) is bonded to one O(5), two equivalent O(1), and two equivalent O(3) atoms to form distorted NaO5 trigonal bipyramids that share  a cornercorner with one K(2)O8 hexagonal bipyramid,  a cornercorner with one Nb(1)O5 trigonal bipyramid, corners with four equivalent Nb(2)O5 trigonal bipyramids, and  a faceface with one K(2)O8 hexagonal bipyramid. The Na(2)-O(5) bond length is 2.46 Å. Both Na(2)-O(1) bond lengths are 2.31 Å. Both Na(2)-O(3) bond lengths are 2.39 Å. Mg(1) is bonded in a trigonal non-coplanar geometry to one O(4) and two equivalent O(2) atoms. The Mg(1)-O(4) bond length is 1.97 Å. Both Mg(1)-O(2) bond lengths are 1.99 Å. There are two inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(6) atoms. Both Pr(1)-O(1) bond lengths are 2.52 Å. Both Pr(1)-O(2) bond lengths are 2.97 Å. Both Pr(1)-O(3) bond lengths are 2.51 Å. Both Pr(1)-O(6) bond lengths are 2.45 Å. In the second Pr site, Pr(2) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(6) atoms. Both Pr(2)-O(1) bond lengths are 2.49 Å. Both Pr(2)-O(3) bond lengths are 2.49 Å. Both Pr(2)-O(6) bond lengths are 2.39 Å. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(5), two equivalent O(2), and two equivalent O(6) atoms to form distorted NbO5 trigonal bipyramids that share  a cornercorner with one K(2)O8 hexagonal bipyramid,  a cornercorner with one Na(2)O5 trigonal bipyramid, and  a faceface with one K(2)O8 hexagonal bipyramid. The Nb(1)-O(5) bond length is 1.87 Å. Both Nb(1)-O(2) bond lengths are 2.03 Å. Both Nb(1)-O(6) bond lengths are 2.01 Å. In the second Nb site, Nb(2) 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 four equivalent Na(2)O5 trigonal bipyramids and edges with two equivalent K(2)O8 hexagonal bipyramids. The Nb(2)-O(4) bond length is 2.00 Å. Both Nb(2)-O(1) bond lengths are 1.97 Å. Both Nb(2)-O(3) bond lengths are 2.07 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(2), one Pr(1), one Pr(2), and one Nb(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one K(2), one Na(1), one Mg(1), one Pr(1), and one Nb(1) atom. In the third O site, O(3) is bonded in a 6-coordinate geometry to one K(1), one K(2), one Na(2), one Pr(1), one Pr(2), and one Nb(2) atom. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one K(1), two equivalent K(2), one Mg(1), and one Nb(2) atom. In the fifth O site, O(5) is bonded in a 6-coordinate geometry to two equivalent K(1), two equivalent K(2), one Na(2), and one Nb(1) atom. In the sixth O site, O(6) is bonded to one Na(1), one Pr(1), one Pr(2), and one Nb(1) atom to form edge-sharing ONaPr2Nb tetrahedra.