K2Na2MgPr2Nb2O10 crystallizes in the monoclinic Cm space group. K(1) is bonded in a 2-coordinate geometry to one O(1), one O(3), and one O(7) atom. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 5-coordinate geometry to one O(2), one O(6), one O(8), and two equivalent O(4) atoms. In the second Na site, Na(2) is bonded to one O(3), one O(5), one O(7), and two equivalent O(1) atoms to form distorted NaO5 trigonal bipyramids that share  a cornercorner with one Nb(1)O5 trigonal bipyramid and corners with four equivalent Nb(2)O5 trigonal bipyramids. Mg(1) is bonded in a distorted trigonal planar geometry to one O(6), one O(7), and one O(8) atom. Pr(1) is bonded in a 7-coordinate geometry to one O(2), one O(5), one O(8), two equivalent O(1), and two equivalent O(4) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(2), one O(7), one O(8), and two equivalent O(4) atoms to form distorted NbO5 trigonal bipyramids that share  a cornercorner with one Na(2)O5 trigonal bipyramid. In the second Nb site, Nb(2) is bonded to one O(3), one O(5), one O(6), and two equivalent O(1) atoms to form NbO5 trigonal bipyramids that share corners with four equivalent Na(2)O5 trigonal bipyramids. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one K(1), one Na(2), two equivalent Pr(1), and one Nb(2) atom. In the second O site, O(2) is bonded to one Na(1), two equivalent Pr(1), and one Nb(1) atom to form distorted ONaPr2Nb tetrahedra that share corners with two equivalent O(5)NaPr2Nb tetrahedra and corners with four equivalent O(8)NaPr2MgNb trigonal bipyramids. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent K(1), one Na(2), and one Nb(2) atom. In the fourth O site, O(4) is bonded in a distorted see-saw-like geometry to one Na(1), two equivalent Pr(1), and one Nb(1) atom. In the fifth O site, O(5) is bonded to one Na(2), two equivalent Pr(1), and one Nb(2) atom to form ONaPr2Nb tetrahedra that share corners with two equivalent O(2)NaPr2Nb tetrahedra and  an edgeedge with one O(8)NaPr2MgNb trigonal bipyramid. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Na(1), one Mg(1), and one Nb(2) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to two equivalent K(1), one Na(2), one Mg(1), and one Nb(1) atom. In the eighth O site, O(8) is bonded to one Na(1), one Mg(1), two equivalent Pr(1), and one Nb(1) atom to form a mixture of distorted corner and edge-sharing ONaPr2MgNb trigonal bipyramids.
K2Na2MgPr2Nb2O10 crystallizes in the monoclinic Cm space group. K(1) is bonded in a 2-coordinate geometry to one O(1), one O(3), and one O(7) atom. The K(1)-O(1) bond length is 3.12 Å. The K(1)-O(3) bond length is 2.54 Å. The K(1)-O(7) bond length is 2.60 Å. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 5-coordinate geometry to one O(2), one O(6), one O(8), and two equivalent O(4) atoms. The Na(1)-O(2) bond length is 2.23 Å. The Na(1)-O(6) bond length is 2.71 Å. The Na(1)-O(8) bond length is 2.41 Å. Both Na(1)-O(4) bond lengths are 2.51 Å. In the second Na site, Na(2) is bonded to one O(3), one O(5), one O(7), and two equivalent O(1) atoms to form distorted NaO5 trigonal bipyramids that share  a cornercorner with one Nb(1)O5 trigonal bipyramid and corners with four equivalent Nb(2)O5 trigonal bipyramids. The Na(2)-O(3) bond length is 2.28 Å. The Na(2)-O(5) bond length is 2.24 Å. The Na(2)-O(7) bond length is 2.83 Å. Both Na(2)-O(1) bond lengths are 2.56 Å. Mg(1) is bonded in a distorted trigonal planar geometry to one O(6), one O(7), and one O(8) atom. The Mg(1)-O(6) bond length is 1.94 Å. The Mg(1)-O(7) bond length is 1.87 Å. The Mg(1)-O(8) bond length is 1.90 Å. Pr(1) is bonded in a 7-coordinate geometry to one O(2), one O(5), one O(8), two equivalent O(1), and two equivalent O(4) atoms. The Pr(1)-O(2) bond length is 2.52 Å. The Pr(1)-O(5) bond length is 2.41 Å. The Pr(1)-O(8) bond length is 2.47 Å. Both Pr(1)-O(1) bond lengths are 2.58 Å. There is one shorter (2.49 Å) and one longer (2.53 Å) Pr(1)-O(4) bond length. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(2), one O(7), one O(8), and two equivalent O(4) atoms to form distorted NbO5 trigonal bipyramids that share  a cornercorner with one Na(2)O5 trigonal bipyramid. The Nb(1)-O(2) bond length is 1.95 Å. The Nb(1)-O(7) bond length is 2.17 Å. The Nb(1)-O(8) bond length is 2.39 Å. Both Nb(1)-O(4) bond lengths are 1.99 Å. In the second Nb site, Nb(2) is bonded to one O(3), one O(5), one O(6), and two equivalent O(1) atoms to form NbO5 trigonal bipyramids that share corners with four equivalent Na(2)O5 trigonal bipyramids. The Nb(2)-O(3) bond length is 1.90 Å. The Nb(2)-O(5) bond length is 2.06 Å. The Nb(2)-O(6) bond length is 1.95 Å. Both Nb(2)-O(1) bond lengths are 1.98 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one K(1), one Na(2), two equivalent Pr(1), and one Nb(2) atom. In the second O site, O(2) is bonded to one Na(1), two equivalent Pr(1), and one Nb(1) atom to form distorted ONaPr2Nb tetrahedra that share corners with two equivalent O(5)NaPr2Nb tetrahedra and corners with four equivalent O(8)NaPr2MgNb trigonal bipyramids. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent K(1), one Na(2), and one Nb(2) atom. In the fourth O site, O(4) is bonded in a distorted see-saw-like geometry to one Na(1), two equivalent Pr(1), and one Nb(1) atom. In the fifth O site, O(5) is bonded to one Na(2), two equivalent Pr(1), and one Nb(2) atom to form ONaPr2Nb tetrahedra that share corners with two equivalent O(2)NaPr2Nb tetrahedra and  an edgeedge with one O(8)NaPr2MgNb trigonal bipyramid. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Na(1), one Mg(1), and one Nb(2) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to two equivalent K(1), one Na(2), one Mg(1), and one Nb(1) atom. In the eighth O site, O(8) is bonded to one Na(1), one Mg(1), two equivalent Pr(1), and one Nb(1) atom to form a mixture of distorted corner and edge-sharing ONaPr2MgNb trigonal bipyramids.