K2Na2MgEu2Nb2O10 crystallizes in the tetragonal P4mm space group. K(1) is bonded in a rectangular see-saw-like geometry to two equivalent O(1) and two equivalent O(2) atoms. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a distorted single-bond geometry to one O(1) and four equivalent O(4) atoms. In the second Na site, Na(2) is bonded in a distorted square co-planar geometry to four equivalent O(3) atoms. Mg(1) is bonded in a 4-coordinate geometry to four equivalent O(4) atoms. Eu(1) is bonded in a body-centered cubic geometry to four equivalent O(3) and four equivalent O(4) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a distorted trigonal bipyramidal geometry to one O(2) and four equivalent O(4) atoms. In the second Nb site, Nb(2) is bonded in a distorted trigonal bipyramidal geometry to one O(1) and four equivalent O(3) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded to four equivalent K(1), one Na(1), and one Nb(2) atom to form distorted OK4NaNb octahedra that share corners with four equivalent O(1)K4NaNb octahedra and corners with four equivalent O(3)NaEu2Nb tetrahedra. The corner-sharing octahedral tilt angles are 11°. In the second O site, O(2) is bonded in a distorted single-bond geometry to four equivalent K(1) and one Nb(1) atom. In the third O site, O(3) is bonded to one Na(2), two equivalent Eu(1), and one Nb(2) atom to form distorted ONaEu2Nb tetrahedra that share  a cornercorner with one O(1)K4NaNb octahedra, corners with four equivalent O(3)NaEu2Nb tetrahedra, and edges with four equivalent O(3)NaEu2Nb tetrahedra. The corner-sharing octahedral tilt angles are 74°. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Na(1), one Mg(1), two equivalent Eu(1), and one Nb(1) atom.
K2Na2MgEu2Nb2O10 crystallizes in the tetragonal P4mm space group. K(1) is bonded in a rectangular see-saw-like geometry to two equivalent O(1) and two equivalent O(2) atoms. Both K(1)-O(1) bond lengths are 2.86 Å. Both K(1)-O(2) bond lengths are 3.05 Å. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a distorted single-bond geometry to one O(1) and four equivalent O(4) atoms. The Na(1)-O(1) bond length is 2.07 Å. All Na(1)-O(4) bond lengths are 2.71 Å. In the second Na site, Na(2) is bonded in a distorted square co-planar geometry to four equivalent O(3) atoms. All Na(2)-O(3) bond lengths are 2.23 Å. Mg(1) is bonded in a 4-coordinate geometry to four equivalent O(4) atoms. All Mg(1)-O(4) bond lengths are 2.12 Å. Eu(1) is bonded in a body-centered cubic geometry to four equivalent O(3) and four equivalent O(4) atoms. All Eu(1)-O(3) bond lengths are 2.47 Å. All Eu(1)-O(4) bond lengths are 2.63 Å. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a distorted trigonal bipyramidal geometry to one O(2) and four equivalent O(4) atoms. The Nb(1)-O(2) bond length is 1.88 Å. All Nb(1)-O(4) bond lengths are 2.04 Å. In the second Nb site, Nb(2) is bonded in a distorted trigonal bipyramidal geometry to one O(1) and four equivalent O(3) atoms. The Nb(2)-O(1) bond length is 1.92 Å. All Nb(2)-O(3) bond lengths are 1.97 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to four equivalent K(1), one Na(1), and one Nb(2) atom to form distorted OK4NaNb octahedra that share corners with four equivalent O(1)K4NaNb octahedra and corners with four equivalent O(3)NaEu2Nb tetrahedra. The corner-sharing octahedral tilt angles are 11°. In the second O site, O(2) is bonded in a distorted single-bond geometry to four equivalent K(1) and one Nb(1) atom. In the third O site, O(3) is bonded to one Na(2), two equivalent Eu(1), and one Nb(2) atom to form distorted ONaEu2Nb tetrahedra that share  a cornercorner with one O(1)K4NaNb octahedra, corners with four equivalent O(3)NaEu2Nb tetrahedra, and edges with four equivalent O(3)NaEu2Nb tetrahedra. The corner-sharing octahedral tilt angles are 74°. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Na(1), one Mg(1), two equivalent Eu(1), and one Nb(1) atom.