MgNb4O10 crystallizes in the monoclinic Pm space group. Mg(1) is bonded to one O(1), one O(3), one O(6), and two equivalent O(2) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent Nb(4)O6 octahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and edges with two equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 27-60°. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(10), one O(2), one O(4), one O(8), and two equivalent O(1) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, edges with two equivalent Nb(4)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 12°. In the second Nb site, Nb(2) is bonded in a 6-coordinate geometry to one O(10), one O(2), one O(4), one O(5), and two equivalent O(3) atoms. In the third Nb site, Nb(3) is bonded in a 5-coordinate geometry to one O(1), one O(6), one O(7), one O(9), and two equivalent O(8) atoms. In the fourth Nb site, Nb(4) is bonded to one O(1), one O(3), one O(7), one O(9), and two equivalent O(10) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(4)O6 octahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and edges with two equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 21°. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Mg(1), one Nb(3), one Nb(4), and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1), one Nb(1), and one Nb(2) atom. In the third O site, O(3) is bonded to one Mg(1), one Nb(4), and two equivalent Nb(2) atoms to form distorted corner-sharing OMgNb3 trigonal pyramids. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one Nb(1) and one Nb(2) atom. In the fifth O site, O(5) is bonded in a single-bond geometry to one Nb(2) atom. In the sixth O site, O(6) is bonded in a linear geometry to one Mg(1) and one Nb(3) atom. In the seventh O site, O(7) is bonded in a bent 120 degrees geometry to one Nb(3) and one Nb(4) atom. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Nb(1) and two equivalent Nb(3) atoms. In the ninth O site, O(9) is bonded in a linear geometry to one Nb(3) and one Nb(4) atom. In the tenth O site, O(10) is bonded in a distorted rectangular see-saw-like geometry to one Nb(1), one Nb(2), and two equivalent Nb(4) atoms.
MgNb4O10 crystallizes in the monoclinic Pm space group. Mg(1) is bonded to one O(1), one O(3), one O(6), and two equivalent O(2) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent Nb(4)O6 octahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and edges with two equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 27-60°. The Mg(1)-O(1) bond length is 2.12 Å. The Mg(1)-O(3) bond length is 2.15 Å. The Mg(1)-O(6) bond length is 1.96 Å. Both Mg(1)-O(2) bond lengths are 2.10 Å. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(10), one O(2), one O(4), one O(8), and two equivalent O(1) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, edges with two equivalent Nb(4)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 12°. The Nb(1)-O(10) bond length is 2.21 Å. The Nb(1)-O(2) bond length is 2.08 Å. The Nb(1)-O(4) bond length is 1.95 Å. The Nb(1)-O(8) bond length is 2.13 Å. Both Nb(1)-O(1) bond lengths are 2.04 Å. In the second Nb site, Nb(2) is bonded in a 6-coordinate geometry to one O(10), one O(2), one O(4), one O(5), and two equivalent O(3) atoms. The Nb(2)-O(10) bond length is 2.53 Å. The Nb(2)-O(2) bond length is 2.16 Å. The Nb(2)-O(4) bond length is 1.95 Å. The Nb(2)-O(5) bond length is 1.74 Å. Both Nb(2)-O(3) bond lengths are 2.12 Å. In the third Nb site, Nb(3) is bonded in a 5-coordinate geometry to one O(1), one O(6), one O(7), one O(9), and two equivalent O(8) atoms. The Nb(3)-O(1) bond length is 2.64 Å. The Nb(3)-O(6) bond length is 1.78 Å. The Nb(3)-O(7) bond length is 2.06 Å. The Nb(3)-O(9) bond length is 1.92 Å. Both Nb(3)-O(8) bond lengths are 2.13 Å. In the fourth Nb site, Nb(4) is bonded to one O(1), one O(3), one O(7), one O(9), and two equivalent O(10) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(4)O6 octahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and edges with two equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 21°. The Nb(4)-O(1) bond length is 2.47 Å. The Nb(4)-O(3) bond length is 2.37 Å. The Nb(4)-O(7) bond length is 1.84 Å. The Nb(4)-O(9) bond length is 1.93 Å. Both Nb(4)-O(10) bond lengths are 2.07 Å. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Mg(1), one Nb(3), one Nb(4), and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1), one Nb(1), and one Nb(2) atom. In the third O site, O(3) is bonded to one Mg(1), one Nb(4), and two equivalent Nb(2) atoms to form distorted corner-sharing OMgNb3 trigonal pyramids. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one Nb(1) and one Nb(2) atom. In the fifth O site, O(5) is bonded in a single-bond geometry to one Nb(2) atom. In the sixth O site, O(6) is bonded in a linear geometry to one Mg(1) and one Nb(3) atom. In the seventh O site, O(7) is bonded in a bent 120 degrees geometry to one Nb(3) and one Nb(4) atom. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Nb(1) and two equivalent Nb(3) atoms. In the ninth O site, O(9) is bonded in a linear geometry to one Nb(3) and one Nb(4) atom. In the tenth O site, O(10) is bonded in a distorted rectangular see-saw-like geometry to one Nb(1), one Nb(2), and two equivalent Nb(4) atoms.