MgNb2(FeO4)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(3), one O(7), and two equivalent O(8) atoms to form MgO5 trigonal bipyramids that share corners with two equivalent Mg(1)O5 trigonal bipyramids,  an edgeedge with one Nb(1)O6 octahedra, edges with two equivalent Nb(2)O6 octahedra, and edges with two equivalent Fe(2)O6 octahedra. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(5), one O(6), one O(7), and two equivalent O(4) atoms to form distorted NbO6 octahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Nb(1)O6 octahedra,  an edgeedge with one Nb(2)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 19-26°. In the second Nb site, Nb(2) is bonded to one O(2), one O(5), one O(6), one O(8), and two equivalent O(3) atoms to form distorted NbO6 octahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra,  an edgeedge with one Nb(1)O6 octahedra,  an edgeedge with one Fe(2)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 3-19°. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(5), one O(7), and two equivalent O(2) atoms. In the second Fe site, Fe(2) is bonded to one O(2), one O(4), one O(6), one O(8), and two equivalent O(1) atoms to form distorted FeO6 octahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Nb(2)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra,  an edgeedge with one Nb(2)O6 octahedra, edges with two equivalent Nb(1)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 3-34°. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Nb(1), one Fe(1), and two equivalent Fe(2) atoms to form distorted OMgNbFe3 trigonal bipyramids that share corners with two equivalent O(1)MgNbFe3 trigonal bipyramids and edges with two equivalent O(2)NbFe3 tetrahedra. In the second O site, O(2) is bonded to one Nb(2), one Fe(2), and two equivalent Fe(1) atoms to form ONbFe3 tetrahedra that share corners with two equivalent O(2)NbFe3 tetrahedra and edges with two equivalent O(1)MgNbFe3 trigonal bipyramids. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), two equivalent Nb(2), and one Fe(1) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to two equivalent Nb(1) and one Fe(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Nb(1), one Nb(2), and one Fe(1) atom. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Nb(1), one Nb(2), and one Fe(2) atom. In the seventh O site, O(7) is bonded in a T-shaped geometry to one Mg(1), one Nb(1), and one Fe(1) atom. In the eighth O site, O(8) is bonded in a distorted square co-planar geometry to two equivalent Mg(1), one Nb(2), and one Fe(2) atom.
MgNb2(FeO4)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(3), one O(7), and two equivalent O(8) atoms to form MgO5 trigonal bipyramids that share corners with two equivalent Mg(1)O5 trigonal bipyramids,  an edgeedge with one Nb(1)O6 octahedra, edges with two equivalent Nb(2)O6 octahedra, and edges with two equivalent Fe(2)O6 octahedra. The Mg(1)-O(1) bond length is 2.01 Å. The Mg(1)-O(3) bond length is 2.04 Å. The Mg(1)-O(7) bond length is 2.10 Å. Both Mg(1)-O(8) bond lengths are 2.06 Å. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(5), one O(6), one O(7), and two equivalent O(4) atoms to form distorted NbO6 octahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Nb(1)O6 octahedra,  an edgeedge with one Nb(2)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 19-26°. The Nb(1)-O(1) bond length is 2.10 Å. The Nb(1)-O(5) bond length is 2.30 Å. The Nb(1)-O(6) bond length is 1.96 Å. The Nb(1)-O(7) bond length is 1.88 Å. There is one shorter (1.98 Å) and one longer (2.04 Å) Nb(1)-O(4) bond length. In the second Nb site, Nb(2) is bonded to one O(2), one O(5), one O(6), one O(8), and two equivalent O(3) atoms to form distorted NbO6 octahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra,  an edgeedge with one Nb(1)O6 octahedra,  an edgeedge with one Fe(2)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 3-19°. The Nb(2)-O(2) bond length is 2.11 Å. The Nb(2)-O(5) bond length is 1.89 Å. The Nb(2)-O(6) bond length is 2.17 Å. The Nb(2)-O(8) bond length is 1.98 Å. Both Nb(2)-O(3) bond lengths are 2.01 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(5), one O(7), and two equivalent O(2) atoms. The Fe(1)-O(1) bond length is 2.64 Å. The Fe(1)-O(3) bond length is 2.46 Å. The Fe(1)-O(5) bond length is 2.08 Å. The Fe(1)-O(7) bond length is 2.14 Å. There is one shorter (2.10 Å) and one longer (2.11 Å) Fe(1)-O(2) bond length. In the second Fe site, Fe(2) is bonded to one O(2), one O(4), one O(6), one O(8), and two equivalent O(1) atoms to form distorted FeO6 octahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Nb(2)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra,  an edgeedge with one Nb(2)O6 octahedra, edges with two equivalent Nb(1)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 3-34°. The Fe(2)-O(2) bond length is 2.13 Å. The Fe(2)-O(4) bond length is 2.40 Å. The Fe(2)-O(6) bond length is 2.05 Å. The Fe(2)-O(8) bond length is 2.44 Å. There is one shorter (2.06 Å) and one longer (2.08 Å) Fe(2)-O(1) bond length. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Nb(1), one Fe(1), and two equivalent Fe(2) atoms to form distorted OMgNbFe3 trigonal bipyramids that share corners with two equivalent O(1)MgNbFe3 trigonal bipyramids and edges with two equivalent O(2)NbFe3 tetrahedra. In the second O site, O(2) is bonded to one Nb(2), one Fe(2), and two equivalent Fe(1) atoms to form ONbFe3 tetrahedra that share corners with two equivalent O(2)NbFe3 tetrahedra and edges with two equivalent O(1)MgNbFe3 trigonal bipyramids. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), two equivalent Nb(2), and one Fe(1) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to two equivalent Nb(1) and one Fe(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Nb(1), one Nb(2), and one Fe(1) atom. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Nb(1), one Nb(2), and one Fe(2) atom. In the seventh O site, O(7) is bonded in a T-shaped geometry to one Mg(1), one Nb(1), and one Fe(1) atom. In the eighth O site, O(8) is bonded in a distorted square co-planar geometry to two equivalent Mg(1), one Nb(2), and one Fe(2) atom.