MgNb4(NO)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one N(2), one O(2), one O(4), and two equivalent O(3) atoms to form MgNO4 trigonal bipyramids that share corners with two equivalent Mg(1)NO4 trigonal bipyramids,  an edgeedge with one Nb(1)N3O3 octahedra, edges with two equivalent Nb(4)N3O3 octahedra, and edges with two equivalent Nb(3)N4O trigonal bipyramids. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one N(1), one N(2), one N(4), one O(2), and two equivalent O(1) atoms to form distorted NbN3O3 octahedra that share corners with two equivalent Nb(1)N3O3 octahedra, corners with three equivalent Nb(3)N4O trigonal bipyramids,  an edgeedge with one Nb(4)N3O3 octahedra, and  an edgeedge with one Mg(1)NO4 trigonal bipyramid. The corner-sharing octahedral tilt angles are 19°. In the second Nb site, Nb(2) is bonded in a 6-coordinate geometry to one N(1), one N(2), two equivalent N(3), one O(2), and one O(4) atom. In the third Nb site, Nb(3) is bonded to one N(3), one N(4), two equivalent N(2), and one O(3) atom to form distorted NbN4O trigonal bipyramids that share  a cornercorner with one Nb(4)N3O3 octahedra, corners with three equivalent Nb(1)N3O3 octahedra, corners with two equivalent Nb(3)N4O trigonal bipyramids,  an edgeedge with one Nb(4)N3O3 octahedra, and edges with two equivalent Mg(1)NO4 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 1-70°. In the fourth Nb site, Nb(4) is bonded to one N(1), one N(3), one N(4), one O(3), and two equivalent O(4) atoms to form distorted NbN3O3 octahedra that share corners with two equivalent Nb(4)N3O3 octahedra,  a cornercorner with one Nb(3)N4O trigonal bipyramid,  an edgeedge with one Nb(1)N3O3 octahedra,  an edgeedge with one Nb(3)N4O trigonal bipyramid, and edges with two equivalent Mg(1)NO4 trigonal bipyramids. The corner-sharing octahedral tilt angles are 26°. There are four inequivalent N sites. In the first N site, N(1) is bonded in a T-shaped geometry to one Nb(1), one Nb(2), and one Nb(4) atom. In the second N site, N(2) is bonded to one Mg(1), one Nb(1), one Nb(2), and two equivalent Nb(3) atoms to form NMgNb4 trigonal bipyramids that share corners with two equivalent N(2)MgNb4 trigonal bipyramids and edges with two equivalent N(3)Nb4 trigonal pyramids. In the third N site, N(3) is bonded to one Nb(3), one Nb(4), and two equivalent Nb(2) atoms to form distorted NNb4 trigonal pyramids that share corners with two equivalent N(3)Nb4 trigonal pyramids and edges with two equivalent N(2)MgNb4 trigonal bipyramids. In the fourth N site, N(4) is bonded in a T-shaped geometry to one Nb(1), one Nb(3), and one Nb(4) atom. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a T-shaped geometry to one Mg(1), one Nb(1), and one Nb(2) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1), one Nb(3), and one Nb(4) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Mg(1), one Nb(2), and two equivalent Nb(4) atoms.
MgNb4(NO)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one N(2), one O(2), one O(4), and two equivalent O(3) atoms to form MgNO4 trigonal bipyramids that share corners with two equivalent Mg(1)NO4 trigonal bipyramids,  an edgeedge with one Nb(1)N3O3 octahedra, edges with two equivalent Nb(4)N3O3 octahedra, and edges with two equivalent Nb(3)N4O trigonal bipyramids. The Mg(1)-N(2) bond length is 2.13 Å. The Mg(1)-O(2) bond length is 2.01 Å. The Mg(1)-O(4) bond length is 2.01 Å. Both Mg(1)-O(3) bond lengths are 2.04 Å. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one N(1), one N(2), one N(4), one O(2), and two equivalent O(1) atoms to form distorted NbN3O3 octahedra that share corners with two equivalent Nb(1)N3O3 octahedra, corners with three equivalent Nb(3)N4O trigonal bipyramids,  an edgeedge with one Nb(4)N3O3 octahedra, and  an edgeedge with one Mg(1)NO4 trigonal bipyramid. The corner-sharing octahedral tilt angles are 19°. The Nb(1)-N(1) bond length is 2.19 Å. The Nb(1)-N(2) bond length is 2.35 Å. The Nb(1)-N(4) bond length is 2.03 Å. The Nb(1)-O(2) bond length is 2.23 Å. There is one shorter (1.97 Å) and one longer (1.98 Å) Nb(1)-O(1) bond length. In the second Nb site, Nb(2) is bonded in a 6-coordinate geometry to one N(1), one N(2), two equivalent N(3), one O(2), and one O(4) atom. The Nb(2)-N(1) bond length is 1.91 Å. The Nb(2)-N(2) bond length is 2.35 Å. There is one shorter (2.10 Å) and one longer (2.11 Å) Nb(2)-N(3) bond length. The Nb(2)-O(2) bond length is 1.94 Å. The Nb(2)-O(4) bond length is 2.78 Å. In the third Nb site, Nb(3) is bonded to one N(3), one N(4), two equivalent N(2), and one O(3) atom to form distorted NbN4O trigonal bipyramids that share  a cornercorner with one Nb(4)N3O3 octahedra, corners with three equivalent Nb(1)N3O3 octahedra, corners with two equivalent Nb(3)N4O trigonal bipyramids,  an edgeedge with one Nb(4)N3O3 octahedra, and edges with two equivalent Mg(1)NO4 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 1-70°. The Nb(3)-N(3) bond length is 2.09 Å. The Nb(3)-N(4) bond length is 1.91 Å. Both Nb(3)-N(2) bond lengths are 2.08 Å. The Nb(3)-O(3) bond length is 2.09 Å. In the fourth Nb site, Nb(4) is bonded to one N(1), one N(3), one N(4), one O(3), and two equivalent O(4) atoms to form distorted NbN3O3 octahedra that share corners with two equivalent Nb(4)N3O3 octahedra,  a cornercorner with one Nb(3)N4O trigonal bipyramid,  an edgeedge with one Nb(1)N3O3 octahedra,  an edgeedge with one Nb(3)N4O trigonal bipyramid, and edges with two equivalent Mg(1)NO4 trigonal bipyramids. The corner-sharing octahedral tilt angles are 26°. The Nb(4)-N(1) bond length is 2.01 Å. The Nb(4)-N(3) bond length is 2.39 Å. The Nb(4)-N(4) bond length is 2.11 Å. The Nb(4)-O(3) bond length is 2.28 Å. Both Nb(4)-O(4) bond lengths are 2.00 Å. There are four inequivalent N sites. In the first N site, N(1) is bonded in a T-shaped geometry to one Nb(1), one Nb(2), and one Nb(4) atom. In the second N site, N(2) is bonded to one Mg(1), one Nb(1), one Nb(2), and two equivalent Nb(3) atoms to form NMgNb4 trigonal bipyramids that share corners with two equivalent N(2)MgNb4 trigonal bipyramids and edges with two equivalent N(3)Nb4 trigonal pyramids. In the third N site, N(3) is bonded to one Nb(3), one Nb(4), and two equivalent Nb(2) atoms to form distorted NNb4 trigonal pyramids that share corners with two equivalent N(3)Nb4 trigonal pyramids and edges with two equivalent N(2)MgNb4 trigonal bipyramids. In the fourth N site, N(4) is bonded in a T-shaped geometry to one Nb(1), one Nb(3), and one Nb(4) atom. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a T-shaped geometry to one Mg(1), one Nb(1), and one Nb(2) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1), one Nb(3), and one Nb(4) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Mg(1), one Nb(2), and two equivalent Nb(4) atoms.