MgNbCrO4 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(1), one O(3), two equivalent O(2), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with four equivalent Mg(1)O6 octahedra,  a cornercorner with one Cr(1)O5 trigonal bipyramid, edges with four equivalent Nb(1)O6 octahedra, and edges with four equivalent Cr(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 7-21°. Nb(1) is bonded to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms to form NbO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra, corners with two equivalent Cr(1)O5 trigonal bipyramids, edges with four equivalent Mg(1)O6 octahedra, and edges with two equivalent Cr(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 10°. Cr(1) is bonded to one O(1), two equivalent O(2), and two equivalent O(4) atoms to form CrO5 trigonal bipyramids that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Cr(1)O5 trigonal bipyramids, edges with two equivalent Nb(1)O6 octahedra, and edges with four equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-77°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a square co-planar geometry to one Mg(1), two equivalent Nb(1), and one Cr(1) atom. In the second O site, O(2) is bonded to two equivalent Mg(1), one Nb(1), and two equivalent Cr(1) atoms to form a mixture of corner and edge-sharing OMg2NbCr2 trigonal bipyramids. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Mg(1) and two equivalent Nb(1) atoms. In the fourth O site, O(4) is bonded to two equivalent Mg(1), one Nb(1), and two equivalent Cr(1) atoms to form a mixture of corner and edge-sharing OMg2NbCr2 trigonal bipyramids.
MgNbCrO4 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(1), one O(3), two equivalent O(2), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with four equivalent Mg(1)O6 octahedra,  a cornercorner with one Cr(1)O5 trigonal bipyramid, edges with four equivalent Nb(1)O6 octahedra, and edges with four equivalent Cr(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 7-21°. The Mg(1)-O(1) bond length is 2.13 Å. The Mg(1)-O(3) bond length is 2.38 Å. Both Mg(1)-O(2) bond lengths are 2.06 Å. Both Mg(1)-O(4) bond lengths are 2.08 Å. Nb(1) is bonded to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms to form NbO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra, corners with two equivalent Cr(1)O5 trigonal bipyramids, edges with four equivalent Mg(1)O6 octahedra, and edges with two equivalent Cr(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 10°. The Nb(1)-O(2) bond length is 2.19 Å. The Nb(1)-O(4) bond length is 2.20 Å. Both Nb(1)-O(1) bond lengths are 2.09 Å. There is one shorter (2.03 Å) and one longer (2.04 Å) Nb(1)-O(3) bond length. Cr(1) is bonded to one O(1), two equivalent O(2), and two equivalent O(4) atoms to form CrO5 trigonal bipyramids that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Cr(1)O5 trigonal bipyramids, edges with two equivalent Nb(1)O6 octahedra, and edges with four equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-77°. The Cr(1)-O(1) bond length is 2.39 Å. Both Cr(1)-O(2) bond lengths are 2.08 Å. Both Cr(1)-O(4) bond lengths are 2.08 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a square co-planar geometry to one Mg(1), two equivalent Nb(1), and one Cr(1) atom. In the second O site, O(2) is bonded to two equivalent Mg(1), one Nb(1), and two equivalent Cr(1) atoms to form a mixture of corner and edge-sharing OMg2NbCr2 trigonal bipyramids. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Mg(1) and two equivalent Nb(1) atoms. In the fourth O site, O(4) is bonded to two equivalent Mg(1), one Nb(1), and two equivalent Cr(1) atoms to form a mixture of corner and edge-sharing OMg2NbCr2 trigonal bipyramids.