Mg2TiNb2O8 crystallizes in the monoclinic C2/c space group. Mg(1) is bonded in a 6-coordinate geometry to three equivalent O(3) and three equivalent O(4) atoms. Ti(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form TiO6 octahedra that share corners with eight equivalent Nb(1)O6 octahedra and edges with two equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-52°. 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 Ti(1)O6 octahedra and edges with two equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-52°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ti(1) and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent Ti(1) and one Nb(1) atom. In the third O site, O(3) is bonded to three equivalent Mg(1) and two equivalent Nb(1) atoms to form distorted OMg3Nb2 trigonal bipyramids that share corners with two equivalent O(3)Mg3Nb2 trigonal bipyramids, corners with three equivalent O(4)Mg3Nb trigonal pyramids, edges with three equivalent O(3)Mg3Nb2 trigonal bipyramids, and edges with four equivalent O(4)Mg3Nb trigonal pyramids. In the fourth O site, O(4) is bonded to three equivalent Mg(1) and one Nb(1) atom to form OMg3Nb trigonal pyramids that share corners with three equivalent O(3)Mg3Nb2 trigonal bipyramids, corners with four equivalent O(4)Mg3Nb trigonal pyramids, edges with four equivalent O(3)Mg3Nb2 trigonal bipyramids, and  an edgeedge with one O(4)Mg3Nb trigonal pyramid.
Mg2TiNb2O8 crystallizes in the monoclinic C2/c space group. Mg(1) is bonded in a 6-coordinate geometry to three equivalent O(3) and three equivalent O(4) atoms. There are a spread of Mg(1)-O(3) bond distances ranging from 2.03-2.37 Å. There are a spread of Mg(1)-O(4) bond distances ranging from 1.96-2.12 Å. Ti(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form TiO6 octahedra that share corners with eight equivalent Nb(1)O6 octahedra and edges with two equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-52°. Both Ti(1)-O(1) bond lengths are 2.05 Å. There are two shorter (2.02 Å) and two longer (2.06 Å) Ti(1)-O(2) bond lengths. 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 Ti(1)O6 octahedra and edges with two equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-52°. The Nb(1)-O(2) bond length is 1.98 Å. The Nb(1)-O(4) bond length is 2.03 Å. There is one shorter (2.04 Å) and one longer (2.10 Å) Nb(1)-O(1) bond length. There is one shorter (2.09 Å) and one longer (2.20 Å) Nb(1)-O(3) bond length. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ti(1) and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent Ti(1) and one Nb(1) atom. In the third O site, O(3) is bonded to three equivalent Mg(1) and two equivalent Nb(1) atoms to form distorted OMg3Nb2 trigonal bipyramids that share corners with two equivalent O(3)Mg3Nb2 trigonal bipyramids, corners with three equivalent O(4)Mg3Nb trigonal pyramids, edges with three equivalent O(3)Mg3Nb2 trigonal bipyramids, and edges with four equivalent O(4)Mg3Nb trigonal pyramids. In the fourth O site, O(4) is bonded to three equivalent Mg(1) and one Nb(1) atom to form OMg3Nb trigonal pyramids that share corners with three equivalent O(3)Mg3Nb2 trigonal bipyramids, corners with four equivalent O(4)Mg3Nb trigonal pyramids, edges with four equivalent O(3)Mg3Nb2 trigonal bipyramids, and  an edgeedge with one O(4)Mg3Nb trigonal pyramid.