MgTi4Pb2O9F2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(4) atoms. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(2), one O(3), one O(5), two equivalent O(1), and one F(1) atom to form distorted TiO5F octahedra that share corners with three equivalent Ti(1)O5F octahedra,  a cornercorner with one Ti(2)O5 trigonal bipyramid, and edges with two equivalent Ti(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 0-29°. In the second Ti site, Ti(2) is bonded to one O(1), one O(4), one O(5), and two equivalent O(2) atoms to form distorted TiO5 trigonal bipyramids that share  a cornercorner with one Ti(1)O5F octahedra, corners with two equivalent Ti(2)O5 trigonal bipyramids, and edges with two equivalent Ti(1)O5F octahedra. The corner-sharing octahedral tilt angles are 9°. Pb(1) is bonded in a 5-coordinate geometry to two equivalent O(4) and three equivalent F(1) atoms. There are five inequivalent O sites. In the first O site, O(1) is bonded in a T-shaped geometry to one Ti(2) and two equivalent Ti(1) atoms. In the second O site, O(2) is bonded to one Mg(1), one Ti(1), and two equivalent Ti(2) atoms to form distorted OMgTi3 trigonal pyramids that share corners with two equivalent O(4)Mg2TiPb2 square pyramids,  a cornercorner with one F(1)TiPb3 tetrahedra, corners with three equivalent O(2)MgTi3 trigonal pyramids, and edges with two equivalent O(4)Mg2TiPb2 square pyramids. In the third O site, O(3) is bonded in a linear geometry to two equivalent Ti(1) atoms. In the fourth O site, O(4) is bonded to two equivalent Mg(1), one Ti(2), and two equivalent Pb(1) atoms to form distorted OMg2TiPb2 square pyramids that share corners with two equivalent O(4)Mg2TiPb2 square pyramids, corners with four equivalent F(1)TiPb3 tetrahedra, corners with two equivalent O(2)MgTi3 trigonal pyramids, edges with three equivalent O(4)Mg2TiPb2 square pyramids,  an edgeedge with one F(1)TiPb3 tetrahedra, and edges with two equivalent O(2)MgTi3 trigonal pyramids. In the fifth O site, O(5) is bonded in a linear geometry to one Ti(1) and one Ti(2) atom. F(1) is bonded to one Ti(1) and three equivalent Pb(1) atoms to form distorted FTiPb3 tetrahedra that share corners with four equivalent O(4)Mg2TiPb2 square pyramids, corners with two equivalent F(1)TiPb3 tetrahedra,  a cornercorner with one O(2)MgTi3 trigonal pyramid,  an edgeedge with one O(4)Mg2TiPb2 square pyramid, and edges with two equivalent F(1)TiPb3 tetrahedra.
MgTi4Pb2O9F2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(4) atoms. Both Mg(1)-O(2) bond lengths are 1.98 Å. All Mg(1)-O(4) bond lengths are 2.34 Å. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(2), one O(3), one O(5), two equivalent O(1), and one F(1) atom to form distorted TiO5F octahedra that share corners with three equivalent Ti(1)O5F octahedra,  a cornercorner with one Ti(2)O5 trigonal bipyramid, and edges with two equivalent Ti(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 0-29°. The Ti(1)-O(2) bond length is 2.18 Å. The Ti(1)-O(3) bond length is 1.87 Å. The Ti(1)-O(5) bond length is 1.92 Å. Both Ti(1)-O(1) bond lengths are 1.94 Å. The Ti(1)-F(1) bond length is 2.44 Å. In the second Ti site, Ti(2) is bonded to one O(1), one O(4), one O(5), and two equivalent O(2) atoms to form distorted TiO5 trigonal bipyramids that share  a cornercorner with one Ti(1)O5F octahedra, corners with two equivalent Ti(2)O5 trigonal bipyramids, and edges with two equivalent Ti(1)O5F octahedra. The corner-sharing octahedral tilt angles are 9°. The Ti(2)-O(1) bond length is 2.05 Å. The Ti(2)-O(4) bond length is 1.96 Å. The Ti(2)-O(5) bond length is 1.79 Å. Both Ti(2)-O(2) bond lengths are 1.97 Å. Pb(1) is bonded in a 5-coordinate geometry to two equivalent O(4) and three equivalent F(1) atoms. Both Pb(1)-O(4) bond lengths are 2.65 Å. There are two shorter (2.50 Å) and one longer (2.68 Å) Pb(1)-F(1) bond length. There are five inequivalent O sites. In the first O site, O(1) is bonded in a T-shaped geometry to one Ti(2) and two equivalent Ti(1) atoms. In the second O site, O(2) is bonded to one Mg(1), one Ti(1), and two equivalent Ti(2) atoms to form distorted OMgTi3 trigonal pyramids that share corners with two equivalent O(4)Mg2TiPb2 square pyramids,  a cornercorner with one F(1)TiPb3 tetrahedra, corners with three equivalent O(2)MgTi3 trigonal pyramids, and edges with two equivalent O(4)Mg2TiPb2 square pyramids. In the third O site, O(3) is bonded in a linear geometry to two equivalent Ti(1) atoms. In the fourth O site, O(4) is bonded to two equivalent Mg(1), one Ti(2), and two equivalent Pb(1) atoms to form distorted OMg2TiPb2 square pyramids that share corners with two equivalent O(4)Mg2TiPb2 square pyramids, corners with four equivalent F(1)TiPb3 tetrahedra, corners with two equivalent O(2)MgTi3 trigonal pyramids, edges with three equivalent O(4)Mg2TiPb2 square pyramids,  an edgeedge with one F(1)TiPb3 tetrahedra, and edges with two equivalent O(2)MgTi3 trigonal pyramids. In the fifth O site, O(5) is bonded in a linear geometry to one Ti(1) and one Ti(2) atom. F(1) is bonded to one Ti(1) and three equivalent Pb(1) atoms to form distorted FTiPb3 tetrahedra that share corners with four equivalent O(4)Mg2TiPb2 square pyramids, corners with two equivalent F(1)TiPb3 tetrahedra,  a cornercorner with one O(2)MgTi3 trigonal pyramid,  an edgeedge with one O(4)Mg2TiPb2 square pyramid, and edges with two equivalent F(1)TiPb3 tetrahedra.