MgCo6(O5F)2 crystallizes in the monoclinic P2 space group. Mg(1) is bonded to two equivalent O(1) and four equivalent O(4) atoms to form MgO6 octahedra that share corners with four equivalent Co(3)O4F square pyramids, edges with two equivalent Mg(1)O6 octahedra, edges with four equivalent Co(1)O6 octahedra, and edges with two equivalent Co(3)O4F square pyramids. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(4) and four equivalent O(1) atoms to form CoO6 octahedra that share corners with four equivalent Co(3)O4F square pyramids, edges with two equivalent Co(1)O6 octahedra, and edges with four equivalent Mg(1)O6 octahedra. In the second Co site, Co(2) is bonded to one O(3), one O(5), two equivalent O(2), and two equivalent F(1) atoms to form CoO4F2 octahedra that share corners with four equivalent Co(4)O6 octahedra, corners with four equivalent Co(3)O4F square pyramids, and edges with two equivalent Co(2)O4F2 octahedra. The corner-sharing octahedral tilt angles range from 50-51°. In the third Co site, Co(3) is bonded to two equivalent O(3), two equivalent O(4), and one F(1) atom to form distorted CoO4F square pyramids that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Co(1)O6 octahedra, corners with four equivalent Co(2)O4F2 octahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with two equivalent Co(3)O4F square pyramids. The corner-sharing octahedral tilt angles range from 35-56°. In the fourth Co site, Co(4) is bonded to two equivalent O(2) and four equivalent O(5) atoms to form CoO6 octahedra that share corners with eight equivalent Co(2)O4F2 octahedra and edges with two equivalent Co(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-51°. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mg(1) and two equivalent Co(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Co(4) and two equivalent Co(2) atoms. In the third O site, O(3) is bonded in a trigonal planar geometry to one Co(2) and two equivalent Co(3) atoms. In the fourth O site, O(4) is bonded to two equivalent Mg(1), one Co(1), and two equivalent Co(3) atoms to form a mixture of distorted corner and edge-sharing OMg2Co3 trigonal bipyramids. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Co(2) and two equivalent Co(4) atoms. F(1) is bonded in a distorted T-shaped geometry to one Co(3) and two equivalent Co(2) atoms.
MgCo6(O5F)2 crystallizes in the monoclinic P2 space group. Mg(1) is bonded to two equivalent O(1) and four equivalent O(4) atoms to form MgO6 octahedra that share corners with four equivalent Co(3)O4F square pyramids, edges with two equivalent Mg(1)O6 octahedra, edges with four equivalent Co(1)O6 octahedra, and edges with two equivalent Co(3)O4F square pyramids. Both Mg(1)-O(1) bond lengths are 1.93 Å. There are two shorter (2.09 Å) and two longer (2.11 Å) Mg(1)-O(4) bond lengths. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(4) and four equivalent O(1) atoms to form CoO6 octahedra that share corners with four equivalent Co(3)O4F square pyramids, edges with two equivalent Co(1)O6 octahedra, and edges with four equivalent Mg(1)O6 octahedra. Both Co(1)-O(4) bond lengths are 1.97 Å. There are two shorter (1.89 Å) and two longer (1.90 Å) Co(1)-O(1) bond lengths. In the second Co site, Co(2) is bonded to one O(3), one O(5), two equivalent O(2), and two equivalent F(1) atoms to form CoO4F2 octahedra that share corners with four equivalent Co(4)O6 octahedra, corners with four equivalent Co(3)O4F square pyramids, and edges with two equivalent Co(2)O4F2 octahedra. The corner-sharing octahedral tilt angles range from 50-51°. The Co(2)-O(3) bond length is 1.94 Å. The Co(2)-O(5) bond length is 1.93 Å. Both Co(2)-O(2) bond lengths are 1.91 Å. There is one shorter (2.08 Å) and one longer (2.09 Å) Co(2)-F(1) bond length. In the third Co site, Co(3) is bonded to two equivalent O(3), two equivalent O(4), and one F(1) atom to form distorted CoO4F square pyramids that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Co(1)O6 octahedra, corners with four equivalent Co(2)O4F2 octahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with two equivalent Co(3)O4F square pyramids. The corner-sharing octahedral tilt angles range from 35-56°. There is one shorter (1.87 Å) and one longer (1.88 Å) Co(3)-O(3) bond length. There is one shorter (2.03 Å) and one longer (2.06 Å) Co(3)-O(4) bond length. The Co(3)-F(1) bond length is 2.07 Å. In the fourth Co site, Co(4) is bonded to two equivalent O(2) and four equivalent O(5) atoms to form CoO6 octahedra that share corners with eight equivalent Co(2)O4F2 octahedra and edges with two equivalent Co(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-51°. Both Co(4)-O(2) bond lengths are 1.88 Å. All Co(4)-O(5) bond lengths are 1.90 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mg(1) and two equivalent Co(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Co(4) and two equivalent Co(2) atoms. In the third O site, O(3) is bonded in a trigonal planar geometry to one Co(2) and two equivalent Co(3) atoms. In the fourth O site, O(4) is bonded to two equivalent Mg(1), one Co(1), and two equivalent Co(3) atoms to form a mixture of distorted corner and edge-sharing OMg2Co3 trigonal bipyramids. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Co(2) and two equivalent Co(4) atoms. F(1) is bonded in a distorted T-shaped geometry to one Co(3) and two equivalent Co(2) atoms.