Ca2Mg5Si8(O11F)2 is Esseneite-derived structured and crystallizes in the monoclinic C2/m space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent F(1) atoms to form MgO4F2 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra,  an edgeedge with one Mg(1)O4F2 octahedra, edges with two equivalent Mg(2)O4F2 octahedra, and edges with two equivalent Mg(3)O6 octahedra. In the second Mg site, Mg(2) is bonded to four equivalent O(2) and two equivalent F(1) atoms to form MgO4F2 octahedra that share corners with four equivalent Si(1)O4 tetrahedra, edges with two equivalent Mg(3)O6 octahedra, and edges with four equivalent Mg(1)O4F2 octahedra. In the third Mg site, Mg(3) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms to form MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra,  an edgeedge with one Mg(2)O4F2 octahedra, and edges with two equivalent Mg(1)O4F2 octahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O4F2 octahedra,  a cornercorner with one Mg(2)O4F2 octahedra,  a cornercorner with one Mg(3)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 59-60°. In the second Si site, Si(2) is bonded to one O(1), one O(3), one O(4), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O4F2 octahedra, corners with two equivalent Mg(3)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 35-57°. There are six inequivalent O sites. In the first O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the second O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), one Mg(1), one Mg(3), and one Si(2) atom. In the third O site, O(5) is bonded in a bent 150 degrees geometry to two equivalent Si(1) atoms. In the fourth O site, O(6) is bonded in a distorted T-shaped geometry to one Ca(1), one Mg(3), and one Si(2) atom. In the fifth O site, O(1) is bonded in a 2-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(2) is bonded to one Mg(1), one Mg(2), one Mg(3), and one Si(1) atom to form a mixture of distorted edge and corner-sharing OMg3Si trigonal pyramids. F(1) is bonded in a distorted trigonal non-coplanar geometry to one Mg(2) and two equivalent Mg(1) atoms.
Ca2Mg5Si8(O11F)2 is Esseneite-derived structured and crystallizes in the monoclinic C2/m space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms. Both Ca(1)-O(1) bond lengths are 2.80 Å. Both Ca(1)-O(3) bond lengths are 2.54 Å. Both Ca(1)-O(4) bond lengths are 2.44 Å. Both Ca(1)-O(6) bond lengths are 2.34 Å. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent F(1) atoms to form MgO4F2 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra,  an edgeedge with one Mg(1)O4F2 octahedra, edges with two equivalent Mg(2)O4F2 octahedra, and edges with two equivalent Mg(3)O6 octahedra. Both Mg(1)-O(2) bond lengths are 2.09 Å. Both Mg(1)-O(4) bond lengths are 2.08 Å. Both Mg(1)-F(1) bond lengths are 2.08 Å. In the second Mg site, Mg(2) is bonded to four equivalent O(2) and two equivalent F(1) atoms to form MgO4F2 octahedra that share corners with four equivalent Si(1)O4 tetrahedra, edges with two equivalent Mg(3)O6 octahedra, and edges with four equivalent Mg(1)O4F2 octahedra. All Mg(2)-O(2) bond lengths are 2.08 Å. Both Mg(2)-F(1) bond lengths are 2.04 Å. In the third Mg site, Mg(3) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms to form MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra,  an edgeedge with one Mg(2)O4F2 octahedra, and edges with two equivalent Mg(1)O4F2 octahedra. Both Mg(3)-O(2) bond lengths are 2.18 Å. Both Mg(3)-O(4) bond lengths are 2.11 Å. Both Mg(3)-O(6) bond lengths are 2.04 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O4F2 octahedra,  a cornercorner with one Mg(2)O4F2 octahedra,  a cornercorner with one Mg(3)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 59-60°. The Si(1)-O(1) bond length is 1.65 Å. The Si(1)-O(2) bond length is 1.63 Å. The Si(1)-O(3) bond length is 1.65 Å. The Si(1)-O(5) bond length is 1.63 Å. In the second Si site, Si(2) is bonded to one O(1), one O(3), one O(4), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O4F2 octahedra, corners with two equivalent Mg(3)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 35-57°. The Si(2)-O(1) bond length is 1.67 Å. The Si(2)-O(3) bond length is 1.69 Å. The Si(2)-O(4) bond length is 1.64 Å. The Si(2)-O(6) bond length is 1.61 Å. There are six inequivalent O sites. In the first O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the second O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), one Mg(1), one Mg(3), and one Si(2) atom. In the third O site, O(5) is bonded in a bent 150 degrees geometry to two equivalent Si(1) atoms. In the fourth O site, O(6) is bonded in a distorted T-shaped geometry to one Ca(1), one Mg(3), and one Si(2) atom. In the fifth O site, O(1) is bonded in a 2-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(2) is bonded to one Mg(1), one Mg(2), one Mg(3), and one Si(1) atom to form a mixture of distorted edge and corner-sharing OMg3Si trigonal pyramids. F(1) is bonded in a distorted trigonal non-coplanar geometry to one Mg(2) and two equivalent Mg(1) atoms.