CaMgB6O17 crystallizes in the monoclinic P2/c space group. Ca(1) is bonded to two equivalent O(6), two equivalent O(7), and four equivalent O(9) atoms to form distorted CaO8 hexagonal bipyramids that share corners with two equivalent B(1)O4 tetrahedra, edges with two equivalent Ca(1)O8 hexagonal bipyramids, and edges with four equivalent B(2)O4 tetrahedra. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. There are three inequivalent B sites. In the first B site, B(1) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form BO4 tetrahedra that share  a cornercorner with one Ca(1)O8 hexagonal bipyramid and  a cornercorner with one B(2)O4 tetrahedra. In the second B site, B(2) is bonded to one O(6), one O(7), one O(8), and one O(9) atom to form BO4 tetrahedra that share  a cornercorner with one B(1)O4 tetrahedra and edges with two equivalent Ca(1)O8 hexagonal bipyramids. In the third B site, B(3) is bonded in a trigonal planar geometry to one O(4), one O(5), and one O(7) atom. There are nine inequivalent O sites. In the first O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one B(1), and one B(2) atom. In the second O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one B(2), and one B(3) atom. In the third O site, O(8) is bonded in a single-bond geometry to one B(2) atom. In the fourth O site, O(9) is bonded in a distorted single-bond geometry to two equivalent Ca(1) and one B(2) atom. In the fifth O site, O(1) is bonded in a bent 150 degrees geometry to two equivalent Mg(1) atoms. In the sixth O site, O(2) is bonded in a bent 120 degrees geometry to one Mg(1) and one O(2) atom. In the seventh O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one B(1) atom. In the eighth O site, O(4) is bonded in a bent 120 degrees geometry to one B(1) and one B(3) atom. In the ninth O site, O(5) is bonded in a bent 120 degrees geometry to one B(1) and one B(3) atom.
CaMgB6O17 crystallizes in the monoclinic P2/c space group. Ca(1) is bonded to two equivalent O(6), two equivalent O(7), and four equivalent O(9) atoms to form distorted CaO8 hexagonal bipyramids that share corners with two equivalent B(1)O4 tetrahedra, edges with two equivalent Ca(1)O8 hexagonal bipyramids, and edges with four equivalent B(2)O4 tetrahedra. Both Ca(1)-O(6) bond lengths are 2.53 Å. Both Ca(1)-O(7) bond lengths are 2.50 Å. There are two shorter (2.47 Å) and two longer (2.48 Å) Ca(1)-O(9) bond lengths. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. Both Mg(1)-O(1) bond lengths are 2.16 Å. Both Mg(1)-O(2) bond lengths are 2.66 Å. Both Mg(1)-O(3) bond lengths are 2.00 Å. There are three inequivalent B sites. In the first B site, B(1) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form BO4 tetrahedra that share  a cornercorner with one Ca(1)O8 hexagonal bipyramid and  a cornercorner with one B(2)O4 tetrahedra. The B(1)-O(3) bond length is 1.45 Å. The B(1)-O(4) bond length is 1.44 Å. The B(1)-O(5) bond length is 1.48 Å. The B(1)-O(6) bond length is 1.49 Å. In the second B site, B(2) is bonded to one O(6), one O(7), one O(8), and one O(9) atom to form BO4 tetrahedra that share  a cornercorner with one B(1)O4 tetrahedra and edges with two equivalent Ca(1)O8 hexagonal bipyramids. The B(2)-O(6) bond length is 1.48 Å. The B(2)-O(7) bond length is 1.48 Å. The B(2)-O(8) bond length is 1.47 Å. The B(2)-O(9) bond length is 1.43 Å. In the third B site, B(3) is bonded in a trigonal planar geometry to one O(4), one O(5), and one O(7) atom. The B(3)-O(4) bond length is 1.35 Å. The B(3)-O(5) bond length is 1.39 Å. The B(3)-O(7) bond length is 1.39 Å. There are nine inequivalent O sites. In the first O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one B(1), and one B(2) atom. In the second O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one B(2), and one B(3) atom. In the third O site, O(8) is bonded in a single-bond geometry to one B(2) atom. In the fourth O site, O(9) is bonded in a distorted single-bond geometry to two equivalent Ca(1) and one B(2) atom. In the fifth O site, O(1) is bonded in a bent 150 degrees geometry to two equivalent Mg(1) atoms. In the sixth O site, O(2) is bonded in a bent 120 degrees geometry to one Mg(1) and one O(2) atom. The O(2)-O(2) bond length is 1.24 Å. In the seventh O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one B(1) atom. In the eighth O site, O(4) is bonded in a bent 120 degrees geometry to one B(1) and one B(3) atom. In the ninth O site, O(5) is bonded in a bent 120 degrees geometry to one B(1) and one B(3) atom.