Mg2B(PO5)2 crystallizes in the monoclinic C2 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(2), one O(3), one O(4), one O(5), one O(7), and one O(9) atom to form MgO6 octahedra that share  a cornercorner with one B(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and edges with two equivalent Mg(2)O6 octahedra. In the second Mg site, Mg(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(8) atom to form MgO6 octahedra that share  a cornercorner with one B(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and edges with two equivalent Mg(1)O6 octahedra. B(1) is bonded to one O(10), one O(6), one O(7), and one O(8) atom to form BO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra,  a cornercorner with one Mg(2)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 43-51°. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Mg(2)O6 octahedra, and  a cornercorner with one B(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 46-58°. In the second P site, P(2) is bonded to one O(1), one O(10), one O(2), and one O(9) atom to form PO4 tetrahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Mg(2)O6 octahedra, and  a cornercorner with one B(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 15-55°. There are ten inequivalent O sites. In the first O site, O(9) is bonded in a linear geometry to one Mg(1) and one P(2) atom. In the second O site, O(10) is bonded in a distorted bent 120 degrees geometry to one B(1) and one P(2) atom. In the third O site, O(1) is bonded in a bent 150 degrees geometry to one Mg(2) and one P(2) atom. In the fourth O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one P(2) atom. In the fifth O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one P(1) atom. In the sixth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one P(1) atom. In the seventh O site, O(5) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one P(1) atom. In the eighth O site, O(6) is bonded in a bent 150 degrees geometry to one B(1) and one P(1) atom. In the ninth O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one B(1) atom. In the tenth O site, O(8) is bonded in a distorted bent 120 degrees geometry to one Mg(2) and one B(1) atom.
Mg2B(PO5)2 crystallizes in the monoclinic C2 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(2), one O(3), one O(4), one O(5), one O(7), and one O(9) atom to form MgO6 octahedra that share  a cornercorner with one B(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and edges with two equivalent Mg(2)O6 octahedra. The Mg(1)-O(2) bond length is 2.12 Å. The Mg(1)-O(3) bond length is 2.12 Å. The Mg(1)-O(4) bond length is 2.18 Å. The Mg(1)-O(5) bond length is 2.11 Å. The Mg(1)-O(7) bond length is 2.22 Å. The Mg(1)-O(9) bond length is 2.01 Å. In the second Mg site, Mg(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(8) atom to form MgO6 octahedra that share  a cornercorner with one B(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and edges with two equivalent Mg(1)O6 octahedra. The Mg(2)-O(1) bond length is 2.02 Å. The Mg(2)-O(2) bond length is 2.07 Å. The Mg(2)-O(3) bond length is 2.13 Å. The Mg(2)-O(4) bond length is 2.10 Å. The Mg(2)-O(5) bond length is 2.12 Å. The Mg(2)-O(8) bond length is 2.20 Å. B(1) is bonded to one O(10), one O(6), one O(7), and one O(8) atom to form BO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra,  a cornercorner with one Mg(2)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 43-51°. The B(1)-O(10) bond length is 1.48 Å. The B(1)-O(6) bond length is 1.45 Å. The B(1)-O(7) bond length is 1.43 Å. The B(1)-O(8) bond length is 1.44 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Mg(2)O6 octahedra, and  a cornercorner with one B(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 46-58°. The P(1)-O(3) bond length is 1.55 Å. The P(1)-O(4) bond length is 1.55 Å. The P(1)-O(5) bond length is 1.55 Å. The P(1)-O(6) bond length is 1.57 Å. In the second P site, P(2) is bonded to one O(1), one O(10), one O(2), and one O(9) atom to form PO4 tetrahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Mg(2)O6 octahedra, and  a cornercorner with one B(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 15-55°. The P(2)-O(1) bond length is 1.53 Å. The P(2)-O(10) bond length is 1.58 Å. The P(2)-O(2) bond length is 1.54 Å. The P(2)-O(9) bond length is 1.51 Å. There are ten inequivalent O sites. In the first O site, O(9) is bonded in a linear geometry to one Mg(1) and one P(2) atom. In the second O site, O(10) is bonded in a distorted bent 120 degrees geometry to one B(1) and one P(2) atom. In the third O site, O(1) is bonded in a bent 150 degrees geometry to one Mg(2) and one P(2) atom. In the fourth O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one P(2) atom. In the fifth O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one P(1) atom. In the sixth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one P(1) atom. In the seventh O site, O(5) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one P(1) atom. In the eighth O site, O(6) is bonded in a bent 150 degrees geometry to one B(1) and one P(1) atom. In the ninth O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one B(1) atom. In the tenth O site, O(8) is bonded in a distorted bent 120 degrees geometry to one Mg(2) and one B(1) atom.