Mg5Al4(PO4)9 is Low Tridymite-derived structured and crystallizes in the monoclinic C2/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(1), one O(11), one O(15), and one O(4) atom to form MgO4 tetrahedra that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra,  a cornercorner with one P(3)O4 tetrahedra, and  a cornercorner with one P(4)O4 tetrahedra. The Mg(1)-O(1) bond length is 1.75 Å. The Mg(1)-O(11) bond length is 1.76 Å. The Mg(1)-O(15) bond length is 1.75 Å. The Mg(1)-O(4) bond length is 1.76 Å. In the second Mg site, Mg(2,3) is bonded to one O(14), one O(18), one O(6), and one O(8) atom to form MgO4 tetrahedra that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(3)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra, and  a cornercorner with one P(5)O4 tetrahedra. The Mg(2,3)-O(14) bond length is 1.75 Å. The Mg(2,3)-O(18) bond length is 1.77 Å. The Mg(2,3)-O(6) bond length is 1.77 Å. The Mg(2,3)-O(8) bond length is 1.75 Å. Al(1,2) is bonded to one O(10), one O(17), one O(3), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra,  a cornercorner with one P(3)O4 tetrahedra, and  a cornercorner with one P(4)O4 tetrahedra. The Al(1,2)-O(10) bond length is 1.76 Å. The Al(1,2)-O(17) bond length is 1.76 Å. The Al(1,2)-O(3) bond length is 1.75 Å. The Al(1,2)-O(7) bond length is 1.75 Å. There are five 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  a cornercorner with one Mg(1)O4 tetrahedra;  a cornercorner with one Mg(2,3)O4 tetrahedra; and corners with two equivalent Al(1,2)O4 tetrahedra. The P(1)-O(3) bond length is 1.51 Å. The P(1)-O(4) bond length is 1.51 Å. The P(1)-O(5) bond length is 1.52 Å. The P(1)-O(6) bond length is 1.50 Å. In the second P site, P(2) is bonded to one O(10), one O(11), one O(12), and one O(9) atom to form PO4 tetrahedra that share  a cornercorner with one Mg(1)O4 tetrahedra;  a cornercorner with one Mg(2,3)O4 tetrahedra; and corners with two equivalent Al(1,2)O4 tetrahedra. The P(2)-O(10) bond length is 1.51 Å. The P(2)-O(11) bond length is 1.52 Å. The P(2)-O(12) bond length is 1.50 Å. The P(2)-O(9) bond length is 1.51 Å. In the third P site, P(3) is bonded to one O(15), one O(16), one O(17), and one O(18) atom to form PO4 tetrahedra that share  a cornercorner with one Mg(1)O4 tetrahedra;  a cornercorner with one Mg(2,3)O4 tetrahedra; and corners with two equivalent Al(1,2)O4 tetrahedra. The P(3)-O(15) bond length is 1.51 Å. The P(3)-O(16) bond length is 1.51 Å. The P(3)-O(17) bond length is 1.52 Å. The P(3)-O(18) bond length is 1.50 Å. In the fourth P site, P(4) is bonded to one O(1), one O(2), one O(7), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Mg(1)O4 tetrahedra;  a cornercorner with one Al(1,2)O4 tetrahedra; and corners with two equivalent Mg(2,3)O4 tetrahedra. The P(4)-O(1) bond length is 1.52 Å. The P(4)-O(2) bond length is 1.50 Å. The P(4)-O(7) bond length is 1.52 Å. The P(4)-O(8) bond length is 1.50 Å. In the fifth P site, P(5) is bonded to two equivalent O(13) and two equivalent O(14) atoms to form PO4 tetrahedra that share corners with two equivalent Mg(2,3)O4 tetrahedra and corners with two equivalent Al(1,2)O4 tetrahedra. Both P(5)-O(13) bond lengths are 1.52 Å. Both P(5)-O(14) bond lengths are 1.50 Å. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Mg(1) and one P(4) atom. In the second O site, O(2) is bonded in a linear geometry to one Mg(2,3) and one P(4) atom. The O(2)-Mg(2,3) bond length is 1.75 Å. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Al(1,2) and one P(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Mg(1) and one P(1) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Al(1,2) and one P(1) atom. The O(5)-Al(1,2) bond length is 1.76 Å. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Mg(2,3) and one P(1) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Al(1,2) and one P(4) atom. In the eighth O site, O(8) is bonded in a linear geometry to one Mg(2,3) and one P(4) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Al(1,2) and one P(2) atom. The O(9)-Al(1,2) bond length is 1.75 Å. In the tenth O site, O(10) is bonded in a bent 150 degrees geometry to one Al(1,2) and one P(2) atom. In the eleventh O site, O(11) is bonded in a bent 150 degrees geometry to one Mg(1) and one P(2) atom. In the twelfth O site, O(12) is bonded in a bent 150 degrees geometry to one Mg(2,3) and one P(2) atom. The O(12)-Mg(2,3) bond length is 1.77 Å. In the thirteenth O site, O(13) is bonded in a bent 150 degrees geometry to one Al(1,2) and one P(5) atom. The O(13)-Al(1,2) bond length is 1.75 Å. In the fourteenth O site, O(14) is bonded in a linear geometry to one Mg(2,3) and one P(5) atom. In the fifteenth O site, O(15) is bonded in a bent 150 degrees geometry to one Mg(1) and one P(3) atom. In the sixteenth O site, O(16) is bonded in a bent 150 degrees geometry to one Al(1,2) and one P(3) atom. The O(16)-Al(1,2) bond length is 1.76 Å. In the seventeenth O site, O(17) is bonded in a bent 150 degrees geometry to one Al(1,2) and one P(3) atom. In the eighteenth O site, O(18) is bonded in a bent 150 degrees geometry to one Mg(2,3) and one P(3) atom. Linkers: 54 [O]P([O])([O])=O. Metal clusters: 30 [Mg] ,24 [Al]. The MOF has largest included sphere 6.59 A, density 1.53 g/cm3, surface area 2938.17 m2/g, accessible volume 0.33 cm3/g