Al2PO8 crystallizes in the orthorhombic Pna2_1 space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2), one O(3), one O(5), one O(6), and one O(7) atom to form AlO5 trigonal bipyramids that share  a cornercorner with one Al(2)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, and  an edgeedge with one Al(2)O6 octahedra. The corner-sharing octahedral tilt angles are 33°. In the second Al site, Al(2) is bonded to one O(1), one O(4), one O(5), one O(6), one O(7), and one O(8) atom to form AlO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra,  a cornercorner with one Al(1)O5 trigonal bipyramid, and  an edgeedge with one Al(1)O5 trigonal bipyramid. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with two equivalent Al(2)O6 octahedra and corners with two equivalent Al(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 17-46°. There are eight inequivalent O sites. In the first O site, O(6) is bonded in a water-like geometry to one Al(1) and one Al(2) atom. In the second O site, O(7) is bonded in a bent 120 degrees geometry to one Al(1) and one Al(2) atom. In the third O site, O(8) is bonded in a single-bond geometry to one Al(2) atom. In the fourth O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Al(2) and one P(1) atom. In the fifth O site, O(2) is bonded in a bent 150 degrees geometry to one Al(1) and one P(1) atom. In the sixth O site, O(3) is bonded in a bent 120 degrees geometry to one Al(1) and one P(1) atom. In the seventh O site, O(4) is bonded in a linear geometry to one Al(2) and one P(1) atom. In the eighth O site, O(5) is bonded in a bent 150 degrees geometry to one Al(1) and one Al(2) atom.
Al2PO8 crystallizes in the orthorhombic Pna2_1 space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2), one O(3), one O(5), one O(6), and one O(7) atom to form AlO5 trigonal bipyramids that share  a cornercorner with one Al(2)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, and  an edgeedge with one Al(2)O6 octahedra. The corner-sharing octahedral tilt angles are 33°. The Al(1)-O(2) bond length is 1.78 Å. The Al(1)-O(3) bond length is 1.86 Å. The Al(1)-O(5) bond length is 1.79 Å. The Al(1)-O(6) bond length is 1.93 Å. The Al(1)-O(7) bond length is 1.83 Å. In the second Al site, Al(2) is bonded to one O(1), one O(4), one O(5), one O(6), one O(7), and one O(8) atom to form AlO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra,  a cornercorner with one Al(1)O5 trigonal bipyramid, and  an edgeedge with one Al(1)O5 trigonal bipyramid. The Al(2)-O(1) bond length is 1.85 Å. The Al(2)-O(4) bond length is 1.82 Å. The Al(2)-O(5) bond length is 1.83 Å. The Al(2)-O(6) bond length is 1.94 Å. The Al(2)-O(7) bond length is 1.92 Å. The Al(2)-O(8) bond length is 1.91 Å. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with two equivalent Al(2)O6 octahedra and corners with two equivalent Al(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 17-46°. The P(1)-O(1) bond length is 1.55 Å. The P(1)-O(2) bond length is 1.54 Å. The P(1)-O(3) bond length is 1.55 Å. The P(1)-O(4) bond length is 1.53 Å. There are eight inequivalent O sites. In the first O site, O(6) is bonded in a water-like geometry to one Al(1) and one Al(2) atom. In the second O site, O(7) is bonded in a bent 120 degrees geometry to one Al(1) and one Al(2) atom. In the third O site, O(8) is bonded in a single-bond geometry to one Al(2) atom. In the fourth O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Al(2) and one P(1) atom. In the fifth O site, O(2) is bonded in a bent 150 degrees geometry to one Al(1) and one P(1) atom. In the sixth O site, O(3) is bonded in a bent 120 degrees geometry to one Al(1) and one P(1) atom. In the seventh O site, O(4) is bonded in a linear geometry to one Al(2) and one P(1) atom. In the eighth O site, O(5) is bonded in a bent 150 degrees geometry to one Al(1) and one Al(2) atom.