BaAl2(PO5)2 crystallizes in the triclinic P-1 space group. Ba(1) is bonded to two equivalent O(1), two equivalent O(2), two equivalent O(4), two equivalent O(5), and four equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with eight equivalent Al(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, edges with two equivalent Ba(1)O12 cuboctahedra, edges with four equivalent P(1)O4 tetrahedra, and faces with two equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-59°. Al(1) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with four equivalent Ba(1)O12 cuboctahedra, corners with four equivalent P(1)O4 tetrahedra,  an edgeedge with one Al(1)O6 octahedra, and  a faceface with one Ba(1)O12 cuboctahedra. 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  a cornercorner with one Ba(1)O12 cuboctahedra, corners with four equivalent Al(1)O6 octahedra, and edges with two equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 44-49°. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Ba(1), one Al(1), and one P(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(1), and one P(1) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Al(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one Ba(1), one Al(1), and one P(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ba(1) and two equivalent Al(1) atoms.
BaAl2(PO5)2 crystallizes in the triclinic P-1 space group. Ba(1) is bonded to two equivalent O(1), two equivalent O(2), two equivalent O(4), two equivalent O(5), and four equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with eight equivalent Al(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, edges with two equivalent Ba(1)O12 cuboctahedra, edges with four equivalent P(1)O4 tetrahedra, and faces with two equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-59°. Both Ba(1)-O(1) bond lengths are 2.97 Å. Both Ba(1)-O(2) bond lengths are 3.24 Å. Both Ba(1)-O(4) bond lengths are 2.89 Å. Both Ba(1)-O(5) bond lengths are 3.12 Å. There are two shorter (2.89 Å) and two longer (3.11 Å) Ba(1)-O(3) bond lengths. Al(1) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with four equivalent Ba(1)O12 cuboctahedra, corners with four equivalent P(1)O4 tetrahedra,  an edgeedge with one Al(1)O6 octahedra, and  a faceface with one Ba(1)O12 cuboctahedra. The Al(1)-O(1) bond length is 1.89 Å. The Al(1)-O(2) bond length is 1.86 Å. The Al(1)-O(3) bond length is 1.94 Å. The Al(1)-O(4) bond length is 1.90 Å. There is one shorter (1.90 Å) and one longer (1.94 Å) Al(1)-O(5) bond length. 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  a cornercorner with one Ba(1)O12 cuboctahedra, corners with four equivalent Al(1)O6 octahedra, and edges with two equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 44-49°. 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 1.57 Å. The P(1)-O(4) bond length is 1.55 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Ba(1), one Al(1), and one P(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(1), and one P(1) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Al(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one Ba(1), one Al(1), and one P(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ba(1) and two equivalent Al(1) atoms.