YAl3O6 crystallizes in the monoclinic C2/c space group. Y(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted YO6 pentagonal pyramids that share corners with four equivalent Al(1)O4 tetrahedra, edges with two equivalent Al(1)O4 tetrahedra, and edges with two equivalent Al(2)O4 tetrahedra. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form AlO4 tetrahedra that share corners with two equivalent Y(1)O6 pentagonal pyramids, corners with two equivalent Al(1)O4 tetrahedra, corners with two equivalent Al(2)O4 tetrahedra, and  an edgeedge with one Y(1)O6 pentagonal pyramid. In the second Al site, Al(2) is bonded to two equivalent O(2) and two equivalent O(3) atoms to form distorted AlO4 tetrahedra that share corners with four equivalent Al(1)O4 tetrahedra and edges with two equivalent Y(1)O6 pentagonal pyramids. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Y(1) and two equivalent Al(1) atoms. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Y(1), one Al(1), and one Al(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Y(1), one Al(1), and one Al(2) atom.
YAl3O6 crystallizes in the monoclinic C2/c space group. Y(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted YO6 pentagonal pyramids that share corners with four equivalent Al(1)O4 tetrahedra, edges with two equivalent Al(1)O4 tetrahedra, and edges with two equivalent Al(2)O4 tetrahedra. Both Y(1)-O(1) bond lengths are 2.36 Å. Both Y(1)-O(2) bond lengths are 2.26 Å. Both Y(1)-O(3) bond lengths are 2.33 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form AlO4 tetrahedra that share corners with two equivalent Y(1)O6 pentagonal pyramids, corners with two equivalent Al(1)O4 tetrahedra, corners with two equivalent Al(2)O4 tetrahedra, and  an edgeedge with one Y(1)O6 pentagonal pyramid. The Al(1)-O(2) bond length is 1.76 Å. The Al(1)-O(3) bond length is 1.77 Å. There is one shorter (1.78 Å) and one longer (1.81 Å) Al(1)-O(1) bond length. In the second Al site, Al(2) is bonded to two equivalent O(2) and two equivalent O(3) atoms to form distorted AlO4 tetrahedra that share corners with four equivalent Al(1)O4 tetrahedra and edges with two equivalent Y(1)O6 pentagonal pyramids. Both Al(2)-O(2) bond lengths are 1.75 Å. Both Al(2)-O(3) bond lengths are 1.80 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Y(1) and two equivalent Al(1) atoms. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Y(1), one Al(1), and one Al(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Y(1), one Al(1), and one Al(2) atom.