Pr9O16 crystallizes in the triclinic P-1 space group. There are five inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a body-centered cubic geometry to one O(2), one O(3), one O(5), one O(6), one O(7), one O(8), and two equivalent O(4) atoms. In the second Pr site, Pr(2) is bonded to one O(1), one O(2), one O(3), two equivalent O(7), and two equivalent O(8) atoms to form distorted PrO7 hexagonal pyramids that share  a cornercorner with one Pr(4)O6 octahedra,  a cornercorner with one Pr(5)O7 pentagonal bipyramid, edges with two equivalent Pr(2)O7 hexagonal pyramids,  an edgeedge with one Pr(4)O6 octahedra, and edges with two equivalent Pr(5)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 58°. In the third Pr site, Pr(3) is bonded in a 7-coordinate geometry to one O(2), one O(4), one O(6), two equivalent O(3), and two equivalent O(5) atoms. In the fourth Pr site, Pr(4) is bonded to two equivalent O(1), two equivalent O(6), and two equivalent O(7) atoms to form a mixture of distorted edge and corner-sharing PrO6 octahedra. In the fifth Pr site, Pr(5) is bonded to one O(2), one O(4), one O(5), one O(6), one O(8), and two equivalent O(1) atoms to form distorted PrO7 pentagonal bipyramids that share  a cornercorner with one Pr(2)O7 hexagonal pyramid,  a cornercorner with one Pr(4)O6 octahedra, edges with two equivalent Pr(2)O7 hexagonal pyramids,  an edgeedge with one Pr(4)O6 octahedra, and  an edgeedge with one Pr(5)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles are 51°. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Pr(2), one Pr(4), and two equivalent Pr(5) atoms to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the second O site, O(2) is bonded to one Pr(1), one Pr(2), one Pr(3), and one Pr(5) atom to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the third O site, O(3) is bonded to one Pr(1), one Pr(2), and two equivalent Pr(3) atoms to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the fourth O site, O(4) is bonded to one Pr(3), one Pr(5), and two equivalent Pr(1) atoms to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the fifth O site, O(5) is bonded to one Pr(1), one Pr(5), and two equivalent Pr(3) atoms to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the sixth O site, O(6) is bonded to one Pr(1), one Pr(3), one Pr(4), and one Pr(5) atom to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the seventh O site, O(7) is bonded to one Pr(1), one Pr(4), and two equivalent Pr(2) atoms to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the eighth O site, O(8) is bonded to one Pr(1), one Pr(5), and two equivalent Pr(2) atoms to form a mixture of edge and corner-sharing OPr4 tetrahedra.
Pr9O16 crystallizes in the triclinic P-1 space group. There are five inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a body-centered cubic geometry to one O(2), one O(3), one O(5), one O(6), one O(7), one O(8), and two equivalent O(4) atoms. The Pr(1)-O(2) bond length is 2.45 Å. The Pr(1)-O(3) bond length is 2.51 Å. The Pr(1)-O(5) bond length is 2.50 Å. The Pr(1)-O(6) bond length is 2.57 Å. The Pr(1)-O(7) bond length is 2.52 Å. The Pr(1)-O(8) bond length is 2.68 Å. There is one shorter (2.45 Å) and one longer (2.51 Å) Pr(1)-O(4) bond length. In the second Pr site, Pr(2) is bonded to one O(1), one O(2), one O(3), two equivalent O(7), and two equivalent O(8) atoms to form distorted PrO7 hexagonal pyramids that share  a cornercorner with one Pr(4)O6 octahedra,  a cornercorner with one Pr(5)O7 pentagonal bipyramid, edges with two equivalent Pr(2)O7 hexagonal pyramids,  an edgeedge with one Pr(4)O6 octahedra, and edges with two equivalent Pr(5)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 58°. The Pr(2)-O(1) bond length is 2.41 Å. The Pr(2)-O(2) bond length is 2.43 Å. The Pr(2)-O(3) bond length is 2.41 Å. There is one shorter (2.43 Å) and one longer (2.56 Å) Pr(2)-O(7) bond length. There is one shorter (2.45 Å) and one longer (2.47 Å) Pr(2)-O(8) bond length. In the third Pr site, Pr(3) is bonded in a 7-coordinate geometry to one O(2), one O(4), one O(6), two equivalent O(3), and two equivalent O(5) atoms. The Pr(3)-O(2) bond length is 2.39 Å. The Pr(3)-O(4) bond length is 2.50 Å. The Pr(3)-O(6) bond length is 2.41 Å. There is one shorter (2.47 Å) and one longer (2.49 Å) Pr(3)-O(3) bond length. There is one shorter (2.41 Å) and one longer (2.57 Å) Pr(3)-O(5) bond length. In the fourth Pr site, Pr(4) is bonded to two equivalent O(1), two equivalent O(6), and two equivalent O(7) atoms to form a mixture of distorted edge and corner-sharing PrO6 octahedra. Both Pr(4)-O(1) bond lengths are 2.35 Å. Both Pr(4)-O(6) bond lengths are 2.41 Å. Both Pr(4)-O(7) bond lengths are 2.39 Å. In the fifth Pr site, Pr(5) is bonded to one O(2), one O(4), one O(5), one O(6), one O(8), and two equivalent O(1) atoms to form distorted PrO7 pentagonal bipyramids that share  a cornercorner with one Pr(2)O7 hexagonal pyramid,  a cornercorner with one Pr(4)O6 octahedra, edges with two equivalent Pr(2)O7 hexagonal pyramids,  an edgeedge with one Pr(4)O6 octahedra, and  an edgeedge with one Pr(5)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles are 51°. The Pr(5)-O(2) bond length is 2.39 Å. The Pr(5)-O(4) bond length is 2.48 Å. The Pr(5)-O(5) bond length is 2.45 Å. The Pr(5)-O(6) bond length is 2.41 Å. The Pr(5)-O(8) bond length is 2.40 Å. There is one shorter (2.45 Å) and one longer (2.55 Å) Pr(5)-O(1) bond length. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Pr(2), one Pr(4), and two equivalent Pr(5) atoms to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the second O site, O(2) is bonded to one Pr(1), one Pr(2), one Pr(3), and one Pr(5) atom to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the third O site, O(3) is bonded to one Pr(1), one Pr(2), and two equivalent Pr(3) atoms to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the fourth O site, O(4) is bonded to one Pr(3), one Pr(5), and two equivalent Pr(1) atoms to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the fifth O site, O(5) is bonded to one Pr(1), one Pr(5), and two equivalent Pr(3) atoms to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the sixth O site, O(6) is bonded to one Pr(1), one Pr(3), one Pr(4), and one Pr(5) atom to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the seventh O site, O(7) is bonded to one Pr(1), one Pr(4), and two equivalent Pr(2) atoms to form a mixture of edge and corner-sharing OPr4 tetrahedra. In the eighth O site, O(8) is bonded to one Pr(1), one Pr(5), and two equivalent Pr(2) atoms to form a mixture of edge and corner-sharing OPr4 tetrahedra.