Pr2W2O9 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 9-coordinate geometry to one O(1), one O(2), one O(4), one O(6), one O(7), one O(8), one O(9), and two equivalent O(3) atoms. In the second Pr site, Pr(2) is bonded in a 9-coordinate geometry to one O(1), one O(5), one O(6), one O(7), one O(9), two equivalent O(2), and two equivalent O(8) atoms. There are two inequivalent W sites. In the first W site, W(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(9) atom to form a mixture of distorted edge and corner-sharing WO6 octahedra. The corner-sharing octahedral tilt angles are 42°. In the second W site, W(2) is bonded to one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom to form a mixture of distorted edge and corner-sharing WO6 octahedra. The corner-sharing octahedral tilt angles are 42°. There are nine inequivalent O sites. In the first O site, O(5) is bonded in a distorted trigonal planar geometry to one Pr(2), one W(1), and one W(2) atom. In the second O site, O(6) is bonded in a 3-coordinate geometry to one Pr(1), one Pr(2), and one W(2) atom. In the third O site, O(7) is bonded in a 3-coordinate geometry to one Pr(1), one Pr(2), and one W(2) atom. In the fourth O site, O(8) is bonded to one Pr(1), two equivalent Pr(2), and one W(2) atom to form edge-sharing OPr3W tetrahedra. In the fifth O site, O(1) is bonded in a 3-coordinate geometry to one Pr(1), one Pr(2), and one W(1) atom. In the sixth O site, O(9) is bonded in a 4-coordinate geometry to one Pr(1), one Pr(2), one W(1), and one W(2) atom. In the seventh O site, O(2) is bonded in a 3-coordinate geometry to one Pr(1), two equivalent Pr(2), and one W(1) atom. In the eighth O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Pr(1) and one W(1) atom. In the ninth O site, O(4) is bonded in a 3-coordinate geometry to one Pr(1), one W(1), and one W(2) atom.
Pr2W2O9 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 9-coordinate geometry to one O(1), one O(2), one O(4), one O(6), one O(7), one O(8), one O(9), and two equivalent O(3) atoms. The Pr(1)-O(1) bond length is 2.49 Å. The Pr(1)-O(2) bond length is 2.60 Å. The Pr(1)-O(4) bond length is 2.76 Å. The Pr(1)-O(6) bond length is 2.57 Å. The Pr(1)-O(7) bond length is 2.38 Å. The Pr(1)-O(8) bond length is 2.42 Å. The Pr(1)-O(9) bond length is 2.64 Å. There is one shorter (2.47 Å) and one longer (2.51 Å) Pr(1)-O(3) bond length. In the second Pr site, Pr(2) is bonded in a 9-coordinate geometry to one O(1), one O(5), one O(6), one O(7), one O(9), two equivalent O(2), and two equivalent O(8) atoms. The Pr(2)-O(1) bond length is 2.51 Å. The Pr(2)-O(5) bond length is 2.45 Å. The Pr(2)-O(6) bond length is 2.47 Å. The Pr(2)-O(7) bond length is 2.63 Å. The Pr(2)-O(9) bond length is 2.66 Å. There is one shorter (2.41 Å) and one longer (3.14 Å) Pr(2)-O(2) bond length. There is one shorter (2.47 Å) and one longer (2.53 Å) Pr(2)-O(8) bond length. There are two inequivalent W sites. In the first W site, W(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(9) atom to form a mixture of distorted edge and corner-sharing WO6 octahedra. The corner-sharing octahedral tilt angles are 42°. The W(1)-O(1) bond length is 1.84 Å. The W(1)-O(2) bond length is 1.88 Å. The W(1)-O(3) bond length is 1.81 Å. The W(1)-O(4) bond length is 2.19 Å. The W(1)-O(5) bond length is 2.02 Å. The W(1)-O(9) bond length is 1.93 Å. In the second W site, W(2) is bonded to one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom to form a mixture of distorted edge and corner-sharing WO6 octahedra. The corner-sharing octahedral tilt angles are 42°. The W(2)-O(4) bond length is 1.87 Å. The W(2)-O(5) bond length is 2.00 Å. The W(2)-O(6) bond length is 1.81 Å. The W(2)-O(7) bond length is 1.83 Å. The W(2)-O(8) bond length is 1.95 Å. The W(2)-O(9) bond length is 2.21 Å. There are nine inequivalent O sites. In the first O site, O(5) is bonded in a distorted trigonal planar geometry to one Pr(2), one W(1), and one W(2) atom. In the second O site, O(6) is bonded in a 3-coordinate geometry to one Pr(1), one Pr(2), and one W(2) atom. In the third O site, O(7) is bonded in a 3-coordinate geometry to one Pr(1), one Pr(2), and one W(2) atom. In the fourth O site, O(8) is bonded to one Pr(1), two equivalent Pr(2), and one W(2) atom to form edge-sharing OPr3W tetrahedra. In the fifth O site, O(1) is bonded in a 3-coordinate geometry to one Pr(1), one Pr(2), and one W(1) atom. In the sixth O site, O(9) is bonded in a 4-coordinate geometry to one Pr(1), one Pr(2), one W(1), and one W(2) atom. In the seventh O site, O(2) is bonded in a 3-coordinate geometry to one Pr(1), two equivalent Pr(2), and one W(1) atom. In the eighth O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Pr(1) and one W(1) atom. In the ninth O site, O(4) is bonded in a 3-coordinate geometry to one Pr(1), one W(1), and one W(2) atom.