K2Pr4O2Cl9 crystallizes in the monoclinic P2_1/m space group. K(1) is bonded in a 5-coordinate geometry to one Cl(2), two equivalent Cl(1), and two equivalent Cl(4) atoms. There are three inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 8-coordinate geometry to two equivalent O(1), one Cl(5), one Cl(6), two equivalent Cl(2), and two equivalent Cl(4) atoms. In the second Pr site, Pr(2) is bonded in a 2-coordinate geometry to two equivalent O(1), one Cl(1), one Cl(3), one Cl(6), two equivalent Cl(2), and two equivalent Cl(4) atoms. In the third Pr site, Pr(3) is bonded in a 8-coordinate geometry to two equivalent O(1), one Cl(3), one Cl(5), two equivalent Cl(1), and two equivalent Cl(4) atoms. O(1) is bonded to one Pr(1), one Pr(3), and two equivalent Pr(2) atoms to form OPr4 tetrahedra that share corners with two equivalent Cl(1)K2Pr2 trigonal pyramids, corners with four equivalent Cl(2)KPr3 trigonal pyramids, edges with two equivalent O(1)Pr4 tetrahedra,  an edgeedge with one Cl(1)K2Pr2 trigonal pyramid, and  an edgeedge with one Cl(2)KPr3 trigonal pyramid. There are six inequivalent Cl sites. In the first Cl site, Cl(1) is bonded to two equivalent K(1), one Pr(2), and one Pr(3) atom to form distorted ClK2Pr2 trigonal pyramids that share corners with two equivalent O(1)Pr4 tetrahedra,  a cornercorner with one Cl(1)K2Pr2 trigonal pyramid, corners with two equivalent Cl(2)KPr3 trigonal pyramids,  an edgeedge with one O(1)Pr4 tetrahedra,  an edgeedge with one Cl(1)K2Pr2 trigonal pyramid, and  an edgeedge with one Cl(2)KPr3 trigonal pyramid. In the second Cl site, Cl(2) is bonded to one K(1), one Pr(1), and two equivalent Pr(2) atoms to form distorted ClKPr3 trigonal pyramids that share corners with four equivalent O(1)Pr4 tetrahedra,  a cornercorner with one Cl(2)KPr3 trigonal pyramid, corners with two equivalent Cl(1)K2Pr2 trigonal pyramids,  an edgeedge with one O(1)Pr4 tetrahedra,  an edgeedge with one Cl(1)K2Pr2 trigonal pyramid, and  an edgeedge with one Cl(2)KPr3 trigonal pyramid. In the third Cl site, Cl(3) is bonded in a 3-coordinate geometry to one Pr(3) and two equivalent Pr(2) atoms. In the fourth Cl site, Cl(4) is bonded in a 6-coordinate geometry to two equivalent K(1), one Pr(1), one Pr(3), and two equivalent Pr(2) atoms. In the fifth Cl site, Cl(5) is bonded in a distorted linear geometry to one Pr(1) and one Pr(3) atom. In the sixth Cl site, Cl(6) is bonded in a 3-coordinate geometry to one Pr(1) and two equivalent Pr(2) atoms.
K2Pr4O2Cl9 crystallizes in the monoclinic P2_1/m space group. K(1) is bonded in a 5-coordinate geometry to one Cl(2), two equivalent Cl(1), and two equivalent Cl(4) atoms. The K(1)-Cl(2) bond length is 3.43 Å. There is one shorter (3.06 Å) and one longer (3.23 Å) K(1)-Cl(1) bond length. There is one shorter (3.03 Å) and one longer (3.09 Å) K(1)-Cl(4) bond length. There are three inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 8-coordinate geometry to two equivalent O(1), one Cl(5), one Cl(6), two equivalent Cl(2), and two equivalent Cl(4) atoms. Both Pr(1)-O(1) bond lengths are 2.40 Å. The Pr(1)-Cl(5) bond length is 3.01 Å. The Pr(1)-Cl(6) bond length is 3.00 Å. Both Pr(1)-Cl(2) bond lengths are 2.90 Å. Both Pr(1)-Cl(4) bond lengths are 3.13 Å. In the second Pr site, Pr(2) is bonded in a 2-coordinate geometry to two equivalent O(1), one Cl(1), one Cl(3), one Cl(6), two equivalent Cl(2), and two equivalent Cl(4) atoms. There is one shorter (2.34 Å) and one longer (2.35 Å) Pr(2)-O(1) bond length. The Pr(2)-Cl(1) bond length is 2.90 Å. The Pr(2)-Cl(3) bond length is 2.98 Å. The Pr(2)-Cl(6) bond length is 3.02 Å. There is one shorter (2.92 Å) and one longer (3.26 Å) Pr(2)-Cl(2) bond length. There is one shorter (3.18 Å) and one longer (3.32 Å) Pr(2)-Cl(4) bond length. In the third Pr site, Pr(3) is bonded in a 8-coordinate geometry to two equivalent O(1), one Cl(3), one Cl(5), two equivalent Cl(1), and two equivalent Cl(4) atoms. Both Pr(3)-O(1) bond lengths are 2.40 Å. The Pr(3)-Cl(3) bond length is 2.97 Å. The Pr(3)-Cl(5) bond length is 2.98 Å. Both Pr(3)-Cl(1) bond lengths are 2.90 Å. Both Pr(3)-Cl(4) bond lengths are 3.17 Å. O(1) is bonded to one Pr(1), one Pr(3), and two equivalent Pr(2) atoms to form OPr4 tetrahedra that share corners with two equivalent Cl(1)K2Pr2 trigonal pyramids, corners with four equivalent Cl(2)KPr3 trigonal pyramids, edges with two equivalent O(1)Pr4 tetrahedra,  an edgeedge with one Cl(1)K2Pr2 trigonal pyramid, and  an edgeedge with one Cl(2)KPr3 trigonal pyramid. There are six inequivalent Cl sites. In the first Cl site, Cl(1) is bonded to two equivalent K(1), one Pr(2), and one Pr(3) atom to form distorted ClK2Pr2 trigonal pyramids that share corners with two equivalent O(1)Pr4 tetrahedra,  a cornercorner with one Cl(1)K2Pr2 trigonal pyramid, corners with two equivalent Cl(2)KPr3 trigonal pyramids,  an edgeedge with one O(1)Pr4 tetrahedra,  an edgeedge with one Cl(1)K2Pr2 trigonal pyramid, and  an edgeedge with one Cl(2)KPr3 trigonal pyramid. In the second Cl site, Cl(2) is bonded to one K(1), one Pr(1), and two equivalent Pr(2) atoms to form distorted ClKPr3 trigonal pyramids that share corners with four equivalent O(1)Pr4 tetrahedra,  a cornercorner with one Cl(2)KPr3 trigonal pyramid, corners with two equivalent Cl(1)K2Pr2 trigonal pyramids,  an edgeedge with one O(1)Pr4 tetrahedra,  an edgeedge with one Cl(1)K2Pr2 trigonal pyramid, and  an edgeedge with one Cl(2)KPr3 trigonal pyramid. In the third Cl site, Cl(3) is bonded in a 3-coordinate geometry to one Pr(3) and two equivalent Pr(2) atoms. In the fourth Cl site, Cl(4) is bonded in a 6-coordinate geometry to two equivalent K(1), one Pr(1), one Pr(3), and two equivalent Pr(2) atoms. In the fifth Cl site, Cl(5) is bonded in a distorted linear geometry to one Pr(1) and one Pr(3) atom. In the sixth Cl site, Cl(6) is bonded in a 3-coordinate geometry to one Pr(1) and two equivalent Pr(2) atoms.