UPr2Se5 crystallizes in the orthorhombic Pna2_1 space group. U(1) is bonded to one Se(3), one Se(4), one Se(5), two equivalent Se(1), and two equivalent Se(2) atoms to form distorted edge-sharing USe7 pentagonal bipyramids. There are two inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), two equivalent Se(3), two equivalent Se(4), and two equivalent Se(5) atoms. In the second Pr site, Pr(2) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), two equivalent Se(3), two equivalent Se(4), and two equivalent Se(5) atoms. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent U(1), one Pr(1), and one Pr(2) atom to form SePr2U2 trigonal pyramids that share corners with two equivalent Se(5)Pr4U square pyramids, corners with four equivalent Se(4)Pr4U square pyramids, corners with two equivalent Se(3)Pr4U trigonal bipyramids, corners with two equivalent Se(1)Pr2U2 trigonal pyramids, corners with four equivalent Se(2)Pr2U2 trigonal pyramids,  an edgeedge with one Se(4)Pr4U square pyramid, edges with two equivalent Se(5)Pr4U square pyramids, edges with two equivalent Se(3)Pr4U trigonal bipyramids, and  an edgeedge with one Se(2)Pr2U2 trigonal pyramid. In the second Se site, Se(2) is bonded to two equivalent U(1), one Pr(1), and one Pr(2) atom to form distorted SePr2U2 trigonal pyramids that share corners with two equivalent Se(5)Pr4U square pyramids, corners with four equivalent Se(4)Pr4U square pyramids, corners with two equivalent Se(3)Pr4U trigonal bipyramids, corners with two equivalent Se(2)Pr2U2 trigonal pyramids, corners with four equivalent Se(1)Pr2U2 trigonal pyramids,  an edgeedge with one Se(4)Pr4U square pyramid, edges with two equivalent Se(5)Pr4U square pyramids, edges with two equivalent Se(3)Pr4U trigonal bipyramids, and  an edgeedge with one Se(1)Pr2U2 trigonal pyramid. In the third Se site, Se(3) is bonded to one U(1), two equivalent Pr(1), and two equivalent Pr(2) atoms to form distorted SePr4U trigonal bipyramids that share  a cornercorner with one Se(5)Pr4U square pyramid, corners with five equivalent Se(4)Pr4U square pyramids, corners with four equivalent Se(3)Pr4U trigonal bipyramids, corners with two equivalent Se(1)Pr2U2 trigonal pyramids, corners with two equivalent Se(2)Pr2U2 trigonal pyramids, edges with two equivalent Se(4)Pr4U square pyramids, edges with four equivalent Se(5)Pr4U square pyramids, edges with two equivalent Se(1)Pr2U2 trigonal pyramids, and edges with two equivalent Se(2)Pr2U2 trigonal pyramids. In the fourth Se site, Se(4) is bonded to one U(1), two equivalent Pr(1), and two equivalent Pr(2) atoms to form SePr4U square pyramids that share corners with four equivalent Se(5)Pr4U square pyramids, corners with five equivalent Se(3)Pr4U trigonal bipyramids, corners with four equivalent Se(1)Pr2U2 trigonal pyramids, corners with four equivalent Se(2)Pr2U2 trigonal pyramids,  an edgeedge with one Se(5)Pr4U square pyramid, edges with two equivalent Se(4)Pr4U square pyramids, edges with two equivalent Se(3)Pr4U trigonal bipyramids,  an edgeedge with one Se(1)Pr2U2 trigonal pyramid,  an edgeedge with one Se(2)Pr2U2 trigonal pyramid, and  a faceface with one Se(5)Pr4U square pyramid. In the fifth Se site, Se(5) is bonded to one U(1), two equivalent Pr(1), and two equivalent Pr(2) atoms to form SePr4U square pyramids that share corners with four equivalent Se(4)Pr4U square pyramids, corners with four equivalent Se(5)Pr4U square pyramids,  a cornercorner with one Se(3)Pr4U trigonal bipyramid, corners with two equivalent Se(1)Pr2U2 trigonal pyramids, corners with two equivalent Se(2)Pr2U2 trigonal pyramids,  an edgeedge with one Se(4)Pr4U square pyramid, edges with four equivalent Se(3)Pr4U trigonal bipyramids, edges with two equivalent Se(1)Pr2U2 trigonal pyramids, edges with two equivalent Se(2)Pr2U2 trigonal pyramids, and  a faceface with one Se(4)Pr4U square pyramid.
UPr2Se5 crystallizes in the orthorhombic Pna2_1 space group. U(1) is bonded to one Se(3), one Se(4), one Se(5), two equivalent Se(1), and two equivalent Se(2) atoms to form distorted edge-sharing USe7 pentagonal bipyramids. The U(1)-Se(3) bond length is 2.92 Å. The U(1)-Se(4) bond length is 3.04 Å. The U(1)-Se(5) bond length is 2.95 Å. There is one shorter (2.81 Å) and one longer (2.87 Å) U(1)-Se(1) bond length. There is one shorter (2.80 Å) and one longer (2.88 Å) U(1)-Se(2) bond length. There are two inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), two equivalent Se(3), two equivalent Se(4), and two equivalent Se(5) atoms. The Pr(1)-Se(1) bond length is 3.05 Å. The Pr(1)-Se(2) bond length is 3.07 Å. There is one shorter (3.13 Å) and one longer (3.24 Å) Pr(1)-Se(3) bond length. There is one shorter (3.08 Å) and one longer (3.11 Å) Pr(1)-Se(4) bond length. There is one shorter (3.07 Å) and one longer (3.11 Å) Pr(1)-Se(5) bond length. In the second Pr site, Pr(2) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), two equivalent Se(3), two equivalent Se(4), and two equivalent Se(5) atoms. The Pr(2)-Se(1) bond length is 3.07 Å. The Pr(2)-Se(2) bond length is 3.06 Å. There is one shorter (3.14 Å) and one longer (3.22 Å) Pr(2)-Se(3) bond length. There is one shorter (3.09 Å) and one longer (3.13 Å) Pr(2)-Se(4) bond length. There is one shorter (3.07 Å) and one longer (3.10 Å) Pr(2)-Se(5) bond length. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent U(1), one Pr(1), and one Pr(2) atom to form SePr2U2 trigonal pyramids that share corners with two equivalent Se(5)Pr4U square pyramids, corners with four equivalent Se(4)Pr4U square pyramids, corners with two equivalent Se(3)Pr4U trigonal bipyramids, corners with two equivalent Se(1)Pr2U2 trigonal pyramids, corners with four equivalent Se(2)Pr2U2 trigonal pyramids,  an edgeedge with one Se(4)Pr4U square pyramid, edges with two equivalent Se(5)Pr4U square pyramids, edges with two equivalent Se(3)Pr4U trigonal bipyramids, and  an edgeedge with one Se(2)Pr2U2 trigonal pyramid. In the second Se site, Se(2) is bonded to two equivalent U(1), one Pr(1), and one Pr(2) atom to form distorted SePr2U2 trigonal pyramids that share corners with two equivalent Se(5)Pr4U square pyramids, corners with four equivalent Se(4)Pr4U square pyramids, corners with two equivalent Se(3)Pr4U trigonal bipyramids, corners with two equivalent Se(2)Pr2U2 trigonal pyramids, corners with four equivalent Se(1)Pr2U2 trigonal pyramids,  an edgeedge with one Se(4)Pr4U square pyramid, edges with two equivalent Se(5)Pr4U square pyramids, edges with two equivalent Se(3)Pr4U trigonal bipyramids, and  an edgeedge with one Se(1)Pr2U2 trigonal pyramid. In the third Se site, Se(3) is bonded to one U(1), two equivalent Pr(1), and two equivalent Pr(2) atoms to form distorted SePr4U trigonal bipyramids that share  a cornercorner with one Se(5)Pr4U square pyramid, corners with five equivalent Se(4)Pr4U square pyramids, corners with four equivalent Se(3)Pr4U trigonal bipyramids, corners with two equivalent Se(1)Pr2U2 trigonal pyramids, corners with two equivalent Se(2)Pr2U2 trigonal pyramids, edges with two equivalent Se(4)Pr4U square pyramids, edges with four equivalent Se(5)Pr4U square pyramids, edges with two equivalent Se(1)Pr2U2 trigonal pyramids, and edges with two equivalent Se(2)Pr2U2 trigonal pyramids. In the fourth Se site, Se(4) is bonded to one U(1), two equivalent Pr(1), and two equivalent Pr(2) atoms to form SePr4U square pyramids that share corners with four equivalent Se(5)Pr4U square pyramids, corners with five equivalent Se(3)Pr4U trigonal bipyramids, corners with four equivalent Se(1)Pr2U2 trigonal pyramids, corners with four equivalent Se(2)Pr2U2 trigonal pyramids,  an edgeedge with one Se(5)Pr4U square pyramid, edges with two equivalent Se(4)Pr4U square pyramids, edges with two equivalent Se(3)Pr4U trigonal bipyramids,  an edgeedge with one Se(1)Pr2U2 trigonal pyramid,  an edgeedge with one Se(2)Pr2U2 trigonal pyramid, and  a faceface with one Se(5)Pr4U square pyramid. In the fifth Se site, Se(5) is bonded to one U(1), two equivalent Pr(1), and two equivalent Pr(2) atoms to form SePr4U square pyramids that share corners with four equivalent Se(4)Pr4U square pyramids, corners with four equivalent Se(5)Pr4U square pyramids,  a cornercorner with one Se(3)Pr4U trigonal bipyramid, corners with two equivalent Se(1)Pr2U2 trigonal pyramids, corners with two equivalent Se(2)Pr2U2 trigonal pyramids,  an edgeedge with one Se(4)Pr4U square pyramid, edges with four equivalent Se(3)Pr4U trigonal bipyramids, edges with two equivalent Se(1)Pr2U2 trigonal pyramids, edges with two equivalent Se(2)Pr2U2 trigonal pyramids, and  a faceface with one Se(4)Pr4U square pyramid.