ULa2Se5 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 La sites. In the first La site, La(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 La site, La(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 La(1), and one La(2) atom to form distorted SeLa2U2 trigonal pyramids that share corners with two equivalent Se(5)La4U square pyramids, corners with four equivalent Se(4)La4U square pyramids, corners with two equivalent Se(3)La4U trigonal bipyramids, corners with two equivalent Se(1)La2U2 trigonal pyramids, corners with four equivalent Se(2)La2U2 trigonal pyramids,  an edgeedge with one Se(4)La4U square pyramid, edges with two equivalent Se(5)La4U square pyramids, edges with two equivalent Se(3)La4U trigonal bipyramids, and  an edgeedge with one Se(2)La2U2 trigonal pyramid. In the second Se site, Se(2) is bonded to two equivalent U(1), one La(1), and one La(2) atom to form distorted SeLa2U2 trigonal pyramids that share corners with two equivalent Se(5)La4U square pyramids, corners with four equivalent Se(4)La4U square pyramids, corners with two equivalent Se(3)La4U trigonal bipyramids, corners with two equivalent Se(2)La2U2 trigonal pyramids, corners with four equivalent Se(1)La2U2 trigonal pyramids,  an edgeedge with one Se(4)La4U square pyramid, edges with two equivalent Se(5)La4U square pyramids, edges with two equivalent Se(3)La4U trigonal bipyramids, and  an edgeedge with one Se(1)La2U2 trigonal pyramid. In the third Se site, Se(3) is bonded to one U(1), two equivalent La(1), and two equivalent La(2) atoms to form distorted SeLa4U trigonal bipyramids that share  a cornercorner with one Se(5)La4U square pyramid, corners with five equivalent Se(4)La4U square pyramids, corners with four equivalent Se(3)La4U trigonal bipyramids, corners with two equivalent Se(1)La2U2 trigonal pyramids, corners with two equivalent Se(2)La2U2 trigonal pyramids, edges with two equivalent Se(4)La4U square pyramids, edges with four equivalent Se(5)La4U square pyramids, edges with two equivalent Se(1)La2U2 trigonal pyramids, and edges with two equivalent Se(2)La2U2 trigonal pyramids. In the fourth Se site, Se(4) is bonded to one U(1), two equivalent La(1), and two equivalent La(2) atoms to form SeLa4U square pyramids that share corners with four equivalent Se(5)La4U square pyramids, corners with five equivalent Se(3)La4U trigonal bipyramids, corners with four equivalent Se(1)La2U2 trigonal pyramids, corners with four equivalent Se(2)La2U2 trigonal pyramids,  an edgeedge with one Se(5)La4U square pyramid, edges with two equivalent Se(4)La4U square pyramids, edges with two equivalent Se(3)La4U trigonal bipyramids,  an edgeedge with one Se(1)La2U2 trigonal pyramid,  an edgeedge with one Se(2)La2U2 trigonal pyramid, and  a faceface with one Se(5)La4U square pyramid. In the fifth Se site, Se(5) is bonded to one U(1), two equivalent La(1), and two equivalent La(2) atoms to form SeLa4U square pyramids that share corners with four equivalent Se(4)La4U square pyramids, corners with four equivalent Se(5)La4U square pyramids,  a cornercorner with one Se(3)La4U trigonal bipyramid, corners with two equivalent Se(1)La2U2 trigonal pyramids, corners with two equivalent Se(2)La2U2 trigonal pyramids,  an edgeedge with one Se(4)La4U square pyramid, edges with four equivalent Se(3)La4U trigonal bipyramids, edges with two equivalent Se(1)La2U2 trigonal pyramids, edges with two equivalent Se(2)La2U2 trigonal pyramids, and  a faceface with one Se(4)La4U square pyramid.
ULa2Se5 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 2.91 Å. The U(1)-Se(4) bond length is 3.05 Å. The U(1)-Se(5) bond length is 2.95 Å. There is one shorter (2.81 Å) and one longer (2.90 Å) U(1)-Se(1) bond length. There is one shorter (2.82 Å) and one longer (2.89 Å) U(1)-Se(2) bond length. There are two inequivalent La sites. In the first La site, La(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 La(1)-Se(1) bond length is 3.10 Å. The La(1)-Se(2) bond length is 3.11 Å. There is one shorter (3.15 Å) and one longer (3.25 Å) La(1)-Se(3) bond length. There is one shorter (3.10 Å) and one longer (3.12 Å) La(1)-Se(4) bond length. There is one shorter (3.09 Å) and one longer (3.14 Å) La(1)-Se(5) bond length. In the second La site, La(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 La(2)-Se(1) bond length is 3.10 Å. The La(2)-Se(2) bond length is 3.09 Å. There is one shorter (3.15 Å) and one longer (3.26 Å) La(2)-Se(3) bond length. There is one shorter (3.10 Å) and one longer (3.12 Å) La(2)-Se(4) bond length. There is one shorter (3.09 Å) and one longer (3.14 Å) La(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 La(1), and one La(2) atom to form distorted SeLa2U2 trigonal pyramids that share corners with two equivalent Se(5)La4U square pyramids, corners with four equivalent Se(4)La4U square pyramids, corners with two equivalent Se(3)La4U trigonal bipyramids, corners with two equivalent Se(1)La2U2 trigonal pyramids, corners with four equivalent Se(2)La2U2 trigonal pyramids,  an edgeedge with one Se(4)La4U square pyramid, edges with two equivalent Se(5)La4U square pyramids, edges with two equivalent Se(3)La4U trigonal bipyramids, and  an edgeedge with one Se(2)La2U2 trigonal pyramid. In the second Se site, Se(2) is bonded to two equivalent U(1), one La(1), and one La(2) atom to form distorted SeLa2U2 trigonal pyramids that share corners with two equivalent Se(5)La4U square pyramids, corners with four equivalent Se(4)La4U square pyramids, corners with two equivalent Se(3)La4U trigonal bipyramids, corners with two equivalent Se(2)La2U2 trigonal pyramids, corners with four equivalent Se(1)La2U2 trigonal pyramids,  an edgeedge with one Se(4)La4U square pyramid, edges with two equivalent Se(5)La4U square pyramids, edges with two equivalent Se(3)La4U trigonal bipyramids, and  an edgeedge with one Se(1)La2U2 trigonal pyramid. In the third Se site, Se(3) is bonded to one U(1), two equivalent La(1), and two equivalent La(2) atoms to form distorted SeLa4U trigonal bipyramids that share  a cornercorner with one Se(5)La4U square pyramid, corners with five equivalent Se(4)La4U square pyramids, corners with four equivalent Se(3)La4U trigonal bipyramids, corners with two equivalent Se(1)La2U2 trigonal pyramids, corners with two equivalent Se(2)La2U2 trigonal pyramids, edges with two equivalent Se(4)La4U square pyramids, edges with four equivalent Se(5)La4U square pyramids, edges with two equivalent Se(1)La2U2 trigonal pyramids, and edges with two equivalent Se(2)La2U2 trigonal pyramids. In the fourth Se site, Se(4) is bonded to one U(1), two equivalent La(1), and two equivalent La(2) atoms to form SeLa4U square pyramids that share corners with four equivalent Se(5)La4U square pyramids, corners with five equivalent Se(3)La4U trigonal bipyramids, corners with four equivalent Se(1)La2U2 trigonal pyramids, corners with four equivalent Se(2)La2U2 trigonal pyramids,  an edgeedge with one Se(5)La4U square pyramid, edges with two equivalent Se(4)La4U square pyramids, edges with two equivalent Se(3)La4U trigonal bipyramids,  an edgeedge with one Se(1)La2U2 trigonal pyramid,  an edgeedge with one Se(2)La2U2 trigonal pyramid, and  a faceface with one Se(5)La4U square pyramid. In the fifth Se site, Se(5) is bonded to one U(1), two equivalent La(1), and two equivalent La(2) atoms to form SeLa4U square pyramids that share corners with four equivalent Se(4)La4U square pyramids, corners with four equivalent Se(5)La4U square pyramids,  a cornercorner with one Se(3)La4U trigonal bipyramid, corners with two equivalent Se(1)La2U2 trigonal pyramids, corners with two equivalent Se(2)La2U2 trigonal pyramids,  an edgeedge with one Se(4)La4U square pyramid, edges with four equivalent Se(3)La4U trigonal bipyramids, edges with two equivalent Se(1)La2U2 trigonal pyramids, edges with two equivalent Se(2)La2U2 trigonal pyramids, and  a faceface with one Se(4)La4U square pyramid.