La2Se2O crystallizes in the orthorhombic Pnma space group. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 3-coordinate geometry to two equivalent Se(2), three equivalent Se(1), and three equivalent O(1) atoms. In the second La site, La(2) is bonded to two equivalent Se(1), three equivalent Se(2), and one O(1) atom to form a mixture of distorted edge and corner-sharing LaSe5O octahedra. The corner-sharing octahedral tilt angles are 67°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent La(2) and three equivalent La(1) atoms to form distorted SeLa5 trigonal bipyramids that share corners with five equivalent O(1)La4 tetrahedra, edges with three equivalent O(1)La4 tetrahedra, and edges with four equivalent Se(1)La5 trigonal bipyramids. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to two equivalent La(1) and three equivalent La(2) atoms. O(1) is bonded to one La(2) and three equivalent La(1) atoms to form OLa4 tetrahedra that share corners with two equivalent O(1)La4 tetrahedra, corners with five equivalent Se(1)La5 trigonal bipyramids, edges with two equivalent O(1)La4 tetrahedra, and edges with three equivalent Se(1)La5 trigonal bipyramids.
La2Se2O crystallizes in the orthorhombic Pnma space group. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 3-coordinate geometry to two equivalent Se(2), three equivalent Se(1), and three equivalent O(1) atoms. Both La(1)-Se(2) bond lengths are 3.29 Å. There is one shorter (3.16 Å) and two longer (3.29 Å) La(1)-Se(1) bond lengths. There is one shorter (2.43 Å) and two longer (2.44 Å) La(1)-O(1) bond lengths. In the second La site, La(2) is bonded to two equivalent Se(1), three equivalent Se(2), and one O(1) atom to form a mixture of distorted edge and corner-sharing LaSe5O octahedra. The corner-sharing octahedral tilt angles are 67°. Both La(2)-Se(1) bond lengths are 2.98 Å. There are two shorter (2.99 Å) and one longer (3.05 Å) La(2)-Se(2) bond length. The La(2)-O(1) bond length is 2.37 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent La(2) and three equivalent La(1) atoms to form distorted SeLa5 trigonal bipyramids that share corners with five equivalent O(1)La4 tetrahedra, edges with three equivalent O(1)La4 tetrahedra, and edges with four equivalent Se(1)La5 trigonal bipyramids. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to two equivalent La(1) and three equivalent La(2) atoms. O(1) is bonded to one La(2) and three equivalent La(1) atoms to form OLa4 tetrahedra that share corners with two equivalent O(1)La4 tetrahedra, corners with five equivalent Se(1)La5 trigonal bipyramids, edges with two equivalent O(1)La4 tetrahedra, and edges with three equivalent Se(1)La5 trigonal bipyramids.