La2SiSeO4 crystallizes in the orthorhombic Pbcm space group. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 6-coordinate geometry to two equivalent Se(1), two equivalent O(2), and four equivalent O(1) atoms. In the second La site, La(2) is bonded in a 6-coordinate geometry to two equivalent Se(1), two equivalent O(1), and four equivalent O(2) atoms. Si(1) is bonded in a tetrahedral geometry to two equivalent O(1) and two equivalent O(2) atoms. Se(1) is bonded in a 4-coordinate geometry to two equivalent La(1) and two equivalent La(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one La(2), two equivalent La(1), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one La(1), two equivalent La(2), and one Si(1) atom.
La2SiSeO4 crystallizes in the orthorhombic Pbcm space group. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 6-coordinate geometry to two equivalent Se(1), two equivalent O(2), and four equivalent O(1) atoms. Both La(1)-Se(1) bond lengths are 3.23 Å. Both La(1)-O(2) bond lengths are 2.54 Å. There are two shorter (2.52 Å) and two longer (2.56 Å) La(1)-O(1) bond lengths. In the second La site, La(2) is bonded in a 6-coordinate geometry to two equivalent Se(1), two equivalent O(1), and four equivalent O(2) atoms. There is one shorter (3.05 Å) and one longer (3.23 Å) La(2)-Se(1) bond length. Both La(2)-O(1) bond lengths are 2.61 Å. There are two shorter (2.51 Å) and two longer (2.53 Å) La(2)-O(2) bond lengths. Si(1) is bonded in a tetrahedral geometry to two equivalent O(1) and two equivalent O(2) atoms. Both Si(1)-O(1) bond lengths are 1.63 Å. Both Si(1)-O(2) bond lengths are 1.64 Å. Se(1) is bonded in a 4-coordinate geometry to two equivalent La(1) and two equivalent La(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one La(2), two equivalent La(1), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one La(1), two equivalent La(2), and one Si(1) atom.