La3NbSe2O4F2 crystallizes in the orthorhombic Pnma space group. There are three inequivalent La sites. In the first La site, La(1) is bonded in a 9-coordinate geometry to two equivalent Se(1), three equivalent Se(2), one O(1), two equivalent O(4), and one F(1) atom. In the second La site, La(2) is bonded in a 9-coordinate geometry to two equivalent Se(1), one O(2), one O(4), two equivalent F(2), and three equivalent F(1) atoms. In the third La site, La(3) is bonded in a 9-coordinate geometry to one Se(1), two equivalent Se(2), one O(1), two equivalent O(2), two equivalent O(3), and one F(2) atom. Nb(1) is bonded to one Se(2), one O(2), one O(3), one O(4), and two equivalent O(1) atoms to form distorted corner-sharing NbSeO5 trigonal bipyramids. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to one La(3), two equivalent La(1), and two equivalent La(2) atoms to form distorted SeLa5 trigonal bipyramids that share corners with two equivalent F(1)La4 tetrahedra, corners with four equivalent O(4)La3Nb tetrahedra,  an edgeedge with one O(4)La3Nb tetrahedra, edges with three equivalent F(1)La4 tetrahedra, and edges with two equivalent Se(1)La5 trigonal bipyramids. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent La(3), three equivalent La(1), and one Nb(1) atom. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one La(1), one La(3), and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to one La(2), two equivalent La(3), and one Nb(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent La(3) and one Nb(1) atom. In the fourth O site, O(4) is bonded to one La(2), two equivalent La(1), and one Nb(1) atom to form OLa3Nb tetrahedra that share  a cornercorner with one F(1)La4 tetrahedra, corners with two equivalent O(4)La3Nb tetrahedra, corners with four equivalent Se(1)La5 trigonal bipyramids, edges with two equivalent F(1)La4 tetrahedra, and  an edgeedge with one Se(1)La5 trigonal bipyramid. There are two inequivalent F sites. In the first F site, F(1) is bonded to one La(1) and three equivalent La(2) atoms to form FLa4 tetrahedra that share  a cornercorner with one O(4)La3Nb tetrahedra, corners with two equivalent F(1)La4 tetrahedra, corners with two equivalent Se(1)La5 trigonal bipyramids, edges with two equivalent O(4)La3Nb tetrahedra, edges with two equivalent F(1)La4 tetrahedra, and edges with three equivalent Se(1)La5 trigonal bipyramids. In the second F site, F(2) is bonded in a trigonal planar geometry to one La(3) and two equivalent La(2) atoms.
La3NbSe2O4F2 crystallizes in the orthorhombic Pnma space group. There are three inequivalent La sites. In the first La site, La(1) is bonded in a 9-coordinate geometry to two equivalent Se(1), three equivalent Se(2), one O(1), two equivalent O(4), and one F(1) atom. Both La(1)-Se(1) bond lengths are 3.15 Å. All La(1)-Se(2) bond lengths are 3.17 Å. The La(1)-O(1) bond length is 2.72 Å. Both La(1)-O(4) bond lengths are 2.51 Å. The La(1)-F(1) bond length is 2.56 Å. In the second La site, La(2) is bonded in a 9-coordinate geometry to two equivalent Se(1), one O(2), one O(4), two equivalent F(2), and three equivalent F(1) atoms. Both La(2)-Se(1) bond lengths are 3.16 Å. The La(2)-O(2) bond length is 2.59 Å. The La(2)-O(4) bond length is 2.54 Å. Both La(2)-F(2) bond lengths are 2.43 Å. There is one shorter (2.54 Å) and two longer (2.63 Å) La(2)-F(1) bond lengths. In the third La site, La(3) is bonded in a 9-coordinate geometry to one Se(1), two equivalent Se(2), one O(1), two equivalent O(2), two equivalent O(3), and one F(2) atom. The La(3)-Se(1) bond length is 3.17 Å. Both La(3)-Se(2) bond lengths are 3.08 Å. The La(3)-O(1) bond length is 2.72 Å. Both La(3)-O(2) bond lengths are 2.64 Å. Both La(3)-O(3) bond lengths are 2.54 Å. The La(3)-F(2) bond length is 2.43 Å. Nb(1) is bonded to one Se(2), one O(2), one O(3), one O(4), and two equivalent O(1) atoms to form distorted corner-sharing NbSeO5 trigonal bipyramids. The Nb(1)-Se(2) bond length is 2.99 Å. The Nb(1)-O(2) bond length is 1.94 Å. The Nb(1)-O(3) bond length is 1.85 Å. The Nb(1)-O(4) bond length is 2.04 Å. Both Nb(1)-O(1) bond lengths are 2.05 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to one La(3), two equivalent La(1), and two equivalent La(2) atoms to form distorted SeLa5 trigonal bipyramids that share corners with two equivalent F(1)La4 tetrahedra, corners with four equivalent O(4)La3Nb tetrahedra,  an edgeedge with one O(4)La3Nb tetrahedra, edges with three equivalent F(1)La4 tetrahedra, and edges with two equivalent Se(1)La5 trigonal bipyramids. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent La(3), three equivalent La(1), and one Nb(1) atom. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one La(1), one La(3), and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to one La(2), two equivalent La(3), and one Nb(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent La(3) and one Nb(1) atom. In the fourth O site, O(4) is bonded to one La(2), two equivalent La(1), and one Nb(1) atom to form OLa3Nb tetrahedra that share  a cornercorner with one F(1)La4 tetrahedra, corners with two equivalent O(4)La3Nb tetrahedra, corners with four equivalent Se(1)La5 trigonal bipyramids, edges with two equivalent F(1)La4 tetrahedra, and  an edgeedge with one Se(1)La5 trigonal bipyramid. There are two inequivalent F sites. In the first F site, F(1) is bonded to one La(1) and three equivalent La(2) atoms to form FLa4 tetrahedra that share  a cornercorner with one O(4)La3Nb tetrahedra, corners with two equivalent F(1)La4 tetrahedra, corners with two equivalent Se(1)La5 trigonal bipyramids, edges with two equivalent O(4)La3Nb tetrahedra, edges with two equivalent F(1)La4 tetrahedra, and edges with three equivalent Se(1)La5 trigonal bipyramids. In the second F site, F(2) is bonded in a trigonal planar geometry to one La(3) and two equivalent La(2) atoms.