La4N2Se3 crystallizes in the monoclinic C2/c space group. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 2-coordinate geometry to two equivalent N(1), one Se(1), and four equivalent Se(2) atoms. In the second La site, La(2) is bonded in a 6-coordinate geometry to two equivalent N(1), two equivalent Se(1), and two equivalent Se(2) atoms. N(1) is bonded to two equivalent La(1) and two equivalent La(2) atoms to form NLa4 tetrahedra that share corners with two equivalent Se(1)La6 octahedra, corners with six equivalent Se(2)La6 octahedra, corners with two equivalent N(1)La4 tetrahedra, edges with two equivalent Se(1)La6 octahedra, edges with three equivalent Se(2)La6 octahedra, and  an edgeedge with one N(1)La4 tetrahedra. The corner-sharing octahedral tilt angles range from 24-82°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent La(1) and four equivalent La(2) atoms to form SeLa6 octahedra that share corners with ten equivalent Se(2)La6 octahedra, corners with four equivalent N(1)La4 tetrahedra, edges with two equivalent Se(1)La6 octahedra, edges with four equivalent N(1)La4 tetrahedra, and faces with two equivalent Se(2)La6 octahedra. The corner-sharing octahedral tilt angles range from 28-63°. In the second Se site, Se(2) is bonded to two equivalent La(2) and four equivalent La(1) atoms to form distorted SeLa6 octahedra that share corners with two equivalent Se(2)La6 octahedra, corners with five equivalent Se(1)La6 octahedra, corners with six equivalent N(1)La4 tetrahedra, edges with six equivalent Se(2)La6 octahedra, edges with three equivalent N(1)La4 tetrahedra, and  a faceface with one Se(1)La6 octahedra. The corner-sharing octahedral tilt angles range from 19-63°.
La4N2Se3 crystallizes in the monoclinic C2/c space group. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 2-coordinate geometry to two equivalent N(1), one Se(1), and four equivalent Se(2) atoms. There is one shorter (2.35 Å) and one longer (2.39 Å) La(1)-N(1) bond length. The La(1)-Se(1) bond length is 3.20 Å. There are a spread of La(1)-Se(2) bond distances ranging from 3.24-3.39 Å. In the second La site, La(2) is bonded in a 6-coordinate geometry to two equivalent N(1), two equivalent Se(1), and two equivalent Se(2) atoms. There is one shorter (2.37 Å) and one longer (2.42 Å) La(2)-N(1) bond length. Both La(2)-Se(1) bond lengths are 3.08 Å. There is one shorter (3.06 Å) and one longer (3.09 Å) La(2)-Se(2) bond length. N(1) is bonded to two equivalent La(1) and two equivalent La(2) atoms to form NLa4 tetrahedra that share corners with two equivalent Se(1)La6 octahedra, corners with six equivalent Se(2)La6 octahedra, corners with two equivalent N(1)La4 tetrahedra, edges with two equivalent Se(1)La6 octahedra, edges with three equivalent Se(2)La6 octahedra, and  an edgeedge with one N(1)La4 tetrahedra. The corner-sharing octahedral tilt angles range from 24-82°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent La(1) and four equivalent La(2) atoms to form SeLa6 octahedra that share corners with ten equivalent Se(2)La6 octahedra, corners with four equivalent N(1)La4 tetrahedra, edges with two equivalent Se(1)La6 octahedra, edges with four equivalent N(1)La4 tetrahedra, and faces with two equivalent Se(2)La6 octahedra. The corner-sharing octahedral tilt angles range from 28-63°. In the second Se site, Se(2) is bonded to two equivalent La(2) and four equivalent La(1) atoms to form distorted SeLa6 octahedra that share corners with two equivalent Se(2)La6 octahedra, corners with five equivalent Se(1)La6 octahedra, corners with six equivalent N(1)La4 tetrahedra, edges with six equivalent Se(2)La6 octahedra, edges with three equivalent N(1)La4 tetrahedra, and  a faceface with one Se(1)La6 octahedra. The corner-sharing octahedral tilt angles range from 19-63°.