Tb4N2Se3 crystallizes in the monoclinic C2/m space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 6-coordinate geometry to one N(1), two equivalent Se(2), and three equivalent Se(1) atoms. In the second Tb site, Tb(2) is bonded in a 6-coordinate geometry to three equivalent N(1), one Se(2), and two equivalent Se(1) atoms. N(1) is bonded to one Tb(1) and three equivalent Tb(2) atoms to form NTb4 tetrahedra that share  a cornercorner with one Se(2)Tb6 octahedra, corners with seven equivalent Se(1)Tb5 square pyramids, corners with two equivalent N(1)Tb4 tetrahedra, edges with two equivalent Se(2)Tb6 octahedra,  an edgeedge with one Se(1)Tb5 square pyramid, and edges with two equivalent N(1)Tb4 tetrahedra. The corner-sharing octahedral tilt angles are 27°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Tb(2) and three equivalent Tb(1) atoms to form SeTb5 square pyramids that share corners with two equivalent Se(2)Tb6 octahedra, corners with seven equivalent N(1)Tb4 tetrahedra, edges with three equivalent Se(2)Tb6 octahedra, edges with four equivalent Se(1)Tb5 square pyramids, and  an edgeedge with one N(1)Tb4 tetrahedra. The corner-sharing octahedral tilt angles are 12°. In the second Se site, Se(2) is bonded to two equivalent Tb(2) and four equivalent Tb(1) atoms to form SeTb6 octahedra that share corners with four equivalent Se(1)Tb5 square pyramids, corners with two equivalent N(1)Tb4 tetrahedra, edges with two equivalent Se(2)Tb6 octahedra, edges with six equivalent Se(1)Tb5 square pyramids, and edges with four equivalent N(1)Tb4 tetrahedra.
Tb4N2Se3 crystallizes in the monoclinic C2/m space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 6-coordinate geometry to one N(1), two equivalent Se(2), and three equivalent Se(1) atoms. The Tb(1)-N(1) bond length is 2.15 Å. Both Tb(1)-Se(2) bond lengths are 2.90 Å. There are two shorter (2.83 Å) and one longer (3.24 Å) Tb(1)-Se(1) bond length. In the second Tb site, Tb(2) is bonded in a 6-coordinate geometry to three equivalent N(1), one Se(2), and two equivalent Se(1) atoms. There is one shorter (2.23 Å) and two longer (2.35 Å) Tb(2)-N(1) bond lengths. The Tb(2)-Se(2) bond length is 2.99 Å. Both Tb(2)-Se(1) bond lengths are 3.05 Å. N(1) is bonded to one Tb(1) and three equivalent Tb(2) atoms to form NTb4 tetrahedra that share  a cornercorner with one Se(2)Tb6 octahedra, corners with seven equivalent Se(1)Tb5 square pyramids, corners with two equivalent N(1)Tb4 tetrahedra, edges with two equivalent Se(2)Tb6 octahedra,  an edgeedge with one Se(1)Tb5 square pyramid, and edges with two equivalent N(1)Tb4 tetrahedra. The corner-sharing octahedral tilt angles are 27°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Tb(2) and three equivalent Tb(1) atoms to form SeTb5 square pyramids that share corners with two equivalent Se(2)Tb6 octahedra, corners with seven equivalent N(1)Tb4 tetrahedra, edges with three equivalent Se(2)Tb6 octahedra, edges with four equivalent Se(1)Tb5 square pyramids, and  an edgeedge with one N(1)Tb4 tetrahedra. The corner-sharing octahedral tilt angles are 12°. In the second Se site, Se(2) is bonded to two equivalent Tb(2) and four equivalent Tb(1) atoms to form SeTb6 octahedra that share corners with four equivalent Se(1)Tb5 square pyramids, corners with two equivalent N(1)Tb4 tetrahedra, edges with two equivalent Se(2)Tb6 octahedra, edges with six equivalent Se(1)Tb5 square pyramids, and edges with four equivalent N(1)Tb4 tetrahedra.