Nd2Se3 crystallizes in the tetragonal I-42d space group. There are three inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), three equivalent Se(2), and three equivalent Se(3) atoms. In the second Nd site, Nd(2) is bonded to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms to form a mixture of distorted face, corner, and edge-sharing NdSe8 hexagonal bipyramids. In the third Nd site, Nd(3) is bonded to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms to form a mixture of distorted face, corner, and edge-sharing NdSe8 hexagonal bipyramids. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Nd(2), two equivalent Nd(1), and two equivalent Nd(3) atoms to form SeNd5 square pyramids that share corners with five equivalent Se(2)Nd6 octahedra, corners with four equivalent Se(1)Nd5 square pyramids, corners with four equivalent Se(3)Nd5 square pyramids, edges with three equivalent Se(2)Nd6 octahedra,  an edgeedge with one Se(1)Nd5 square pyramid, edges with four equivalent Se(3)Nd5 square pyramids,  a faceface with one Se(2)Nd6 octahedra, and  a faceface with one Se(1)Nd5 square pyramid. The corner-sharing octahedral tilt angles range from 23-49°. In the second Se site, Se(2) is bonded to one Nd(3), two equivalent Nd(2), and three equivalent Nd(1) atoms to form distorted SeNd6 octahedra that share corners with three equivalent Se(2)Nd6 octahedra, corners with five equivalent Se(1)Nd5 square pyramids, corners with seven equivalent Se(3)Nd5 square pyramids, edges with two equivalent Se(2)Nd6 octahedra,  an edgeedge with one Se(3)Nd5 square pyramid, edges with three equivalent Se(1)Nd5 square pyramids, faces with two equivalent Se(2)Nd6 octahedra,  a faceface with one Se(1)Nd5 square pyramid, and faces with two equivalent Se(3)Nd5 square pyramids. The corner-sharing octahedral tilt angles range from 18-49°. In the third Se site, Se(3) is bonded to one Nd(2), one Nd(3), and three equivalent Nd(1) atoms to form distorted SeNd5 square pyramids that share corners with seven equivalent Se(2)Nd6 octahedra, corners with four equivalent Se(1)Nd5 square pyramids, corners with five equivalent Se(3)Nd5 square pyramids,  an edgeedge with one Se(2)Nd6 octahedra, edges with four equivalent Se(1)Nd5 square pyramids, faces with two equivalent Se(2)Nd6 octahedra, and  a faceface with one Se(3)Nd5 square pyramid. The corner-sharing octahedral tilt angles range from 14-54°.
Nd2Se3 crystallizes in the tetragonal I-42d space group. There are three inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), three equivalent Se(2), and three equivalent Se(3) atoms. There is one shorter (2.95 Å) and one longer (3.19 Å) Nd(1)-Se(1) bond length. There are a spread of Nd(1)-Se(2) bond distances ranging from 2.98-3.34 Å. There are a spread of Nd(1)-Se(3) bond distances ranging from 2.95-3.18 Å. In the second Nd site, Nd(2) is bonded to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms to form a mixture of distorted face, corner, and edge-sharing NdSe8 hexagonal bipyramids. Both Nd(2)-Se(1) bond lengths are 2.97 Å. Both Nd(2)-Se(3) bond lengths are 3.17 Å. There are two shorter (2.99 Å) and two longer (3.17 Å) Nd(2)-Se(2) bond lengths. In the third Nd site, Nd(3) is bonded to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms to form a mixture of distorted face, corner, and edge-sharing NdSe8 hexagonal bipyramids. Both Nd(3)-Se(2) bond lengths are 3.26 Å. Both Nd(3)-Se(3) bond lengths are 3.01 Å. There are two shorter (2.99 Å) and two longer (3.17 Å) Nd(3)-Se(1) bond lengths. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Nd(2), two equivalent Nd(1), and two equivalent Nd(3) atoms to form SeNd5 square pyramids that share corners with five equivalent Se(2)Nd6 octahedra, corners with four equivalent Se(1)Nd5 square pyramids, corners with four equivalent Se(3)Nd5 square pyramids, edges with three equivalent Se(2)Nd6 octahedra,  an edgeedge with one Se(1)Nd5 square pyramid, edges with four equivalent Se(3)Nd5 square pyramids,  a faceface with one Se(2)Nd6 octahedra, and  a faceface with one Se(1)Nd5 square pyramid. The corner-sharing octahedral tilt angles range from 23-49°. In the second Se site, Se(2) is bonded to one Nd(3), two equivalent Nd(2), and three equivalent Nd(1) atoms to form distorted SeNd6 octahedra that share corners with three equivalent Se(2)Nd6 octahedra, corners with five equivalent Se(1)Nd5 square pyramids, corners with seven equivalent Se(3)Nd5 square pyramids, edges with two equivalent Se(2)Nd6 octahedra,  an edgeedge with one Se(3)Nd5 square pyramid, edges with three equivalent Se(1)Nd5 square pyramids, faces with two equivalent Se(2)Nd6 octahedra,  a faceface with one Se(1)Nd5 square pyramid, and faces with two equivalent Se(3)Nd5 square pyramids. The corner-sharing octahedral tilt angles range from 18-49°. In the third Se site, Se(3) is bonded to one Nd(2), one Nd(3), and three equivalent Nd(1) atoms to form distorted SeNd5 square pyramids that share corners with seven equivalent Se(2)Nd6 octahedra, corners with four equivalent Se(1)Nd5 square pyramids, corners with five equivalent Se(3)Nd5 square pyramids,  an edgeedge with one Se(2)Nd6 octahedra, edges with four equivalent Se(1)Nd5 square pyramids, faces with two equivalent Se(2)Nd6 octahedra, and  a faceface with one Se(3)Nd5 square pyramid. The corner-sharing octahedral tilt angles range from 14-54°.